JP2017066523A - Al-Mg BASED HOT-DIP METAL COATED STEEL MATERIAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Mg based hot-dip metal coated steel material capable of remarkably improving corrosion resistance and workability.SOLUTION: The Al-Mg based hot-dip metal coated steel material includes a steel material and a metal coated layer including an Al-Fe alloy layer and Al-Mg alloy layer arranged on the surface of the steel material. The Al-Fe alloy layer is formed on the steel material surface and has a thickness of 100 nm or more and 15 μm or less. The Al-Mg alloy layer is formed on the Al-Fe alloy layer and includes 5 vol.% or more of an eutectic structure including a quasicrystal phase having an average circle equivalent diameter of more than 1 μm and an Al phase dispersed in the quasicrystal phase and having a crystal grain size of 2 μm. The chemical component composition of the Al-Mg alloy layer includes Zn:5-83% and Mg:2.5-35% by mass%.SELECTED DRAWING: None

Description

  The present invention relates to an Al—Mg hot-dip galvanized steel material excellent in corrosion resistance and workability.

  In the building materials field, a wide variety of hot dip plated steel sheets are used. Most of them are Zn-based plated steel sheets, but in recent years, the use of hot-dip plated steel sheets in which Al is added to the Zn-based plated layer to improve corrosion resistance has begun. In the field of building materials where a longer service life is desired, further high corrosion resistance technology is required, and plating disclosed in Patent Document 1 and Patent Document 2 has also been developed as a plated steel sheet that achieves high corrosion resistance by adding Mg. ing.

  The present inventors have been studying Zn-Al-based hot dipping containing Mg at a high concentration. Such plating is expected to exhibit unprecedented high corrosion resistance. If a hot-dip plated steel material containing Mg at a high concentration could be realized, the possibility of being applied to a field where high corrosion resistance was conventionally emphasized and hot-dip plated steel material could not be applied increased. One example of such an environment is the use of hot dip plated steel in the beach area.

  Since many marine-derived chlorides adhere to the plating surface of hot-dipped steel used in the beach area, even in the past, even if it is a highly corrosion-resistant Al-containing Zn plating layer, alumina on the plating surface layer Since the film becomes unstable due to adhesion of chloride, it was difficult to use in such an environment. When Mg is contained at a high concentration, the corrosion resistance is improved, so that it can be used in such an environment.

  On the other hand, since high corrosion resistance plated steel materials contain corrosion resistant elements in the plating layer, the formation of intermetallic compounds by alloying these elements with Zn, Al, or the like proceeds, resulting in the hardening of the plating layer. As a result, ductility is reduced, and the possibility of powdering and flaking phenomenon that the plating layer peels off during complicated processing is increasing. Even in the building material field, various processes such as bent bending and roll forming are applied to the plated steel material. However, when powdering and flaking occur, the application field of the plated steel material is limited.

  In order to avoid powdering and flaking phenomenon, it is necessary to introduce a phase having excellent ductility into the plating layer in order to soften the plating layer and improve ductility. Usually, in order to realize these, it is preferable that the plating layer is composed of a simple metal phase close to a pure metal. However, the introduction of these phases goes against the trend of high corrosion resistance technology by element addition that has been carried out so far, and generally the corrosion resistance tends to deteriorate.

  Therefore, until now, hot dip plated steel materials that have both excellent corrosion resistance and workability have not been realized.

JP 2008-255464 A JP 2009-91652 A

  The problem to be solved by the present invention is to provide an Al—Mg-based hot dipped galvanized steel material with dramatically improved corrosion resistance and workability.

  As a result of intensive studies by the present inventors to solve the above-mentioned problems, it has been found that the corrosion resistance that has not been obtained by hot dipping has been developed by containing a large amount of a quasicrystalline phase in the plating layer. .

On the other hand, since the quasicrystalline phase has low workability, in order to improve the workability in the hot-dip plated layer containing the quasicrystalline phase, an Al phase is introduced into the plating layer and the quasicrystalline phase including the quasicrystalline phase and the Al phase is included. It has been found that the workability of the plating layer is enhanced by forming a crystal structure in the plating layer.
The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) A steel material and a plating layer including an Al—Fe alloy layer and an Al—Mg alloy layer disposed on the surface of the steel material are provided,
The Al-Fe alloy layer is formed on the surface of the steel material, and has a thickness of 100 nm or more and 15 μm or less.
The Al—Mg alloy layer is formed on the Al—Fe alloy layer, and includes a quasicrystalline phase having an average equivalent circle diameter of more than 1 μm and an Al phase having a crystal grain size of 2 μm or less dispersed in the quasicrystalline phase. Containing eutectic structure containing 5% by volume or more,
The chemical component composition of the Al-Mg alloy layer is mass%,
Zn: 5% to 83%,
Mg: 2.5% to 35%,
Ca: 0% to 5%,
Y: 0% to 3.5%,
La: 0% to 3.5%,
Ce: 0% to 3.5%
Si: 0% to 10%,
Cr: 0% to 2.5%
Ti: 0% to 2.5%,
Ni: 0% to 2.5%,
Co: 0% to 0.5%,
V: 0% to 0.5%,
Nb: 0% to 0.5%,
Cu: 0% to 2.5%,
Sn: 0% to 2.5%
Fe: 0% to 3%,
Mn: 0% to 2.5%
Sr: 0% to 0.5%,
Sb: 0% to 0.5%,
Pb: 0% to 0.5%
An Al—Mg based hot-dip galvanized steel material satisfying Ca + Y + La + Ce ≦ 5, and the balance being made of Al and impurities.
(2) The chemical composition of the Al-Mg alloy layer is
Zn: 5% to 65%
Mg: 2.5% to 30%,
Ca: 0.1% to 3%,
Y: 0% to 3%
La: 0% to 3%,
Ce: satisfies the condition of 0% to 3%,
The Al—Mg alloy layer includes 10 volume% or more of primary crystal Al phase and 5 volume% or more of the eutectic structure, and the primary crystal Al phase and the eutectic structure total 70 volumes. % Al-Mg hot-dip galvanized steel as described in (1).
(3) The chemical composition of the Al-Mg alloy layer is
Zn: 5% to 58%
Mg: satisfying the condition of 2.5% to 25%,
The Al—Mg alloy layer contains 35% by volume or more of primary crystal Al phase and 5% by volume or more of the eutectic structure, and the primary crystal Al phase and the eutectic structure total 85 volumes. % Al-Mg-based hot dipped galvanized steel material according to (1) or (2).
(4) The Al—Mg hot-dip galvanized steel material according to any one of (1) to (3), wherein the thickness of the Al—Fe alloy layer is 5 μm or less.
(5) The Al—Mg hot-dip galvanized steel material according to any one of (1) to (4), wherein the hardness of the Al—Mg alloy layer is 100 Hv or more.

  ADVANTAGE OF THE INVENTION According to this invention, the Al-Mg type hot dip plated steel material excellent in corrosion resistance and workability can be provided.

It is an electron beam diffraction image obtained from the quasicrystal phase contained in the Al-Mg system hot-dip plated steel material which is embodiment of this invention. It is an optical microscope photograph of the plating layer cross section of the Al-Mg system hot-dipped steel material which is embodiment of this invention. It is an optical microscope photograph of the plating layer cross section of the Al-Mg system hot-dipped steel material which is embodiment of this invention. It is a reflection electron image by the electron microscope of the plating layer cross section of the Al-Mg system hot-dipped steel material which is embodiment of this invention.

Hereinafter, embodiments of the present invention will be described.
The Al—Mg hot-dip plated steel material (hereinafter referred to as “plated steel material”) according to this embodiment includes a steel material and a plating layer formed on the surface of the steel material. The plated layer formed on the steel material surface includes an Al—Fe alloy layer having a thickness of 100 nm to 15 μm and an Al—Mg alloy layer having a thickness of 2 μm to 50 μm.

  The upper limit of the thickness of the entire plating layer is, for example, 60 μm or less. Since the thickness of the plating layer depends on the plating conditions, the lower limit of the thickness of the entire plating layer is not particularly limited. For example, the normal hot dipping method relates to the viscosity and specific gravity of the plating bath, and Since the basis weight is adjusted by the pulling speed of the plated member and the strength of wiping, the lower limit is about 2 μm.

  That is, the plating layer of the plated steel material of the present embodiment has a two-layer configuration of an Al—Fe alloy layer and an Al—Mg alloy layer. Hereinafter, the steel material and the plating layer will be sequentially described.

  There are no particular restrictions on the material of the steel material used as the base for plating. Although details will be described later, general steel, Ni pre-plated steel, and the like can be used without particular limitation, Al killed steel and some high alloy steels can also be applied, and there is no particular limitation on the shape. . By applying a hot dipping method, which will be described later, to the steel material, a plating layer including an Al—Fe alloy layer and an Al—Mg alloy layer is formed.

The Al—Fe alloy layer is formed on the surface of the steel material, and mainly contains an Al ₃ Fe phase as a structure. The Al—Fe alloy layer is formed by mutual atomic diffusion of the base iron and the plating bath. Al ₃ Fe phase is formed most because Al is contained at a certain concentration or more in the plating bath. However, it takes time for atomic diffusion, and there is a portion where Fe concentration is high near the iron Therefore, in some cases, a small amount of AlFe phase may be included, and in a portion close to the Al—Mg alloy layer, a small amount of Al ₅ Fe ₂ phase may be included. In addition, since a certain concentration of Zn is contained in the plating bath, the Al—Fe alloy layer may contain a small amount of Zn. Even when a pre-plated steel sheet is used as a plating original sheet, a small amount of a pre-plating element may be contained. Note that the corrosion resistance of the Al ₃ Fe phase, AlFe phase, and Al ₅ Fe ₂ phase is not significantly different. The thickness of the Al-Fe alloy layer in the plating layer is small, and the corrosion resistance is low compared to the Al-Mg alloy layer, so the overall corrosion resistance difference is not much different even if the ratio of these phases is changed. .

The chemical composition of the Al—Fe alloy layer is that the Al ₃ Fe phase is mainly contained in the Al—Fe alloy layer, so that the average composition is Fe: 30 to 50%, Al: 50 to 70%, and more than 0% to 5%. The following Zn and inevitable impurities are used. In this embodiment, since the thickness of the Al—Mg alloy layer is larger than the thickness of the Al—Fe alloy layer that is the interface alloy layer, the contribution of the Al—Fe alloy layer to the corrosion resistance is compared with that of the Al—Mg alloy layer. However, since the Al—Fe alloy layer contains Al and Zn, which are corrosion resistant elements, at a certain concentration or more, the sacrificial anticorrosive ability and the corrosion barrier effect are provided to some extent with respect to the ground iron. When a pre-plated steel sheet is used as the plating base plate, the pre-plating element remains on the plating base plate even after hot dipping, and a small amount of pre-plating element is detected in the Al-Fe alloy layer in the vicinity of the interface with the base iron. However, it exists as a solid solution that replaces the Fe element, and the thickness and concentration in the Al—Fe alloy layer are extremely low. Therefore, the sacrificial anticorrosive ability and the barrier effect are not affected.

  In order to accurately grasp the components of the Al-Fe alloy layer, a calibration curve for quantitative analysis is prepared with a high-frequency glow discharge optical emission spectrometer (GDS) using an alloy whose components have been determined in advance, and the target plating layer The element concentration distribution in the depth direction is grasped to determine the component concentration. For example, in the φ5 mm GDS analysis, the component at the place where the component intensity in the depth direction becomes almost flat is grasped, and the average value may be adopted from the measurement results at five or more locations. Although the component grasping by GDS can be applied to the upper Al—Mg alloy layer in addition to the Al—Fe alloy layer, a certain thickness or more, for example, 1 μm or more is often required for accurate component measurement. In the case of less than 1 μm, EPMA or TEM-EDS analysis quantitative analysis is often more accurate.

  When a hot-dip plated layer containing Al is produced, an Al—Fe alloy layer as an interface alloy layer is inevitably formed. Although the lower limit of the thickness of the Al—Fe alloy layer is not particularly limited, in the present embodiment, the thickness when the formation of the interface alloy layer is most suppressed is about 100 nm, and therefore 100 nm is set as the lower limit. If the Al—Fe alloy layer is 100 nm or more, sufficient adhesion between the plating layer and the ground iron can be secured.

  On the other hand, the upper limit of the thickness of the Al—Fe alloy layer is preferably 15 μm or less, more preferably 5 μm or less, and even more preferably 2 μm or less. From the viewpoint of preventing corrosion, it is preferable that the Al—Fe alloy layer is thick, but an Al—Fe alloy layer that is too thick causes the workability of the plating layer to deteriorate significantly. Moreover, when the Al—Fe alloy layer is thick, the Al component of the Al—Mg alloy layer formed on the Al—Fe alloy layer is insufficient, and the plating adhesion and workability tend to be extremely deteriorated. Therefore, the upper limit of the thickness of the Al—Fe alloy layer is preferably in the above range. In particular, by setting the thickness to 5 μm or less, it is possible to reduce the number of cracks in plating generated starting from an Al—Fe alloy layer generated in a V-bending test or the like.

  Once the Al—Fe alloy layer is formed, it tends to cause flaking in which the plating layer peels off the wire in a V-bending test or the like. As will be described later, exfoliation starting from the interface due to the Al-Fe alloy layer, etc. is suppressed rather than the exfoliation of the plating layer due to the presence of a primary quasicrystalline phase with poor workability in the Al-Mg alloy layer difficult. This is because the amount of powdering tends to be slightly increased because the interfacial alloy layer is formed on the entire plating layer with respect to the partially existing primary crystal quasicrystal. Therefore, in order to avoid powdering, it is indispensable to make the Al—Fe alloy layer thin.

  Next, the Al—Mg alloy layer will be described. The Al—Mg alloy layer is laminated on the Al—Fe alloy layer, and includes a quasicrystalline phase having an average equivalent circle diameter of more than 1 μm and an Al phase having a crystal grain size of 2 μm or less dispersed in the quasicrystalline phase. The structure contains 5% by volume or more.

  In order to form a eutectic structure consisting of a quasicrystalline phase and an Al phase in the Al—Mg alloy layer, the chemical composition of the Al—Mg alloy layer is, by mass, Zn: 5% to 83%, It is necessary to satisfy at least Mg: 2.5% to 35%. The balance is Al and impurities. A composition outside this range is basically a composition in which quasicrystals are hardly obtained, and the plating layer tends to be hard, or the melting point is very high, and plating peeling is likely to occur and is suitable as a hot dipping. There is no composition range. Since Al, Mg, and Zn are elements constituting quasicrystals, it is necessary to always include a predetermined amount in the Al—Mg alloy layer. In the composition range disclosed in the present embodiment, the eutectic structure including the quasicrystalline phase and the Al phase may be included in the Al-Mg alloy layer by manufacturing the hot dip plating under appropriate manufacturing conditions. it can. Since the quasicrystalline phase is contained in the eutectic structure, if the eutectic structure is included at a volume fraction of 5% or more, at least half of the quasicrystalline phase is contained at 3% or more. When outside the above composition range, intermetallic compounds other than the quasicrystalline phase increase in the Al—Mg alloy layer, and the workability tends to be inferior like the quasicrystalline phase.

<Zn> 5 to 83%
The Zn concentration is set to 5 to 83% because it is necessary to provide corrosion resistance in the Al-Mg alloy layer, form quasicrystals, and suitability for a Zn-based general paint and chemical conversion treatment. When Zn is less than 5%, an Mg phase that deteriorates the corrosion resistance tends to precipitate. In order to improve the corrosion resistance, the precipitation of the quasicrystalline phase is indispensable, and when the Zn concentration is lowered, the growth of the quasicrystal becomes dull. In addition, the Mg or Mg ₅₁ Zn ₂₀ phase, which has an excessive sacrificial anticorrosive ability, is more easily formed than necessary, and the compatibility with various Zn-based paints and chemical conversion treatments deteriorates. Therefore, the lower limit of the Zn content is 5% or more. On the other hand, if the Zn content exceeds 83%, the Zn phase tends to precipitate in the plating layer, and the alkali corrosion resistance becomes extremely poor. Further, almost no quasicrystal is formed. Therefore, the upper limit of Zn is 83% or more. A more preferable range of the Zn content is 5 to 65%, and a more preferable range is 5 to 58%. From the viewpoint of corrosion resistance and workability of the plating layer, the Zn concentration in the plating layer tends to be preferably higher in a range not exceeding the Al concentration.

<Mg> 2.5% to 35%
Mg is an element greatly related to the formation of quasicrystals. If Mg is less than 2.5%, it becomes difficult to sufficiently form a quasicrystalline phase. The quasicrystalline phase formation condition is particularly related to the Al concentration, Zn concentration, Ca, Y, La, and Ce concentration in addition to the Mg concentration. In general, the formation of the quasicrystalline phase is strongly related to the formation region of the Frank-Kasper phase, which will be described later. Therefore, the higher the Al concentration, the easier it is to form the quasicrystalline phase even if the Mg concentration is small. As the concentration increases, a higher Mg concentration is required. Further, since Ca, Y, La, and Ce are substituted with Mg in the quasicrystalline phase, it can be used as a substitute for Mg. The inventors have empirically found that when the Al concentration is 90% or higher, the total value of concentration components ([Mg concentration] + [Ca, Y, La, Ce concentration]) is 2.5% or higher and the Al concentration is 80%. If it does not satisfy 5% or more at ˜90%, 9% or more when Al concentration is 80 to 50%, and 10% or less when less than 50%, a quasicrystalline phase cannot be obtained, and the structure of the plating layer according to the present invention It was found that it cannot be formed.
On the other hand, if Mg exceeds 35%, a large amount of dross is generated in the plating bath, and plating becomes difficult. A more preferable range of the amount of Mg is 2.5 to 30%, and a more preferable range is 2.5 to 25%. Further, from the viewpoint of corrosion resistance and workability, the ratio of the quasicrystalline phase is required to be a certain level or more, the eutectic structure needs to be increased, that is, the Al primary crystal needs to be reduced, and Mg is preferably 10% or more. However, in this case, the Al concentration is more preferably less than 80%. In terms of component composition, the Mg concentration in the plating layer is preferably a high concentration within a range not exceeding the concentrations of Al and Zn.

<Al> Remainder Al is the remainder of the chemical component of the Al—Mg alloy layer, but Al in the Al—Mg alloy layer is an element greatly related to the formation of a quasicrystal that imparts corrosion resistance. When Al is small, MgZn ₂ is a large amount of formed relatively quasicrystalline phase becomes difficult to obtain. Further, when Al is excessive, an Al-based intermetallic compound is formed and the alkali corrosion resistance and compatibility with the Zn-based paint tend to be deteriorated. Accordingly, the remaining Al is preferably contained in an amount of 1% or more, more preferably 40% or more, and even more preferably 55% or more. If Al is contained in an amount of 40% or more, it becomes a condition that an Al phase is likely to precipitate as an initial crystal, and the workability is improved. However, as described above, if there is an excessive amount of Al in the plating layer, an Al-based intermetallic compound is formed. Therefore, a decrease in alkali corrosion resistance and a tendency to deteriorate the compatibility with the Zn-based coating are observed. The Al concentration is preferably 75% or less, and more preferably 65% or less.

In order to form a sufficient amount of eutectic structure in the Al—Mg alloy layer, the Al concentration needs to be 8.2% or more. More preferably 16% or more. Even when the eutectic structure is obtained when the Al concentration is low, if it is less than 16%, Zn must be 70% or more, or Mg must satisfy 20% or less. The eutectic structure can be obtained only in a limited composition range.
Since the primary Al phase is formed after the fine Al phase is sufficiently contained in the eutectic structure, 40% or more of Al is necessary to obtain the primary Al phase.

  In addition, when a plated steel material is manufactured by the hot dipping method, Fe may be mixed in the Al—Mg alloy layer as an inevitable impurity in the vicinity of the Al—Fe alloy layer, up to about 3%. Since there is almost no Fe diffusing up to, it does not affect the performance of the Al-Mg alloy layer.

  Further, in the Al—Mg alloy layer, as addition selection elements, Ca: 0 to 5%, Y: 0% to 3.5%, La: 0% to 3.5%, Ce: 0% to 3.5% 1 type or 2 types or more of% may be contained. However, it is necessary to satisfy Ca + Y + La + Ce ≦ 5%.

<Ca> 0-5%
Ca, like Al, is an element that greatly affects the formation of quasicrystals. Since Ca has an atomic radius close to that of Mg, it is substituted at the position of Mg in the quasicrystalline phase. Although a quasicrystalline phase can be formed without adding Ca, 0.1% or more is preferably added. On the other hand, when Ca exceeds 5%, an intermetallic compound phase having poor corrosion resistance is formed. Moreover, when the cooling rate at the time of solidification of a plating layer is quick, the amorphous phase which is a kind of non-equilibrium phase forms. Furthermore, planar corrosion resistance and suitability for Zn-based paints also tend to decrease. Therefore, the upper limit concentration of Ca is set to 5% or less.

<Y: 0% to 3.5%, La: 0% to 3.5%, Ce: 0% to 3.5%>
These elements have an atomic radius that is relatively close to Ca atoms, and the effects are estimated to be equivalent to Ca. On the other hand, if it is added in an amount equivalent to Ca due to the specific gravity, melting point, and compatibility of Zn and Mg, the amount of dross formed in the plating bath increases, making it difficult to produce a plated steel sheet. As a result, the corrosion resistance is extremely deteriorated. Therefore, the upper limit concentration of these elements is 3.5% or less. More preferably, it is 1 to 3%, respectively.

In particular, it is necessary to control the thickness of the above-described Al—Fe alloy layer in order to achieve good workability by more severe processing. Furthermore, it is necessary to increase the Al phase ratio in the Al—Mg alloy layer and suppress the precipitation of Al ₄ Ca, Al ₂ Zn ₂ Ca, Al ₃ ZnCa, and the like. Therefore, it is preferable to limit the concentration of components such as Ca, La, and Ce to 3% or less.

  As described above, the quasicrystalline phase is more easily formed when Ca, Y, La, and Ce are contained in the plating layer. On the other hand, when the Ca concentration is high or when the total concentration of Ca, Y, La, and Ce is high, the quasicrystalline phase is not formed immediately. Moreover, when Y, La, and Ce exceed the upper limit values, it is difficult to form a quasicrystalline phase, which may adversely affect the performance of plating itself.

  Further, in the Al—Mg alloy layer, Si: 0% to 10%, Cr: 0% to 2.5%, Ti: 0% to 2.5%, Ni: 0% to 2. 5%, Co: 0% to 0.5%, V: 0% to 0.5%, Nb: 0% to 0.5%, Cu: 0% to 2.5%, Sn: 0% to 2. One or two of 5%, Mn: 0% to 2.5%, Sr: 0% to 0.5%, Sb: 0% to 0.5%, Pb: 0% to 0.5% You may further contain the above.

<Cr: 0% to 2.5%, Ti: 0% to 2.5%>
Ti and Cr may be contained as necessary in order to preferably form a quasicrystalline phase in the plating layer. When a small amount of Ti and Cr are contained in the plating layer, it is considered that a quasicrystalline phase is easily generated and the structure of the quasicrystalline phase is stabilized.

<Si>
It has been confirmed that when Si is contained in the plating layer at a concentration of 10% or less, a quasicrystalline phase is likely to be generated in the same manner as Ti and Cr. Further, it has been confirmed that the growth of the Al—Fe alloy layer is slowed when added in excess of 0.1%, and inclusion of Si in the plating layer has an adverse effect on the plating workability. This is an effective means for suppressing the alloy layer.

However, Si forms an intermetallic compound with Mg, Ca, Y, La, and Ce contained in the plating bath, and tends to precipitate. For example, Ca ₂ Si, (Ca, La) ₂ Si, and the like are representative examples of intermetallic compounds formed by combining Ca and Si in the plating layer. _{Furthermore, Al 4 Ca, Al 2 Zn} 2 Ca, is a small amount in Al 3 intermetallic compound such ZnCa tends Si is a solid solution. And since these intermetallic compounds containing Si are the most active among the substances contained in the plating layer, the cause of the color change (yellowing, blackening) of the plating layer in a high humidity environment or an environment where a salt content comes in. It is easy to become. For this reason, in order to provide a product with excellent appearance quality, it is better not to add Si. In order to completely avoid these phenomena, it is preferable to strictly limit the concentration, and it is preferable to control the concentration to less than 0.01%.

  Moreover, when Si addition density | concentration exceeds 5%, it will become easy to form bottom dross in a plating bath, and operativity may fall. From the viewpoint of operation, the Si concentration is 5% or less, more preferably less than 1%.

As described above, when workability is particularly required for the plated steel material, the amount of Si in the Al—Mg alloy layer is preferably 10% or less in order to suppress the growth of the Al—Fe alloy layer. In order to improve operability, the Si content is preferably 5% or less. The lower limit when adding Si is preferably 0.01% or more, and more preferably 0.1% or more.
Further, from the viewpoint of the plating performance of the plated steel material, that is, from the viewpoint of satisfying all of the corrosion resistance, workability, discoloration resistance and operability in a well-balanced manner, the Si concentration is preferably controlled to less than 0.01%.

<Ni: 0% to 2.5%, Co: 0% to 0.5%, V: 0% to 0.5%, Nb: 0% to 0.5%, Cu: 0% to 2.5% , Sn: 0% to 2.5%>
Co, Ni, V, Nb, Cu, and Sn are elements that are effective in the stable generation of quasicrystals, like the above-described Si, Ti, and Cr. Although it is an element that is effective in the formation of quasicrystals, detailed studies have revealed that it has an additive effect different from the effects of elements such as Si, Ti, and Cr. When these elements are added to the plating layer, the diffusion of Fe element into the plating layer is extremely suppressed. These elements tend to be dissolved in the Al ₃ Fe intermetallic compound mainly in the vicinity of the interface between the steel material and the plating layer. At the same time, an intermetallic compound of Fe ₁₁ Zn ₄₀ is easily formed. As a result, the formation of the Al—Fe-based intermetallic compound as the interface alloy layer is suppressed, and factors that inhibit the formation of the quasicrystalline phase in the plating layer, such as the reduction of the Al component in the plating layer, are reduced. Since the formation of the interfacial alloy layer that does not affect the corrosion resistance and the formation of the quasicrystalline phase is suppressed, the original corrosion resistance of the plating layer is exhibited. In the SST test or the like, usually, the smaller the thickness of the interface alloy layer, the longer the red rust occurrence time.

  These elements are added in advance by pre-plating the steel plate that is the original plate by electroplating or vapor deposition, and incorporating the elements into the plating layer when forming the plating layer, and adding these elements to the plating bath There is a way to do it. Many refractory metals such as Ni and Co remain in the vicinity of the interface, but generally, pre-plating tends to be a little more incorporated into the plating layer, and also has an effect of suppressing the formation of the interface alloy layer. high. When it is concentrated near the interface and the plating layer is 6 μm or less, it is about 0.5% to 1.0% and may exceed 0.5%, but many concentrate near the interface. The Ni concentration detected from the plating layer main layer is often less than 0.5%. On the other hand, Cu, Sn, trace amounts of Nb, etc. are easily dissolved even when added to the plating bath, are relatively easily taken into the plating layer, and an effect of suppressing the interface alloy layer is also observed.

<Mn: 0% to 2.5%>
In recent years, high-tensile steel (high-strength steel) has come to be used as a steel material that is a base material for plated steel. When a plated steel material is manufactured using high-tensile steel, elements such as Si and Mn contained in the high-tensile steel may diffuse into the plated layer. Of Si and Mn, Mn does not have the above-described effects of Si. However, even if about 2.5% of Mn is contained in the plating layer, there is little possibility of affecting the quasicrystal generation behavior and the corrosion resistance of the plating layer. Therefore, the Mn content of the plating layer may be 0% to 2.5%.

<Sr: 0% to 0.5%, Sb: 0% to 0.5%, Pb: 0% to 0.5%>
Sr, Sb, and Pb are elements that improve the plating appearance. In order to obtain this effect, the Sr content of the plating layer may be 0% to 0.5%, the Sb content may be 0% to 0.5%, and the Pb content may be 0% to 0.5%. . When the Sr content, Sb content, and Pb content are in the above ranges, there is almost no influence on the corrosion resistance.

Next, the structure constituting the Al—Mg alloy layer will be described.
In the component composition disclosed in the present embodiment, the following structures have been confirmed for the Al-Mg alloy layer. That is, it is a eutectic structure including the primary crystal Al phase, primary crystal quasicrystalline phase, quasicrystalline phase and Al phase. Further, there is a case where the type of the selected _{elements, Al 4 Ca, Al 2 Zn} 2 Ca, include Al 3 ZnCa like. Furthermore, MgZn ₂ phase, Mg ₂ Zn ₃ phase (sometimes referred to as Mg ₄ Zn ₇ in some literature, but treated as the same substance), Mg ₅₁ Zn ₂₀ phase, Mg Phase and MgZn phase.

  The quasicrystalline phase is a phase containing a quasicrystal. The quasicrystal is a crystal structure first discovered by Daniel Schuchman in 1982 and has an icosahedral atomic arrangement. This crystal structure is a non-periodic crystal structure with a unique rotational symmetry that cannot be obtained with ordinary metals and alloys, for example, a 5-fold symmetry, and is equivalent to an aperiodic structure represented by a three-dimensional Penrose pattern. Known as a crystal structure. In order to identify this metal material, it is usually confirmed by obtaining a radial regular decagonal electron beam diffraction image resulting from the regular icosahedron structure from the target phase by electron beam observation by TEM observation. For example, the electron diffraction image shown in FIG. 1 is obtained only from a quasicrystal and cannot be obtained from any other crystal structure.

Further, the quasicrystalline phase obtained from the component composition disclosed in the present embodiment is simply defined as the Mg ₃₂ (Zn, Al) ₄₉ phase in terms of chemical composition, and spreads to the Zn, Al ratio. And X-ray diffraction shows a diffraction peak that can be identified by JCPDS card: PDF # 00-019-0029 or # 00-039-0951. It may also be called a Frank-Kasper phase. A diffraction peak is often observed around 36.3 to 8 °.
It is said that the formation of the quasicrystal icosahedral crystal structure is influenced by the formation of a Mg ₃₂ (Zn, Al) ₄₉ phase having a rhomboid polyhedron structure having clusters. The crystal structure of the icosahedral quasicrystalline phase has been reported to include three or more types of crystal structures, such as the Mackay cluster, Bergman cluster, and cocoon cluster types, and the crystal structure is still under study. In addition, it has been pointed out that the Mg ₃₂ (Zn, Al) ₄₉ phase is an approximate crystal that is the same as the quasicrystal from the early stage of the quasicrystal research, and the cluster structure changes partially due to the cooling method at the time of formation. A different icosahedron structure shown in FIG. The definition of the quasicrystalline phase in the present invention refers to an approximate crystal and is defined as a variant from the Mg ₃₂ (Zn, Al) ₄₉ phase, including a substance having a cluster structure equivalent to the quasicrystal. In some cases, a coarse crystal having a regular icosahedron structure with a size of several tens of μm or more can be obtained, and only a few nanometers can be obtained (that is, the electron beam shown in FIG. Although a diffraction image can be obtained from any place, an electron diffraction image of the Mg ₃₂ (Zn, Al) ₄₉ phase can be obtained, and the image of FIG. At present, it is technically impossible to clearly distinguish the crystal phase from the approximate crystal. It is presumed that a quasicrystalline phase is included in the Mg ₃₂ (Zn, Al) ₄₉ phase, but it is difficult to partially cut out the quasicrystal. It is presumed to be based on the expression of a unique crystal structure resulting from the structure, and the Mg ₃₂ (Zn, Al) ₄₉ phase, which is an approximate crystal, can be treated as the same quality as the quasicrystal. Therefore, in a simple case, when searching for an approximate crystal Mg ₃₂ (Zn, Al) ₄₉ phase by XRD, obtaining the same performance as a quasicrystal, and searching for a quasicrystal structure in more detail The crystal structure of the target crystal phase may be searched in detail by TEM.

  Further, from the crystal structure, the quasicrystal is a very hard substance, the hardness of the quasicrystalline phase itself is considered to be 350 to 450 Hv, and the plating layer becomes hard as the content thereof increases. The plating hardness of the plating layer is 100 Hv or more, more specifically, in the range of about 120 to 450 Hv. When a large amount of the quasicrystalline phase is contained, the plastic deformability of the plating layer is rapidly lost. Therefore, in order to maintain the plastic deformability, it is necessary to introduce a soft structure such as a eutectic structure including an Al phase according to the present embodiment into the plating layer.

  When the quasicrystalline phase is contained in the plating layer, the corrosion resistance of the plating is increased, and the corrosion resistance is dramatically improved in the exposure test and the combined cycle corrosion test. In particular, corrosion weight loss in seawater tends to be small. For example, when immersed in artificial seawater for a long time, the corrosion weight loss becomes extremely smaller than a plated steel material that does not contain a quasicrystalline phase. This is presumably because Al, which has a weak film barrier property with respect to chlorine, contains a quasicrystalline phase, which makes it stable in seawater and further strengthens the film barrier. This effect is confirmed if the quasicrystalline phase contains 3% or more of the volume fraction, that is, if the eutectic structure contains 5% or more, the corrosion thickness reduction in artificial seawater is reduced. it can. If no quasicrystalline phase is contained, this effect cannot be confirmed. Also, it is more preferable that the Al concentration is usually higher.

  The Al—Mg alloy layer of the present embodiment includes 5% by volume or more of a eutectic structure including a quasicrystalline phase and an Al phase. In addition, the Al—Mg alloy layer of the present embodiment may include either the primary crystal Al phase or the primary crystal quasicrystalline phase in addition to the eutectic structure of 5% by volume or more. The primary crystal Al phase is distinguished as being formed before the Al phase in the eutectic structure is precipitated. When the cross section of the plating layer is observed with a microscope, an Al phase that does not clearly constitute a eutectic structure may be determined as a primary Al phase. The primary crystal quasicrystalline phase is distinguished as being formed before the quasicrystalline phase in the eutectic structure is precipitated. When the cross section of the plating layer is observed with a microscope, a quasicrystalline phase that does not contain an Al phase with an equivalent circle diameter of 2 μm or less may be determined to be a primary quasicrystalline phase.

  There are two forms of quasicrystal precipitation in the Al—Mg alloy layer. The primary crystal quasicrystalline phase which is the first form is precipitated in the Al—Mg alloy layer as a massive structure because the quasicrystalline phase is precipitated as the primary crystal. Usually, the average equivalent circular diameter of the primary crystal massive structure is about 1 μm to 300 μm. The shape is often a polygon.

  The quasicrystalline phase in the eutectic structure which is the second form exists as a eutectic structure with the Al phase. The quasicrystalline phase in the eutectic structure preferably has an average equivalent circle diameter of more than 1 μm. A quasicrystalline phase having an average equivalent circle diameter of 1 μm or less tends to have a reduced corrosion resistance. When a quasicrystalline phase exists as a eutectic structure, an Al phase having an equivalent circular diameter and a crystal grain size of 2 μm or less is dispersed in the quasicrystalline phase at a volume fraction of about 20 to 50%. Further, since the melting point of the Al phase is higher than that of the quasicrystalline phase, the eutectic structure has a structure in which the Al phase is precipitated from the quasicrystal. However, as the Al concentration increases, the volume fraction of the Al phase dispersed in the quasicrystal increases. The crystal grain size of 2 μm or less is a numerical value obtained experimentally, and no larger Al phase is formed, and even if formed, it does not affect the corrosion resistance. It may be determined that an Al phase having a crystal grain size exceeding 2 μm does not constitute a eutectic structure but constitutes a primary crystal Al phase.

  The structure of the eutectic structure also affects the cooling rate at the time of plating production. If the cooling rate at the time of solidification of the plating layer is slow, the Al phase repeats bonding and growth, and the Al phase that precipitates as the primary crystal increases. The volume fraction contained in the Al phase in the eutectic structure is slightly reduced. On the other hand, if the plating layer is rapidly cooled during solidification, the volume fraction of the Al phase contained in the eutectic structure slightly increases.

  There are also two forms of precipitation of the Al phase in the Al-Mg alloy layer. The primary crystal Al phase which is the first form is precipitated in the Al—Mg alloy layer as a bulk structure because the Al phase is precipitated as the primary crystal. Usually, the average equivalent circular diameter of the primary crystal massive structure is about 1 μm to 300 μm. The shape is often elliptical.

  The Al phase in the eutectic structure which is the second form exists as a eutectic structure with the quasicrystalline phase and is as described above.

  In the present embodiment, the quasicrystalline phase is precipitated as the primary crystal or the Al phase is precipitated at the eutectic line existing between Al concentration of 35 to 45%. There is almost no case where the primary crystal Al phase coexists. That is, whether the Al phase or the quasicrystalline phase is precipitated as the primary crystal is determined by the amount of Al in the Al—Mg alloy layer.

  As an example, FIG. 2 shows an optical microscope image of a plating layer composed of a primary crystal quasicrystalline phase and a eutectic structure. FIG. 3 shows, as another example, an optical microscope image of a plating layer composed of a primary crystal Al phase and a eutectic structure. FIG. 4 shows a backscattered electron image of the eutectic structure. In FIG. 2, the primary crystal quasicrystalline phase is precipitated at the position indicated by arrow 1, and the eutectic structure is precipitated at the position indicated by arrow 2. Further, in FIG. 3, the primary crystal Al phase is precipitated at the position indicated by the arrow 3, and the eutectic structure is precipitated at the position indicated by the arrow 4. Further, in FIG. 4, it can be seen that a quasicrystalline phase is precipitated at a position indicated by an arrow 5 and an Al phase is precipitated at a position indicated by an arrow 6.

  The volume fractions of the primary crystal Al phase, primary crystal quasicrystalline phase, eutectic structure, etc. in the Al—Mg alloy layer are directly linked to the workability of plating. The workability of plating can be easily evaluated by a V bending test or the like. The V bending test refers to an evaluation by a V block method (bending test evaluation) in JIS standards (terms JIS G 202, JIS Z2248) relating to steel product testing. In the V-bending test used for evaluation in the present invention, the smaller the inner radius R value, the narrower the region to which plastic deformation is applied. A larger R value tends to increase the amount of powdering because the region to which plastic deformation is applied is wider. This is because the quasicrystalline phase is a very brittle substance and easily breaks with a small amount of strain.

  When the eutectic structure is contained in an amount of 5% by volume or more, plastic deformability starts to occur in the plating layer. For example, the amount of powdering in valley tape peeling in a 1R-90 ° V bending process test is reduced. When the eutectic structure is less than 5% by volume, the workability improvement effect is small. The volume fraction of the eutectic structure is preferably large, preferably 30% by volume or more, more preferably 50% by volume or more, and still more preferably 80% by volume or more. In the eutectic structure, it is preferable that the volume fraction of the quasicrystal is low and the volume fraction of the Al phase is high. By including an Al phase as a eutectic structure, generation of powdering during processing can be suppressed.

  In addition, when the primary crystal quasicrystalline phase is contained in the Al—Mg alloy layer, partial peeling tends to occur during processing. Although the primary crystal quasicrystalline phase depends on the size of the crystal grain, if the primary crystal quasicrystalline phase is located at the processing site, it may cause intragranular cracking, and the plating layer may be lost as it is, causing powdering peeling. is there. Although the amount of peeling varies depending on the volume fraction and the area of the processed part, it is preferable that the primary crystal quasicrystalline phase does not exist from the viewpoint of processing.

Further, when the primary crystal Al phase is contained in the Al—Mg alloy layer, plastic deformation is possible even in processing with a low R value. It is preferable that the primary crystal Al phase contained in the Al—Mg alloy layer is larger. If the primary crystal Al phase is contained in an amount of 10% by volume or more, the amount of powdering in the valley tape peeling in the 5R-V bending test is reduced. More preferably, the primary Al phase is contained in an amount of 35% by volume or more. By containing 35% by volume or more of the primary Al phase, the amount of powdering is reduced for more severe processing. For example, the amount of powdering can be reduced in bending back after V bending.
When the workability between the eutectic structure and the primary Al phase is compared, the Al phase is richer in workability. In the composition disclosed in the present invention, it is impossible to make an Al phase single phase, but in the vicinity of a eutectic line (eutectic composition existing between 35% to 45% Al concentration), a single phase eutectic structure is used. It is possible.

The primary crystal Al phase, primary crystal quasicrystalline phase, Al phase and quasicrystalline phase in the eutectic structure contained in the Al—Mg alloy layer all contribute to the corrosion resistance of the plated layer. All have a strong passive film, and the occurrence of rust in the accelerated corrosion test is suppressed. In particular, the Al-Mg alloy layer, which has improved workability due to the coexistence of the primary Al phase, suppresses plating peeling and cracking at severely processed parts in the processed part corrosion resistance. Is improved.
Since the Al—Mg alloy layer contains Zn and Mg having a high sacrificial anticorrosive ability at a certain concentration or more, there is no problem with deterioration of corrosion resistance due to cracks generated in the plating layer. This is because cracks are immediately closed with corrosion products in the early stage of corrosion, and the progress of corrosion is suppressed. Further, if the powdering of the plating layer is partially less than 5% of the processed part area, the surrounding plating is corroded and covered, and the corrosion rate is slightly increased, but the plating performance is not greatly impaired. On the other hand, when the plating layer peels off from the interface between the base metal and the plating layer, and a peeling of 20% or more with respect to the processed part area is seen, the corrosion rate of the plating layer becomes extremely large, and the powdering part Red rust tends to occur more quickly.

  Further, when the total volume fraction of the primary crystal Al phase or primary crystal quasicrystalline phase in the Al-Mg alloy layer and the eutectic structure becomes 70% by volume or more, the corrosion resistance inside the V-bending specimen is further improved. Improved. More preferably, it is 85% or more.

  In particular, in the present embodiment, in order to impart plastic deformability to the plating layer, it is necessary to contain the primary crystal Al phase as a phase that imparts plastic deformability in the plating layer. The primary Al phase is a structure that is more excellent in workability than the eutectic structure. The composition disclosed in the present embodiment is a composition range in which an Al phase can be contained at the same time that a quasicrystal is obtained.

  In particular, the chemical composition of the Al-Mg alloy layer is Zn: 5% to 65%, Mg: 2.5% to 30%, Ca: 0.1% to 3%, Y: 0% to 3%, La : When satisfying the conditions of 0% to 3% and Ce: 0% to 3%, in the Al-Mg alloy layer, the primary crystal Al phase of 10% by volume or more and the eutectic structure of 5% by volume or more are contained. In addition, the total amount of primary Al phase and eutectic structure is 70% by volume or more. The plated steel material provided with such an Al—Mg alloy layer has good workability. In this case, the amount of Al is preferably 40% or more.

  Further, when the chemical composition of the Al—Mg alloy layer satisfies the conditions of Zn: 5% to 58% and Mg: 2.5% to 25%, the Al—Mg alloy layer has an initial content of 35% by volume or more. The crystal Al phase and the eutectic structure of 5% by volume or more are contained, and the primary crystal Al phase and the eutectic structure contain 85% by volume or more in total. The plated steel material provided with such an Al—Mg alloy layer is further improved in workability. Specifically, the amount of powdering is suppressed in a V-bending test or the like. In this case, the Al content is preferably 55% or more.

  Next, the manufacturing method of the plated steel material of this embodiment is demonstrated in detail.

  In the present embodiment, there is no problem even if any steel material such as ordinary steel, aluminum killed steel, high-tensile steel, etc. is used as the steel plate to be the plating original plate, and the steel material type is not particularly limited. There is no problem in using a pre-plated steel plate as the original plate.

  As the plating bath, alloys having a predetermined component composition prepared in a vacuum melting furnace or the like are used, and these alloys are melted in the atmosphere. Usually, in order to carry out hot dip plating, it is necessary to make the plating bath temperature 15 to 20 ° C. higher than the melting point of the alloy. In the plating bath of this embodiment, the operation near the melting point is that the viscosity of the plating becomes high, and because the quasicrystalline phase precipitates and easily precipitates in the plating bath, either the melting point of the alloy + 20 ° C. or 500 ° C. Or higher temperature. More preferably, the alloy melting point + 15 ° C. or 540 ° C. or higher, whichever is higher. Moreover, in order to avoid bottom dross formation and precipitation, it is preferable that the inside of the plating bath is sufficiently stirred.

In particular, in the low melting point alloy with an Al concentration of 30% or more, the specific gravity of the entire plating bath is light, while the quasicrystal containing a large amount of Zn has a high specific gravity, so that the bath temperature is below the precipitation temperature of the quasicrystal. Precipitation occurs immediately, and the plating bath separates into two phases from the lower part (quasicrystal) and the upper part (liquid phase plating bath), making it difficult to maintain the components of the plating bath. Moreover, many solid and granular dross will adhere also to the plated steel plate to manufacture. Also, from the viewpoint of structure control, unless the structure control is performed from a sufficiently small quasicrystal precipitated from the liquid phase, coarse quasicrystalline phases may be scattered in the plating layer, which may cause inferior workability. From the viewpoint of operability and structure control, it is preferable to set the bath temperature to 540 ° C. or higher at which the quasicrystalline composition is completely dissolved.
In a high-temperature bath of 540 ° C. or higher, an Al—Fe alloy layer formed by the reaction between the base iron and the plating bath is excessively formed. Therefore, as will be described later, the reaction time of the Al—Fe alloying reaction is shortened. It is necessary to take measures to suppress the growth of the Fe alloy layer.

However, under high temperature conditions where the bath temperature exceeds 540 ° C, the reaction with Al and the iron in the plating bath becomes intense, and an excessively thick Al-Fe alloy layer is formed, and the consumption of Al in the plating layer is promoted. Therefore, the component balance is lost, and the tissue control becomes difficult. For this reason, when the alloy melting point exceeds 525 ° C. and the plating bath temperature exceeds 540 ° C., it is preferable that the bath temperature is not excessively increased from 540 ° C.
For example, considering the temperature drop width of wiping during plating, for plating baths with a melting point of 535 ° C or higher, the bath temperature should be set so that wiping is completed at a temperature close to the melting point as much as possible with a melting point of + 15 ° C Is good. In order to reduce the temperature drop at the time of wiping, if the wiping part is heated with a heater and cooling with N ₂ hot gas is used, it is possible to have a melting point + 10 ° C., etc. In the case of, the temperature drop in wiping can be almost ignored, and sufficient hot dipping is possible even at a melting point of + 5 ° C.

For the production of the plated steel material, it is preferable to employ the Sendzimer method, and the steel material reduced with hydrogen at 800 ° C. in a non-oxidizing environment is immersed in the plating bath as it is. The immersion time also affects the thickness of the Al—Fe alloy layer of the plating layer, but usually 0.5 seconds is sufficient. After the immersion, the amount of adhesion is adjusted by spraying N ₂ gas.

  In addition, when a plated steel material is manufactured by the manufacturing method of the present embodiment, the component composition ratio of the plating bath is the chemical component composition of the Al—Mg alloy layer. The reduction of the Al component and the Zn component of the Al—Mg alloy layer due to the formation of the Al—Fe alloy layer during immersion in the plating bath is usually slight. This is because the thickness of the Al—Fe alloy layer is usually sufficiently smaller than that of the Al—Mg alloy layer, and the Al—Mg alloy layer contains sufficient Al element. Therefore, what is necessary is just to adjust the component composition of a plating bath so that the Al-Mg alloy layer of a desired composition may be obtained.

When the steel material whose surface is reduced is immersed in a plating bath having a relatively high Al concentration, Fe and Al immediately react to form an Al—Fe alloy layer which is an interface alloy layer. Since the Al-Fe alloy layer is explosively formed to reduce the Al concentration in the plating layer and adversely affect the formation of the quasicrystalline phase, eutectic structure, and Al phase, it is necessary to strictly control the cooling time. . The higher the temperature, the greater the reaction rate.
The time for cooling the plating layer to 500 ° C. or less including the immersion time is preferably at least 5 seconds or less. For example, when the plating bath temperature is 600 ° C., it must be cooled to 500 ° C. or less at an average cooling rate of 20 ° C./second or more. For those longer than 5 seconds, the Al component of the Al-Mg alloy layer decreases due to the growth of the Al-Fe alloy layer, making it difficult to obtain a quasicrystalline structure and a eutectic structure, as well as deterioration in corrosion resistance and workability. And the surface appearance is also deteriorated.
At a temperature of 500 ° C. or lower, the temperature is low for the growth of the Al—Fe alloy layer, and the solidification reaction starts depending on the components of the plating bath, so that the growth of the Al—Fe alloy layer is extremely suppressed. . In order to ensure the adhesion of the plating, it is necessary to form an Al—Fe alloy layer with a certain thickness, but by setting the temperature region of 500 ° C. or more to 0.5 seconds or more, the thickness is sufficient for the adhesion. An Al—Fe alloy layer is formed.

Furthermore, in this embodiment, in order to produce a plating layer including a quasicrystalline phase or a eutectic structure, it is necessary to adjust the cooling rate in a temperature range of 500 ° C. or lower.
The quasicrystalline phase is composed of Al, Mg, and Zn, and further includes a cluster structure (regular icosahedron, rhombohedral polyhedron, etc.), and thus can contain a variety of elements in the cluster structure atom and the inside thereof. Moreover, it is the area | region which 500-400 degreeC can exist stably. The eutectic structure according to the present embodiment is a structure formed by Al separating from the quasicrystalline phase, and atomic diffusion is required for the formation. When quenching from a molten state, a quasicrystalline phase or a supersaturated solid solution may be formed, and a eutectic structure is not formed. For this reason, it is essential to control the cooling rate in forming a eutectic structure. Further, the solidification mechanism of the plating layer varies depending on the Al concentration of the plating bath. Hereinafter, the case where the Al concentration is less than 40% and the case where it exceeds 40% will be described.

<When Al concentration is less than 40%>
When the Al concentration of the plating bath is less than 40%, the first phase formed during solidification of the plating layer is a quasicrystalline phase. Precipitation of the quasicrystalline phase which is the primary crystal is almost completed by the melting point to about 470 ° C. Thereafter, a liquid phase eutectic reaction occurs at around 470 ° C., and the Al phase is gradually separated from the quasicrystalline phase to form a eutectic structure. Generation of a eutectic structure due to phase separation of the Al phase occurs until the temperature drops to 200 ° C. In the temperature range of 470 ° C. to 200 ° C., the phase-separated Al phase grows by repeated bonding.

  When rapid cooling such as water cooling or strong mist cooling is performed, Al contained in supersaturation in the quasicrystalline phase cannot be separated, and a quasicrystalline phase tends to be formed in a large amount, and a eutectic structure is not formed. In addition, the aging effect of the component elements contained in supersaturation gradually separating and precipitating near room temperature, and the generation of residual stress due to a sudden change in thermal expansion coefficient, a large number of cracks are formed in the quasicrystals in the plating layer. However, it is not preferable from the viewpoint of workability. Accordingly, the upper limit value of the average cooling rate from 470 ° C. to 200 ° C. is set to 30 ° C./second. More preferably, 20 ° C./second and 10 ° C./second are better. Since water cooling, mist cooling, etc. usually obtain a cooling rate of 50 to 1000 ° C./second, the use of these cooling means is not preferred. That is, in order to suppress the formation of the Al—Fe alloy layer up to 500 ° C., the rapidly cooled plating layer forms a eutectic structure including a healthy quasicrystal in the plating layer. A cooling process needs to be carried out. However, when it is slowly cooled in the temperature range of 470 ° C. to 200 ° C., the phase separation of the Al phase repeats bonding, and the proportion of the eutectic structure excellent in ductility becomes extremely reduced by becoming a coarse Al phase, The cooling rate in the temperature range of 470 ° C. to 200 ° C. is set to 3 ° C./second or more. That is, the temperature range of 470 ° C. to 200 ° C. is a range in which a eutectic structure is formed, and at the same time is a range in which the Al phase is solid-phase separated and bonded, so that it should not be kept for a long time. Therefore, a cooling rate of 5 to 20 ° C./second is appropriate as a cooling rate in this temperature range.

<When Al concentration is 40% or more>
When the Al concentration of the plating bath is 40% or more, the first phase formed during solidification of the plating layer is the Al phase. Precipitation of the Al phase as the primary crystal is almost completed by the melting point to about 470 ° C. Thereafter, a liquid phase eutectic reaction occurs at around 470 ° C., and the Al phase is gradually separated from the quasicrystalline phase to form a eutectic structure. Formation of a eutectic structure by the phase separation of Al occurs until the temperature drops to 200 ° C. From 470 ° C. to 200 ° C., the phase-separated Al phase repeats bonding and grows.

When the rapid cooling is performed, the quasicrystal does not grow, and a supersaturated solid solution Al phase containing Mg and Zn in a supersaturation tends to be formed in a large amount, so that a eutectic structure is not formed. The component separation is necessary for the formation of the eutectic structure as in the case where the quasicrystalline phase contains a component element. Therefore, the upper limit of the average cooling rate from 470 to 200 ° C. is set to 30 ° C./second.
Since water cooling, mist cooling, etc. usually obtain a cooling rate of 50 to 1000 ° C./second, the use of these cooling means is not preferred. On the other hand, when slowly cooling in the temperature range of 470 ° C. to 200 ° C., the phase separation of the Al phase repeats bonding, and the proportion of the eutectic structure excellent in ductility becomes extremely reduced as a coarse Al phase, The cooling rate in the temperature range of 470 ° C. to 200 ° C. is set to 3 ° C./second or more. As for the temperature range of the optimum condition, the cooling rate of 5 to 20 ° C./second is the same as the cooling rate in this temperature range.

For cooling in a temperature range of 200 ° C. or lower, the structure has already been determined, so the structure in the plating layer does not change due to the temperature history, but when cooling in the atmosphere, the surface of the plating layer is gentle. In combination with oxygen in the air, an oxide film is formed. The oxide film also causes a subsequent chemical conversion treatment and a poor appearance. Therefore, it is preferable that the formation of an oxide film is suppressed by rapid cooling (mist cooling or water cooling) to 100 ° C. or lower, more preferably close to room temperature. For example, when cooling from 200 ° C. to 100 ° C. at 10 ° C./second or more, it is confirmed that the oxide film formed on the surface of the plating layer is less than 200 nm, and does not affect the subsequent performance and appearance.
The plated steel material of this embodiment is manufactured by the above.

Next, a plating layer analysis means will be described.
TEM observation is essential to specify the quasicrystalline phase. A TEM sample is prepared from the plated steel material using FIB processing, and the presence of the quasicrystalline phase can be confirmed by a diffraction pattern of the Mg ₃₂ (Zn, Al) ₄₉ phase or a radial regular decagonal electron diffraction pattern. . Depending on the plating component, the Mg ₃₂ (Zn, Al) ₄₉ phase diffraction image may be partially a regular decagon within the crystal or a regular decagonal electron beam diffraction image may appear at the grain boundary or the like. There is also. In addition, XRD (X-ray diffraction) is performed in advance, and it is simply identified with Mg ₃₂ (Zn, Al) ₄₉ phase, JCPDS card: PDF # 00-019-0029 or # 00-039-0951. It is preferable to confirm that it matches the diffraction peak that can be formed. If these diffraction peaks and diffraction images are obtained, it can be confirmed that the Mg ₃₂ (Zn, Al) ₄₉ phase and quasicrystal having a cluster structure exist.

A method for measuring the volume fraction of each phase in the Al—Mg alloy layer will be described. An arbitrary cross section of the plating layer, at least 3 fields of view (500 × 500 μm) is taken with an SEM-reflected electron image. The quasicrystalline phase, eutectic structure, and Al phase in the SEM-reflected electron image are specified from the experimental results obtained separately by TEM observation. In a predetermined field of view, the component mapping image is grasped, the same component composition location as the quasicrystalline phase in the plating layer is specified, and each phase in the plating layer is specified by image processing. An image in which the range of the quasicrystalline phase region is selected is prepared by an image analyzer, and the ratio of each phase in the Al—Mg alloy layer is measured. The area ratio of the quasicrystalline phase in the plating layer is adopted as the volume fraction from the average value from three similarly processed visual fields. The observation magnification of the SEM-reflected electron image may be adjusted so that the shape and size of the tissue to be observed can be specified, and the resolution of component mapping may be adjusted so that the component of the tissue to be analyzed can be specified.

  The component composition of each phase in the plating layer is determined by quantitative analysis using SEM-EDS, EPMA or the like in the cross section of the plating layer. In order to grasp the components of the plating layer, the components are grasped by point analysis from the location of the same structure in at least three different visual fields, and the average value is adopted. When there is tissue spread, it is possible to obtain an accurate value from the EPMA mapping image by adopting the average value of the composition in a specific range.

  In order to grasp the component composition of the entire plating layer, it is preferable to dissolve the plating layer in an acid solution to which an inhibitor that suppresses corrosion of the base iron is added, and to confirm the component by ICP (high frequency inductively coupled plasma) emission spectroscopy. In addition to the element added intentionally, in the measurement of the impurity element concentration which is usually less than 0.1% which is not intended, it is possible to grasp the component up to the minimum concentration of about 0.005%. When the thickness of the Al—Fe alloy layer is 1 μm or more, the acid solution time must be shortened to prepare a measurement solution so as not to dissolve the Al—Fe alloy layer. In addition, it is preferable to use a quantitative analysis method by GDS or to grasp the component by EPMA line mapping or the like as multiple times.

  Vickers hardness is used to measure the hardness of the plating layer. If a 30-point average hardness is obtained from an indentation from the plating surface with a μ Vickers measuring device or the like, the approximate hardness of the plating layer can be estimated.

  The workability of the plating layer is preferably a V-bending test using the press described above. In the evaluation of workability in the present invention, the amount of powdering tends to increase in V bending with a large R value as described above. When more severe processing is evaluated, it is preferable to perform a bending and bending back test in which a V-bending, 180 ° C. bending, and 0T bending test is performed and the tape is peeled after returning to a flat plate again.

  When evaluating the corrosion resistance of the plating layer, it is most preferable to check the corrosion status by an exposure test, but it is also possible to evaluate in a short time using a salt spray test (SST), a combined cycle corrosion test (CCT), etc. It is. We give superiority or inferiority in corrosion resistance by evaluating the occurrence of white rust and red rust after a predetermined period of time and evaluating corrosion weight loss.

  Hereinafter, examples of the present invention will be described, but the conditions in the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  A predetermined amount of pure metal ingot was used in a vacuum melting furnace so as to have the plating layer composition shown in Table 1A and Table 1C, and this was melted to build a plating bath in the atmosphere. It was confirmed that the plating bath components were the same using ICP emission spectroscopy, and that the plating layer components produced from the plating bath were the same components as the plating bath. In the plating components shown in Tables 1A and 1C, a blank column indicates that the component element is not added and the concentration is less than 0.005%. In addition, for the Si concentration, the ICP analysis value was displayed regardless of the intention of addition.

  A batch-type hot dipping apparatus was used for the production of the plated steel material. The plating bath temperature was a melting point + 15 ° C. However, those having a melting point of 535 ° C. or lower were all set to 550 ° C. in consideration of operability and structure control.

This device has a structure that assumes a hot dipping line, and the plating plate heating part, snout part, hot dipping bath part, wiping part, and cooling part can all be performed in an N ₂ -5% H ₂ environment. . The oxygen concentration in the snout in contact with the plating bath was set to 20 ppm or less. The plating bath temperature is shown in Table 1B and Table 1D.

A cold-rolled steel plate (carbon concentration: 0.2% by mass) having a thickness of 0.8 mm was used as the plating original plate. The steel plate cut to 100 mm × 200 mm was subjected to plating. The plate temperature during the hot dipping was monitored at the center of the plating plate. In Table 1A and Table 1C, the test example in which Ni is described in the column of the original plate is a Ni-plated steel plate in which Ni plating is applied to the cold-rolled steel plate in a Watt bath in advance with an adhesion amount of about 2.0 g / m ^2. It was.

Before immersion in the plating bath, the surface of the plating original plate is reduced by holding it at 800 ° C. for 1 minute in a furnace having an oxygen concentration of 20 ppm or less with N ₂ -5% H ₂ gas, and then cooled with N ₂ gas to cool the immersion plate temperature. After reaching the melting point + 40 ° C., it was immersed in a plating bath for about 3 seconds. After immersion in the plating bath, the film was pulled up at a pulling rate of 100 mm / sec. At the time of pulling up, the plating adhesion amount was adjusted with N ₂ wiping gas. The wiping is completed within + 5 ° C. just above the melting point. The plating thickness was adjusted to 20 μm (± 2 μm). During cooling, N ₂ gas cooling was performed, and the plated steel sheets were cooled to the cooling rates shown in Tables 1A and 1C to room temperature. Thus, various plated steel materials were manufactured.

First, a 10 mm square was cut out from the plated steel material, FIB sampling was performed from three places, and “○” was not confirmed for those in which the quasicrystalline phase defined in this specification having an equivalent circle diameter of 1 μm or more was confirmed. The thing was set as "x". The results are shown in Table 1B and Table 1D.
Among the quasicrystals, those in which the Al phase was not dispersed in the phase or were polygonal, and those that were considered to be primary crystal quasicrystals were observed as “◯”.

  Furthermore, in order to measure the volume fraction of the constituent phase inside the plating layer, after embedding and polishing the plating layer cross section, SEM-EPMA cross section observation is performed, the structure is identified from the backscattered electron image, quantitative / point analysis, and the plating layer cross section The eutectic structure and the Al phase area ratio were calculated by computer image analysis. Three samples were taken from the same plated steel sheet, and the average value of the three fields of view was taken as the volume ratio (area ratio). The results are shown in Table 1B and Table 1D. The primary Al phase was clearly distinguishable from Al contained in the eutectic structure.

A 30 mm square was cut out from the plated steel sheet, and the Vickers hardness was measured on the plated surface. The load was 10 gf, and an average of 30 points was Vickers hardness.
In order to investigate the seawater resistance of the plating layer, a plated steel sheet with a 50 mm square window is prepared with tape and immersed in an artificial seawater (manufactured by Yashima Pharmaceutical) and a water tank provided with an average flow rate of 3 m / min. Soaked for 70 hours. After immersion, the corrosion products adhering to the surface of the plated steel sheet were removed with 5% citric acid, and the corrosion weight loss was measured. Seawater resistance was evaluated in terms of corrosion weight loss and density, converted to corrosion thickness reduction. The evaluation criteria were as follows. The results are shown in Table 1B and Table 1D.

AAA: Corrosion thickness is less than 1 μm A: Corrosion thickness is 1 to 3 μm
B: Corrosion thickness is over 3μm

  In order to evaluate the workability of the plating layer, V bending (JIS Z 2248) was used. The plated steel plate was cut into 50 × 90 mm, and the molded body was used with a 1R-90 ° V-shaped die press. In order to evaluate more severe workability, the molded body was used with a 5R-90 ° V-shaped die press. In a hard plated steel sheet containing a quasicrystal, the peeled area tends to increase when the R value is looser. Tape peeling was performed in the valley. A cellophane tape having a width of 24 mm was pressed against the bent portion and pulled apart, and a 90 mm long portion of the cellophane tape was visually determined. The evaluation criteria were as follows. The results are shown in Table 1B and Table 1D.

AAA: Peeling part does not occur AA: Peeling part is partly peeled off (less than 5% with respect to the processed part area)
A: There is a part where the peeled part is peeled on the line (less than 5 to 20% with respect to the processed part area)
B: Exfoliation part is almost exfoliation (20% or more with respect to the processing part area)

  In order to evaluate more severe processing, after molding with a 2R-90 ° V-shaped die press, a flat plate is further bent back into a flat plate. After processing the V-shape, a cellophane tape having a width of 24 mm was pressed against the place where it was a valley, and the cellophane tape was pulled apart to visually determine the portion of the cellophane tape having a length of 90 mm. The evaluation criteria were as follows. The results are shown in Table 1B and Table 1D.

AAA: Peeling part does not occur AA: Peeling part is partly peeled off (less than 5% with respect to the processed part area)
A: There is a part where the peeled part is peeled on the line (less than 5 to 20% with respect to the processed part area)
B: Exfoliation part is almost exfoliation (20% or more with respect to the processing part area)

  The processed portion corrosion resistance was evaluated using a sample 5R-90 ° V-bend sample after V-shaped processing and a 2R-90 ° bent-back flat plate sample (samples subjected to tape peeling test were used). . JASOM 609-91 was used with the V-bent valley as the upper surface, or the valley-back bent back portion as the upper surface, and in each case, determination was made based on the occurrence of red rust from the processed portion. The evaluation criteria were as follows. The results are shown in Table 1B and Table 1D.

AAA: No red rust after 240 cycles of JASO A: No red rust after 180-240 cycles of JASO B: Red rust occurs in less than 180 cycles of JASO

  In order to confirm the change in appearance of the plating under high humidity environment, the plated steel sheet sample (50x50mm) was left in a constant temperature and humidity chamber at 85 ° C and 98% humidity for 2 weeks in the atmospheric environment. The appearance of was visually evaluated. The results are shown in Table 1B and Table 1D.

AAA: Yellowing / blackening not observed (yellowing area less than 5%)
AA: Yellowing present (yellowing area 5% or more)
A: In addition to yellowing, blackening (yellowing or blackening area 5% or more)

As shown in Table 1A to Table 1D, it can be seen that the plated steel material of the present invention is excellent in both corrosion resistance and workability.
In particular, no. 28, 34, 35, 36, 40 and 45, the chemical composition of the Al—Mg alloy layer is Zn: 5% to 65%, Mg: 2.5% to 30%, Ca: 0.1% to 3 %, Y: 0% to 3%, La: 0% to 3%, Ce: 0% to 3%, 10% by volume or more of primary Al phase and 5% by volume or more of eutectic In addition, since the primary Al phase and the eutectic structure are 70% by volume or more in total, the corrosion resistance and workability are further improved.
No. 42, 43, 47, 50, 52, 53, 54, 55, 58, 59, 60, 61, 62, 63, 64, 65 and 66, the chemical composition of the Al-Mg alloy layer is Zn: 5% ~ 58%, Mg: satisfying the conditions of 2.5% to 25%, and containing 35% by volume or more of primary Al phase and 5% by volume or more of eutectic structure, primary crystal Al phase and eutectic Since the structure is 85% by volume or more in total, the corrosion resistance and workability are further improved.

  On the other hand, the plated steel material of the comparative example included “B” evaluation in the evaluation items of corrosion resistance and workability, and either or both of corrosion resistance and workability were not satisfied.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Quasicrystalline phase, 2 ... Eutectic structure, 3 ... Al phase, 4 ... Eutectic structure, 5 ... Quasicrystalline phase, 6 ... Al phase.

Claims (5)

A steel material, and a plating layer including an Al-Fe alloy layer and an Al-Mg alloy layer disposed on the surface of the steel material,
The Al-Fe alloy layer is formed on the surface of the steel material, and has a thickness of 100 nm or more and 15 μm or less.
The Al—Mg alloy layer is formed on the Al—Fe alloy layer, and includes a quasicrystalline phase having an average equivalent circle diameter of more than 1 μm and an Al phase having a crystal grain size of 2 μm or less dispersed in the quasicrystalline phase. Containing eutectic structure containing 5% by volume or more,
The chemical component composition of the Al-Mg alloy layer is mass%,
Zn: 5% to 83%,
Mg: 2.5% to 35%,
Ca: 0% to 5%,
Y: 0% to 3.5%,
La: 0% to 3.5%,
Ce: 0% to 3.5%
Si: 0% to 10%,
Cr: 0% to 2.5%
Ti: 0% to 2.5%,
Ni: 0% to 2.5%,
Co: 0% to 0.5%,
V: 0% to 0.5%,
Nb: 0% to 0.5%,
Cu: 0% to 2.5%,
Sn: 0% to 2.5%
Fe: 0% to 3%,
Mn: 0% to 2.5%
Sr: 0% to 0.5%,
Sb: 0% to 0.5%,
Pb: 0% to 0.5%
An Al—Mg based hot-dip galvanized steel material satisfying Ca + Y + La + Ce ≦ 5, and the balance being made of Al and impurities. The chemical component composition of the Al-Mg alloy layer is
Zn: 5% to 65%
Mg: 2.5% to 30%,
Ca: 0.1% to 3%,
Y: 0% to 3%
La: 0% to 3%,
Ce: satisfies the condition of 0% to 3%,
The Al—Mg alloy layer includes 10 volume% or more of primary crystal Al phase and 5 volume% or more of the eutectic structure, and the primary crystal Al phase and the eutectic structure total 70 volumes. The Al—Mg hot-dip galvanized steel material according to claim 1, which includes at least%. The chemical component composition of the Al-Mg alloy layer is
Zn: 5% to 58%
Mg: satisfying the condition of 2.5% to 25%,
The Al—Mg alloy layer contains 35% by volume or more of primary crystal Al phase and 5% by volume or more of the eutectic structure, and the primary crystal Al phase and the eutectic structure total 85 volumes. The Al—Mg-based hot-dip galvanized steel material according to claim 1 or claim 2 containing at least%.   The thickness of the said Al-Fe alloy layer is 5 micrometers or less, The Al-Mg type hot dip plated steel material as described in any one of Claim 1 thru | or 3.   The Al-Mg system hot-dip plated steel material according to any one of claims 1 to 4, wherein the hardness of the Al-Mg alloy layer is 100 Hv or more.