WO2013187419A1 - Magnesium alloy plate and magnesium alloy member - Google Patents

Abstract

Provided are a magnesium alloy plate which is excellent in terms of workability concerning plastic working, e.g., pressing, and a magnesium alloy member. The magnesium alloy plate is a plate obtained by rolling a magnesium alloy and has a cross section which is parallel with the thickness direction thereof and in which if the crystal grains present in the cross section are each examined for major-axis length and minor-axis length and for aspect ratio, which is the ratio of the major-axis length to the minor-axis length, i.e., (major-axis length)/(minor-axis length), and if the crystal grains having an aspect ratio of 3.85 or higher are taken as elongated grains, then the area fraction of the elongated grains in the cross section is 3-20%.

Description

Magnesium alloy plate and magnesium alloy member

The present invention relates to a magnesium alloy sheet that has been rolled, and a magnesium alloy member formed from the magnesium alloy sheet. In particular, it relates to a magnesium alloy plate excellent in plastic workability.

A magnesium alloy that is lightweight and excellent in specific strength and specific rigidity has been used as a constituent material for various members such as casings of portable electric and electronic devices such as mobile phones and notebook personal computers and automobile parts.

The magnesium alloy typically has a dense hexagonal crystal structure, and the sliding surface at a low temperature such as room temperature is only the bottom surface. Therefore, the conventional magnesium alloy member is typically a cast material obtained by die casting or thixomolding.

In recent years, as described in Patent Documents 1 and 2, it has been studied to perform rolling on a magnesium alloy and to perform plastic working such as press working on the obtained rolled plate. When plastic processing such as rolling or pressing is performed on a magnesium alloy, the material is heated as described in Patent Document 1, or a processing jig such as a rolling roller or a press die is heated. Plastic workability can be improved by using inter-process.

JP 2011-131274 A JP-A-2005-298888

Development of magnesium alloy plates with excellent plastic workability is desired in the production of plastic working members such as press-formed bodies composed of magnesium alloys. In addition, it is desired to develop a magnesium alloy plate capable of producing a plastic processed member having excellent mechanical properties such as strength and impact resistance.

Patent Document 1 discloses that a rolled sheet having excellent plastic workability can be obtained by performing warm rolling while controlling both the material and the rolling roller at a specific temperature. This rolled plate is sufficiently deformed due to rolling and has suppressed crystal grain coarsening by the above-described temperature control, resulting in dynamic recrystallization during press working and plastic working. Excellent in properties. Here, the mechanical properties of the magnesium alloy generally depend on the grain size. The finer the crystal grains, the better the strength and elongation. The rolled sheet has suppressed crystal grain coarsening, that is, the crystal grains are fine. Therefore, the rolled plate is excellent in strength and elongation, and a press-molded body made of the rolled plate is also excellent in strength and impact resistance.

However, when a magnesium alloy having a dense hexagonal structure is rolled, the c-axis of the crystal (the axis perpendicular to the (0001) plane that is the bottom surface) is formed on the rolling surface (of the surface of the material in contact with the rolling roller). Oriented perpendicular to the surface. That is, the rolled sheet has a structure in which the (0001) plane is oriented parallel to the rolled plane. For this reason, this rolled sheet has anisotropy with respect to plastic working, is difficult to bend in an arbitrary direction, and is inferior in plastic workability. Therefore, it is desired to develop a magnesium alloy sheet with relaxed anisotropy for plastic working.

Patent Document 2 discloses a method for manufacturing a magnesium alloy sheet in which both the treatment with a roller leveler and the recrystallization heat treatment are sequentially performed a plurality of times after warm rolling. The rolled sheet obtained by this manufacturing method can be bent and formed at a low temperature because the c-axis ({0002} plane) is inclined with respect to the rolled surface. On the other hand, it is inferior in mechanical properties (particularly strength and rigidity), easily deforms even at room temperature, and dent deformation can occur due to impact such as dropping.

In addition, a magnesium alloy to which Li is added in an amount of about 10.5 mass% to 16 mass% has a cubic crystal structure and can be pressed at room temperature. However, this magnesium alloy is also easily deformed at room temperature and is inferior in strength and impact resistance. In addition, this magnesium alloy is inferior in corrosion resistance due to a large amount of Li.

Therefore, one of the objects of the present invention is to provide a magnesium alloy sheet that can build a magnesium alloy member that is excellent in strength and impact resistance and that is excellent in plastic workability. Another object of the present invention is to provide a magnesium alloy member having excellent strength and impact resistance.

The magnesium alloy plate of the present invention is obtained by rolling a magnesium alloy, takes a cross section parallel to the thickness direction of the magnesium alloy plate, and obtains a major axis and a minor axis for each crystal grain in the cross section, A section in which the ratio of the major axis to the minor axis is an aspect ratio, and the crystal grains having the aspect ratio of 3.85 or more are elongated grains, and the area ratio of the elongated grains to the section is 3% or more and 20% or less. Have

The magnesium alloy sheet of the present invention is excellent in plastic workability.

(A) shows sample No. 2 is a reverse pole figure orientation map (IPF Map) and (B) of the elongated grains by SEM-EBSD method. 2 is a graph showing the relationship between the aspect ratio of the crystal grains and the existence frequency in (C). 2 is a pole figure of the (0001) plane of elongated grains in FIG. Sample No. (A) is an angle graph of the rolling direction (RD direction) in a crystal grain whose angle in the plate width direction from the normal direction is within 5 °, (B) It is an angle graph of the plate | board width direction (TD direction) in the crystal grain whose angle of the rolling direction from a normal line direction is less than 20 degrees. (A) is explanatory drawing used for description of the operation | work which extracts an expansion | extension grain, (B) is explanatory drawing used for description of the operation | work which extracts the crystal grain of a specific angle from the pole figure of (0001) plane. (A) shows sample No. 3 is a reverse pole figure orientation map (IPF Map) of the elongated grains by SEM-EBSD method. 3 is a graph showing the relationship between the crystal grain aspect ratio and the existence frequency in FIG. 3 is a pole figure of the (0001) plane of elongated grains in FIG. Sample No. (A) is an angle graph of the rolling direction (RD direction) in a crystal grain in which the angle in the plate width direction from the normal direction is within 5 °, (B) It is an angle graph of the plate | board width direction (TD direction) in the crystal grain whose angle of the rolling direction from a normal line direction is less than 20 degrees. (A) shows sample No. 4 is a reverse pole figure orientation map (IPF Map) and (B) of the elongated grains by the SEM-EBSD method. 4 is a graph showing the relationship between the aspect ratio of the crystal grains and the existence frequency in FIG. 4 is a pole figure of the (0001) plane of elongated grains in FIG. Sample No. (A) is an angle graph of the rolling direction (RD direction) in a crystal grain in which the angle in the plate width direction from the normal direction is within 5 °, (B) It is an angle graph of the plate | board width direction (TD direction) in the crystal grain whose angle of the rolling direction from a normal line direction is less than 20 degrees.

[Description of Embodiment of the Present Invention]
The inventors of the present invention produced rolled plates made of a magnesium alloy under various conditions, and performed press work using the rolled plates as raw material plates to examine workability. As a result, it was found that a material plate from which a molded body having excellent surface properties was obtained, having a specific structure, hardly cracked or roughened even when subjected to strong processing. Moreover, the obtained molded object acquired the knowledge that it was excellent in intensity | strength and impact resistance. Furthermore, the inventors have found that this material plate can be manufactured by using a material composed of a specific structure as a material for rolling, and by subjecting the material for rolling to warm rolling under specific conditions. The present invention is based on the above findings. First, embodiments of the present invention will be listed and described.

(1) The magnesium alloy plate according to the embodiment is obtained by rolling a magnesium alloy, takes a cross section parallel to the thickness direction of the magnesium alloy plate, and has an area ratio of elongated grains to the cross section of 3 % And 20% or less. Elongated grains are obtained by determining the major axis and minor axis for each crystal grain in the cross section, and the ratio of the major axis to the minor axis: the major axis / minor axis is the aspect ratio, and the aspect ratio is 3.85 or more. To do.

The above-mentioned long and narrow crystal grains having a specific size: The structure in which elongated grains exist in the specific range can be said to be a structure in which the orientation is disturbed to some extent. The magnesium alloy plate of the embodiment composed of such a specific structure can relax anisotropy with respect to plastic working and has excellent plastic workability as compared with a structure in which all crystal grains are oriented in a certain direction. . Further, in the magnesium alloy plate of the embodiment, the crystal grains other than the elongated grains are fine and have a certain orientation by rolling (a structure in which the c-axis is oriented perpendicular to the rolling surface). Is building. Therefore, the magnesium alloy plate of the embodiment can suppress a decrease in strength due to the presence of elongated grains, and can have high strength and elongation due to a finely oriented structure, and thus is excellent in strength, elongation, and impact resistance. In addition, the section where the area ratio of the elongated grains is 3% or more and 20% or less typically includes a section parallel to the rolling direction.

(2) As an example of the magnesium alloy plate of the embodiment, a pole figure of the (0001) plane of the elongated grain is taken, and a crystal whose angle θ _TD in the sheet width direction on the (0001) plane of the elongated grain is within 5 ° When the grain is extracted and the angle θ _RD in the rolling direction on the (0001) plane of the extracted crystal grain is viewed, the peak of the angle θ _{RD in} the rolling direction is 9 ° or more from the normal direction. .

Simply speaking, it can be said that the above-mentioned form has many crystal grains (hereinafter referred to as RD inclined elongated grains) in which the (0001) plane is inclined in the rolling direction. That is, the above form can be said to be a somewhat random structure in which crystal grains having different orientation directions (RD inclined elongated grains) exist, and thus is substantially composed only of crystal grains in which the c-axis is oriented perpendicular to the rolling surface. Compared to the structure, the anisotropy to plastic working can be sufficiently relaxed, and the plastic workability is excellent.

(3) As an example of a magnesium alloy plate embodiments, take the pole figure of the elongated grains (0001) plane, the crystal grain angle theta _RD in the rolling direction in the extension grains (0001) plane is within 20 ° extracting, when viewed angle theta _TD in the plate width direction of the extracted crystal grains (0001) plane, crystal grains and the normal direction angle theta _TD of the plate width direction is -20 ° or less from the normal direction To 20% or more and 70% or less with respect to the whole elongated grains.

Simply speaking, it can be said that the above-mentioned form has crystal grains (hereinafter referred to as TD inclined elongated grains) whose (0001) plane is greatly inclined in the plate width direction in a specific range. That is, since it can be said that the crystal grains having different orientation directions (TD inclined elongated grains) are present to some extent, the above configuration is substantially composed only of crystal grains in which the c-axis is oriented perpendicular to the rolling surface. Compared to the structure, the anisotropy to plastic working can be sufficiently relaxed, and the plastic workability is excellent. And since the content of TD inclination extension grain is in a specific range, the above-mentioned form controls the fall of the mechanical property by existence of TD inclination extension grain, and is excellent in intensity or impact resistance.

(4) As an example of the magnesium alloy plate of the embodiment, there is a form in which the average cross-sectional area of the elongated grains is 600 μm ² or less.

The above form is excellent in plastic workability because the elongated grains are small and it is difficult to become a starting point of cracking during plastic working.

(5) As an example of the magnesium alloy plate of the embodiment, a form in which the magnesium alloy contains aluminum (Al) in an amount of 8.3% by mass to 9.5% by mass.

A magnesium alloy containing Al in the above specific range (hereinafter referred to as a high Al magnesium alloy) is excellent in mechanical properties (particularly strength) and corrosion resistance. Therefore, the above-mentioned form is excellent in plastic workability by being a specific structure having the above-described elongated grains, and is excellent in mechanical properties (particularly strength) and corrosion resistance by being a specific composition.

An example of the magnesium alloy sheet (6) embodiment, the cross-sectional area of the elongated particle can be cited embodiment is 25 [mu] m ² Ultra 5000 .mu.m ² or less.

The above-mentioned form is excellent in plastic workability because each elongated grain is small and hardly becomes a starting point of cracking during plastic working.

(7) The magnesium alloy member according to the embodiment is formed by pressing at least a part of the magnesium alloy plate of the embodiment.

The magnesium alloy member of the embodiment is excellent in productivity as well as in shape accuracy and dimensional accuracy by using the magnesium alloy plate of the embodiment excellent in plastic workability as a raw material. Moreover, the magnesium alloy member of the embodiment is excellent in mechanical properties such as strength, rigidity, and impact resistance by being configured from the magnesium alloy plate of the embodiment that is also excellent in mechanical properties such as strength and elongation.

[Details of the embodiment of the present invention]
Hereinafter, the magnesium alloy plate and the magnesium alloy member according to the embodiment will be described in detail.

[Magnesium alloy plate]
(composition)
The magnesium alloy plate of the embodiment and the magnesium alloy member of the embodiment are composed of magnesium alloys having various compositions containing various additive elements in Mg (remainder: Mg and impurities, Mg: 50% by mass or more).

The additive element is selected from, for example, Al, Zn, Mn, Si, Be, Ca, Sr, Y, Cu, Ag, Sn, Li, Zr, Ce, Ni, Au, and rare earth elements (excluding Y and Ce). 1 type or more elements. In particular, an Mg—Al alloy containing Al is excellent in strength, rigidity, impact resistance, and corrosion resistance. As for Al content, 0.1 mass% or more is mentioned. As the Al content increases, the strength and corrosion resistance tend to be excellent. However, when the content exceeds 12% by mass, the plastic workability is deteriorated. Therefore, the content of Al is preferably 12% by mass or less, and more preferably 11% by mass or less.

Examples of the content of each element other than Al include 0.01% by mass to 10% by mass, and further 0.1% by mass to 5% by mass. In particular, a total of at least one element selected from Si, Sn, Y, Ce, Ca and rare earth elements (excluding Y and Ce) is 0.001% by mass or more, preferably a total of 0.1% by mass or more and 5% by mass. % Or less of the magnesium alloy is excellent in heat resistance and flame retardancy. Examples of the impurities in the magnesium alloy include Fe.

More specific compositions of the Mg—Al based alloy include, for example, AZ based alloy (Mg—Al—Zn based alloy, Zn: 0.2 mass% to 1.5 mass%), AM based alloy ( Mg-Al-Mn alloy, Mn: 0.15% to 0.5% by mass), AS alloy (Mg-Al-Si alloy, Si: 0.2% to 6.0% by mass) ), AX alloy (Mg—Al—Ca alloy, Ca: 0.2 mass% to 6.0 mass%), AJ alloy (Mg—Al—Sr alloy, Sr: 0.2 mass% or more) 7.0% by mass or more). In addition, Mg-Al-RE alloys (RE: rare earth elements, RE: 0.001% by mass to 5% by mass, preferably 0.1% by mass or more), and the like can be given.

Among Mg-Al alloys, alloys containing Al in excess of 7.2% by mass, especially alloys containing Al in the range of 8.3% by mass to 9.5% by mass, have mechanical properties such as strength and impact resistance. , And further excellent in corrosion resistance. Specific examples of the composition include AZ91 alloy and AZX911 alloy containing 0.5% by mass or more and 1.5% by mass or less of Zn in addition to Al.

(shape)
The magnesium alloy plate of the embodiment typically includes a rectangular plate having a rectangular planar shape. By appropriately cutting or punching, a plate having a desired planar shape such as a circle, an ellipse, or a polygon can be obtained. Moreover, it can also be set as the coil material which wound up the elongate rectangular board in the spiral shape.

(Thickness / width / length)
The magnesium alloy plate of the embodiment is typically in the form of the same thickness throughout. The thickness can be appropriately selected. When it uses for the raw material of a plastic working member, the thickness of a plastic working member substantially maintains the thickness of a raw material board. Therefore, as the magnesium alloy plate is thinner, the plastic working member can be made thinner, smaller, and lighter. Specific thicknesses are 0.1 mm or more and 2.5 mm or less, 2 mm or less, especially 1.5 mm or less, and 0.3 mm or more and 1.2 mm or less are particularly easy to use. In addition, it is allowed to have a portion having a partially different thickness, such as a through hole, a groove, or a protrusion.

Width and length of the magnesium alloy plate of the embodiment (in the case of a deformed plate such as a circular plate, an elliptical plate, or a polygonal plate, the maximum distance connecting two points on the contour line) can be selected as appropriate. For example, in the case of a rectangular plate, if it is a wide plate having a width of 100 mm or more, further 200 mm or more, particularly 250 mm or more, it can be transported from a small component such as a portable device component when used as a material for a plastic working member. Plastic working members of various sizes can be manufactured up to large ones such as equipment parts. In addition, for example, in the case of a rectangular plate, if the length plate is 50 m or more, further 100 m or more, 200 m or more, 400 m or more, when the material is used as a material for a plastic working member, the material is continuously connected to the plastic working device. It can be supplied, and plastic parts can be mass-produced. If such a long plate is a coil material wound up in a spiral shape, it is easy to carry and supply it to a plastic working apparatus.

(Form)
The magnesium alloy plate of the embodiment is at least rolled. Specifically, a rolled sheet as it is rolled and a treated sheet subjected to the following treatments after rolling are exemplified. The above treatments include heat treatment (annealing) to remove distortion introduced during rolling, anticorrosion treatment such as polishing, straightening, chemical conversion treatment and anodizing treatment, painting, decorative processing such as hairline processing, diamond cutting and etching, etc. Can be mentioned. Each of these treatments is performed in a temperature range below the recrystallization temperature of the alloy constituting the magnesium alloy plate, so that the treatment plate substantially maintains the structure immediately after rolling (a specific structure in which elongated grains exist). .

(mechanical nature)
The magnesium alloy plate of the embodiment is excellent in mechanical properties as compared with a cast plate made of a magnesium alloy having the same composition because it has a specific structure described later and is rolled. Depending on the composition, for example, when composed of a high Al magnesium alloy such as AZ91 alloy, the tensile strength: 270 MPa to 450 MPa, 0.2% proof stress: 220 MPa to 350 MPa, the elongation at break: 1% The form which satisfy | fills 15% or less is mentioned (all are room temperature). In addition, being comprised from a high Al magnesium alloy, and tensile strength and 0.2% yield strength satisfy | filling the above-mentioned range become one of the grounds which showed that rolling was performed.

(Organization)
The magnesium alloy plate of the embodiment basically has a dense hexagonal crystal structure, and at least one elongated crystal grain called an elongated grain exists. This magnesium alloy plate is comprised from the structure | tissue which contains the said elongate grain in a specific range (specific area ratio).

Elongated grains are obtained by cutting the magnesium alloy plate along a plane parallel to the thickness direction of the magnesium alloy plate, taking the minor axis and major axis of the crystal grains present on the cut surface, and taking the major axis / minor axis as the aspect ratio. , Crystal grains satisfying an aspect ratio of 3.85 or more. Details of the method of taking a cross section, the measuring method of the major axis and minor axis, and the extracting method of elongated grains will be described later. As a result of investigations by the present inventors, a rolled sheet rolled under specific conditions to be described later has a very large number of crystal grains having an aspect ratio of about 1.4 to 3.4 and some crystal grains having a large aspect ratio. Existed (area ratio 20% or less). Since the crystal grains that affect the plastic workability are considered to be elongated to some extent, in the magnesium alloy plate of the embodiment, the crystal grains satisfying an aspect ratio of 3.85 or more are defined as elongated grains. If the crystal grains excluding the elongated grains are small to some extent (preferably, the average crystal grain size is about 10 μm or less), the aspect ratio may be a large value such as 10 or more.

Elongated grains tend to be stretched in the rolling direction (advancing direction of the material) with rolling. Therefore, in order to properly extract the elongated grains, take a cross section (so-called vertical cross section) of the magnesium alloy sheet cut along a plane parallel to both the thickness direction and the rolling direction, and the minor axis of the crystal grains It can be said that measuring the major axis is appropriate. When the rolling direction of the magnesium alloy sheet can be discriminated, a cross section (that is, a longitudinal cross section) parallel to both the thickness direction and the rolling direction may be used as the measurement cross section. When the magnesium alloy plate is wound in a coil shape, for example, since the longitudinal direction usually corresponds to the rolling direction, a cross section parallel to the longitudinal direction may be used as the measurement cross section. When the magnesium alloy plate is a rectangular plate or a disc, and the rolling direction cannot be determined, an elongated grain having an aspect ratio of 3.85 or more with an arbitrary cross section parallel to the thickness direction as the measurement cross section The presence / absence of a cross section having a ratio of 3% to 20% (hereinafter, this cross section is referred to as a corresponding cross section) is determined. When it has an applicable cross section, let the direction parallel to this applicable cross section be a rolling direction of a magnesium alloy plate, and let the direction orthogonal to both a rolling direction and a thickness direction be a plate width direction.

The area ratio of the elongated grains is the sum of the areas of at least one elongated grain existing in an arbitrary field of view in the cross section, and is the ratio of the total area of the elongated grains to the area of the field of view. When the area ratio of the elongated grains is 3% or more, these elongated grains can relieve anisotropy with respect to plastic working and enhance the plastic workability, and can increase the limit drawing ratio, for example. The larger the area ratio of the elongated grains, the better the plastic workability, and it is possible to increase the limit drawing ratio and suppress the generation of cracks. However, if there are too many elongated grains, the elongated grains themselves become the starting point of cracking, causing cracks, or rough skin based on the unevenness of the elongated grains, resulting in deterioration of surface properties and productivity. Therefore, the area ratio of the elongated grains is 20% or less. The area ratio of the elongated grains is more preferably 5% or more and 15% or less.

If the elongated grains are too large, cracks and rough skin are easily caused as described above, and therefore the average cross-sectional area of the elongated grains is preferably 600 μm ² or less. If the elongated grains are too small, it is difficult to obtain an anisotropic relaxation effect on the plastic working. Therefore, it is considered that the average sectional area of the elongated grains is preferably about 100 μm ² or more. Further, the cross-sectional area of the elongated particle is preferably 25 [mu] m ² Ultra 5000 .mu.m ² or less. Area extension grains per piece is easy to suppress the smaller cracks and rough skin, 5000 .mu.m ² or less, is considered more 4800Myuemu ² or less, particularly 4500Myuemu ² or less. Area extension grains per piece is too small, since it becomes difficult to obtain the effect of alleviating the anisotropy with respect to plastic working, 25 [mu] m ² than it is believed that further 30 [mu] m ² or more.

In the dense hexagonal magnesium alloy, the elongated grains are not parallel to the surface of the magnesium alloy plate (typically, the rolling surface formed in contact with the rolling roller), the (0001) surface being a slip surface, It is preferable that it is inclined. Typically, it is preferable that the (0001) plane is inclined in at least one of the rolling direction and the sheet width direction. For example, taking a pole figure of the (0001) plane of the elongated grains, a crystal grain having a small angle θ _TD in the plate width direction on the (0001) plane (a crystal grain whose inclination from the normal direction is within 5 °) (0001) ) When the peak of the angle θ _RD in the rolling direction on the surface is seen, there is a form in which this peak exists at a position shifted from the normal direction, specifically, a form in which the peak position is 9 ° or more. In this form, since there are many crystal grains in which the (0001) plane of the elongated grains is tilted in the rolling direction, an anisotropic relaxation effect on plastic working due to the presence of the tilt-oriented crystal grains can be obtained. Excellent plastic workability. The angle of the peak position (absolute value) is preferably larger in the range of 90 ° or less.

For example, taking a pole figure of the (0001) plane of elongated grains, a crystal grain having a rolling direction angle θ _RD in the (0001) plane within a specific range (a crystal grain whose inclination from the normal direction is within 20 ° )), When the angle θ _TD in the plate width direction in the (0001) plane is viewed, the elongated grains having a large angle θ _{TD in the} plate width direction (elongated grains that are 20 ° or more from the normal direction: TD inclined elongated grains) have an area. The form which is 20% or more and 70% or less by a ratio is mentioned. The TD inclined elongated grains are crystal grains in which the (0001) plane is greatly inclined particularly in the plate width direction. The presence of 20% by area or more of such TD inclined elongated grains as a whole makes it possible to obtain an anisotropic relaxation effect on the plastic working due to the presence of the TD inclined elongated grains. Even better. The larger the area ratio of the TD inclined elongated grains, the easier it is to obtain the above-mentioned anisotropic relaxation effect. However, 70% by area or less is preferable because it causes a decrease in strength and impact resistance and deterioration of surface properties. The area ratio of the TD inclined elongated grains is more preferably 25 area% or more and 50 area% or less.

The crystal grains other than the elongated grains are all fine and have a structure in which the (0001) plane is oriented parallel to the rolled surface (structure in which the c-axis is oriented perpendicular to the rolled surface). The average crystal grain size of the crystal grains excluding the elongated grains is, for example, 1 μm or more and 10 μm or less.

[Magnesium alloy members]
The magnesium alloy member of the embodiment is a molded body in which plastic working (particularly press working) is performed on at least a part of the magnesium alloy plate of the above embodiment. For example, a member in which plastic working is performed only on a part of the magnesium alloy plate, such as a form in which plastic processing is performed on the entire magnesium alloy plate such as a cylindrical member, or an L shape or a cross-section]. A typical example of plastic working is warm working. The material temperature at the time of plastic working is 350 ° C. or less, preferably 300 ° C. or less, particularly 150 ° C. or more and 280 ° C. or less, and further 150 ° C. or more and 220 ° C. or less. In plastic processing (secondary processing) such as press processing, the time for maintaining the material at the above-described material temperature is relatively short (typically about several seconds to several minutes depending on the processing). Therefore, the magnesium alloy member of the embodiment after plastic working substantially maintains the composition and structure of the magnesium alloy plate of the embodiment, and is excellent in strength, rigidity, and impact resistance like the magnesium alloy plate of the embodiment. .

The magnesium alloy member of the embodiment is a form in which at least a part is subjected to a treatment such as a corrosion prevention treatment such as polishing, chemical conversion treatment or anodizing treatment, coating, hairline processing, decoration processing such as diamond cut processing or etching, A form having a through hole, a groove, a protrusion, or the like, or a form in which a resin molded body is joined can be used.

[Manufacturing method of magnesium alloy sheet]
The magnesium alloy plate of the embodiment having the specific structure described above can be manufactured, for example, by a manufacturing method including the following steps.
Casting process: A process of continuously casting a magnesium alloy to prepare a cast plate.
Solution treatment step: a step of subjecting the cast plate to a solution treatment to produce a solution plate.
Rolling step: A step of subjecting the solution plate to warm rolling for one pass or more.
In particular, the solution treatment is performed so that the average crystal grain after the solution treatment is more than 15 μm and less than 60 μm. In the warm rolling, the preheating temperature of the material is 220 ° C. or more and 280 ° C. or less, the temperature of the rolling roller is 200 ° C. or more and 300 ° C. or less, and the rolling reduction per pass is 30% or less.

(Casting process)
Conventionally, what cast an ingot and a thick slab as a cast material used as a rolling material is used (ingot in patent documents 2). Since the continuous casting method can be rapidly solidified, it is possible to reduce oxides and segregation and to suppress the formation of coarse crystal precipitates of more than 10 μm. That is, it is possible to reduce foreign matter that can be a starting point of cracking during rolling. In addition, since the average crystal grain size can be reduced to some extent, it is easy to suppress the generation of very coarse elongated grains (for example, one having an area of more than 600 μm ² ) or excessive elongated grains. The average crystal grain size of the cast plate is preferably 15 μm or more and 50 μm or less, and the cooling rate (in consideration of the composition of the magnesium alloy and the thickness of the cast plate so that the average crystal grain size of the cast plate is in the above range. (Casting speed) is controlled. In particular, the twin-roll continuous casting method is preferable because it is easy to form a cast plate having excellent rigidity and thermal conductivity, little segregation, and excellent rollability. The continuous casting method can easily produce a long cast plate. By using a long cast plate as a rolling material, a long rolled plate can be manufactured, and productivity of the magnesium alloy plate of the embodiment can be improved.

The thickness, width, and length of the cast plate can be selected as appropriate. For example, when the thickness is 10 mm or less, further 7 mm or less, particularly 5 mm or less, miniaturization by quenching or suppression of segregation can be achieved, and a cast plate having excellent strength can be easily obtained. For example, a long cast plate having a length of 30 m or more, further 50 m or more, particularly 100 m or more, or a wide cast plate having a width of 100 mm or more, further 200 mm or more, particularly 250 mm or more, and these are used as a rolling material. Thus, a long rolled plate or a wide rolled plate can be produced.

(Solution process)
By subjecting the cast plate to a solution treatment, it is possible to homogenize the composition, improve mechanical properties and rollability by solid solution of precipitates, and control the size of crystal grains. Solution conditions include heating temperature: 350 ° C. or higher and 420 ° C. or lower, holding time: 1 hour or longer and 15 hours or shorter. Since the solution treatment is performed at a relatively high temperature as described above, the longer the holding time, the easier the crystal grains grow. As a result, elongated grains are easily generated, leading to excessive generation of elongated grains and generation of coarse elongated grains. Therefore, the holding time in the solution treatment is shortened. Although it depends on the composition and thickness of the cast plate and the rolling conditions in the next step, the holding time is more preferably 2 hours or longer and 12 hours or shorter.

The holding time is adjusted within the above range so that the average crystal grain size of the heat-treated plate (solution-treated plate) after solution treatment is more than 15 μm and less than 60 μm. When the average crystal grain size of the solution plate is 15 μm or less, crystal grains before rolling are too small, and elongated grains are not generated sufficiently after rolling. Here, when a strain is introduced by rolling, recrystallization may occur due to the strain. If the crystal before recrystallization is too small, it does not grow sufficiently even if recrystallization is performed, and it is considered that it is difficult to form elongated grains. On the other hand, if the average crystal grain size of the solution plate is more than 60 μm, the crystal grains before rolling are too large, leading to excessive generation of elongated grains and generation of coarse elongated grains. The reason for this is that the crystals before rolling are too large, and strain due to rolling is difficult to accumulate, and recrystallization due to strain energy does not occur sufficiently, so that coarse crystals remain as they are, or coarse crystals are caused by rolling. This is considered to be further stretched. The average crystal grain size of the solution plate is more preferably 20 μm or more and 50 μm or less.

(Rolling process)
Rolling a solution plate for one pass or more improves mechanical properties by work hardening, improves workability of secondary processing (plastic processing such as press processing) by controlling the crystal structure, reduces plate thickness, etc. Can be achieved. In particular, at least one pass of rolling is warm rolling. The conditions for the warm rolling are a material preheating temperature: 220 ° C. or more and 280 ° C. or less, a rolling roller temperature: 200 ° C. or more and 300 ° C. or less, and a rolling reduction per pass: 30% or less. By subjecting a solution plate having an average crystal grain size in a specific range to warm rolling under the above-mentioned specific conditions, in a structure composed of fine crystal grains in which the c-axis is oriented perpendicular to the rolling surface. Thus, the magnesium alloy plate of the embodiment having a structure in which elongated grains exist in a specific range is obtained. In addition, when warm rolling is performed under the above-mentioned specific conditions, (1) the plastic workability of the material can be improved and cracking of the edge can be reduced, (2) the rolling reduction per pass can be increased (for example, 10% or more), the productivity can be improved, (3) surface property deterioration due to seizure or the like can be suppressed, and (4) thermal deterioration of the rolling roller can be suppressed.

If the heating (preheating) of the material is performed by separately providing a heating furnace, it is easy to uniformly heat the entire material. However, the temperature of the raw material can be lowered between the heating furnace and the contact with the rolling roller. Therefore, it is preferable to adjust the transport distance and transport time, to provide a heat insulating cover on the transport path, or to control the temperature of the atmosphere so that the material temperature immediately before contacting the rolling roller is 180 ° C. or higher. .

Although all passes in rolling may be warm rolling, cold rolling can be performed when performing rolling with a small reduction ratio by finish rolling or the like.

In rolling, it is preferable to use a lubricant because the friction between the material and the rolling roller can be reduced and the rolling can be performed satisfactorily.

When performing multiple-pass rolling, as described in Patent Document 1, if reverse rolling is performed, a long rolled plate can be manufactured with high productivity. When reverse rolling is performed, as described in Patent Document 1, it is preferable to construct a rolling system including a reel that feeds out a material, a reel that winds up the material, and a rolling roller disposed between both reels. Using this system, reverse rolling of multiple passes can be performed by reversing both reels. When each reel is configured to be housed in a heating furnace that preheats the material, a large amount of material can be preheated at a time, and the time until the preheated material is introduced between a pair of rolling rollers arranged opposite to each other is set. It can be shortened and the temperature drop of the material can be suppressed. When reverse rolling is performed, a coil material wound in a spiral shape is used as the material. Moreover, when performing reverse rolling, the coil material by which the rolled sheet was wound up in the shape of a spiral is obtained.

[Test example]
Magnesium alloy sheets were produced under various conditions, and the cross-sectional structure was examined. Further, the obtained magnesium alloy plate was subjected to press working to evaluate plastic workability.

In this test, a molten magnesium alloy having a composition equivalent to AZ91 alloy (Mg-8.7% Al-0.65% Zn, all by mass%) was prepared, and a cast plate having a thickness of 4 mm was obtained by a twin roll casting machine. Were continuously produced and wound up to produce a cast coil material. Here, the casting speed was adjusted so that the average grain size was about 15 μm to 50 μm. The produced cast coil material was housed in a heating furnace (batch furnace) and subjected to a solution treatment to produce a solution plate (solution solution coil material). Here, the solution treatment conditions were varied to vary the crystal grain size after the solution treatment. The heating temperature for the solution treatment was selected from the range of 350 ° C. to 420 ° C., and the holding time was varied. Sample No. The holding time of 100 is the shortest (0.5 hours). The retention time of 200 is the longest (100 hours). 1-No. For No. 4, the holding time was selected from the range of 1 to 15 hours, and the holding time was shortened as the sample number was smaller.

The average crystal grain size of each solutionized plate obtained after the solution treatment was measured as follows. The results are shown in Table 1. A sample for embedding is cut out from each solution-treated plate so that a cross-section parallel to the casting direction and a cross-section parallel to the plate width direction can be observed for each solution-formed plate. The cut sample for embedding is embedded in a resin, subjected to mirror polishing and etching in order, and each cross section is observed with an optical microscope, and the crystal grain size is measured by a line method. For each of the cross section in the casting direction and the cross section in the plate width direction, a micrograph with an observation magnification of 100 is taken. Three line segments corresponding to 1500 μm are drawn on the photographed micrograph, and the number of crystal particles present on each line segment is counted. Value obtained by dividing the line segment length by the number of crystal grains: The line segment length / the number of crystal grains is defined as the crystal grain size in this segment. The average value of the crystal grain size for the three line segments in the cross section in the casting direction and the crystal grain size for the three line segments in the cross section in the plate width direction is defined as the average crystal grain size.

The obtained solution coil material was rewound and subjected to multiple passes of warm rolling to produce a rolled plate (rolled coil material). Here, a rolled coil material made of a rolled plate having a thickness of 0.8 mm, a width of 250 mm, and a length of 760 m was produced (total rolling reduction: 80%). Further, here, a reverse rolling system having two heating furnaces with a built-in reel and a rolling roller disposed between both heating furnaces was used. Then, the material was preheated in a heating furnace for each pass, the material in a heated state was supplied to the rolling roller, and each reel was reversed, so that the rolling direction of the material was changed to perform reverse rolling of a plurality of passes. For all the samples, the rolling conditions were 20% to 25% reduction per pass, the preheating temperature of the material was 260 ° C., and the temperature of the rolling roller was 250 ° C.

The obtained rolled coil material was appropriately cut to prepare a structure observation sheet. Each sheet is cut along a plane parallel to both the thickness direction and the rolling direction to obtain a longitudinal section. The longitudinal section is observed with an FE-SEM (field emission scanning electron microscope), and an observation image is obtained by an EBSD method (electronic Decompose and measure by line backscatter diffraction method. Specifically, for an arbitrary field of view in the longitudinal section (here, one field of 3.16 × 10 ⁵ μm ² (0.316 mm ² )), particle grains are identified by crystal grain orientation, The area of crystal grains is obtained for all crystal grains. Further, the outline of each crystal grain is approximated by an ellipse to obtain a major axis (length in the major axis direction): a and a minor axis (length in the minor axis direction): b, respectively. Ellipse approximation is performed by a known method using the following mathematical formula.

The distance d _ij between the points x _j and y _j on the ellipse is obtained by the following formula 1. The maximum value of the distance d _ij is equal to the length of the ellipse in the major axis direction: a. The angle γ formed by the long axis and the horizontal axis can be obtained by the following formula 2. In Equation 2, x _j ^max , y _j ^max , x _i ^max , and y _i ^max are two coordinate points and take the maximum distance. The center coordinates of the ellipse are expressed by Equations 3 and 4 below. In Equations 3 and 4, x _k and y _k are coordinate points of all data included in the crystal grains. In order to obtain the length in the minor axis direction: b, Equations 5 and 6 are used to convert x _k and y _k into an elliptical basic coordinate system. And the length of short axis: b is calculated | required using the average formula shown in the following Numerical formula 7.

The aspect ratio: major axis / minor axis is determined using the major axis: a and minor axis: b of each crystal grain. Based on the aspect ratio, elongated grains are extracted from the visual field in the longitudinal section. Here, in addition to the aspect ratio, the area of crystal grains was also taken into account to extract elongated grains. Specifically, the average of the area of all crystal grains: S _ave and the standard deviation of the area of all crystal grains: σ _S were determined, and S _ave + 3σ _S was determined as the area threshold. Then, crystal grains satisfying both the aspect ratio of 3.85 or more and the area of the threshold value: S _ave + 3σ _S or more (crystal grains existing in a region surrounded by a broken-line rectangular frame in FIG. 3A). Elongated grains were used. It is considered that the elongated crystal grains can be more appropriately extracted by extracting the elongated grains in consideration of the area of the crystal grains. Note that crystal grains having an aspect ratio of 3.85 or more may be extracted as elongated grains without considering the area. Moreover, about the extracted extended grain, the average (average cross-sectional area) was calculated | required using the area of each extended grain. Furthermore, among the extracted elongated grains, the cross-sectional area of the grains having the minimum area (minimum cross-sectional area) and the cross-sectional area of the grains having the maximum area (maximum cross-sectional area) were determined. These results are shown in Table 1.

1 (A), 4 (A), and 6 (A) all show reverse pole figure orientation maps of elongated grains (FIG. 1 (A): Sample No. 2, FIG. 4 (A): Sample No. .3, FIG. 6 (A): Sample No. 4). The color key of the crystal orientation image is shown below each map. 1 (B), 4 (B), and 6 (B) all show graphs showing the relationship between the aspect ratio of crystal grains and the existence frequency (FIG. 1 (B): Sample No. 2, FIG. 4). (B): Sample No. 3, FIG. 6 (B): Sample No. 4).

For the extracted elongated grains, a pole figure about the (0001) plane of the elongated grains, where the thickness direction in the structure observation sheet is the ND direction (normal direction), the rolling direction is the RD direction, and the sheet width direction is the TD direction. Created. 1C, FIG. 4C, and FIG. 6C all show pole figures of the (0001) plane of the elongated grains (FIG. 1C: Sample No. 2, FIG. 4C): Sample No. 3, Fig. 6 (C): Sample No. 4).

In each prepared pole figure, a crystal grain having an angle θ _TD of 5 ° or less in the plate width direction: TD direction in the (0001) plane of the elongated grain is extracted. Specifically, as shown in FIG. 3B, crystal grains existing in a range where the angle θ _TD in the TD direction is −5 ° or more and + 5 ° or less are extracted. Then, the extracted grains (0001) rolling in the plane direction: creating a graph for RD direction at an angle theta _RD. 2A, 5A, and 7A are graphs showing the abundance of the angle θ _{RD in} the RD direction (FIG. 2A: Sample No. 2 and FIG. ): Sample No. 3, FIG. 7 (A): Sample No. 4). Using the created graph, the presence or absence of a peak at an angle θ _{RD in} the RD direction was examined, and the angle from the normal direction at the peak (inclination angle θ _P ) was examined. The results are shown in Table 1. Here, since there are a plurality of peaks, the maximum value (large) and the minimum value (small) of the inclination angle θ _P (absolute value) are shown in Table 1.

In each pole diagram created, the rolling direction of elongation grains (0001) plane: RD direction at an angle theta _RD extracts the crystal grains is within 20 °. Specifically, extracts the grains angle theta _RD of RD direction as shown in FIG. 3 (B) is present in the range of -20 ° or + 20 ° or less. Then, the extracted grains (0001) plate width direction of surface: creating a graph for TD direction at an angle theta _TD. FIG. 2 (B), the FIG. 5 (B), the FIG. 7 (B) is a graph showing the presence frequency of the angle theta _RD of both the TD direction (FIG. 2 (B): Sample No.2, Fig. 5 (B ): Sample No. 3, FIG. 7B: Sample No. 4). Using the created graph, the total area ratio ΣS ₂₀ of the crystal grains having an angle θ _{TD in the} TD direction of −20 ° or less from the normal direction and the crystal grains having the angle of + 20 ° or more was examined. The total area was obtained by integrating the hatched regions in FIGS. 2B, 5B, and 7B. The results are shown in Table 1.

Crystal grain area, ellipse approximation, calculation of major axis / minor axis / aspect ratio, extraction of elongated grains, creation of pole figure, tilt angle θ _{P at} peak of angle _{RD in} RD direction, total area ratio of crystal grains ΣS ₂₀ can be easily and automatically performed by using commercially available calculation software attached to a commercially available SEM-EBSD system. Here, SUPRA35VP manufactured by Carl Zeiss was used as the SEM, and OIM Analysis 5.31 manufactured by EDAX-TSL was used as the EBSD software.

After correcting the obtained rolled coil material, surface polishing was performed, and the obtained polishing plate was subjected to press working to evaluate press formability as plastic workability. For the correction, a known roller leveler device (see Patent Document 1) was used, and it was warm (roll temperature: 250 ° C.). Polishing was performed wet using a polishing belt (polishing amount: about 30 μm in total on both sides).

The press formability was evaluated based on (1) limit drawing ratio, (2) cracking due to pressing, and (3) surface roughness of the pressed portion. The press working conditions are shown below.

(1) Limit drawing ratio: A cylindrical deep drawing test is performed warm (250 ° C.) using a cylindrical punch having a diameter of 50 mm and a shoulder R = 2 mm. As the drawing material, the above polishing plate was cut into a circular shape, and circular plates with various diameters D (mm) were prepared. Then, the limit drawing ratio (LRD) was examined. The limit drawing ratio is assumed to be material diameter: Dmax / punch diameter: d (here, 50 mm).

(2) Cracking by pressing: A right-angle bending test is performed warm (250 ° C.) using a prismatic punch with a punch R = 0 mm. As a bending material, a rectangular plate (length: 200 mm) obtained by cutting the above polishing plate into a predetermined length was prepared. Then, after bending at a right angle, the presence or absence of cracks on the outer peripheral surface of the bent portion was examined by visual confirmation. Evaluate as ◯ that there is no crack.

(3) Surface roughness of the pressed portion: The surface roughness of the outer peripheral surface of the bent portion was measured in the material subjected to the right-angle bending test of (2) above. The surface roughness was measured according to JIS B 0601 (2001) / ISO 4287 (1997) using a commercially available roughness measuring device, with an arithmetic average roughness Ra.

As shown in Table 1, there are a plurality of elongated grains having an aspect ratio of 3.85 or more, and a cross section having an area ratio of 3% or more and 20% or less (here, parallel to both the thickness direction and the rolling direction). Sample No. having a cross section). 1-No. 4 shows that it is excellent in workability of plastic working such as press working. Here, Sample No. 1-No. It can be seen that No. 4 has a large limit drawing ratio of more than 2 and is capable of strong working, and that cracks hardly occur even when bending at right angles, the bent portion is smooth, and the surface properties are excellent.

And, as shown in FIGS. 1 (A), (B), FIGS. 4 (A), (B), FIGS. 6 (A), (B), etc., the magnesium alloy plate excellent in plastic workability as described above, It can be said that it has a structure in which fine crystal grains having a small aspect ratio and elongated crystal grains: elongated grains are mixed. From this, sample no. 1-No. No. 4 contains irregularly shaped crystal grains in a specific range, so that the anisotropy to plastic working is relaxed and the plastic workability is lower than the case of being composed of fine crystal grains with a uniform shape. It is thought that it was raised. Further, many of the elongated grains here can be said to be crystal grains in which the (0001) plane is inclined with respect to both the rolling direction and the sheet width direction, that is, the c-axis is inclined with respect to the rolling plane. Specifically, the inclination angle θ _P satisfies 9 ° or more (here, both the maximum value and the minimum value of the inclination angle θ _P are 9 ° or more), or the total area ratio ΣS ₂₀ is 20% or more and 70%. Satisfy the following: By containing crystal grains in which the c-axis is inclined with respect to the rolling surface in a specific range, the sample No. 1-No. It is considered that No. 4 was able to further relax the anisotropy with respect to plastic working and further improved the plastic workability. In addition, since the average cross-sectional area of the elongated grains is 600 μm ² or less, it is considered that the elongated grains are less likely to become the starting point of cracking, and the plastic workability is improved. Further, when the individual elongated grains are viewed, since the cross-sectional area of the elongated grains is more than 25 μm ^{2 and} less than or equal to 5000 μm ^2, it is considered that the elongated grains are less likely to become a starting point of cracking and the plastic workability is improved.

Test pieces were prepared from the prepared polishing plates, and the tensile strength (room temperature) and 0.2% proof stress (room temperature) were measured using a commercially available tensile test apparatus. As a result, sample no. 1-No. All of No. 4 were high strength, with tensile strength: 270 MPa or more and 0.2% proof stress: 220 MPa or more. The reason for such a result is that the content of the elongated grains in which the c-axis is oriented non-orthogonally with respect to the rolling surface is within a specific range, and substantially all of the crystal grains other than the elongated grains are: It is considered that high strength was maintained by being fine and having the c-axis oriented perpendicular to the rolling surface. Further, by using such a high-strength magnesium alloy plate as a raw material, the magnesium alloy member subjected to the above-described press working is also expected to be high-strength and excellent in impact resistance and difficult to dent.

And the magnesium alloy plate excellent in plastic workability as described above is subjected to a solution treatment on the continuous cast material, the crystal grain size after the solution treatment is in a specific range, and the preheating temperature of the material during rolling and It can be said that it can be manufactured by controlling the temperature of the rolling roller to a specific temperature.

In addition, this invention is not limited to embodiment mentioned above, In the range which does not deviate from the summary of this invention, it can change suitably. For example, magnesium alloy composition, sheet thickness / width / length, manufacturing conditions (solution temperature / holding time, rolling reduction per pass, material temperature / rolling roller temperature during rolling, total rolling reduction), etc. It can be changed as appropriate.

The magnesium alloy sheet of the present invention can be suitably used as a material for a magnesium alloy member that has been subjected to various plastic workings such as press working such as bending, drawing, and shearing, forging, and upsetting. The magnesium alloy member of the present invention is a constituent member of various electric / electronic devices (more specifically, a portable or small electric / electronic device casing or reinforcing material), a transport device such as an automobile or an aircraft. It can be suitably used for structural members, exterior members such as various cases and covers, skeleton members, bags, and the like.

Claims (7)

1. A magnesium alloy sheet obtained by rolling a magnesium alloy,
   Taking a cross section parallel to the thickness direction of the magnesium alloy plate, the major axis and the minor axis are obtained for each crystal grain in the section, the ratio of the major axis to the minor axis is the aspect ratio, and the aspect ratio is 3.85 or more. A magnesium alloy plate having a cross section in which an area ratio of the elongated grains to the cross section is 3% or more and 20% or less when a certain crystal grain is an elongated grain.
2. Taking a pole figure of the (0001) plane of the elongated grain, a crystal grain whose angle θ _TD in the plate width direction on the (0001) plane of the elongated grain is within 5 ° is extracted, and (0001) of the extracted grain 2. The magnesium alloy sheet according to claim 1, wherein when the angle θ _RD in the rolling direction on the surface is viewed, the peak of the angle θ _{RD in} the rolling direction exists at 9 ° or more from the normal direction.
3. Taking a pole figure of the (0001) plane of the elongated grain, extracting a crystal grain having a rolling direction angle θ _RD within 20 ° in the (0001) plane of the elongated grain, and (0001) plane of the extracted grain When the angle θ _TD in the plate width direction is viewed, the total area ratio of the crystal grains in which the angle θ _{TD in the} plate width direction is −20 ° or less from the normal direction and the crystal grains that are + 20 ° or more from the normal direction The magnesium alloy sheet according to claim 1 or 2, wherein is 20% or more and 70% or less with respect to the entire elongated grains.
4. The magnesium alloy sheet according to any one of claims 1 to 3, wherein an average cross-sectional area of the elongated grains is 600 袖 m ² or less.
5. The magnesium alloy sheet according to any one of claims 1 to 4, wherein the magnesium alloy contains 8.3 mass% or more and 9.5 mass% or less of Al.
6. Magnesium alloy sheet according to any one of claims 1 to 5 cross-sectional area of the elongated particle is 25 [mu] m ² Ultra 5000 .mu.m ² or less.
7. A magnesium alloy member obtained by pressing at least a part of the magnesium alloy plate according to any one of claims 1 to 6.

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