JP5385025B2 - Aluminum alloy wire rod for high-strength bolt excellent in formability and manufacturing method thereof, high-strength flange bolt and manufacturing method thereof - Google Patents

Description

  The present invention relates to an Al—Mg—Si-based aluminum alloy wire rod for high-strength bolts and a method for manufacturing the same, a flange bolt using the aluminum alloy wire rod as a material, and a method for manufacturing the flange bolt. The wire rod material referred to in the present invention is a wire rod material as a material for high-strength bolts, a rolled wire rod material subjected to hot rolling in the production process thereof, a wire material having a relatively small diameter, A generic term for bars with relatively large diameters. Hereinafter, aluminum is also referred to as Al, and Al—Mg—Si is also referred to as 6000.

  Conventionally, fasteners such as steel bolts and screws are generally used to fasten aluminum parts and magnesium parts of automobile parts that have been reduced in weight using light alloys such as aluminum alloys and magnesium alloys (hereinafter collectively referred to as generic names). (Also simply called bolts).

  On the other hand, in recent years, in connection with the weight reduction of automobile bodies, wire rods having a circular cross-section such as aluminum alloy wires and rods are also formed on these bolts in order to reduce the weight of automobile parts. There is a demand to use aluminum alloy bolts manufactured in this way.

  Moreover, aluminum alloy bolts for fastening automotive parts such as aluminum materials and magnesium materials have a relatively small diameter of M12 or less in terms of the nominal diameter of the bolts in terms of the design of automotive parts, as well as aluminum materials and magnesium materials, etc. It is required that the stress concentration from the bolt head on the joint surface of the fastened component is small. If the bolt has the small diameter, the diameter of the head is naturally reduced, and stress is easily concentrated from the bolt head to the joint surface of the component to be fastened.

  Here, the bolts having a nominal diameter of M6 to M12 are hexagonal bolts with a head hexagonal flat diameter of 13 mm or 12 mm, M8 bolts, 10 mm M6 bolts, 14 mm M10 bolts, and 17 mm M12 bolts. Say. The nominal diameter of the bolt is also referred to as the name of the screw, the nominal diameter of the screw, the nominal diameter of the screw, or the like, and the diameter, size, or nominal diameter of the male screw portion may be referred to as M6 to M12. All point to the same bolt.

  Usually, in order to alleviate and suppress the stress concentration from the bolt head to the joint surface of the fastened component (the surface of the fastened component that receives a load from the bolt head), A washer is interposed between the joint surface and the bolt head. However, when such a washer is interposed, the number of steps for attaching the washer is greatly increased at the time of fastening the bolt, and the bolt fastening process cannot be made efficient.

  On the other hand, there is a flange bolt (bolt with flange) as a bolt that can omit the washer. As shown in the perspective view of FIG. 1 as a whole, this flange bolt has an overall shape of a male threaded portion 3 that is a threaded shaft portion and a hexagonal bolt head as in a normal hexagonal bolt. It consists of two. However, it has a structure in which a flange (flange portion, collar) 4 is integrally provided in advance on the lower peripheral edge of the bolt head 2.

  And this flange 4 contacts the joining surface of a to-be-fastened part instead of the said washer, and can relieve | moderate and suppress the stress concentration from a bolt head to the to-be-joined surface of a to-be-fastened part. When this flange bolt is used, the washer can be omitted, and there is an advantage that the number of steps for installing the washer in the bolt fastening process can be greatly reduced. Therefore, such an aluminum alloy flange bolt is required for fastening aluminum materials, magnesium materials, and the like of automobile parts where efficiency is important.

On the other hand, conventionally, as an aluminum alloy bolt, a high-strength 6000 series aluminum alloy screw (including a bolt) used for assembling aluminum alloy structures such as window sashes and automobile bodies has been patented. It is proposed in Document 1 and the like. The aluminum alloy bolt disclosed in Patent Document 1 is not a flange bolt, but only a normal hexagon bolt. However, such as header workability of a bolt head and thread rolling processability to a small M4 bolt or the like. Formability and corrosion resistance are also issues. The mechanical properties (mechanical characteristics) of the screw are as follows. The yield strength is 300 N / mm ² or more, the elongation is 6% or more, and the torsion strength is JIS-B-1057-1989 AL3 (A6061-T6). In order to obtain a value higher by 10% or more, a 6000 series aluminum alloy extruded material having a specific composition is used. Specifically, in wt%, Mg: 0.5-1.5%, Si: 0.5-1.5%, Cu: 0.5-1.5%, Mn: 0.2-0. Al—Mg— containing 5%, Ti: 0.005 to 0.1%, B: 0.001 to 0.05%, Zr: 0.05 to 0.25%, and remaining aluminum and inevitable impurities Si-based aluminum alloy composition.

  This Patent Document 1 is significant in that a 6000 series aluminum alloy wire rod material is selected as a material for fastening aluminum alloy bolts such as window sashes and automobile bodies. This aluminum alloy other than 6000 series has the following problems for practical use as an aluminum alloy for fasteners, as described in Patent Document 1.

  For example, 5000 series aluminum alloys such as 5052 and 5056 have a large amount of alloys such as Mg, are inferior in recyclability and low in strength compared to 6000 series. Moreover, the header processability to a fastener is also inferior. Although 7000 series aluminum alloys such as 7N01 and 7075 have high strength, they have a large amount of alloys such as Zn and Cu and are inferior in recyclability. Moreover, since there are many alloy quantities, such as Zn and Cu, it is easy to corrode and lacks reliability. And molding and workability are inferior, and it is easy to break during flange molding at the time of header processing. Although 2000 series aluminum alloys, such as 2024, have high heat resistance, when there are many alloy quantities, such as Cu, there exists a problem which is inferior to recyclability and is easy to corrode. Moreover, it is inferior in molding and workability and easily breaks during header processing. The same applies to AA2618 which is a typical heat-resistant aluminum alloy. This alloy has already been used for several decades, and examples of applications include the body of a supersonic aircraft Concorde. The heat-resistant temperature is about 120 ° C., which is the highest among practical aluminum alloys. However, the corrosion resistance is low, and it is necessary to take measures against corrosion resistance for its use. For this reason, the usage environment is limited, and the alloy is not easy to use.

  However, even in the case of a 6000 series aluminum alloy, the existing alloys such as A6061 and A6056 used as the fasteners are still inferior in molding and workability, are easily broken during header processing, and are subjected to artificial age hardening treatment. Even when I went there, the strength itself was low. Patent Document 1 also attempts to improve these problems of the 6000 series aluminum alloy.

Japanese Patent No. 3939414

  The basic characteristics required for the 6000 series aluminum alloy bolts for fastening such as aluminum parts and magnesium materials of the automobile parts described above are the same as the normal 6000 series aluminum alloy bolts intended by the above-mentioned Patent Document 1, and are sag resistant. These include excellent stability, securing a stable axial force during tightening, no loosening due to a decrease in axial force during use after tightening, or no breakage. In order for the 6000 series aluminum alloy bolts to exhibit these characteristics, the aluminum alloy wire rod with a circular cross-section as the material has mechanical properties such as high strength and header processing on the bolts. It is necessary to have moldability such as thread rolling and corrosion resistance.

  However, in the case of the flange bolt as an object of the present invention, in addition to the basic characteristics such as sag resistance required for the bolt, a thin-walled flange is formed at the time of header processing (forming) on the head of the characteristic bolt. The molding process becomes complicated and the molding conditions become more strict, such as an overhang process for forming. This is a point that is greatly different from a normal (hexagonal) bolt as intended by Patent Document 1.

  For this reason, in the case of the flange bolt, in the 6000 series aluminum alloy wire rod manufactured by the extrusion process as described in Patent Document 1, the thin flange portion is cracked when the bolt head is processed. Occasionally, molding may not be possible. Therefore, the extruded material of Patent Document 1 cannot be used for the flange bolt which is the object of the present invention, particularly in terms of formability.

  In particular, the flange bolt targeted by the present invention has not only a complicated shape in which a thin flange is integrally provided on the bolt head, but also a nominal diameter of the bolt of M6 to M12. . Moreover, as described above, in order to satisfy the basic characteristics such as sag resistance required for aluminum alloy flange bolts, the most important thing is high strength, and aluminum alloy wire rods must also have high strength. Absent. For this reason, these complicated shapes, small diameters, and high strengths make the formation by header processing even more difficult than ordinary hexagon bolts and large diameter bolts.

  As a countermeasure, the formability of the flange bolt head can be improved by reducing the strength of the 6000 series aluminum alloy wire rod. However, there is a limit to the strength that can be improved by the heat treatment after molding, and the strength of flange bolts is reduced, and the basic characteristics required for the aluminum alloy bolts (ensuring stable axial force when tightening, use after tightening) (The prevention of loosening due to a decrease in the internal axial force, no breakage) is sacrificed. Further, if the flange bolt has a large diameter, the flange diameter can be secured, but the weight increases accordingly. In addition, the design of the automobile part needs to be changed, which is not allowed in the design of the automobile part.

  In addition, particularly when manufacturing a 6000 series aluminum alloy wire rod having a circular cross section, the manufacturing method by hot extrusion as described in Patent Document 1, as described later, causes problems with the flange of the wire rod as described later. This is also due to the fact that there is a big limit to the formability of the bolt head itself and the improvement of the formability.

  The present invention has been made in view of such a problem, and provides a 6000 series aluminum alloy flange bolt that is easy to form and has high strength without impairing the basic characteristics such as sag resistance, and a method for manufacturing the same. Objective.

In order to achieve the above object, the gist of the aluminum alloy wire rod for a high-strength bolt excellent in formability of the present invention has the following requirements a to e.
a. The said aluminum alloy wire rod is mass%, Mg: 0.5-1%, Si: 0.7-1.2%, Cu: 0.4-0.8%, Mn: 0.05-0 .6%, Ti: 0.01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, respectively, and the balance Al and inevitable impurities Al A wire rod material having a diameter of 12 mmφ or less, produced by hot rolling, wire drawing and heat treatment of an ingot of a Mg—Si composition.
b. The average crystal grain size of the center portion of the aluminum alloy wire rod before forming the bolt head is 50 μm or less, the tensile strength is 150 MPa or more and 300 MPa or less, and is measured and calculated by a drop test under the following conditions. The deformation resistance value is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. The aluminum alloy wire rod is formed into a bolt having a tensile strength of 350 MPa or more by heat treatment after the bolt head is formed.

Moreover, the summary of the manufacturing method of the aluminum alloy wire rod material for high-strength bolts excellent in formability of this invention for achieving the said objective has the requirements of the following ae.
a. In mass%, Mg: 0.5 to 1%, Si: 0.7 to 1.2%, Cu: 0.4 to 0.8%, Mn: 0.05 to 0.6%, Ti: 0.00. A casting of Al-Mg-Si composition comprising 01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, and the balance being Al and inevitable impurities After the ingot is melted and the ingot is homogenized and heat-treated, hot rolling with a processing rate of 70% or more is performed at a processing start temperature in the range of 320 to 470 ° C. The aluminum alloy wire rod is 12 mmφ or less.
b. The average grain size of the aluminum alloy wire rod before forming the bolt head is 50 μm or less, the tensile strength is 150 MPa or more and 300 MPa or less, and is measured and calculated by a drop test under the following conditions. The deformation resistance value is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. The aluminum alloy wire rod is formed into a bolt having a tensile strength of 350 MPa or more by heat treatment after the bolt head is formed.

The gist of the high-strength flange bolt of the present invention to achieve the above object is a flange bolt having a nominal diameter of M6 to M12 and formed of an aluminum alloy wire rod having the following requirements a to e. It is characterized by becoming.
a. The said aluminum alloy wire rod is mass%, Mg: 0.5-1%, Si: 0.7-1.2%, Cu: 0.4-0.8%, Mn: 0.05-0 .6%, Ti: 0.01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, respectively, and the balance Al and inevitable impurities Al A diameter of 12 mmφ or less is produced by hot rolling, wire drawing, and heat treatment of an ingot of a Mg—Si composition.
b. The average crystal grain size of the center portion of the aluminum alloy wire rod before forming the bolt head is 50 μm or less, the tensile strength is 150 MPa or more and 300 MPa or less, and is measured and calculated by a drop test under the following conditions. The deformation resistance value is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. The flange bolt has a tensile strength of 350 MPa or more by heat treatment after the bolt head is formed.

The gist of the manufacturing method of the high-strength flange bolt of the present invention for achieving the above object is a manufacturing method of a flange bolt having a nominal diameter of M6 to M12 having the following requirements a to e. And
a. In mass%, Mg: 0.5 to 1%, Si: 0.7 to 1.2%, Cu: 0.4 to 0.8%, Mn: 0.05 to 0.6%, Ti: 0.00. A casting of Al-Mg-Si composition comprising 01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, and the balance being Al and inevitable impurities The ingot is melted and the ingot is homogenized and heat-rolled, and then hot-rolling with a processing rate of 70% or more is performed at a processing start temperature in the range of 320 to 470 ° C. Aluminum alloy wire rod.
b. When this aluminum alloy wire rod is processed into a header to form a flanged head of the flange bolt, the average grain size of the center portion of this aluminum alloy wire rod is 50 μm or less, and the tensile strength is In addition to 150 MPa or more and 300 MPa or less, the deformation resistance value measured and calculated by a drop test under the following conditions is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. After forming the flanged head portion of the flange bolt, the tensile strength of the flange bolt is set to 350 MPa or more by heat treatment.

  Here, the aluminum alloy wire rod material referred to in the present invention is a wire rod material having a diameter of 12 mmφ or less by hot rolling, wire drawing and heat treatment in the production process as described above, It is a wire rod material as a bolt material on which a bolt head is molded, such as a flanged head of a flange bolt. Therefore, the above-mentioned average crystal grain size (structure) and mechanical properties (characteristics) in the aluminum alloy wire rod material are defined as follows. The state of this wire rod material before the bolt head is formed.

  The wire rod material as the bolt material of the present invention may be a bolt other than the flange bolt. Further, the cross section of the wire rod material of the present invention is mainly intended for a circular wire rod material, but the cross sectional shape is not limited to a perfect circle as long as it can be applied to a bolt material. A circular cross-sectional shape is also appropriately selected according to the bolt application.

  The present inventor believes that the composition and structure of a 6000 series aluminum alloy wire rod, which is a material of the bolt, has the complex shape, small diameter, and formability of a high-strength flange bolt. We found that there is a deep correlation between sex.

  First, the composition of the 6000 series aluminum alloy wire rod is a high-strength flange bolt, and the basic characteristics required for the aluminum alloy bolt (sag resistance, securing a stable axial force during tightening, after tightening, This is indispensable to ensure that the axial force is not loosened during use and prevents breakage. If the composition deviates, the strength of the flange bolt is lowered, and the basic characteristics required for the aluminum alloy bolt cannot be guaranteed.

  Next, the structure of the 6000 series aluminum alloy wire rod is a hot-rolled rolled structure. By adopting this rolled structure, due to the uniformity of the structure from the surface of the bar material to the inside, which is peculiar to this rolled structure, the formability of the flange bolt having a complicated shape and high strength and a small diameter, in particular, The formability of the flanged head is improved.

  Moreover, using a rolled structure is also effective for refining the crystal grains (average crystal grain size) of the wire rod structure. If the crystal grains of the 6000 series aluminum alloy wire rod structure, which is the material of the bolt, can be refined, the form of the flange bolt having a complicated shape, high strength, and small diameter, particularly the flanged head The moldability of the part is improved. Further, if the crystal grains can be refined, the basic characteristics such as sag resistance required for the aluminum alloy bolt can be guaranteed, and corrosion resistance such as intergranular corrosion resistance can be improved.

  In the case of a wire rod having a round cross-section as the object of the present invention, the shape is simple, unlike the case of a shape having a complicated shape. For this reason, in the hot extrusion process, the shape of the die is simplified, and the center part of the billet (ingot) is extruded as it is as the center part of the wire rod material without being processed by the die. The billet cast structure tends to remain as it is in the center of the material. Even if the cast structure does not remain as it is, the center portion of the wire rod material has a remarkably low processing rate, and even if it becomes an extruded structure, the crystal grains tend to be coarse.

  Also, in the hot extrusion process, contrary to the center part of this wire rod material, the surface of the billet becomes stronger and the temperature tends to increase, and the crystallized material present on the billet surface with a relatively low melting point melts locally. It becomes easy to adhere to dies. For this reason, the surface of the wire rod material during extrusion is peeled off, causing a phenomenon called mushy, and the surface failure of the wire rod material called pickup tends to occur. In order to prevent such defects of the extruded material, it is necessary to increase the soaking temperature or reduce the amount of transition elements in order to reduce the crystallized matter on the surface. However, when the soaking temperature is raised, the dispersed particles become coarse, and when the amount of transition elements is reduced, the dispersed particles are reduced and the density is reduced, and there is a problem that the crystal grains cannot be refined as defined in the present invention.

  For these reasons, the uniformity of the structure from the surface of the wire rod to the inside is inferior to that of the rolled structure at the surface and the center of the wire rod manufactured by hot extrusion. Further, it is difficult to make the crystal grains fine as defined in the present invention. In particular, when manufacturing a 6000 series aluminum alloy wire rod having a circular cross section, the manufacturing method by hot extrusion as described in Patent Document 1 may cause the flange bolt head to be formed due to problems specific to the extruded material. This is the reason why there is a big limit to the improvement of the properties and the moldability.

  In the present invention, the formability of the 6000 series aluminum alloy wire rod material to the flange bolt head is further improved, and the complicated shape, high strength and small diameter of the flange bolt head are ensured. Therefore, the tensile strength and the deformation resistance value of the wire rod are defined within a specific range.

  As described above, it is well known that an aluminum alloy has a certain correlation between strength and formability. However, according to the knowledge of the present inventors, the present invention 6000 series aluminum alloy wire rod having the specific composition that has been hot rolled (hereinafter referred to as a rolled material) is a known 6000 series aluminum alloy such as 6061. Despite having higher strength than wire rod material (rolled material), flange having low deformation resistance value by the specific measuring method, complex shape, high strength and small diameter The formability of the bolt head is excellent. This is a peculiar phenomenon, and according to the above technical common sense, a known 6000 series aluminum alloy wire rod (rolled material) such as low strength 6061 should have better formability of the flange bolt head. It is. Further, the 6000 series aluminum alloy wire rod (rolled material) of the present invention has lower strength than known 6000 series aluminum alloy wire rod (rolled material) such as 6056, but it depends on the specific measuring method. The deformation resistance value is low, and the formability of the flange bolt head having the complicated shape, high strength, and small diameter is excellent.

  Therefore, in the rolled material field of 6000 series aluminum alloy as in the present invention, the strength and the deformation resistance value have a certain correlation with the formability of the flange bolt head. That is, it can be said that the strength and the deformation resistance value are in a contradictory relationship with the formability of the flange bolt head. Therefore, as long as the strength and the deformation resistance value do not satisfy the range defined in the present invention, both the high strength required for the aluminum alloy flange bolt and the formability to the aluminum alloy flange bolt are satisfied. I can't. On the other hand, this invention can satisfy both the high intensity | strength requested | required of the said aluminum alloy flange bolt, and the moldability to the said flange bolt. In other words, it is possible to provide a high-strength 6000 series aluminum alloy flange bolt and a method for producing the same without impairing the basic characteristics such as sag resistance required for the aluminum alloy bolt.

It is a perspective view which shows the whole flange bolt. It is explanatory drawing which shows the aspect of the drop test which measures the said deformation resistance value. It is explanatory drawing which shows the aspect of a tensile testing machine.

  Hereinafter, embodiments of the present invention will be specifically described in order from the composition of the 6000 series (Al-Mg-Si series) aluminum alloy wire rod in the present invention. In addition, in the following description, it demonstrates in relation to a flange bolt especially among bolts. In the following description, the 6000 series aluminum alloy wire rod in the present invention is also referred to as an aluminum alloy wire rod or simply a wire rod.

a. composition:
First, the chemical component composition of a 6000 series aluminum alloy wire rod as a bolt material in the present invention will be described. The present invention is directed to a relatively small flange bolt having a nominal diameter of M12 or less, and as described above, the flange bolt is used as a fastening bolt for automotive parts such as aluminum and magnesium. Basic characteristics are required. The basic characteristics are high strength and high sag resistance, ensuring a stable axial force during tightening, no loosening due to a decrease in axial force during use after tightening, or no breakage. In addition, it is necessary to have both formability and corrosion resistance on the flange bolt.

  In order to satisfy such a requirement, an aluminum alloy rolled wire rod is made of a specific Al as a rolled wire rod on the premise that the ingot is subjected to hot rolling, wire drawing and heat treatment in the production process. -It is set as a Mg-Si type aluminum alloy composition. That is, in mass%, Mg: 0.5 to 1%, Si: 0.7 to 1.2%, Cu: 0.4 to 0.8%, Mn: 0.05 to 0.6%, Ti: A specific composition comprising 0.01 to 0.05%, Zr: 0.05 to 0.25%, and Cr: 0.05 to 0.25%, respectively, and the balance being Al and unavoidable impurities. Here, the% display of the content of each element means the mass%, including the content of each element described below.

  Since the specific alloy composition has a high strength of 350 MPa or more as the flange bolt, the type and content of alloy elements are relatively large for the composition of the 6000 series aluminum alloy. Normally, if the type and content of the alloy elements are relatively large, coarse crystal precipitates are inevitably formed in the ingot. For this reason, when a wire rod material is manufactured by hot extrusion or the like, seizure with a die is likely to occur during extrusion. In order to prevent such seizure, it is necessary to reduce the extrusion speed, which reduces productivity. Further, if the extrusion speed is increased excessively, the surface of the extruded material is damaged, which is likely to cause broken lines and surface cracks during wire processing.

  On the other hand, in the rolled wire rod material, the alloy element is balanced by the combination of the selected alloy element and the amount of the alloy element as described above in spite of the relatively large type and content of the alloy element. ing. In addition, the wire rod material is made into a rolled structure by a combination or synergistic effect of hot rolling, wire drawing and heat treatment in the production process of the aluminum alloy wire rod, and then the wire rod material. The crystal grain size is reduced to an average crystal grain size of 50 μm or less. As a result, the aluminum alloy wire rod of the present invention has high formability to bolts and can satisfy the basic characteristics such as sag resistance as the high-strength bolts.

  At the same time, if the balance is made by the combination of the selected alloy element and the amount of the alloy element, as in the chemical component composition described above, the type and content of the alloy element is not enough for the chemical component composition of the 6000 series aluminum alloy. Despite being relatively large, the corrosion resistance can also be improved.

  Other elements other than these are basically impurities, and the content (allowable amount) at each element level in accordance with AA to JIA standards and the like.

  However, from the viewpoint of recycling, not only high-purity Al bullion but also 6000 series alloys, other aluminum alloy scrap materials, low-purity Al bullion, etc. are used as melting materials. There is a high possibility that other elements other than the above will also be mixed. Further, performing the process of further reducing these impurity elements increases the manufacturing cost, and it is necessary to allow a certain amount of inclusion. On the other hand, there is an element whose content is better regulated within a range not hindering the object and effect of the present invention described above.

  For example, Fe is allowed to contain 0.5% or less, Ag is 0.2% or less, and Sn is 0.2% or less. On the other hand, Zn is particularly harmful to corrosion resistance, and it is preferable to regulate the content as low as possible to 0.05% or less.

  The preferable content range and significance of each element, or the allowable amount will be described below for each element.

Si: 0.7-1.2%
Si, together with Mg, partly dissolves in the matrix and strengthens the aluminum alloy wire rod. In addition, the high strength required to exhibit the age-hardening ability to form aging precipitates that contribute to strength improvement during artificial aging treatment and to satisfy the basic characteristics such as sag resistance required for bolts. It is an essential element for obtaining. In order to exhibit the excellent age-hardening ability in the artificial aging treatment, an excess Si type 6000 series aluminum containing Mg / Si in a mass ratio of 1.73 or less and containing Si excessively with respect to Mg. An alloy composition is preferable.

  If the Si content is too small, the absolute amount is insufficient, so that the solid solution strengthening and age hardening ability are insufficient. As a result, the required high strength cannot be obtained. On the other hand, if the Si content is too large, coarse crystals and precipitates are formed, and the required high strength cannot be obtained. Moreover, the hot workability to a wire rod material and the moldability to a bolt are remarkably inhibited. Therefore, the Si content is in the range of 0.7 to 1.2%.

Mg: 0.5 to 1%
Mg is required to satisfy the basic characteristics required for bolts by forming an aging precipitate that contributes to strength improvement together with Si during solid solution strengthening and the artificial aging treatment, and exhibits age hardening ability. , An essential element for obtaining the high strength.

  If the Mg content is too small, the absolute amount is insufficient, so that the solid solution strengthening and age hardening ability are insufficient. As a result, the required high strength cannot be obtained. On the other hand, if the Mg content is too large, coarse crystals and precipitates are formed, and the required high strength cannot be obtained. Therefore, the Mg content is in the range of 0.5 to 1%.

Cu: 0.4 to 0.8%
Cu contributes to strength improvement together with Mg and Si. If the Cu content is too small, the effect cannot be sufficiently obtained, and the basic characteristics required for the bolt cannot be obtained. On the other hand, when there is too much Cu content, intensity | strength will fall on the contrary. Further, the formability to the bolt and the corrosion resistance are greatly reduced. Therefore, the Cu content is in the range of 0.4 to 0.8%, preferably in the range of 0.45 to 0.85%.

Mn: 0.05 to 0.6%
Mn partially dissolves in the matrix and strengthens the aluminum alloy wire rod. Further, during the homogenization heat treatment of the ingot, Al—Mn-based dispersed particles can be formed, and the crystal grains of the wire rod material structure can be refined, and the strength, formability, corrosion resistance, and the like can be improved.

  If the Mn content is too small, the effect cannot be sufficiently obtained, and the high strength necessary for satisfying the basic characteristics required for the bolt cannot be obtained. On the other hand, when there is too much Mn content, intensity | strength falls on the contrary. In addition, the formability and corrosion resistance of the bolt are greatly reduced. Therefore, the Mn content is in the range of 0.05 to 0.6%, preferably in the range of 0.1 to 0.5%.

Ti: 0.01 to 0.05%
Ti, together with B, has the effect of refining the crystal grains of the ingot. This improves casting and rolling cracks in the production process of the aluminum alloy wire rod. In addition, the average grain size of the crystal grains of the 6000 series aluminum alloy wire rod structure is refined to 50 μm or less, which contributes to improvement in strength and formability to bolts. If the Ti content is too small, the effect cannot be obtained sufficiently, cracking is likely to occur, and productivity is significantly inhibited. In addition, there is a limit to the refinement of crystal grains. On the other hand, when there is too much Ti content, a coarse intermetallic compound will be formed and an intensity | strength will fall on the contrary. Moreover, the moldability to a bolt also falls significantly. Therefore, the Ti content is in the range of 0.01 to 0.05%.

  Further, since B is contained in the mother alloy for Ti addition, it is easy to be mixed at the same time when Ti is added, and has the same effect as Ti as described above. Therefore, it is not rational and economical to positively exclude the B content, and a 0.05% or less content that does not impair the strength and formability of the bolt is allowed.

Zr: 0.05 to 0.25%
Zr forms dispersed particles containing the respective elements in the same manner as Mn, and has the effect of preventing crystal grains from becoming coarse during the heat treatment of the aluminum alloy wire rod and making the crystal grains finer. As a result, the average grain size of the crystal grains of the 6000 series aluminum alloy wire rod structure is refined to 50 μm or less, which contributes to improvement in strength and formability to bolts.

  When there is too little Zr content, the improvement effect of the intensity | strength and the moldability to a volt | bolt cannot fully be acquired. On the other hand, when there is too much Zr content, intensity | strength will be reduced on the contrary, and the moldability to a bolt will also be reduced significantly. Therefore, the Zr content is in the range of 0.05 to 0.25%.

Cr: 0.05-0.25%
Since Cr forms dispersed particles in the same manner as Mn and Zr, it has the effect of preventing the crystal grains from becoming coarse during the heat treatment of the aluminum alloy wire rod and miniaturizing the crystal grains. Contributes to improving strength and formability to bolts. Cr also has the effect of improving corrosion resistance. If the Cr content is too small, the effect of crystal grain refinement cannot be expected. On the other hand, when there is too much content of Cr, a coarse crystallization thing will be formed and an intensity | strength will fall on the contrary. Moreover, the moldability to a bolt is also reduced significantly. Therefore, the Cr content is in the range of 0.05 to 0.25%.

b. Strength and deformation resistance value:
In the present invention, as described above, the formability of a high-strength 6000 series aluminum alloy flange bolt, particularly the bolt head 2 shown in FIG. 1, without impairing the basic characteristics such as sag resistance required for the bolt. The flange portion 4 can be easily formed. For this purpose, the tensile strength and deformation resistance value of the aluminum alloy wire rod material as the bolt material are defined within a certain range.

That is, in the present invention, when the flanged head portion of the flange bolt is formed, the tensile strength of the 6000 series aluminum alloy wire rod having the specific composition subjected to the hot rolling, wire drawing and heat treatment is 150 MPa or more. , 300 MPa or less. At the same time, the deformation resistance value measured and calculated by a drop test under the following conditions of this aluminum alloy wire rod is set to 350 kg / mm ² or less.

  Thus, in the present invention, the strength and deformation resistance value of the 6000 series aluminum alloy wire rod having the specific composition that has been hot-rolled, drawn, and heat-treated are specified, and although the strength is high, First, the formability of the flange bolt head having a complicated shape, high strength, and a small diameter is improved. In this regard, in the present invention, in the macro sense, instead of observing a microscopic structure such as SEM or TEM, the structure of the 6000 series aluminum alloy wire rod is similar to the average crystal grain size described below. It can be said that it is defined by strength and deformation resistance value.

  In the field of rolled material as in the present invention, the strength and formability of the 6000 series aluminum alloy wire rod (rolled material) are interestingly related to the formability of the flanged head of the flange bolt. It is different from general correlation. That is, it cannot always be said that the lower the strength, the higher the moldability.

  As will be described later, the 6000 series aluminum alloy wire rod (rolled material) of the present invention has higher strength than known 6000 series aluminum alloy wire rod (rolled material) such as 6061. Nevertheless, the deformation resistance value by the specific measuring method is low, and the complex bolt shape, high strength, and small diameter flange bolt head formability are excellent. This is a peculiar phenomenon, and according to the technical common sense, a known 6000 series aluminum alloy wire rod (rolled material) such as 6061 having a lower strength is superior in formability of the flange bolt head. It should be.

  The 6000 series aluminum alloy wire rod (rolled material) of the present invention has a lower strength than known 6000 series aluminum alloy wire rod (rolled material) such as 6056, but is deformed by the specific measurement method. The resistance value is low, and the formability of the flange bolt head having a complicated shape, high strength, and a small diameter is excellent.

Strength:
As will be explained in the examples described later, the tensile strength of the aluminum alloy wire rod (rolled material) is set to 150 MPa in order to obtain the complex shape and the formability of the flange bolt head having a high strength and a small diameter. As mentioned above, it is necessary to make it 300 MPa or less, preferably 250 MPa or less. On the other hand, in order to set the tensile strength of the flange bolt to 350 MPa or more, it is necessary to set the tensile strength of the aluminum alloy wire rod before forming the flange bolt head to 150 MPa or more. When the tensile strength is less than 150 MPa, the tensile strength of the material is too low, and the flange bolt has a tensile strength of 350 MPa or more even by artificial age hardening after molding of the flanged head of the flange bolt. It can not be.

Deformation resistance value:
Moreover, in addition to the tensile strength of this aluminum alloy wire rod material, as demonstrated in the examples described later, in order to obtain the complex shape and formability of the flange bolt head having a high strength and a small diameter, The deformation resistance value measured and calculated by the drop test under the following conditions needs to be 350 kg / mm ² or less, preferably 300 kg / mm ² or less, more preferably 250 kg / mm ² or less.

  As described above, in the 6000 series aluminum alloy wire rod having the specific composition that has been hot-rolled, drawn, and heat-treated, the strength and the deformation resistance value are constant with respect to the formability of the flange bolt head. There is a correlation. That is, both the high strength required for the aluminum alloy flange bolt and the formability to the aluminum alloy flange bolt are satisfied unless the strength and the deformation resistance value satisfy the range defined in the present invention. I can't.

c. Test material for drop test:
The test material for the drop test is the flange whose tensile strength and deformation resistance value are adjusted and tempered after the hot rolling, wire drawing and, in the case of the present invention, after wire drawing or by annealing in the middle. The wire rod material before forming the bolt head. Here, the length of the test material is kept constant at 12 mm. In order to improve the measurement accuracy and reproducibility of the deformation resistance value measured in the drop test, it is originally preferable that not only the length of the test material but also the diameter is constant. However, the product diameter of the wire rod material to be drawn varies, and in the actual continuous wire drawing process, it is practically impossible to collect from the middle of the process before making the final wire diameter. .

c. Dropping test:
The drop test for measuring the deformation resistance value simulates the header processing (molding) of the head 2 with the flange 4 of the flange bolt 1, but as described above, this header workability (bolt head formability). ) And the deformation resistance value measured in the drop test. In order to further ensure the test accuracy and reproducibility of the drop test data, the specific conditions shown in FIG. That is, as shown in FIG. 2, in a state where the cylindrical test material 5 is erected on a rigid body 6 made of steel or the like, a weight 7 weighing 70 kg from above is placed on the rigid body 6 toward the cylindrical test material 5. To the weight 7 is set to 1200 mm, and the free fall is performed.

d. Deformation resistance value:
The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm). This condition is intended to process the test material 5 (wire rod material) by 50% in order to further correlate (simulate) the drop test with respect to the header processing in consideration of the processing amount of the header processing. It is a numerical condition. That is, in actual header machining, for example, in machining M8 bolts, a φ7 strand is machined to form a bolt head with a flange diameter of φ17.5 to φ14.5. did.

b. Structure-grain refinement:
In the present invention, the average grain size of the crystal grains of the 6000 series aluminum alloy wire rod material structure as the bolt material is refined to 50 μm or less as described above, and the above-described strength and formability to the bolt are improved. In addition, corrosion resistance such as intergranular corrosion resistance is also improved. When the average grain size of the crystal grains exceeds 50 μm and becomes coarse, the above-described strength and formability to bolts are lowered. In addition, corrosion resistance such as intergranular corrosion resistance is reduced.

Measurement of average grain size:
The average crystal grain size of the center part (shaft center part) of the wire rod is measured by the following method. The crystal grain size referred to here is a crystal grain size in the rolling direction (axial direction) in a cross section cut along the rolling direction (axial direction) of the wire rod. The crystal grain size is observed using a 50 × optical microscope after a longitudinal section in the rolling direction of the wire rod material is pretreated by mechanical polishing and electrolytic etching. At this time, a straight line is drawn in the rolling direction, and a section length of each crystal grain positioned on the straight line is measured by a cutting method (line intercept method) in which each crystal grain size is measured. This is measured at 10 arbitrary locations, and the average crystal grain size is calculated. At this time, the length of one measurement line is 0.5 mm or more, and three measurement lines per one visual field are observed, and five visual fields are observed per one measurement point. The average grain size measured sequentially for each measurement line is averaged sequentially per field of view (3 measurement lines), per 5 fields of view / 1 measurement point, and 10 measurement points, and the average crystal grain referred to in the present invention. The diameter.

Structure-crystal precipitates and dispersed particles:
Here, in order to guarantee the quality of the aluminum alloy wire rod and bolt, it is premised that there are no coarse crystal precipitates and dispersed particles in the structure of the aluminum alloy wire rod (bolt). Due to the inclusion of the alloy elements described above, crystal precipitates and dispersed particles are inevitably generated in the structure of the aluminum alloy wire rod and bolt. When these crystal precipitates and dispersed particles are coarsened, the formability to the bolt is remarkably lowered, and the basic characteristics of the bolt, such as sag resistance, are significantly impaired. When producing the aluminum alloy wire rod, if the production method and conditions such as hot rolling are performed within the preferable condition range as described later, the crystal precipitates and the dispersed particles are usually not coarsened. Incidentally, as a guideline for the absence of coarse crystal precipitates and dispersed particles, the average density of coarse crystal precipitates having a maximum length of 10 μm or more is 500 pieces / mm ² or less, and the maximum length is 800 nm. No over dispersed particles are observed.

Production method:
The method for producing an aluminum alloy rolled wire rod as a bolt material in the present invention will be described below in the order of steps. The structure and characteristics of the above-described 6000 series aluminum alloy wire rod can be manufactured by a combination or synergistic effect of the above-described 6000 series aluminum alloy with the specific composition and processing into a wire rod by hot rolling.

  That is, as a premise for obtaining the structure and characteristics of the wire rod material, the structure of the wire rod material having the specific composition is a rolled structure. After such hot rolling, the 6000 series aluminum alloy wire rod before being formed into a bolt after further drawing is performed to obtain a wire rod material having a predetermined diameter and shape and heat treatment. The structure and characteristics of the material are the above-described structure and characteristics.

(Dissolution, casting cooling rate)
First, in the melting and casting process, a molten aluminum alloy melt-adjusted within the above-mentioned 6000 series component composition range is cast by appropriately selecting a normal melting casting method such as a semi-continuous casting method (DC casting method).

(Homogenization heat treatment)
Prior to hot rolling, the cast aluminum alloy billet (ingot) is subjected to homogenization heat treatment (soaking) in the range of 470 to 565 ° C. to homogenize the structure (segregation within the crystal grains in the ingot structure). Etc.). The soaking temperature is selected from the range of 470 to 565 ° C., and the homogenization time is selected from the range of 2 hours or more.

  If the soaking temperature is too high, the dispersed particles in the wire rod material structure become coarse, and the average grain size of the crystal grains cannot be reduced to 50 μm or less. Further, the softening resistance is also lowered. On the other hand, even if this soaking temperature is too low, fine dispersed particles are insufficient, and the average grain size of crystal grains cannot be reduced to 50 μm or less. Further, the softening resistance is also lowered.

  After this soaking, it is preferable to forcibly quench the billet (ingot) with a fan or the like to increase the cooling rate. If the cooling rate is slow, such as letting the billet (ingot) cool, there is a risk that the MgSi compound (crystal precipitates) will become coarse during the cooling process. The standard of the average cooling rate in such rapid cooling is preferably 80 ° C./hr or higher up to a temperature of 300 ° C. or lower including room temperature.

(Hot rolling)
As a premise for obtaining the structure and characteristics of the wire rod material, the wire rod material structure is a rolled structure. At this time, in order to refine crystal grains, it is preferable to perform hot rolling at low temperature and strong processing on the billet after the homogenization treatment. For this reason, the hot rolling start temperature (hot rolling start temperature) is in the range of 320 to 520 ° C., preferably in the range of 320 to 485 ° C., depending on the composition of the aluminum alloy and the size of the ingot. It is preferably selected from the lowest possible temperature in the range of 320 to 470 ° C. When the hot rolling start temperature is too high, the rolling is not performed at a low temperature, and there is a high risk that the crystal grains cannot be refined as defined in the present invention. On the other hand, if the hot rolling start temperature is too low as less than 320 ° C., the rolling load is particularly excessive in the hot rolling in the strong working, and the rolling of the wire rod itself becomes difficult. In the present invention, the hot rolling start temperature is inevitably lower than the soaking temperature. Therefore, after the soaking, cooling is performed from the homogenizing heat treatment temperature, and hot rolling is started as the hot rolling start temperature. To do. Further, after the homogenization heat treatment, it may be once cooled to room temperature, reheated to the hot rolling start temperature, and hot rolling may be started at this reheating temperature.

  The hot rolling processing rate is also selected from the range of 70% or higher processing rate as high as possible depending on the composition of the aluminum alloy and the relationship between the ingot size and the wire rod diameter. If the processing rate is too small, there is a possibility that the crystal grains cannot be refined as defined in the present invention.

  Here, hot rolling is a hot extrusion method in which a wire rod having a circular cross section (round) can be produced without causing new problems or other problems with the structure and characteristics of the present invention. It is much better than For example, in the case of a wire rod having a round cross-sectional shape as the object of the present invention, the shape is simple in extrusion, unlike the case of a shape having a complicated shape. For this reason, the shape of the die is also simplified, and the center portion of the billet (ingot) is extruded as it is as the center portion of the wire rod material without being processed by the die, and the center portion of the wire rod material is The cast structure of the billet tends to remain as it is. In other words, in the central part of the wire rod produced by hot extrusion, the coarse crystal grain structure present in the cast structure of the billet remains coarse and is crystallized as defined in the present invention. The grains cannot be refined.

  Contrary to this central portion, the billet surface is more strongly processed and easily heated, and the crystallized material having a relatively low melting point present on the billet surface is locally melted and easily adhered to a die or the like. For this reason, the surface of the wire rod material during extrusion is peeled off, causing a phenomenon called mushy, and the surface failure of the wire rod material called pickup tends to occur. In order to prevent such defects of the extruded material, it is necessary to increase the soaking temperature or reduce the amount of transition elements in order to reduce the crystallized matter on the surface. However, as described above, when the soaking temperature is increased, the dispersed particles become coarse, and when the amount of the transition element is decreased, the dispersed particles are reduced and the density is reduced, and the crystal grains cannot be refined as defined in the present invention. . Thus, in the hot extrusion process, it is difficult to produce a wire rod having a structure and characteristics as in the present invention. This is the reason why when manufacturing a wire rod having a circular cross section for a flange bolt, the conventional manufacturing by extrusion as in Patent Document 1 has a large problem in the formability to the flange bolt.

(Heat treatment of wire rod)
When wire rod material that has been coiled and coiled after hot rolling is further cold drawn, heat treatment such as annealing treatment for wire rod material during or after wire drawing (Tempering) is performed, and the strength and deformation resistance value of the wire rod material before forming into the flange bolt are mainly adjusted within the range specified in the present invention. In addition, during this wire drawing or after wire drawing, a solution treatment and a rapid cooling (quenching) treatment described later may be performed.

(Molding)
The wire rod material whose strength, deformation resistance value, and average crystal grain size are adjusted within the scope of the present invention is formed into the flange bolt (flanged bolt) shown in FIG. In this forming, first, the head of the flange bolt 1 is formed by header processing of a wire rod cut to an appropriate bolt length. That is, a head structure in which a hexagonal bolt head 2 and a flange 4 are integrally provided on the lower peripheral edge of the bolt head 2 is formed. Next, the male screw portion 3 that is a shaft portion into which a screw (thread) has been cut is formed, usually by an economical thread rolling process or by a thread cutting process with high shape accuracy but high cost. At this time, whether or not to cut the screw over the entire length of the male screw portion 3 (full screw) is appropriately selected according to the application. Also, the bolt head periphery shape is not only a regular hexagon, but also a square or a circle, and the bolt head groove shape is also appropriately selected according to the application when there is no minus groove, plus (cross) groove, or no groove. The A well-known thing can be used for the said header processing machine, a thread rolling processing machine, or processing conditions. Note that these header processing machine and screw rolling processing machine are also disclosed in FIG. 1 of Patent Document 1 as a simple hexagon bolt forming machine having no flange at the head.

(Bolt heat treatment)
The flange bolt thus formed is subjected to a heat treatment (tempering) such as a solution treatment or an artificial age hardening treatment, so that the flange bolt satisfies the basic characteristics such as strength and sag resistance. Of course, the tempering may be performed before the male thread portion 3 is molded, such as the rolling process.

  The solution treatment is preferably performed at a temperature of 500 ° C. in order to sufficiently precipitate aging precipitates that contribute to strength improvement by the artificial age hardening treatment after flange bolt forming and the relationship with the composition of the aluminum alloy. 570 is performed under the condition of holding for a predetermined time. Immediately after the solution treatment, rapid cooling (quenching) is performed at a cooling rate of 10 ° C./second or more. When the cooling rate of the rapid cooling treatment after the solution treatment is slow, Si, MgSi compounds and the like are likely to precipitate on the grain boundaries, and mechanical properties and formability are deteriorated.

  The artificial age hardening treatment of the flange bolt after the flange bolt molding is preferably performed at a high temperature aging treatment at 150 to 200 ° C. in order to improve mechanical properties such as the strength of the wire rod. By such an aging treatment, the tensile strength of the flange bolt is set to 350 MPa or more.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  Next, examples of the present invention will be described. After casting the 6000 series aluminum alloy shown in Table 1, it is subjected to hot rolling at a soaking temperature, a hot rolling start temperature and a hot rolling process rate shown in Table 2, and then by drawing and annealing after this drawing, And wire rods having different cross-sections and different cross-sections were manufactured. And various characteristics, such as the moldability to the bolt with a flange of these wire rod materials, the mechanical characteristic of a bolt with a flange, and corrosion resistance, were evaluated.

Bar material manufacturing conditions:
More specific production conditions for the aluminum alloy wire rod are as follows. A 6000 series aluminum alloy having each composition shown in Table 1 was cast into a billet (ingot) by a semi-continuous casting method. These billets were changed in diameter in order to change the hot rolling rate, and were soaked for 4 hours (hr) in common at the soaking temperature shown in Table 2. And after cooling to room temperature once after that, it reheats to each hot rolling start temperature shown in Table 2, it hot-rolls with the processing rate shown in Table 2, and the cross section of 13 mm diameter is circular in common. Manufactured. Here, the billet after the soaking was forcibly quenched by a fan, and the average cooling rate up to 300 ° C. or less was set to 150 ° C./hr.

  Further, after the hot-rolled wire rod was peeled, the wire rod was cold-drawn at a working rate shown in Table 2 to a wire rod with a 3.5 mmφ cross-section in a cold state. The thinned wire rod material was annealed in common at the annealing temperatures shown in Table 2 for 4 hours (hr), and finally tempered (adjusted) the tensile strength and deformation resistance value. .

Bar material structure and properties:
The average crystal grain size (μm), tensile strength (MPa), deformation resistance value (kg / mm ² ) of these aluminum alloy wire rods before header processing for forming the flanged head of the flange bolt Each was measured by the method described above. In addition, the tensile strength was measured on the same conditions as the tensile test of the flange bolt after the shaping | molding mentioned later. These results are also shown in Table 2. Here, the deformation resistance value was obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (2649 mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).

Here, the presence or absence of coarse crystal precipitates and dispersed particles was examined in the structure of these aluminum alloy wire rods. As a result, in all of the inventive examples including the comparative example, the average density of coarse crystal precipitates having a maximum length of 10 μm or more is 500 pieces / mm ² or less, and dispersed particles having a maximum length exceeding 800 nm are observed. There wasn't. The measurement surface of the average density of the crystal precipitates is the central part of any cross section parallel to the longitudinal direction (axial direction) of the aluminum alloy wire rod, and the scanning electron microscope (SEM) of the structure at the position of the central part of these parallel cross sections ) And observed at 1000 times magnification. The measurement surface of the dispersed particles is the same as that of the crystal precipitate, and a thin film sample is prepared from the central part of these parallel cross sections, and the magnification is 5000 times using a TEM (transmission electron microscope) attached to the component analyzer. And observed.

Rod material molding:
The 7 mm wire rod after the tempering is cut to a predetermined length, the header is processed in the cold, and the bolt head of the flange bolt of FIG. 200 pieces were molded. At this time, the hexagonal flat diameter of the head 2 was 12 mm, the diameter of the flange 4 was 15 mm, the thickness of the tip was 1 mm, and the length was 50 mm. Thereafter, the thread of the male thread portion 3 was further formed by rolling with all screws. In addition, in the case of header processing, those in which a crack or the like occurred in the flange 4 or the head 2 were not subjected to subsequent rolling processing. These molding conditions correspond to the complex shape and diameter described above and the moldability of high-strength flange bolts.

Formability of rod material:
Even when these flange bolts are formed, the formability (header processability) of the bolt head is evaluated, and even if it is efficiently processed at a normal header processing speed, defects such as cracks do not occur in the flange 4. In addition, an example in which 100 heads of a total amount of bolts could be processed soundly was evaluated as ◯. On the other hand, when processing at the normal header processing speed, several defects such as cracks occur, and even if the header processing conditions are relaxed by reducing the degree of processing, the defects such as cracks are An example where it still occurred and it was judged that the moldability of the head was poor (impossible) was evaluated as x. In addition, although the defect such as the crack is generated and the formability is poor, if it is determined that the processing of the header portion of the header can be eased by reducing the degree of processing, etc. evaluated. Further, the rolling processability of the thread of the male screw portion 3 was also evaluated based on the same criteria. These results are also shown in Table 2.

Tempering after rolling:
The flange bolt after the rolling process (formed) was subjected to a solution treatment at 5760 ° C. for 3 hours, then water-quenched to room temperature, and then immediately subjected to a high temperature aging treatment at 180 ° C. for 9 hours. These are tempering treatments for increasing the strength to obtain the basic characteristics such as sag resistance as flange bolts. Then, the mechanical properties and corrosion resistance of these tempered flange bolts were measured and evaluated. These results are also shown in Table 2.

mechanical nature:
As for the mechanical properties, a tensile test was performed on the flange bolt after the tempering at a crosshead speed of 5 mm / min at room temperature until breakage using a tensile tester shown in FIG. From the stress-strain rate, tensile strength (MPa) and 0.2% yield strength (MPa) were measured. Elongation (%) was calculated from the spacing of the marking lines before and after the tensile test of the flange bolt during the tensile test (interval of 10 mm before the tensile test). In addition, these measured values were made into the average value of each measured value of three flange bolts in each example.

Corrosion resistance:
In order to evaluate the corrosion resistance, a corrosion test was carried out in accordance with the method described in the section 4.4.3 of the JIS-W1103 method of each test material. That is, the corrosion test conditions were as follows. First, the sample was immersed in an etching solution at 93 ° C. (composition of 70% concentrated nitric acid 50 ml, 48%, hydrofluoric acid 5 ml, distilled water 945 ml), washed with distilled water and dried. It was. Thereafter, it was immersed in a corrosion accelerating solution at 30 ° C. (57 g of NaCl, 10 ml of 30% hydrogen peroxide solution diluted to 1 liter with distilled water) for 6 hours. Then, the test specimen parallel section was immersed in an etching solution (composition of 70% concentrated nitric acid 2.5 ml, concentrated hydrochloric acid 1.5 ml, 48% hydrofluoric acid 1.0 ml, distilled water 95.0 ml) for 10 seconds, followed by distillation. Washed with water and dried. The corrosion state of this test piece parallel cross section was observed with a 200-fold metal microscope. In the observation of the corrosion, the degree of corrosion was judged using 6061-T6 as a comparative material in the microscope field of view, distinguishing it from other pitting corrosion and general corrosion. That is, the case where the degree of corrosion was large as compared with the comparative material was evaluated as x, equal to or less than or equal to ○.

  The aluminum alloy of each invention example of the alloy numbers 1-8 of Table 1 is in this invention component composition range. Inventive Examples 1 to 8 in Table 2 using these are hot-rolled and tempered at a low temperature and with a strong work within the above-described preferable condition range. For this reason, as shown in Table 2, the wire rods of these invention examples have a structure and characteristics that satisfy the ranges of the average crystal grain size, tensile strength, and deformation resistance defined in the present invention.

  As a result, as shown in Table 2, each invention example is excellent in the above-described complicated shape, small diameter and high-strength flange bolt formability, in particular, flange bolt head formability (the header workability), The rolling processability of the thread of the male thread is also excellent. In addition, the heat treatment after molding provides a high strength of 350 MPa or more as a flange bolt, and is excellent in corrosion resistance, satisfying the basic characteristics such as sag resistance required for the bolt.

On the other hand, the aluminum alloy of each comparative example of alloy numbers 9 to 18 in Table 1 has a component composition outside the scope of the present invention.
The comparative example 9 has too little Mn content (it does not contain Mn).
The comparative example 10 has too little Cu content (it does not contain Cu).
Comparative Example 11 has too little Zr content (does not contain Zr).
Comparative Example 12 has too much Cr content and Comparative Example 13 has too much Si content.
Comparative Example 14 has too much Mg content.
The comparative example 15 has too little Mg content.
The comparative example 16 has too little Si content.
Comparative Example 17 is a conventional 6061 alloy composition in which the Si content is too low and the Mg content is too high.
Comparative Example 18 is a conventional 6056 alloy composition in which the contents of Cu, Mn, and Zn are too large.

  Therefore, as shown in Table 2, wires of Comparative Examples 9 to 16, 19 (17, 6061 alloy of Table 1), 20 (18, 6056 alloy of Table 1) using the comparative example alloys of Table 1 above. Although the rod is subjected to hot rolling and tempering at a low temperature and strong processing within the above-mentioned preferable condition range, it satisfies the range of the average crystal grain size, tensile strength, and deformation resistance defined in the present invention. It doesn't have organization and characteristics. As a result, as shown in Table 2, the wire rod material of each comparative example is inferior in the formability of the above-mentioned complicated shape, small diameter and high strength flange bolt, or as a flange bolt by heat treatment after molding. A high strength with a tensile strength of 350 MPa or more has not been obtained. There are also cases where the corrosion resistance is poor. Therefore, the basic characteristics required for bolts are not satisfied.

  In particular, the 6061 alloy example of Comparative Example 20 satisfies the range of the average crystal grain size, tensile strength, and deformation resistance defined in the present invention in the characteristics before flange bolt head forming, but the heat treatment after bolt forming. However, the tensile strength is low as a flange bolt, and a high strength of 350 MPa or more is not obtained. Further, the 6056 alloy example of Comparative Example 21 is a characteristic before forming the flange bolt head, which is outside the range of the deformation resistance value defined in the present invention. As a result, as shown in Table 2, the wire rod material of this 6056 alloy example is inferior in formability of the above-described complicated shape, small diameter, and high strength flange bolt. Moreover, since these are the results of the rolled material, in the case of extruded materials of these alloys, these properties are still inferior or cannot be obtained because the uniformity of the structure is inferior to that of the rolled material. Can easily be expected.

  Further, Comparative Examples 17 and 18 in Table 2 use the alloy of Alloy No. 1 that is within the composition range of the present invention shown in Table 1, but in the above-mentioned preferable condition range, hot rolling at low temperature and strong working Is not done. In Comparative Example 17, the hot rolling start temperature is too high. In Comparative Example 18, the hot rolling start temperature is low, but the hot rolling reduction is too low. For this reason, as shown in Table 2, the wire rod materials of these comparative examples do not have the structure and characteristics satisfying the range of the average crystal grain size, tensile strength, and deformation resistance value defined in the present invention. As a result, as shown in Table 2, the wire rod material of each comparative example is inferior in the formability of the above-mentioned complicated shape, small diameter and high strength flange bolt, or as a flange bolt by heat treatment after molding. A high strength with a tensile strength of 350 MPa or more has not been obtained. There are also cases where the corrosion resistance is poor. Therefore, the basic characteristics required for bolts are not satisfied.

  Therefore, from the results of the above examples, the critical significance for satisfying the basic characteristics as the flange bolt, the formability to the flange bolt of each component of the wire rod material in the present invention, the structure, and the characteristics requirements. The effect is supported. Further, the critical significance or effect for obtaining the structure and characteristics of the wire rod material in the present invention in the preferable production conditions of the wire rod material is supported.

  According to the present invention, a 6000 series aluminum alloy wire rod excellent in formability, a method for producing the same, and a high strength 6000 series aluminum alloy flange satisfying the basic characteristics such as sag resistance by this wire rod material. A bolt and a manufacturing method thereof can be provided. Therefore, the present invention can be suitably used as a fastening bolt that does not require a washer, such as an aluminum material or a magnesium material of an automobile part that has been reduced in weight.

1: flange bolt, 2: hexagonal bolt head, 3: male thread, 4: flange, 5: cylindrical test material, 6: rigid body, 7: weight

Claims (11)

An aluminum alloy wire rod for a high-strength bolt excellent in formability, characterized by having the following requirements a to e.
a. The said aluminum alloy wire rod is mass%, Mg: 0.5-1%, Si: 0.7-1.2%, Cu: 0.4-0.8%, Mn: 0.05-0 .6%, Ti: 0.01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, respectively, and the balance Al and inevitable impurities Al A wire rod material having a diameter of 12 mmφ or less, produced by hot rolling, wire drawing and heat treatment of an ingot of a Mg—Si composition.
b. The average crystal grain size of the center portion of the aluminum alloy wire rod before forming the bolt head is 50 μm or less, the tensile strength is 150 MPa or more and 300 MPa or less, and is measured and calculated by a drop test under the following conditions. The deformation resistance value is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. The aluminum alloy wire rod is formed into a bolt having a tensile strength of 350 MPa or more by heat treatment after the bolt head is formed.   The aluminum alloy wire rod for high-strength bolts with excellent formability according to claim 1, wherein the aluminum alloy wire rod has a tensile strength of 150 MPa or more and 250 MPa or less. The aluminum alloy wire rod for a high-strength bolt excellent in formability according to claim 1 or 2, wherein the high-strength bolt is a flange bolt having a nominal diameter of M6 to M12.   The aluminum alloy wire rod for a high-strength bolt excellent in formability according to any one of claims 1 to 3, wherein the high-strength bolt is a hexagon bolt.   The aluminum alloy wire rod for a high-strength bolt with excellent formability according to any one of claims 1 to 4, wherein the high-strength bolt fastens a magnesium material or an aluminum material without interposing a washer. The manufacturing method of the aluminum alloy wire rod material for high strength bolts excellent in the moldability characterized by having the requirements of following ae.
a. In mass%, Mg: 0.5 to 1%, Si: 0.7 to 1.2%, Cu: 0.4 to 0.8%, Mn: 0.05 to 0.6%, Ti: 0.00. A casting of Al-Mg-Si composition comprising 01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, and the balance being Al and inevitable impurities After the ingot is melted and the ingot is homogenized and heat-treated, hot rolling with a processing rate of 70% or more is performed at a processing start temperature in the range of 320 to 470 ° C. The aluminum alloy wire rod is 12 mmφ or less.
b. The average grain size of the aluminum alloy wire rod before forming the bolt head is 50 μm or less, the tensile strength is 150 MPa or more and 300 MPa or less, and is measured and calculated by a drop test under the following conditions. The deformation resistance value is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. The aluminum alloy wire rod is formed into a bolt having a tensile strength of 350 MPa or more by heat treatment after the bolt head is formed. A high-strength flange bolt having a nominal diameter of M6 to M12 and formed of an aluminum alloy wire rod having the following requirements a to e.
a. The said aluminum alloy wire rod is mass%, Mg: 0.5-1%, Si: 0.7-1.2%, Cu: 0.4-0.8%, Mn: 0.05-0 .6%, Ti: 0.01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, respectively, and the balance Al and inevitable impurities Al A diameter of 12 mmφ or less is produced by hot rolling, wire drawing, and heat treatment of an ingot of a Mg—Si composition.
b. The average crystal grain size of the center portion of the aluminum alloy wire rod before forming the bolt head is 50 μm or less, the tensile strength is 150 MPa or more and 300 MPa or less, and is measured and calculated by a drop test under the following conditions. The deformation resistance value is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. The flange bolt has a tensile strength of 350 MPa or more by heat treatment after the bolt head is formed.   The high strength flange bolt according to claim 7, wherein the tensile strength of the aluminum alloy wire rod is 150 MPa or more and 250 MPa or less.   The high-strength flange bolt according to claim 7 or 8, wherein the high-strength bolt is a hexagon bolt.   The high-strength flange bolt according to any one of claims 7 to 9, wherein the high-strength flange bolt fastens a magnesium material or an aluminum material without interposing a washer. A manufacturing method of a flange bolt having a nominal diameter of M6 to M12 having the following requirements a to e.
a. In mass%, Mg: 0.5 to 1%, Si: 0.7 to 1.2%, Cu: 0.4 to 0.8%, Mn: 0.05 to 0.6%, Ti: 0.00. A casting of Al-Mg-Si composition comprising 01 to 0.05%, Zr: 0.05 to 0.25%, Cr: 0.05 to 0.25%, and the balance being Al and inevitable impurities The ingot is melted and the ingot is homogenized and heat-rolled, and then hot-rolling with a processing rate of 70% or more is performed at a processing start temperature in the range of 320 to 470 ° C. Aluminum alloy wire rod.
b. When this aluminum alloy wire rod is processed into a header to form a flanged head of the flange bolt, the average grain size of the center portion of this aluminum alloy wire rod is 50 μm or less, and the tensile strength is In addition to 150 MPa or more and 300 MPa or less, the deformation resistance value measured and calculated by a drop test under the following conditions is 350 kg / mm ² or less.
c. In the drop test, the aluminum alloy wire rod material is erected on a rigid body as a test material, and a weight weighing 70 kg from above is applied to the test material, and the drop height from the rigid body to the weight is measured. Is set to 1200 mm and allowed to fall freely.
d. The deformation resistance value is obtained by the following equation. Deformation resistance value (kg / mm ² ) = (M × H) / [V × In (h0 / h1)], where M is the weight of the weight (70 kg), and H is the weight drop height (1200 mm ), V: test material volume (mm ³ ), h0: height of test material before drop test (12 mm), h1: height of test material after drop test (mm).
e. After forming the flanged head portion of the flange bolt, the tensile strength of the flange bolt is set to 350 MPa or more by heat treatment.

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