JPH1030147A - Aluminum-zinc-magnesium alloy extruded material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit recrystallization by T6 treatment after plastic working of an Al-Zn-Mg alloy extruded material and to improve strength, toughness, and stress corrosion cracking resistance by the same. SOLUTION: The Al-Zn-Mg alloy extruded material has a composition consisting of, by weight, 4.00-6.50% Zn, 0.5-1.50% Mg, 0.1-0.5% Cu, 0.10-0.50% Zr, further either or both of 0.05-0.20% Mn and 0.05-0.20% Cr, and the balance Al with inevitable impurities. In this case, the value of (elongation)/(tensile strength) of the T6-treated material is regulated to >=0.030, and further, sectional structure is all formed into fiber structure or recrystallized structure is allowed to exist in the part not higher than the position at a depth of 300μm in the surface layer, by which toughness and stress corrosion cracking resistance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an Al—Zn—Mg based material which is excellent in workability with an annealed material (0 material) and excellent in toughness and stress corrosion cracking resistance in a solution age hardened material (T6 material). The present invention relates to an alloy extruded material and a method for producing the same, and more particularly to a molded member for an automobile, such as a bumper, a main frame for a two-wheeled vehicle, a swing arm, or the like, which is used for electric and mechanical parts by cutting and forging, etc. The present invention relates to an extruded Mg-based alloy (extruded bar, extruded bar) and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, extruded profiles have a complicated cross-sectional shape and are hollow due to the needs of the industry, and are mainly subjected to forming (plastic working) such as bending, swaging, expansion, and bulging. Has become. The extruded rod is also subjected to secondary processing such as cutting and cold forging to obtain a predetermined shape, and then subjected to a heat treatment, that is, an age hardening treatment after a solution treatment (the material thus treated is hereinafter referred to as a T6 material). Therefore, the characteristic required of the Al alloy material is that the extruded material is excellent in various workability, and therefore, it is necessary to use a material softened by annealing treatment after extrusion (hereinafter referred to as "0 material"). However, in the case of Al-Zn-Mg-based conventional alloys, which are heat-treated alloys, if the T6 treatment is performed after plasticizing the softened extruded material, recrystallization occurs on the entire surface or most of the cross-section, resulting in extrusion. In addition to the occurrence of defects such as orange peel on the surface layer of the material and the occurrence of stress corrosion cracking, it is common that T6 treatment after plastic working is not performed. T6 treatment after forming processing results in excellent strength and toughness, and A material having excellent stress corrosion cracking properties could not be obtained.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems.
Improves various plastic workings (bending, swaging, bulge, upsetting, etc.) of the extruded Mg-based alloys with zero material, and the strength, toughness, and metal structure of T6 treated materials of such processed materials An Al-Zn-Mg based alloy extruded material having improved stress corrosion cracking resistance and a method for producing the same.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned situation, the present invention has made intensive studies and as a result, improved the workability by examining the alloy components and the conditions of the 0-piece annealing treatment after extrusion.
By examining the treatment conditions, the strength and toughness, structure, and stress corrosion cracking resistance of the extruded material after T6 treatment were improved. That is, the invention of claim 1 for solving the above-mentioned problem is based on Zn
4.00 to 6.50 wt%, Mg 0.50 to 1.50 w
t%, Cu 0.10 to 0.50 wt%, Zr 0.10
0.50wt%, Mn0.05 ~ 0.20wt%, Cr
An extruded Al alloy material containing 0.05 to 0.20 wt%, the balance being Al and unavoidable impurities, wherein the ratio of elongation / tensile strength of the T6 treated material is 0.03.
Al—Zn—Mg characterized by being excellent in toughness and stress corrosion cracking resistance in which the cross-sectional structure is not less than 0 and the entire cross-sectional structure is a fibrous structure or the recrystallized structure has a surface layer depth of 300 μm or less.
Extruded alloy

[0005] The invention according to claim 2 is based on Zn 4.00.
6.50 wt%, Mg 0.50 to 1.50 wt%, Cu
0.10-0.50wt%, Zr0.10-0.50w
t%, Mn0.05 ~ 0.20wt%, Cr0.05 ~
An Al alloy ingot containing 0.20 wt%, the balance being Al and unavoidable impurities, was cast at a temperature of 420 to 520 ° C.
After performing the homogenization heat treatment for ~ 24 hours, 430-520 ° C
Extrusion at a temperature of 300-420 ° C.
A method of producing an extruded Al-Zn-Mg alloy, characterized in that an annealing treatment is performed at a temperature of 30 ° C., and the material is cooled to room temperature at a cooling rate of 30 ° C./hr or less to obtain a material excellent in formability. And

A third aspect of the present invention relates to a method for manufacturing ZnO of 4.00 to 6.5.
0 wt%, Mg 0.50 to 1.50 wt%, Cu0.1
0 to 0.50 wt%, Zr 0.10 to 0.50 wt%,
Mn 0.05-0.20 wt%, Cr 0.05-0.2
An Al alloy ingot containing 0 wt% and the balance consisting of Al and unavoidable impurities was cast at a temperature of 420 to 520 ° C. for 2 to 24 hours.
After the homogenizing heat treatment for a time, extrusion is performed at a temperature of 430 to 520 ° C., and then an annealing treatment is performed at a temperature of 300 to 420 ° C., which is cooled to room temperature at a cooling rate of 30 ° C./hr or less. After cooling, this is subjected to a forming process. Subsequently, it is subjected to a solution treatment at a temperature of 400 to 500 ° C., and is cooled to room temperature at a cooling rate of 50 ° C./hr or more.
The first-stage aging treatment at a temperature of 90 to 110 ° C. for 2 to 12 hours and the second-stage aging treatment at a temperature of 120 to 180 ° C. for 5 to 24 hours give a material having a ratio of elongation / tensile strength. An Al—Zn—Mg material having a cross-sectional structure of at least 0.030 and a fibrous structure or a recrystallized structure having a surface layer depth of 300 μm or less and having excellent toughness and stress corrosion cracking resistance. This is a method for producing an extruded alloy.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, the invention of claim 1 is an extruded material of an Al—Zn—Mg-based alloy.
This is a material obtained by subjecting a g-based alloy extruded material to molding and subjecting it to T6 treatment. First, the Al-Z according to the present invention
The reason for limiting the alloy composition of the extruded n-Mg alloy will be described. Zn has an effect of improving mechanical properties.
If the amount is less than 4.00% by weight, there is no effect, while if it exceeds 6.50% by weight, stress corrosion cracking resistance (hereinafter also referred to as SCC resistance), moldability and extrusion processability deteriorate, and productivity increases. Also decrease. Therefore, in the present invention, the amount of Zn added is limited to 4.00 to 6.50 wt%. Mg is
Although it is an element that improves mechanical properties, its effect is small when the amount of addition is less than 0.50 wt%.
If it is added in excess of 0 wt%, the stress corrosion cracking resistance, moldability and extrudability deteriorate, and productivity also decreases. Therefore, in the present invention, the addition amount of Mg is limited to 0.50 to 1.50 wt%.

[0008] Cu has the effect of improving mechanical properties and stress corrosion cracking resistance. If the amount is less than 0.10% by weight, the effect is not obtained. On the other hand, if the amount exceeds 0.50% by weight, the corrosion resistance is harmed. Therefore, in the present invention, the addition amount of Cu is 0.10 to 0.50.
wt%. Zr has the effect of suppressing the coarsening of the recrystallized grains in the alloy, stabilizing the structure with the crystal grains as a fibrous structure, and improving the formability such as bending and swaging. If the addition amount is less than 0.10 wt%, the effect is small. On the other hand, if the addition amount exceeds 0.50 wt%, a coarse Al-Zr-based intermetallic compound is formed to deteriorate toughness and the like. Therefore, in the present invention, the addition amount of Zr is set to 0.1.
It was limited to 10 to 0.50 wt%.

Mn and Cr coexist to prevent the recrystallization of the fibrous structure finely dispersed in the aluminum base, stabilize the structure, and extrude after forming such as bending and swaging. It has the effect of preventing orange peel-like roughening of the surface of the material. If the added amount is less than 0.05 wt%, the effect is small. Conversely, if the added amount exceeds 0.20 wt%, the effect is saturated, but a coarse intermetallic compound is formed or quenching sensitivity is increased. In addition, it has an adverse effect on strength and extrudability. Therefore, in the present invention, the addition amounts of Mn and Cr are each limited to 0.05 to 0.20 wt%. Further, impurities such as Ti, Ni, and B may be contained as long as each is 0.05 wt% or less, since the effects of the present invention are not adversely affected.

Next, the present material is a material obtained by subjecting an annealed material to bending, swaging or the like, and further performing a T6 treatment. The material has an elongation / tensile strength ratio of 0.030. The material limited to the above is intended for a structural member such as a molded member for an automobile, for example, a bumper, a main frame for a two-wheeled vehicle, and a swing arm. Due to the nature of the product, the material has toughness, that is, toughness. It is necessary. In the present invention, the ratio of elongation / tensile strength of the material was used as a measure of the toughness characteristics. In the present invention,
The reason why the cross-sectional structure of the material is all fibrous structure or recrystallized structure is limited to a surface layer depth of 300 μm or less is to improve the toughness characteristics and stress corrosion cracking resistance. In addition,
If the recrystallized structure has a surface layer depth of 300 μm or less, it can be removed by subsequent surface processing (processing with a buff, processing with a shot, etc.), so that there is no problem in the final product.

[0011] The invention of claim 2 is a method for producing A
The present invention relates to a method for producing an extruded l-Zn-Mg alloy. As described above, the extruded material is subjected to a forming process such as bending and swaging. In the present invention, particularly, in the cooling after annealing of the hot extruded material, the cooling rate is extremely slowed down. The moldability is improved. Further, the invention according to claim 3 is characterized in that, after the forming process, T
Al-Z according to the first aspect of the present invention.
The present invention relates to a method for producing an extruded n-Mg alloy.

In general, an extruded material of an Al—Zn—Mg alloy is generally subjected to press quenching or separate solution treatment of a homogenized heat-treated ingot by hot extrusion, followed by artificial aging treatment and hot extrusion. It is manufactured by a method of performing an annealing process after working, performing plastic working, and then performing a T6 process. The production method of the present invention achieves the object by using the Al alloy according to the present invention to limit the temperature conditions and processing time conditions at each stage of the latter production.

Hereinafter, the manufacturing conditions of each step in the manufacturing method of the second and third aspects will be described in detail. First, a homogenizing heat treatment is applied to the Al alloy ingot according to the present invention. The homogenizing heat treatment is performed at a relatively high temperature in order to finely and uniformly disperse compounds such as Zr, Mn, and Cr. However, 52
If the treatment is carried out at a temperature exceeding 0 ° C. or for more than 24 hours, recrystallization of the surface layer of the cross section after extrusion is promoted, or the precipitate is coarsened to deteriorate properties such as extrudability and quenching sensitivity. On the other hand, 42
If the treatment is performed at less than 0 ° C. or for less than 2 hours, homogenization is insufficient. Therefore, in the present invention, the homogenization heat treatment is performed in the range of 420 to 5 hours.
It is performed under the condition of 20 ° C. × 2 to 24 hours.

Next, the ingot is reheated to an extrusion temperature to perform hot extrusion. The extrusion temperature is set so that a thin hollow member having a large extrusion ratio, which is difficult to extrude, can be processed.
Perform at a high temperature of 0-520 ° C. When a conventional alloy is extruded at such a high temperature, recrystallization progresses and coarse recrystallized grains are generated, so that stress corrosion cracking resistance is significantly reduced, and coarse intermetallic compounds are formed. Workability, formability, corrosion resistance, etc. are deteriorated. However, in the alloy having the composition according to the present invention, the addition of Zr results in a fibrous structure without recrystallized grains, the progress of recrystallization is suppressed by dispersing Mn and Cr finely, and the addition of Cu further reduces the SC resistance.
Extrusion processing at high temperature is made possible by greatly improving the C property. If the extrusion temperature is lower than 430 ° C., it is difficult to extrude the hollow profile, and if it exceeds 520 ° C., the recrystallization of the surface layer of the cross section after extrusion is promoted, or the precipitates become coarse and extrudability, quenching sensitivity, etc. Characteristics are deteriorated. Therefore, the extrusion temperature is set to 430 to 520 ° C.

Next, the extruded material is subjected to an annealing treatment. Annealing is performed by bending, swaging, bulging, upsetting, etc. after annealing due to the coarse precipitation of solute elements in solid solution and the reduction of mechanical properties and hardness due to the formation of coarse intermetallic compounds. Plastic working becomes possible. However, annealing at a temperature exceeding 420 ° C. induces recrystallization and promotes an increase in strength due to insensitivity to quenching. Meanwhile, 3
If the temperature is lower than 00 ° C., the annealing treatment becomes insufficient. In addition, when cooling to room temperature after the annealing treatment, it is necessary to suppress the cooling rate to 30 ° C./hr or less. This is because if the cooling rate exceeds 30 ° C./hr, it is difficult to obtain a sufficient hardness of 0 material because the quenching sensitivity is insensitive. Therefore, the annealing conditions are 300 to 420.
It is necessary to anneal at a temperature of ° C and cool at a cooling rate of 30 ° C / hr or less.

Next, after the annealing, plastic working such as bending, swaging, bulging, upsetting and the like is performed. After the plastic working, it is necessary to perform T6 treatment (solution treatment and artificial aging treatment) like a normal heat treatment type alloy to improve mechanical properties. In the solution treatment, it is necessary to form a supersaturated solid solution in which a solute element is sufficiently dissolved in an aluminum base. However, if the solution treatment temperature exceeds 500 ° C., eutectic melting (burning) occurs, causing defects in the metal structure and deteriorating mechanical properties. On the other hand, if the temperature is lower than 400 ° C., the solution is insufficient. Note that the cooling rate after the solution treatment needs to be performed at 50 ° C./hr or more. Because 50 ℃
When the cooling rate is less than / hr, a supersaturated solid solution sufficient for imparting strength cannot be obtained, and further, the entire cross section of the extruded material is recrystallized, or coarse recrystallization occurs in the surface layer. Therefore, the solution treatment condition is performed at a temperature of 400 to 500 ° C., and the solution treatment needs to be cooled at a cooling rate of 50 ° C./hr or more.

Next, these materials are subjected to an artificial age hardening treatment. In this artificial aging treatment, a precipitate is finely deposited by heating the supersaturated solid solution obtained by the solution treatment at a low temperature. Specifically, the second stage aging is performed, and the fine precipitate of MgZn ₂ is uniformly dispersed by the first stage aging, and is grown into a coarse GP zone or an intermediate phase by the second stage aging. The first-stage artificial aging is performed at 90 to 110 ° C. for 2 to 12 hours in order to sufficiently finely precipitate and disperse and precipitate while preventing coarsening of the precipitate. The second-stage aging treatment is performed at a higher temperature than the first stage.
If the treatment is carried out at a temperature exceeding 80 ° C., MgZn ₂ precipitates coarsely and the formability and corrosion resistance deteriorate. On the other hand, if the treatment is performed at a temperature lower than 120 ° C., the growth into the GP zone or the intermediate phase becomes insufficient, and the strength becomes insufficient. Further considering the productivity, in the present invention, the aging treatment in the second stage is 120
The reaction is performed at a temperature of 180 ° C. for 5 to 24 hours.

As described above, the Al—Zn—Mg based alloy extruded material according to the production method of the present invention is subjected to plastic working (bending, swaging, bulge, upsetting, etc.) after annealing, and subsequently to Even when the T6 treatment is performed, the cross-sectional structure of the material can be all a fibrous structure or the recrystallized structure can have a surface layer depth of 300 μm or less. If the recrystallized structure has a surface layer depth of 300 μm or less, it can be removed by subsequent surface processing (processing with a buff, processing with a shot, etc.), so that there is no problem in the final product. Further, such a material is excellent in strength and toughness, and also excellent in stress corrosion cracking resistance.

[0019]

EXAMPLES Next, examples of the present invention (examples of the present invention) will be described in more detail in comparison with comparative examples and conventional examples. Table 1
Examples of the present invention (Nos. 1 to 4) and Comparative Examples (N
o. 5-7), and the alloy of the conventional example (No. 8-10) was DC
It was cast into an ingot for extrusion having a diameter of 219 mm by casting, and subjected to homogenization heat treatment under the conditions shown in Table 1. Thereafter, each was heated again to the extrusion temperature shown in Table 1, and was extruded into a hollow material (cross section: width 60 mm × height 60 mm × wall thickness 3.0 mm) and an extruded rod of φ20 mm. After the extrusion, annealing was performed under the annealing treatment conditions shown in Table 1, and then cooled to room temperature at a cooling rate shown in Table 1 to produce an annealed material (0 material). Only the 0-member shaped material after annealing was plastically worked into a square tube having a cross section of 40 mm wide × 40 mm high × 2.5 mm thick by square tube swaging, and then subjected to the solution treatment conditions shown in Table 1. (Considering the cooling rate). After the solution treatment, a two-stage artificial aging treatment shown in Table 1 was performed to prepare a test material.

[0020]

[Table 1]

Of these test materials, mechanical properties, swaging workability, and upsetting workability were evaluated for the 0 material, and the mechanical properties, metal structure, stress corrosion cracking test (salt water) for the T6 material were evaluated. Spray test and chromic acid accelerated test) were evaluated. The mechanical properties of the No. 0 material and the T6 material were determined by taking a JIS No. 5 tensile test specimen from the extrusion longitudinal direction and performing a tensile test.
Evaluation was made based on tensile strength, proof stress, and elongation. Further, for the T6 material, the ratio of elongation / tensile strength was determined. The higher the value, the more the material has toughness, and was used as a measure of the presence or absence of toughness. As described above, the swaging process is performed from a hollow profile (a square tube having a cross section of width 60 mm × height 60 mm × thickness 3.0 mm) with a cross section of width 40 mm × height 40 mm × thickness 2.5.
A plastic tube was subjected to plastic working, and the surface state after the working was visually observed and evaluated. For the upsetting process, use a 0-member extrusion rod,
The blank having a diameter of 20 mm and a height of 50 mm was subjected to upsetting in a cold state, and the rate of reduction in the height direction up to the crack limit was shown. Regarding the metal structure after T6, the cross-sectional microstructure of the surface layer of the material subjected to the T6 treatment after the swaging of the square tube was observed. The stress corrosion cracking test was evaluated by two kinds of tests, a salt spray test and a chromate accelerated test. In the salt spray test, stress was applied in a 3.5% NaCl solution by three-point bending (95% of the proof stress), and after one month of standing, the presence or absence of cracks was observed. In the chromic acid accelerated test, stress was applied to the chromic acid boiling solution by three-point bending (95% of the proof stress), and after holding for 12 hours, the presence or absence of cracks was observed. Table 2 shows the test results of these characteristics.

[0022]

[Table 2]

As is clear from Table 2, the present invention example No.
Nos. 1 to 4 are Comparative Example Nos. 5 to 7 and Conventional Example Nos. 8-10
Compared with No. 0, the workability such as swaging and upsetting is excellent due to the high elongation. In addition, the present invention example No. Nos. 1 to 4 also clearly show that the T6 material also has a high elongation / tensile strength ratio, excellent toughness of the material, and significantly improved metallographic structure and stress corrosion cracking resistance.

[0024]

As described in detail above, the conventional Al-Zn
-When extruded Mg-based alloys are subjected to T6 treatment after plastic working, recrystallization occurs on the entire surface or most of the cross-section, causing defects such as orange peel on the extruded material surface and stress corrosion cracking. Therefore, the T6 treatment after the plastic working is generally not performed, and a high-strength material subjected to the T6 treatment cannot be obtained.
6 treatments became possible. That is, the present invention relates to Al-Zn-M
It is excellent in various plastic working (bending, swaging, bulge, upsetting, etc.) of 0 g-alloy extruded material, and T6 treated material of such processed material has high strength and excellent toughness, Al-Zn with no problem in metal structure and stress corrosion cracking resistance
-An Mg-based alloy material is obtained, which has an industrially remarkable effect.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C22F 1/00 630 8719-4K C22F 1/00 630K 640 8719-4K 640A 682 8719-4K 682 683 8719 -4K 683 691 8719-4K 691C 8719-4K 691B 692 8719-4K 692A 694 8719-4K 694B

Claims (3)

[Claims] 1. 4.00 to 6.50 wt% of Zn, Mg
0.50 to 1.50 wt%, Cu 0.10 to 0.50 w
t%, Zr 0.10-0.50 wt%, Mn0.05-
An extruded Al alloy material containing 0.20 wt%, Cr 0.05 to 0.20 wt%, and the balance being Al and unavoidable impurities.
The tensile strength ratio is 0.030 or more, and the cross-sectional structure is all fibrous structure or recrystallized structure has a surface layer depth of 300 μm.
An Al-Zn-Mg based alloy extruded material characterized by having the following excellent toughness and stress corrosion cracking resistance. 2. 4.00 to 6.50 wt% of Zn, Mg
0.50 to 1.50 wt%, Cu 0.10 to 0.50 w
t%, Zr 0.10-0.50 wt%, Mn0.05-
After subjecting an Al alloy ingot containing 0.20 wt% and Cr 0.05 to 0.20 wt%, the balance being Al and unavoidable impurities, to homogenization heat treatment at a temperature of 420 to 520 ° C. for 2 to 24 hours, Extrusion is performed at a temperature of 430 to 520 ° C., then annealed at a temperature of 300 to 420 ° C., and cooled to room temperature at a cooling rate of 30 ° C./hr or less. A characterized in that
A method for producing an extruded l-Zn-Mg alloy. 3. 4.00 to 6.50 wt% of Zn, Mg
0.50 to 1.50 wt%, Cu 0.10 to 0.50 w
t%, Zr 0.10-0.50 wt%, Mn0.05-
After subjecting an Al alloy ingot containing 0.20 wt% and Cr 0.05 to 0.20 wt%, the balance being Al and unavoidable impurities, to homogenization heat treatment at a temperature of 420 to 520 ° C. for 2 to 24 hours, Extrusion is performed at a temperature of 430 to 520 ° C., then annealed at a temperature of 300 to 420 ° C., and cooled to room temperature at a cooling rate of 30 ° C./hr or less. And then apply this to 400
A solution treatment is performed at a temperature of up to 500 ° C.
After cooling to room temperature at a cooling rate of hr or more, 90-110
First stage aging treatment for 2 to 12 hours at a temperature of ° C.
A second-stage aging treatment is performed at a temperature of 20 to 180 ° C for 5 to 24 hours, and the ratio of elongation / tensile strength of the material is 0.030 or more, and the cross-sectional structure is all a fibrous structure or a recrystallized structure. Characterized by having a surface layer having a depth of 300 μm or less and having excellent toughness and stress corrosion cracking resistance.
A method for producing an extruded Mg-based alloy.