CN113825850A

CN113825850A - Magnesium alloy sheet material, press-formed body, and method for producing magnesium alloy sheet material

Info

Publication number: CN113825850A
Application number: CN202080003635.0A
Authority: CN
Inventors: 吉田雄; 吉田克仁; 中田大贵; 大桥秀亮; 镰土重晴
Original assignee: Sumitomo Electric Industries Ltd; Nagaoka University of Technology NUC
Current assignee: Sumitomo Electric Industries Ltd; Nagaoka University of Technology NUC
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-12-21
Also published as: WO2021214890A1; JPWO2021214890A1

Abstract

A magnesium alloy sheet material comprising a magnesium-based alloy, wherein the magnesium-based alloy has: a composition containing 2.0 mass% or more and less than 4.5 mass% of Al; and the following organization: when the crystal orientation is measured by the EBSD method, fb/fa satisfies 10 or more where fa is the proportion of the number of pixels having a bottom surface inclined at 0 DEG to 10 DEG with respect to the plate surface, fb is the proportion of the number of pixels having a crystal orientation inclined at 25 DEG to 45 DEG with respect to the plate surface, and mD is the Schmidt factor of bottom surface slip in the stretching direction in the direction orthogonal to both the plate width direction and the plate thickness direction, mC is the Schmidt factor of bottom surface slip in the stretching direction in the plate width direction, and mD is the Schmidt factor of bottom surface slip in the stretching direction in the direction inclined at 45 DEG, and mL/mC and mL/mD satisfy 0.9 or more and less than 1.3, and the maximum value of the relative intensity of the crystal orientation of the bottom surface satisfies 5.2 or less.

Description

Magnesium alloy sheet material, press-formed body, and method for producing magnesium alloy sheet material

Technical Field

The present disclosure relates to a magnesium alloy sheet material, a press-formed body, and a method for manufacturing a magnesium alloy sheet material.

Background

The magnesium alloy sheet material of patent document 1 is produced by heating an alloy sheet material containing 1.0 mass% or more and 10.0 mass% or less of Al at 490 to 566 ℃ to perform hot rolling, and annealing at 300 to 450 ℃ after rolling.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2010-133005

Disclosure of Invention

The magnesium alloy sheet to which the present disclosure relates is a magnesium alloy sheet comprising a magnesium-based alloy, wherein,

the magnesium-based alloy has:

a composition containing 2.0 mass% or more and less than 4.5 mass% of Al; and

the following organization: the crystal orientation is measured by the EBSD method, wherein fb/fa satisfies 10 or more when the ratio of the number of pixels in which the crystal orientation of the bottom surface among all the pixels in one field of view is inclined by 0 DEG to 10 DEG with respect to the plate surface is fa, the ratio of the number of pixels in which the crystal orientation is inclined by 25 DEG to 45 DEG with respect to the plate surface is fb, the Schmidt factor of bottom surface slip in which the direction orthogonal to both the plate width direction and the plate thickness direction is the stretching direction is mL, the Schmidt factor of bottom surface slip in which the plate width direction is the stretching direction is mC, and the Schmidt factor of bottom surface slip in which the direction inclined by 45 DEG with respect to both the orthogonal direction and the plate width direction is the stretching direction is mD, and mL/mC and mL/mD satisfy 0.9 or more and less than 1.3, and the maximum value of the relative strength of the crystal orientation of the bottom surface satisfies 5.2 or less.

The present disclosure relates to pressed shapes comprising the magnesium alloy sheet of the present disclosure.

The method for producing a magnesium alloy sheet material according to the present disclosure includes:

a step for producing a plate-like casting material containing a magnesium-based alloy;

a step of performing a first heat treatment on the cast material to produce a treated material;

a step of rolling the treatment material with a plurality of passes by a rolling roll to produce a rolled material; and

a step of subjecting the rolled material to a second heat treatment, wherein

In the step of producing the above-mentioned cast material,

the magnesium-based alloy has a composition containing 2.0 mass% or more and less than 4.5 mass% of Al,

the cooling rate during casting is 100 ℃/sec or more and 2000 ℃/sec or less,

the thickness of the cast material is 2mm to 6mm,

the first heat treatment is performed by heating the casting material to 460 ℃ to 510 ℃,

in the step of producing the rolled material described above,

the preheating temperature of the treatment material and the temperature of the rolling rolls are heated to 170 ℃ to 270 ℃,

a plurality of passes from the rolling of the k-th pass to the rolling of the n-th pass as the final pass are performed under specific conditions,

the specific conditions are as follows:

the temperature of the plate immediately after the plate comes out of the rolling rolls in each pass is made lower than the recrystallization temperature of the magnesium-based alloy,

the reduction ratio from the k-th pass to the n-th pass is 40% or more,

k is an integer of 1 to n-1,

the second heat treatment is performed by heating the rolled material to 180 ℃ or higher and 425 ℃ or lower.

Drawings

Fig. 1 is a perspective view schematically showing a magnesium alloy plate material according to an embodiment.

Fig. 2 is a perspective view showing an outline of crystals of a magnesium alloy plate material according to an embodiment.

Fig. 3 is a perspective view schematically showing a press-molded body according to an embodiment.

Fig. 4 is a view for explaining a manufacturing process of the method for manufacturing a magnesium alloy sheet material according to the embodiment.

Fig. 5 is a diagram illustrating a cooling rate in a casting process in the method for producing a magnesium alloy plate material according to the embodiment.

Fig. 6 is a view illustrating a twin roll casting apparatus used in the method of manufacturing a magnesium alloy sheet according to the embodiment.

Fig. 7 is a diagram illustrating a rolling apparatus used in the method for producing a magnesium alloy sheet material according to the embodiment.

Fig. 8 is a bottom polar view obtained by the EBSD method of sample No. 1.

FIG. 9 is a bottom polar view of sample No. 11 obtained by the EBSD method.

Fig. 10 is an explanatory view illustrating a method of determining a total angle occupied by an area in which a relative intensity between a point inclined by 25 ° and a point inclined by 45 ° is 2.0 or more and less than 5.7 in a bottom surface polar diagram.

Detailed Description

[ problem to be solved by the present disclosure ]

The magnesium alloy sheet material is preferably excellent in plastic workability at room temperature and small in anisotropy of strength. The anisotropy of strength means that the strength differs depending on the direction of the magnesium alloy sheet material. When the anisotropy of strength is large, the stress at the start of deformation changes depending on the direction of load, for example, in the case of performing a simulation of press working or the like. Therefore, the difficulty in design such as the setting of parameters becomes complicated is increased. Therefore, the ease of use of the magnesium alloy sheet material is deteriorated.

Accordingly, an object of the present disclosure is to provide a magnesium alloy sheet material having excellent plastic workability at normal temperature and small anisotropy of strength.

In addition, another object of the present disclosure is to provide a press-formed body including the above magnesium alloy sheet material.

Another object of the present disclosure is to provide a method for producing a magnesium alloy sheet material that can produce a magnesium alloy sheet material having excellent plastic workability at room temperature and small strength anisotropy.

[ Effect of the present disclosure ]

The magnesium alloy sheet material according to the present disclosure is excellent in plastic workability at room temperature and has a small anisotropy of strength.

The press-formed body according to the present disclosure is excellent in productivity.

The method for producing a magnesium alloy sheet according to the present disclosure can produce a magnesium alloy sheet having excellent plastic workability at room temperature and small anisotropy of strength.

Description of embodiments of the present disclosure

First, embodiments of the present disclosure will be described by way of example.

(1) A magnesium alloy sheet according to one embodiment of the present disclosure is a magnesium alloy sheet including a magnesium-based alloy, wherein,

the magnesium-based alloy has:

a composition containing 2.0 mass% or more and less than 4.5 mass% of Al; and

The magnesium alloy sheet is excellent in plastic workability at normal temperature and has a small anisotropy of strength. The reason why the plastic workability at room temperature is excellent is that when fb/fa satisfies 10 or more, the crystal orientation of the bottom surface, that is, the proportion of the number of crystals whose crystal orientation of the (0001) plane is inclined by 25 ° or more and 45 ° or less with respect to the plate surface is large, and the proportion of the number of crystals whose crystal orientation of the (0001) plane is inclined by 0 ° or more and 10 ° or less with respect to the plate surface is small. The reason why the anisotropy of strength is small is that crystals having a crystal orientation of the bottom surface inclined at 25 ° or more and 45 ° or less with respect to the plate surface exist substantially uniformly in any one of the orthogonal direction, the plate width direction, and the inclined direction by making the maximum value of the relative strength of mL/mC and mL/mD and the crystal orientation of the bottom surface satisfy a specific range. Therefore, the magnesium alloy sheet material easily exhibits the same bending strength against deformation in various load directions. Further, since the magnesium alloy sheet material contains Al in the above range, the plastic workability at normal temperature is not easily deteriorated, and the strength and corrosion resistance are excellent.

(2) As an embodiment of the magnesium alloy sheet material described above,

mention may be made of: the average crystal grain diameter of the structure measured by the EBSD method is 2 to 7 μm.

When the average crystal grain size is 2 μm or more, the magnesium alloy sheet material is excellent in plastic workability. In addition, the magnesium alloy sheet material is easily work hardened to improve strength. Further, the magnesium alloy sheet material can have a uniform elongation. The magnesium alloy sheet material is excellent in strength if the average crystal grain size is 7 μm or less.

(3) As an embodiment of the magnesium alloy sheet material described above,

mention may be made of: the fa is 2 or less.

When fa is 2 or less, the magnesium alloy sheet material has a small proportion of the number of crystals having an inclination of 0 DEG to 10 DEG of the (0001) plane with respect to the sheet surface, and therefore has excellent plastic workability at room temperature.

(4) As an embodiment of the magnesium alloy sheet material described above,

mention may be made of: when the 0.2% yield strength in the orthogonal direction is represented by α and the 0.2% yield strength in the plate width direction is represented by β, α and β are 140MPa or more, and the difference between α and β is 15MPa or less.

The magnesium alloy sheet material is excellent in strength in the orthogonal direction and the sheet width direction, and has small anisotropy of strength in the orthogonal direction and the sheet width direction.

(5) As an embodiment of the magnesium alloy sheet material described above,

mention may be made of: the Erichsen value at room temperature is 8.5mm or more.

The magnesium alloy sheet has a large ericsson value at normal temperature, and therefore has excellent plastic workability at normal temperature.

(6) As an embodiment of the magnesium alloy sheet material described above,

mention may be made of: the composition further contains 0.01 to 2.0 mass% of Zn.

When the Zn content is 0.01 mass% or more, the strength of the magnesium alloy sheet material is excellent. The reason for this is that the strength-improving effect by solid-solution strengthening is easily obtained by increasing the Zn content. If the Zn content is 2.0 mass% or less, the magnesium alloy sheet material is less likely to have reduced plastic workability and strength at room temperature. The reason for this is that the content of Zn is not excessive, and thus the intermetallic compound is not easily formed.

(7) As an embodiment of the magnesium alloy sheet material described above,

mention may be made of: the above composition further contains at least one element selected from the group consisting of Ca, Sr, Sn, Zr and rare earth elements,

the content of each of the at least one element is 0.1 mass% or more and 1.0 mass% or less.

If the content of each of the at least one element is 0.1% by mass or more, the strength of the magnesium alloy sheet material is excellent. This is because the effect of refining crystal grains is easily obtained. If the content of each of the at least one element is 1.0% by mass or less, the plastic workability and strength at room temperature of the magnesium alloy sheet material are less likely to be reduced. The reason for this is that the content of each of the at least one element is not too large, and therefore, it is difficult to form an intermetallic compound.

(8) As an embodiment of the magnesium alloy sheet material described above,

mention may be made of: the composition further contains 0.1 to 1.0 mass% of Mn.

When the Mn content is 0.1 mass% or more, the strength and corrosion resistance of the magnesium alloy sheet material are excellent. This is because, since Mn is contained in a relatively large amount, the crystal grain diameter is likely to become fine. That is, the effect of improving the strength due to the miniaturization of crystal grains is easily obtained. In addition, this is because the effect of improving the corrosion resistance due to the inclusion of Mn is easily obtained by including a relatively large amount of Mn. When the Mn content is 1.0 mass% or less, the magnesium alloy sheet material is excellent in mechanical properties. This is because, since an appropriate amount of Mn is contained, not only the grain size is less likely to become coarse, but also the formation of intermetallic compounds is easily suppressed.

(9) A press-formed body according to an embodiment of the present disclosure includes any one of the magnesium alloy sheet materials described in (1) to (8) above.

The press-formed article is excellent in productivity because it contains a magnesium alloy sheet material which is excellent in plastic workability at room temperature and has small anisotropy of strength.

(10) A method for producing a magnesium alloy sheet material according to an embodiment of the present disclosure includes:

a step of subjecting the rolled material to a second heat treatment, wherein

In the step of producing the above-mentioned cast material,

the thickness of the cast material is 2mm to 6mm,

in the step of producing the rolled material described above,

the specific conditions are as follows:

the reduction ratio from the k-th pass to the n-th pass is 40% or more,

k is an integer of 1 to n-1,

The method for producing a magnesium alloy plate material described above is a method for easily producing a magnesium alloy plate material having a structure in which the maximum values of the relative strengths of the fb/fa, mL/mC, mL/mD, and the crystal orientation of the bottom surface satisfy specific ranges, respectively, by using a casting material having a composition containing 2.0 mass% or more and less than 4.5 mass% of Al and performing the steps in the temperature ranges described above. That is, the above-described method for producing a magnesium alloy sheet material can produce a magnesium alloy sheet material having not only excellent plastic workability at normal temperature but also small anisotropy of strength. The reason for this is as follows. By the rapid solidification method, a cast material having a structure in which the crystal orientation of the bottom surface is inclined in various directions with respect to the plate surface can be easily obtained. Therefore, even if the first heat treatment is performed on the treatment material, the bottom surface is less likely to follow the plate surface. Further, by rolling under specific conditions, as will be described in detail later, it is easy to maintain a state in which the crystal orientation of the bottom surface is inclined in various directions with respect to the plate surface. Therefore, the crystal orientation of the rolled material after the second heat treatment is more likely to be random than that of a mold cast material described later.

Detailed description of embodiments of the present disclosure

The following describes in detail embodiments of the present disclosure. The same symbols in the drawings denote the same names.

Detailed description of the preferred embodiments

[ magnesium alloy sheet ]

A magnesium alloy plate material 1 according to an embodiment will be described with reference to fig. 1 and 2. The magnesium alloy sheet 1 contains a magnesium-based alloy. One of the characteristics of the magnesium alloy sheet material 1 is a structure having a specific composition and characteristics. The following description will be made in detail.

[ composition ]

The magnesium-based alloy contains Al (aluminum) as an additive element. The magnesium-based alloy may further contain at least one element selected from the group consisting of Mn (manganese), Zn (zinc), Ca (calcium), Sr (strontium), Sn (tin), Zr (zirconium), and rare earth elements as an additive element. The rare earth element is at least one rare earth element selected from the group consisting of group 3 elements of the periodic table, i.e., scandium (Sc), yttrium (Y), lanthanoid elements, and actinoid elements, and also includes a Misch Metal (MM) which is an alloy containing a plurality of rare earth elements. The magnesium-based alloy is allowed to contain inevitable impurities other than Mg (magnesium) and additive elements. The Mg content is 88 mass% or more, further 93 mass% or more, and particularly 95 mass%. The content of the inevitable impurities may be 1% or less, further 0.5% or less by mass, and particularly 0.2% or less by mass. When the element contained as the inevitable impurity is plural, the content of the inevitable impurity is the total content.

Examples of the type of the magnesium-based alloy include AM-based alloys, AZ-based alloys, AMJ-based alloys, AMX-based alloys, and AME-based alloys expressed in accordance with ASTM standards. The AM-based alloy contains Al and Mn as additive elements, and for example, AM30 can be mentioned. The AZ-based alloy contains Al and Zn as additive elements, and examples thereof include AZ31 and AZ 41. The AMJ-based alloy contains Al, Mn, and Sr as additive elements, and for example, AMJ300 is cited. The AMX-based alloy contains Al, Mn, and Ca as additive elements, and includes, for example, AMX 300. The AME-based alloy contains Al, Mn, and a rare earth element as additive elements, and may be exemplified by AME 300.

(Al)

Al improves the strength and corrosion resistance of the magnesium alloy sheet 1. The strength referred to herein includes tensile strength in a tensile test, 0.2% yield strength, and the like. The corrosion resistance includes a rating number in a salt spray test, a corrosion reduction amount, and the like. The content of Al is 2.0 mass% or more and less than 4.5 mass%. By setting the Al content to 2.0 mass% or more, the magnesium alloy sheet material 1 is excellent in strength and corrosion resistance. When the Al content is less than 4.5 mass%, the plastic workability at normal temperature of the magnesium alloy sheet material 1 is hardly lowered. The ordinary temperature may be 20. + -. 15 ℃. The content of Al is further 2.5 mass% or more and 4.25 mass% or less, and particularly 3.0 mass% or more and 4.0 mass% or less. The Al content is a value obtained when the total content of elements contained in the magnesium-based alloy is 100 mass%. This is also the same for the contents of Mn, Ca, Sr, Sn, Zr and rare earth elements described later.

(Mn)

Mn improves the strength and corrosion resistance of the magnesium alloy sheet 1. The content of Mn is preferably 0.1 mass% or more and 1.0 mass% or less, for example. When the Mn content is 0.1 mass% or more, the magnesium alloy sheet material 1 is excellent in strength and corrosion resistance. If the Mn content is 1.0 mass% or less, generation of coarse intermetallic compounds can be suppressed, and therefore, the plastic workability and strength at normal temperature of the magnesium alloy sheet material 1 are less likely to be reduced. As the intermetallic compound, an intermetallic compound containing Al and Mn can be cited. The coarse particles may be, for example, those having a diameter equivalent to a circle of equal area exceeding 10 μm. The content of Mn is preferably 0.2 mass% or more and 0.8 mass% or less, more preferably 0.2 mass% or more and 0.4 mass% or less, and particularly preferably 0.2 mass% or more and 0.3 mass% or less.

(Zn)

Zn improves the strength of the magnesium alloy sheet 1. The Zn content is preferably 0.01 mass% or more and 2.0 mass% or less, for example. When the Zn content is 0.01 mass% or more, the strength of the magnesium alloy sheet material 1 is excellent. The reason for this is that the strength-improving effect by solid-solution strengthening is easily obtained by the large Zn content. If the Zn content is 2.0 mass% or less, the formation of intermetallic compounds is easily suppressed, and therefore, the plastic workability and strength at normal temperature of the magnesium alloy sheet material 1 are less likely to be reduced. The Zn content is more preferably 0.1 mass% or more and 1.5 mass% or less, and particularly preferably 0.15 mass% or more and 1.0 mass% or less.

(Ca, Sr, Sn, Zr and rare earth elements)

Ca. Sr, Sn, Zr and rare earth elements improve the strength of the magnesium alloy plate 1. Ca. The content of each of Sr, Sn, Zr, and the rare earth element is, for example, preferably 0.1 mass% or more and 1.0 mass% or less. If the content of each element is 0.1 mass% or more, the crystal grains become finer than in the case where each element is not contained, and therefore the strength of the magnesium alloy sheet material 1 is excellent. If the content of each element is 1.0 mass% or less, an intermetallic compound is difficult to form, and therefore, the magnesium alloy sheet material 1 is likely to suppress a decrease in plastic workability and a decrease in strength at normal temperature. The content of each element is more preferably 0.15% by mass or more and 0.5% by mass or less, and particularly preferably 0.2% by mass or more and 0.3% by mass or less. Further preferably, the total content of Ca, Sr, Sn, Zr and the rare earth element satisfies, for example, 0.1 mass% or more and 1.0 mass% or less. The total content is more preferably 0.15 mass% or more and 0.5 mass% or less, and particularly preferably 0.2 mass% or more and 0.3 mass% or less.

The composition of the magnesium-based alloy can be confirmed by, for example, ICP Emission Spectrometry (Inductively Coupled Plasma Optical Emission Spectrometry).

[ tissue ]

The magnesium alloy plate material 1 has a structure in which fb/fa, mL/mC, mL/mD, and the relative strengths of the crystal orientations of the bottom surfaces satisfy specific ranges, respectively.

(fb/fa)

fb/fa satisfies 10 or more. fa is a ratio of the number of pixels in which the crystal orientation of the bottom surface is inclined by 0 ° or more and 10 ° or less with respect to the plate surface among all the pixels. fb is a ratio of the number of pixels in which the crystal orientation of the bottom surface is inclined by 25 ° or more and 45 ° or less with respect to the plate surface among all the pixels. As described later, all pixels refer to all pixels in one field of view. The bottom surface is (0001) surface. The plate surface is a surface orthogonal to the plate thickness direction 22 shown in fig. 1. When fb/fa is 10 or more, the magnesium alloy sheet material 1 has excellent plastic workability at room temperature. The reason for this is that the ratio of the number of crystals 12 is large and the ratio of the number of crystals 11 is small as shown in fig. 2. The

crystals

11 and 12 are hexagonal crystals. The crystal 12 is a crystal in which the crystal orientation of the bottom surface is inclined by 25 ° or more and 45 ° or less with respect to the plate surface. The crystal 11 is a crystal in which the crystal orientation of the bottom surface is inclined by 0 ° or more and 10 ° or less with respect to the plate surface. fb/fa more preferably satisfies 15 or more, particularly preferably 18 or more. The upper limit value of fb/fa is about 40 in practical use. That is, fb/fa may be 10 or more and 40 or less, further 15 or more and 40 or less, and particularly 18 or more and 40 or less.

In particular, fa preferably satisfies 2 or less. The magnesium alloy plate material 1 satisfying fa 2 or less has excellent plastic workability at room temperature because the proportion of the number of crystals 11 is small and the proportion of the number of crystals 12 is large. fa is more preferably 1.9 or less, and particularly preferably 1.8 or less. The fa is preferably 0.5 or more. The magnesium alloy plate material 1 in which fa is 0.5 or more is easy to satisfy both of plastic workability and strength at room temperature because the ratio of the number of crystals 11 is not too small. fa is more preferably 0.7 or more, and particularly preferably 1.0 or more. That is, fa is 0.5 to 2 inclusive, further 0.7 to 1.9 inclusive, and particularly 1.0 to 1.8 inclusive.

(mL/mC、mL/mD)

mL/mC and mL/mD satisfy 0.9 or more and less than 1.3. mL is a schmitt factor of bottom surface slippage in a stretching direction in a direction 23 perpendicular to both the width direction 21 and the thickness direction 22. The magnesium alloy sheet material 1 is subjected to rolling processing in the manufacturing process as described in detail later. When the magnesium alloy sheet material 1 is viewed in plan and the longitudinal direction of the magnesium alloy sheet material 1 is the rolling direction 25, the sheet width direction 21 is a direction orthogonal to the longitudinal direction of the magnesium alloy sheet material 1. That is, the orthogonal direction 23 is the rolling direction 25 in the process of manufacturing the magnesium alloy sheet material 1. mC means schmitt factor of bottom surface slip with the sheet width direction 21 as the stretching direction. mD is a schmitt factor of bottom surface slippage in which the stretching direction is the oblique direction 24 that is inclined by 45 ° with respect to both the orthogonal direction 23 and the sheet width direction 21.

When mL/mC and mL/mD satisfy 0.9 or more and less than 1.3, the anisotropy of strength of the magnesium alloy sheet material 1 is small. The small anisotropy of strength as referred to herein means that the difference between the strength in an arbitrary direction in the plane of the plate and the strength in other directions is small. The reason for this is that the crystal orientation of the bottom surface is inclined by 25 ° or more and 45 ° or less with respect to the plate surface, and the crystal 12 (fig. 2) exists substantially uniformly in any one of the orthogonal direction 23, the plate width direction 21, and the inclined direction 24. mL/mC further preferably satisfies 0.95 to 1.25, and particularly preferably satisfies 0.95 to 1.20. The mL/mD is more preferably 0.95 to 1.15, particularly preferably 0.95 to 1.10.

(relative intensity)

The maximum value of the relative strength of the crystal orientation of the bottom surface satisfies 5.2 or less. The relative intensity is an index used in the polar diagram, and is an index indicating the degree of aggregation of the relative crystal orientations with respect to the random crystal orientations. The higher the relative intensity, the more the crystal orientation is indicated. The magnesium alloy sheet material 1 having the small maximum value has small anisotropy of strength and elongation. The reason for this is that by setting the maximum value to 5.2 or less, the proportion of the crystal orientation of the bottom surface that is aligned in a specific direction is small. That is, when the maximum value of the relative intensity is low, the random orientation is approached. The maximum value is more preferably 5.0 or less, and particularly preferably 4.8 or less.

Referring to fig. 8, the total angle occupied by the region having a relative strength of 5.2 or less in the circumferential direction between a 25 ° point 82 and a 45 ° point 83 in the pole point diagram described later is preferably 200 ° or more, more preferably 230 ° or more, and particularly preferably 250 ° or more. The method of calculating the total angle is the same as the method described later.

(average grain size)

The average grain size of the structure is preferably 2 μm or more and 7 μm or less, for example. When the average crystal grain size is 2 μm or more, the magnesium alloy sheet material 1 is excellent in plastic workability. In addition, the magnesium alloy sheet material 1 is easily increased in strength by work hardening. Further, the magnesium alloy sheet material 1 may have a uniform elongation. When the average crystal grain size is 7 μm or less, the magnesium alloy sheet material 1 is excellent in plastic workability and strength at normal temperature. The average crystal grain diameter is more preferably 3 μm or more and less than 7 μm, and particularly preferably 4 μm or more and 6.5 μm or less.

As described in detail later, fa, fb, mL, mC, mD and average crystal grain diameter can be measured using a mapping image obtained by color-dividing crystal orientations of respective crystal grains by an EBSD method. As described in detail later, the maximum value of the relative strength of the crystal orientation of the bottom surface can be obtained by obtaining a pole point diagram of the bottom surface in each crystal grain by the EBSD method.

[ Properties ]

The magnesium alloy sheet material 1 preferably satisfies the following range in at least one of the ericsson value and the 0.2% yield strength. The magnesium alloy sheet material 1 preferably satisfies both the ericsson value and the 0.2% yield strength in the following ranges.

(Elickson value)

The Erichsen value of the magnesium alloy sheet material 1 may be set to 8.5mm or more, for example. By setting the Elrichsen value to 8.5mm or more, the plastic workability at normal temperature is excellent. The ericsson value may be set to be greater than 8.5mm, further 8.7mm or more, and particularly 9.0mm or more. The upper limit of the number of ericsson is about 11mm in practical use. That is, the ericsson value is 8.5mm or more and 11mm or less, further 8.7mm or more and 11mm or less, and particularly 9.0mm or more and 11mm or less. The ericsson value is determined in accordance with the JIS standard described later.

(0.2% yield strength)

Preferably, the magnesium alloy sheet material 1 has a 0.2% yield strength in the orthogonal direction 23 and a 0.2% yield strength in the sheet width direction 21 that satisfy 140MPa or more, and a difference between the 0.2% yield strength in the orthogonal direction 23 and the 0.2% yield strength in the sheet width direction 21 that satisfies 15MPa or less. The magnesium alloy sheet material 1 is excellent in strength in the orthogonal direction 23 and the sheet width direction 21, and has small anisotropy of strength in the orthogonal direction 23 and the sheet width direction 21. The 0.2% yield strength in the orthogonal direction 23 and the 0.2% yield strength in the plate width direction 21 further preferably satisfy 145MPa or more, and particularly preferably satisfy 150MPa or more. The upper limit value of the 0.2% yield strength in the orthogonal direction 23 and the upper limit value of the 0.2% yield strength in the plate width direction 21 may be about 220MPa in practical use. That is, the 0.2% yield strength in the orthogonal direction 23 and the 0.2% yield strength in the plate width direction 21 may be 140MPa or more and 220MPa or less, further 145MPa or more and 220MPa or less, and particularly 150MPa or more and 220MPa or less. The difference in 0.2% yield strength is more preferably 12MPa or less, and particularly preferably 10MPa or less. The difference between 0.2% yield strength means the absolute value of the difference. As described in detail later, the 0.2% yield strength in each direction was determined in accordance with JIS standard.

[ use ]

The magnesium alloy plate material 1 of the present embodiment can be suitably used for structural members of transportation means such as automobiles, airplanes, railways, and the like, structural members of electric and electronic devices, and the like. In particular, the magnesium alloy sheet material 1 of the present embodiment can be suitably used for a press-formed body, for example. The press-formed body can be produced by press-working the magnesium alloy sheet material 1. The press working includes drawing, support pressing, bending, stretch flange working, and the like. Fig. 3 shows an example of the press-molded body 10. The shape of the press-formed body 10 of fig. 3 is an example. The shape of the press-molded body 10 is not particularly limited to the U shape shown in fig. 3. The press-formed body 10 is excellent in productivity because it contains the magnesium alloy sheet material 1 excellent in plastic workability at normal temperature and small in strength anisotropy.

[ Effect ]

The magnesium alloy sheet material 1 of the present embodiment is excellent in plastic workability at room temperature and has small anisotropy of strength. The reason why the plastic workability at room temperature is excellent is that the ratio of the number of crystals 12 having the crystal orientation of the bottom surface inclined at 25 DEG to 45 DEG to the plate surface is large by satisfying 10. ltoreq. fb/fa. The reason why the anisotropy of strength is small is as follows. The maximum values of the relative intensities of the crystal orientations of mL/mC, mL/mD, and the bottom face satisfy specific ranges. Therefore, the crystal 12 having the crystal orientation of the bottom surface inclined by 25 ° or more and 45 ° or less with respect to the plate surface is substantially uniformly present in any one of the orthogonal direction 23, the plate width direction 21, and the inclined direction 24. Therefore, the magnesium alloy sheet material 1 of the present embodiment is easily plastically deformed in various directions. Further, the magnesium alloy sheet material 1 of the present embodiment has high strength. The reason for this is that not only the average crystal grain diameter is small, but also the 0.2% yield strength in the orthogonal direction 23 and the 0.2% yield strength in the plate width direction 21 are large.

[ method for producing magnesium alloy sheet Material ]

A method for manufacturing a magnesium alloy sheet material according to an embodiment will be described with reference to fig. 4 to 7. As shown in fig. 4, a method for manufacturing a magnesium alloy plate material according to an embodiment includes: a casting process S1, a first heat treatment process S2, a rolling process S3, and a second heat treatment process S4. The casting step S1 produces a plate-like cast material containing a magnesium-based alloy. The first heat treatment step S2 is a step of performing a first heat treatment on the cast material to produce a treated material. The rolling step S3 rolls the treated material with the rolls to produce a rolled material. The second heat treatment step S4 heat-treats the rolled material. One of the characteristics of the method for producing a magnesium alloy sheet material according to the present embodiment is that the four steps are performed under specific conditions. Hereinafter, the casting step S1 to the second heat treatment step S4 will be described in order.

[ casting step S1]

This step produces a plate-like casting material containing a magnesium-based alloy. The cast material is produced by a rapid solidification method. In fig. 5, a temperature curve 71 of the rapid solidification method is shown by a solid line, and a temperature curve 72 of the gravity casting method, the continuous casting method, or the like is shown by a two-dot chain line. The horizontal axis of fig. 5 represents time, and the vertical axis of fig. 5 represents temperature. As shown in fig. 5, the cooling rate of the quench solidification method is very high as compared with the cooling rate of the gravity casting method or the like. For convenience of explanation, the temperature curves 71 and 72 in fig. 5 are simplified and do not necessarily correspond to actual temperature curves.

As the rapid solidification method, for example, a twin roll casting method can be cited. The twin roll casting method is a method of making a cast material 42 from a melt 41, for example, using a twin roll casting apparatus 30 as shown in fig. 6. The twin roll casting apparatus 30 includes: a melting furnace 31, a conveying pipe 32, a holding furnace 33, a supply part 34, a liquid injection port 35, and a pair of rollers 36. The melting furnace 31 produces and stores a melt 41 of a magnesium-based alloy. The composition of melt 41 is as described above. The composition of the melt 41 is maintained at the composition of the magnesium alloy sheet material 1 (fig. 1) produced through the second heat treatment step S4 described later. The transfer pipe 32 transfers the melt 41 from the melting furnace 31 to the holding furnace 33. Holding furnace 33 holds melt 41. The supply section 34 supplies the melt 41 between the pair of rollers 36. The liquid pouring port 35 opens between the pair of rollers 36. The melt 41 is cooled and solidified between the pair of rolls 36, thereby producing a casting material 42.

The cooling rate is 100 ℃/sec or more. If the cooling rate is 100 ℃/sec or more, the cooling rate is high, and therefore solute atoms are sufficiently dissolved in a solid solution, so that not only is the formation of coarse crystal grains suppressed, but also the crystal grains are likely to become fine, and crystals inclined with respect to the plate surface are likely to be formed. The cooling rate is more preferably 500 ℃/sec or more, and particularly preferably 1000 ℃/sec or more. The upper limit of the cooling rate is 2000 ℃/sec in practical use. That is, the cooling rate may be 100 ℃/sec or more and 2000 ℃/sec or less, more preferably 500 ℃/sec or more and 2000 ℃/sec or less, and particularly preferably 1000 ℃/sec or more and 2000 ℃/sec or less.

By the rapid solidification method, a cast material 42 having a structure in which the crystal orientation of the bottom surface is not aligned in a specific direction, for example, the long side direction of the plate, the short side direction of the plate, the plate thickness direction, and the like, but is inclined in various directions with respect to the plate surface is obtained. Therefore, the magnesium alloy sheet material 1 (fig. 1) can be easily produced through the subsequent steps. The bottom surface is (0001) surface.

The thickness of the casting material 42 is, for example, preferably 2mm to 6mm, more preferably 2.5mm to 5.5mm, and particularly preferably 3mm to 5 mm.

[ first Heat treatment Process S2]

In this step, a plate-shaped casting material 42 containing a magnesium-based alloy is subjected to a first heat treatment to prepare a plate-shaped treatment material. The first heat treatment may be performed by, for example, a continuous heat treatment furnace, a batch heat treatment furnace, or the like. The first heat treatment is a homogenization treatment.

The first heat treatment is performed so that the temperature of the cast material 42 becomes 460 ℃ to 510 ℃. If the temperature of the casting material 42 is 460 ℃ or higher, the solute atoms are easily dissolved sufficiently. If the temperature of the cast material 42 is 510 ℃ or lower, the temperature of the cast material 42 does not become too high, and a treated material having excellent surface properties, such as no discoloration due to excessive oxidation or no spot defects due to melting of intermetallic compounds, can be easily produced. The temperature of the casting material 42 may be set to 470 ℃ or higher and 500 ℃ or lower, and particularly, may be set to 480 ℃ or higher and 500 ℃ or lower. The cooling rate of the treatment material is as high as possible, but it is sufficient to cool the treatment material to 300 ℃ at about 3 ℃/sec or more.

[ Rolling Process S3]

This step rolls the treatment material to produce a rolled material in a plate shape. The rolling process may be any of reversible rolling and tandem rolling. The rolling process may be performed by using a rolling device 50 shown in fig. 7, for example. The rolling device 50 includes a pair of rolling rolls 51 disposed to face each other in the vertical direction. The material to be treated 61 is inserted between the pair of reduction rolls 51 to pass through the material to be treated, thereby producing a material to be rolled 62. For each of the reduction rolls 51, rolls having the same diameter and having a rotation axis not eccentrically positioned at the roll center can be used. The rotation speed of each of the reduction rolls 51 is set to be the same.

The treatment material 61 supplied between the pair of reduction rolls 51 is preheated to a specific temperature, and the pair of reduction rolls 51 is heated to a specific temperature. The preheating temperature of the treatment material 61 and the temperature of the reduction rolls 51 may be 170 ℃ to 270 ℃. The preheating temperature of the processing material 61 is the surface temperature of the processing material 61 in the preheating furnace, which is not shown. That is, the preheating temperature of the treatment material 61 is the surface temperature of the treatment material 61 before the 1 st pass rolling. The temperature of the reduction roll 51 means the surface temperature of the reduction roll 51. By setting the preheating temperature of the treatment material 61 and the temperature of the reduction rolls 51 to 170 ℃ or higher, the rolled material 62 having fine crystal grains can be easily produced. When the preheating temperature of the treated material 61 and the temperature of the reduction rolls 51 are 270 ℃ or lower, the crystal grains of the rolled material 62 are less likely to be coarsened. The preheating temperature of the treatment material 61 and the temperature of the reduction rolls 51 may be further set to 180 ℃ or more and 260 ℃ or less, and particularly may be set to 200 ℃ or more and 250 ℃ or less. The preheating temperature of the processing material 61 and the temperature of the reduction rolls 51 may be the same or different. If the preheating temperature of the processed material 61 is the same as the temperature of the reduction rolls 51, the temperature of the sheet material does not change during the reduction processing, and the rolled material 62 having a uniform structure over the entire length can be easily produced.

The rolling process is performed in a plurality of passes. The reduction ratio R per 1 pass is preferably 10% or more and 35% or less, for example. Pressure per 1 passLower rate R through { (t)₂-t₁)/t₂Find out (X100). t is t₂The thickness was measured before 1 pass rolling. t is t₁The thickness of the plate after 1 pass of rolling. The reduction ratios in the respective passes may be the same, and may be different from each other within the above range. The reduction ratio R per 1 pass is more preferably 15% or more and 30% or less, and particularly preferably 20% or more and 30% or less.

The total rolling reduction ratio Rt after the rolling in the nth pass, which is the final pass, is preferably 50% or more and 90% or less, for example. Total reduction ratio Rt by { (t)_b-t_a)/t_bFind out (X100). t is t_bThe thickness of the processed material 61 before rolling. t is t_aThe thickness of the rolled material 62 after the rolling is completed. The total reduction ratio Rt is more preferably 60% or more and 90% or less, and particularly preferably 70% or more and 90% or less.

The rolling process is a process in which a plurality of passes from the k-th pass rolling to the n-th pass rolling are performed under specific conditions. k is an integer of 1 to n-1. That is, each rolling of at least two passes including the rolling of the final pass and the rolling of 1 pass before the final pass is performed under specific conditions. Rolling may be performed in all passes from the 1 st pass rolling to the n th pass rolling under specific conditions.

The specific conditions are such that the temperature of the plate material immediately after the exit from the reduction rolls 51 is lower than the recrystallization temperature of the magnesium-based alloy constituting the plate material, and the rolling reduction Rs from the k-th pass to the n-th pass is 40% or more. Immediately after the exit of the reduction rolls 51, the vertical distance from the immediate lower side of the reduction rolls 51 to the surface at the center in the width direction of the sheet material is 200mm to 500 mm. The reduction rate Rs is defined by { (t)_b-t_k-1)/t_bFind out (X100). t is t_k-1The thickness of the plate before the rolling until the k-th pass, that is, the thickness after the rolling of the k-1 th pass.

E.g. t_k-1T when k is 1₀。t₀Is the thickness t of the treated material 61 before rolling_b. That is, for the treated material 61 before rolling, each rolling until the total reduction ratio Rt is reached is performed in accordance with the plate material immediately after coming out from the rolling rolls 51At a temperature lower than the recrystallization temperature of the magnesium-based alloy constituting the sheet.

Among the calendering under specific conditions, mention may be made of: the temperature of the plate material immediately after the exit from the reduction rolls 51 in the reduction of each pass after the 2 nd pass is made lower than the temperature of the plate material immediately after the exit from the reduction rolls 51 in the reduction before the 1 st pass. In this case, the temperature of the plate material immediately after the exit from the reduction rolls 51 gradually decreases as the number of passes increases. The temperature of the sheet material immediately after the exit from the reduction rolls can be gradually lowered by appropriately adjusting the traveling speed of the sheet material, the time until the sheet material is sent out, and the like.

The cooling rate D of the plate material per 1 pass is preferably 0.1% or more and 15% or less, for example. The temperature reduction rate D per 1 pass is { (T)₁-T₂)/T₁Find out (X100). T is₁The temperature of the plate immediately after the exit from the reduction rolls 51 in the rolling before 1 pass. T is₂Is the temperature of the sheet immediately after the exit from the reduction roll 51 in the current pass of the reduction. The temperature reduction rate D of the plate material in each pass may be the same, or may be different within the above range. The temperature decrease rate D is more preferably 0.2% or more and 13% or less, and particularly preferably 0.3% or more and 12% or less.

The total temperature decrease rate Dt of the plate material after the nth rolling is preferably 0.5% or more and 50% or less, for example. The total temperature reduction rate Dt is defined by { (T)_k-1-T_n)/T_k-1Find out (X100). T is_k-1The temperature of the plate immediately after the exit from the reduction roll 51 in the k-1 th pass of the rolling is shown. T is_nThe temperature of the plate immediately after the exit from the reduction roll 51 in the n-th reduction is shown. The total temperature lowering rate Dt is more preferably 0.7% or more and 40.0% or less, and particularly preferably 1.0% or more and 30.0% or less.

By this rolling, after the second heat treatment step described later, nuclei for forming a structure in which the crystal orientation of the bottom surface is inclined in the sheet width direction, the rolling direction, and the direction between the sheet width direction and the rolling direction can be formed. The reason for this is as follows. By performing rolling under specific conditions, it is easy to suppress accumulated distortion from being removed during rolling in the rolled sheet material. That is, dynamic recrystallization, which is a cause of the bottom surface following the plate surface, is suppressed, and the rolled material 62 having a large amount of strain accumulated is produced. By this deformation, a large number of the nuclei can be introduced. In addition, the rolled material 62 having a large number of cores can be obtained by a large amount of deformation caused by the rolling processing. The rolled material 62 has a longitudinal direction as a rolling direction and a direction orthogonal to the longitudinal direction as a sheet width direction in a plan view of the sheet material. In other words, the rolling direction is the direction in which the sheet travels during rolling. The sheet width direction is a direction orthogonal to the rolling direction and along the plane direction of the sheet, i.e., a direction along the axial direction of the reduction rolls 51.

[ second Heat treatment Process S4]

This process heats the rolled material 62 so as to satisfy a specific temperature range. By this heating, the strain introduced in the rolling step is removed, and recrystallized grains grow from the nuclei, so that a structure in which the crystal orientation of the bottom surface is inclined in the sheet width direction, the rolling direction, and the direction between the sheet width direction and the rolling direction can be formed. The second heat treatment may be performed in, for example, a continuous heat treatment furnace, a batch heat treatment furnace, or the like. Through these steps, although the detailed mechanism is not known, a magnesium alloy plate material 1 (fig. 1) having a structure in which the relative strengths of the crystal orientations of fb/fa, mL/mC, mL/mD and the bottom surface satisfy specific ranges is produced.

The heating temperature of the rolled material 62 is, for example, 180 ℃ to 425 ℃. The heat treatment time is, for example, 0.5 hours or more and 4.0 hours or less. By setting the heating temperature of the rolled material 62 to 180 ℃ or higher and the heat treatment time to 0.5 hours or longer, the strain of the rolled material 62 can be easily removed. By setting the heating temperature of the rolled material 62 to 425 ℃ or lower and setting the heat treatment time to 4.0 hours or less, coarsening of crystal grains of the rolled material 62 is easily suppressed. The heating temperature of the rolled material 62 is more preferably 200 ℃ or more and 400 ℃ or less, and particularly preferably 220 ℃ or more and 350 ℃ or less. The heat treatment time is more preferably 1.0 hour or more and 4.0 hours or less, and particularly preferably 2.0 hours or more and 4.0 hours or less.

[ use ]

The method for producing a magnesium alloy sheet material according to the present embodiment can be suitably used for producing the above-described various constituent members.

[ Effect ]

In the method of manufacturing a magnesium alloy plate material according to the present embodiment, by using the casting material 42 containing 2.0 mass% or more and less than 4.5 mass% of Al, and setting each of the three steps to a specific temperature range, it is possible to manufacture the magnesium alloy plate material 1 (fig. 1) having a structure in which the maximum values of the relative strengths of the fb/fa, mL/mC, mL/mD and the crystal orientation of the bottom surface satisfy specific ranges, respectively. That is, the method for producing a magnesium alloy sheet material according to the present embodiment can produce the magnesium alloy sheet material 1 having not only excellent plastic workability at normal temperature but also small anisotropy of strength.

Experimental examples

In the test examples, the plastic workability at normal temperature of the magnesium alloy sheet material was evaluated.

[ sample No. 1 to sample No. 16]

The magnesium alloy plate material of each sample was produced by successively passing through a casting step, a first heat treatment step, a rolling step, and a second heat treatment step in the same manner as in the above-described method for producing a magnesium alloy plate material.

[ casting Process ]

This step produces a plate-like casting material containing a magnesium-based alloy. As the casting material, a casting material produced by a quench solidification method and a casting material produced by pouring a molten metal into a mold without quenching and naturally cooling the molten metal were prepared. The cooling rate of the quench solidification method corresponds to the cooling rate shown in the temperature curve 71 of fig. 5. The cooling rate of the free cooling corresponds to the cooling rate shown by the temperature curve 72 of fig. 5. In the following description, a cast material produced by a quench solidification method is referred to as a quench solidified plate, and a cast material produced without quenching and naturally cooled is referred to as a die cast plate.

The quench solidified sheet was made by a twin roll casting process at a cooling rate of 1000 ℃/sec. The thickness of the quenched solidified plate was the same as the value shown in the column of the plate thickness before rolling in table 3. The die cast sheet is prepared by cutting from an ingot made by die casting. The thickness of the die cast plate was set to 10 mm. The kinds of the additive elements and the contents of the additive elements in the casting materials of the respective samples are shown in table 1. The kind of the additive element and the content of the additive element in the casting material of each sample were determined by ICP emission spectrometry. The content of the additive elements shown in table 1 is a value when the total content of the elements contained in the magnesium-based alloy is 100 mass%. The "-" shown in the column of the additional element of table 1 indicates that the additional element is not contained. In any of the cast materials, the balance other than the additive elements is Mg and inevitable impurities. The content of inevitable impurities was 1% or less in any of the samples.

[ first Heat treatment Process ]

In this step, a first heat treatment is performed on the cast material to produce a treated material. As the first heat treatment, homogenization treatment for heating the cast material of each sample was performed. The heating of the cast material was performed in such a manner that the temperature of the cast material became a temperature selected from the range of 400 ℃ to 500 ℃ as shown in table 2. The treatment time was set to 5 hours to 12 hours as shown in table 2.

[ Rolling Process ]

This step rolls the treatment material to produce a rolled material in a plate shape. The rolling process is performed by inserting the treatment material between a pair of vertically opposed rolling rolls in a rolling device. For each calender roll, a roll having the same diameter as each other and having a rotation axis which is not eccentrically located at the center of the roll is used. The rotation speed of each calendering roller is the same. The rolling process is performed in a plurality of passes.

The temperature of the calender roll in each pass is set to a temperature selected from the range of 180 ℃ to 280 ℃. The temperature of the calender rolls was the same in each pass. The preheating temperature of the treatment material is brought to a temperature selected from the range of 180 ℃ to 280 ℃. The preheating temperature of the treatment material means the surface temperature of the treatment material in the preheating furnace. The surface temperature of the treated material before rolling after the 2 nd pass is not set. The preheating temperature of the treatment material was the same as the temperature of the reduction rolls in each pass. The preheating temperature of the treatment material and the temperature of the reduction rolls are collectively shown as the reduction temperature in table 2.

The rolling process was carried out as follows: in each of the plurality of passes from the k-th pass to the n-th pass, which is the final pass, the temperature of the sheet material immediately after the exit from the reduction rolls is made lower than the recrystallization temperature of the magnesium-based alloy constituting the sheet material. In this case, the rolling reduction Rs from the k-th pass to the n-th pass is 40% or more.

The recrystallization temperature of AM30 was 181 ℃.

The recrystallization temperature of AZ31 was 180 ℃.

The recrystallization temperature of AZ41 was 177 ℃.

The recrystallization temperature of AMJ300, AMX300, AME300 is substantially the same as AM 30.

The recrystallization temperature of M1 was 189 ℃.

The recrystallization temperature of ZX10 was 186 ℃.

In sample No. 1, rolling was performed for 6 passes, and rolling from 2 nd pass to 6 th pass was performed under specific conditions. In the rolling under the specific conditions, the temperature of the sheet immediately after the exit from the reduction rolls is made lower than the temperature of the sheet immediately after the exit from the reduction rolls before the 1-pass rolling.

In sample nos. 2, 3, 7 to 9, and 13 to 15, rolling was performed for 6 passes in the same manner as in sample No. 1, and rolling from 2 nd pass to 6 th pass was performed under specific conditions. In sample No. 4, 5 passes of rolling were performed, and rolling from the 1 st pass to the 5 th pass was performed under specific conditions. In sample nos. 5 and 6, the rolling was performed for 5 passes, and the rolling was performed from the 2 nd pass to the 5 th pass under specific conditions. In sample nos. 10 to 12, rolling was performed for 6 passes, and rolling from the 1 st pass to the 6 th pass was performed under specific conditions. In sample nos. 2 to 15, in the same manner as in sample No. 1, in the rolling under the specific conditions, the temperature of the plate material immediately after the exit from the reduction rolls was made lower than the temperature of the plate material immediately after the exit from the reduction rolls before the 1-pass rolling.

In sample nos. 1 to 15, the plate thickness of the treated material supplied to rolling is shown in the column of the plate thickness before rolling in table 3, and the plate thickness of the rolled material after rolling is shown in the column of the plate thickness after rolling in table 3. The reduction ratios R, the average value of the reduction ratios R, the reduction ratios Rs and the total reduction ratio Rt per 1 pass of sample nos. 1 to 15 are shown in table 3. In sample nos. 4 to 6, since 5 passes of rolling were performed and no 6 th pass was performed, the column of the 6 th pass in table 3 is "-".

In sample No. 16, rolling was performed for 9 passes. In sample No. 16, a rolled material of 1mm was produced using a treated material having a thickness of 10 mm. The average value of the rolling reductions R of sample No. 16 was 20%, and the total rolling reduction Rt was 90%.

The average values of the temperature decrease rate D and the total temperature decrease rate Dt for each 1 pass of sample nos. 1 and 4 and 12 to 15 are shown in table 4. The average value of the temperature decrease rate D is an average value of the rate of change between the temperature of the plate material immediately after the exit from the reduction roll in the rolling before 1 pass and the temperature of the plate material immediately after the exit from the reduction roll in the current pass in each pass of the specific conditions. The total temperature decrease rate Dt is a temperature decrease rate from the 1 st pass rolling to the final pass rolling under specific conditions. That is, the average value of the temperature decrease rate D of sample No. 1 is the average value of the rate of change between the temperature of the plate material immediately after the exit from the rolling roll before 1 pass and the temperature of the plate material immediately after the exit from the rolling roll of the current pass in each of the 2 nd to 6 th passes. The total temperature decrease rate Dt of sample No. 1 is a rate of change between the temperature of the plate material immediately after the 1 st pass rolling roll and the temperature of the plate material immediately after the 6 th pass rolling roll. The average values of the cooling rate D, the cooling rate D per 1 pass, and the total cooling rate Dt for sample nos. 2, 3, 5 to 10 were the same as for sample No. 1. The average value of the temperature decrease rate D per 1 pass of sample No. 11 and the total temperature decrease rate Dt was the same as that of sample No. 12.

[ second Heat treatment Process ]

In this step, the rolled material is heated. The heating was performed in such a manner that the temperature of the rolled material reached 250 ℃ or 350 ℃ as shown in table 2. The heating time was set to 1.5 hours or 4 hours as shown in table 2.

[ tissue analysis ]

As the structure analysis of the magnesium alloy sheet material of each sample, fb/fa, mL/mC, mL/mD, the maximum value of the relative strength of the crystal orientation of the bottom surface, and the average crystal grain diameter were determined as follows.

A piece for texture analysis was produced from the magnesium alloy plate material of each sample.

Before polishing, the measurement piece was fixed to the polishing jig so that a cross section orthogonal to the plate width direction was a polishing surface. The polishing jig was attached to IS-POLISHER manufactured by POUCHI CORPORATION, and the measurement piece was subjected to surface polishing, intermediate polishing, and finish polishing in this order. For surface polishing, polishing paper having silicon carbide as abrasive grains was used. The numbers of the abrasive papers were set to three types of #400, #1200, and # 2000. The intermediate grinding uses alumina having a particle size of 0.3 μm as a grinding agent. The finish grinding used silica having a particle size of 0.04 μm as a grinding agent. After finish grinding, the surface was cleaned with ethanol to prepare a measurement piece for tissue analysis.

Each measurement piece was inserted into an FE-SEM (field emission type scanning electron microscope). The FE-SEM device used JSM-7000F manufactured by Japan Electron Ltd. The sample chamber of the FE-SEM was evacuated. The measurement conditions were room temperature and the acceleration voltage was 10 kV. An observation field was taken from the above cross section of each measurement piece. The size of the observation field was set to 1200. mu. m.times.600. mu.m for a sample having an average crystal grain size of 10 μm or more. The size of the observation field was set to 600. mu. m.times.600. mu.m for a sample having an average crystal grain diameter of less than 10 μm. The method of finding the average crystal grain diameter is explained below. By the EBSD method, a mapping image obtained by color-dividing each crystal grain according to the crystal orientation is obtained for each observation field of each measurement piece. The spot diameter of the irradiated electron beam was about 0.05 μm. The scanning interval of the electron beam is set to 1 μm here. Image analysis of the mapping image was performed using oim (Imaging microscopy)5.3.1 manufactured by TSL Solutions co. Data points with a Confidence Index (Confidence Index: CI value) of 0.1 or more in the analysis software were used. The confidence index is an index indicating the reliability of the result of the indexing/orientation calculation by the EBSD method, and CI values of 0.1 or more indicate that 95% or more of the accurate indexing/orientation calculation was performed.

(fb/fa)

Fb/fa was obtained by calculating a ratio fa of the number of pixels in which the crystal orientation of the bottom surface is inclined by 0 ° or more and 10 ° or less with respect to the plate surface among all the pixels in one field of view and a ratio fb of the number of pixels in which the crystal orientation of the bottom surface is inclined by 25 ° or more and 45 ° or less with respect to the plate surface among all the pixels in one field of view. The bottom surface is (0001) surface. The center of each pixel corresponds to the point of electron beam irradiation. Each pixel has a regular hexagonal shape. The equivalent circle diameter of one pixel was set to 1.05 μm. When fb/fa is large, it means that the crystal orientation of the bottom surface is inclined at 25 ° or more and 45 ° or less to the plate surface, and the crystal orientation of the bottom surface is inclined at 0 ° or more and 10 ° or less to the plate surface, and is small. The results are shown in table 5.

(mL/mC、mL/mD)

From the image analysis of the cross section, a schmitt factor mL of bottom surface slip in the rolling direction as the stretching direction, a schmitt factor mC of bottom surface slip in the sheet width direction as the stretching direction, and a schmitt factor mD of bottom surface slip in the stretching direction inclined at 45 ° to both the rolling direction and the sheet width direction were obtained.

The schmitt factor mL is obtained by setting the stress component σ RD in the stress tensor to 1, setting the other stress components to 0, and setting the slip plane and the slip direction to the (0001) plane and the [11-20] direction so as to apply the tensile load parallel to the orthogonal direction 23 (fig. 1) in the analysis software. The stress component σ RD in the stress tensor is 1 and the other stress component is 0, which means a uniaxial tensile stress state in which the orthogonal direction 23 is the tensile direction. The slip plane and slip direction are (0001) plane and the [11-20] direction refers to bottom surface slip. In the representation of the slip direction, the combination of "-" and "-following numbers" is an alternative representation of the combination of "numbers and upper dash". For example, "-2" is a combination of "2 and an upper dash".

The schmitt factor mC is obtained by setting the stress component σ TD in the stress tensor to 1, setting the other stress components to 0, and setting the slip plane and the slip direction to the (0001) plane and the [11-20] direction so as to apply the tensile load parallel to the sheet width direction 21 (fig. 1) in the analysis software. The stress component σ TD in the stress tensor is 1 and the other stress component is 0, which means a uniaxial tensile stress state in which the sheet width direction 21 is the stretching direction.

The schmitt factor mD is set to the average of the schmitt factor mD1 and the schmitt factor mD 2. First, the analysis software performs an operation of rotating the crystal orientations of all pixels by 45 ° with the plate thickness direction 22 (fig. 1) as an axis. The rotation direction may be either left rotation or right rotation. The schmidt factor mD1 is obtained by setting the stress component σ RD in the stress tensor to 1, the other stress components to 0, and the slip plane and the slip direction to the (0001) plane and the [11-20] direction so as to apply the tensile load parallel to the orthogonal direction 23. As described above, the stress component σ RD in the stress tensor is 1 and the other stress component is 0, which means a uniaxial tensile stress state in which the orthogonal direction 23 is the stretching direction. The schmidt factor mD2 is obtained by setting the stress component σ TD in the stress tensor to 1, setting the other stress components to 0, and setting the slip plane and the slip direction to the (0001) plane and the [11-20] direction so as to apply a tensile load parallel to the sheet width direction 21. As described above, the stress component σ TD in the stress tensor is 1 and the other stress component is 0, which means a uniaxial tensile stress state in which the sheet width direction 21 is the stretching direction.

Note that the [11-20] direction is equivalent to the [1-210] direction, [ -2110] direction, [ -1-120] direction, [ -12-10] direction, and [2-1-10] direction, and therefore, in the above analysis software, any direction can be specified as the slip direction.

From the obtained Schmitt factor mL, Schmitt factor mC and Schmitt factor mD, mL/mC and mL/mD were obtained. The results are shown in table 5. The closer to 1 the mL/mC and mL/mD are, the smaller the anisotropy is.

(maximum value of relative intensity of crystal orientation of bottom surface)

The maximum value of the relative intensity in the crystal orientation of the bottom surface is obtained by obtaining a polar diagram of the crystal orientation of the bottom surface of each pixel by the EBSD method.

(average grain size)

The average crystal grain diameter is calculated by the following procedure. First, the number of crystal grains included in one field of view is determined by image analysis of the cross section. Here, a pixel aggregate in which the difference in crystal orientation between adjacent pixels is less than 15 ° is defined as one crystal grain. For one pixel, the same aggregate is set if the crystal orientation difference of even only one of the adjacent six pixels is less than 15 °. Next, the average area a of the crystal grains, which is a value obtained by dividing the measurement area by the number of crystal grains, is obtained. Then, {4 × (A/π) }was obtained^1/2The average grain size is defined as the value thereof. The number of crystal grains at the boundary of the measurement range is also set as one crystal grain. The results are shown in table 5.

[ evaluation of Plastic workability ]

The plastic workability of the magnesium alloy sheet material of each sample at room temperature was evaluated by measuring the ericsson value at room temperature. The ericsson value is determined in accordance with "ericsson tester JIS B7729 (2005)" and "ericsson test method JIS Z2247 (2006)". The results are shown in table 5.

[ evaluation of Strength ]

The strength of the magnesium alloy sheet material of each sample was evaluated by measuring the 0.2% yield strength in the rolling direction and the sheet width direction of the magnesium alloy sheet material as described below. Two kinds of test pieces, i.e., a first test piece and a second test piece, were produced from the magnesium alloy sheet material of each sample. Each test piece was set as a small test piece having a distance between the standard points of 20mm and a width of 4 mm. The first test piece had a length direction along the rolling direction of the magnesium alloy sheet material. The second test piece had a length direction along the width direction of the magnesium alloy plate. A tensile force was applied to each test piece in the longitudinal direction thereof at room temperature in accordance with "metal material tensile test method JIS Z2241 (2011)". The absolute values of the 0.2% yield strength in the rolling direction, the 0.2% yield strength in the sheet width direction, and the difference between the 0.2% yield strengths are shown in table 5.

As shown in Table 5, the magnesium alloy sheet materials of sample No. 1, sample No. 4 to sample No. 9, and sample No. 12 to sample No. 14 all satisfied the four requirements of 10. ltoreq. fb/fa, 0.9. ltoreq. mL/mC <1.3, 0.9. ltoreq. mL/mD <1.3, and the maximum value of the relative strength of the crystal orientation of the bottom surface < 5.2. The magnesium alloy sheet materials of these samples had an average crystal grain size of 2 μm to 7 μm. It is found that the magnesium alloy sheet materials of these samples are excellent in plastic workability at room temperature and have small anisotropy of strength.

The magnesium alloy sheet materials of sample No. 1, sample No. 4, sample No. 7, sample No. 8, sample No. 9 and sample No. 12 satisfy fa ≦ 2. That is, the magnesium alloy sheet materials of sample nos. 1, 4, 7, 8, 9 and 12 are excellent in plastic workability at room temperature. The magnesium alloy sheet materials of sample nos. 1 and 4 had an erichson value of 8.5mm or more. That is, the magnesium alloy sheet materials of sample No. 1 and sample No. 4 are excellent in plastic workability at room temperature. In particular, the magnesium alloy sheet material of sample No. 1 has an Elrichsen value of 9.5mm, and can have plastic workability comparable to that of a sheet material made of 5000 series aluminum alloy. The magnesium alloy sheet materials of sample No. 1, sample nos. 4 to 9, and sample nos. 12 to 14 had a 0.2% yield strength in the rolling direction of 140MPa or more, a 0.2% yield strength in the sheet width direction of 140MPa or more, and a difference in 0.2% yield strength of 15MPa or less. That is, the magnesium alloy sheet materials of sample No. 1, sample nos. 4 to 9, and sample nos. 12 to 14 have high strength and small anisotropy of strength.

In these samples, the magnesium alloy sheet materials of sample No. 2, sample No. 3, sample No. 10 and sample No. 15 satisfy two requirements of 0.9. ltoreq. mL/mC <1.3 and 0.9. ltoreq. mL/mD <1.3 among the above four requirements, but do not satisfy the other two requirements of 10. ltoreq. fb/fa and the requirement that the maximum value of the relative strength of the crystal orientation of the bottom surface is 5.2 or less. That is, the magnesium alloy sheet material of sample No. 2 was inferior in plastic workability at room temperature and high in anisotropy of strength. The magnesium alloy sheet material of sample No. 11 satisfies the above four requirements of 10. ltoreq. fb/fa and the maximum value of the relative strength of the crystal orientation of the bottom surface of 5.2 or less, but does not satisfy the other two requirements of 0.9. ltoreq. mL/mC <1.3 and 0.9. ltoreq. mL/mD < 1.3. That is, the magnesium alloy sheet material of sample No. 11 had large anisotropy of strength. The magnesium alloy sheet material of sample No. 16 satisfied 10. ltoreq. fb/fa, 0.9. ltoreq. mL/mC <1.3, and 0.9. ltoreq. mL/mD <1.3 among the above four requirements, but did not satisfy the requirement that the maximum value of the relative strength of the crystal orientation of the other one bottom surface was 5.2 or less. That is, the magnesium alloy sheet material of sample No. 16 had large anisotropy of strength.

The fa of the magnesium alloy sheet materials of sample No. 2, sample No. 3, sample No. 10 and sample No. 15 was more than 2. The magnesium alloy sheet material of sample No. 2 had an Elickson value of less than 8.5 mm. Further, the difference in 0.2% yield strength of the magnesium alloy sheet material of sample No. 2 was more than 15 MPa. The magnesium alloy sheet material of sample No. 3 had an Elickson value of less than 8.5 mm. The magnesium alloy sheet material of sample No. 10 had an Elickson value of less than 8.5 mm. Further, the magnesium alloy sheet material of sample No. 10 had a 0.2% yield strength in the rolling direction of less than 140MPa and a 0.2% yield strength in the sheet width direction of less than 140 MPa. The magnesium alloy sheet material of sample No. 11 had an average crystal grain diameter of more than 7 μm, a 0.2% yield strength in the rolling direction of less than 140MPa, a 0.2% yield strength in the sheet width direction of less than 140MPa, and a difference in 0.2% yield strength of more than 15 MPa. The magnesium alloy sheet material of sample No. 16 had an Elickson value of less than 8.5 mm. Further, the difference in 0.2% yield strength of the magnesium alloy sheet material of sample No. 16 was more than 15 MPa.

Fig. 8 and 9 are typical pole point diagrams of the bottom surfaces of sample No. 1 and sample No. 11 obtained by the EBSD method. Each pole figure represents the distribution of the crystal orientation of the bottom surface in gray scale. Specifically, the relative intensity changes from black to white in the order from high to low. The center of each polar diagram indicates a state in which the crystal orientation of the bottom surface is inclined by 0 ° with respect to the plate surface, and the circumference indicates a state in which the crystal orientation of the bottom surface is inclined by 90 ° with respect to the plate surface. RD is the rolling direction, and TD is the sheet width direction. As described above, the relative intensity is an index indicating the degree of aggregation of the relative crystal orientations with respect to the random crystal orientations, and a higher relative intensity indicates a larger crystal orientation. In each polar diagram, for convenience of explanation, a point 81 where the crystal orientation of the bottom surface is inclined by 10 ° with respect to the plate surface, a point 82 where the crystal orientation is inclined by 25 °, and a point 83 where the crystal orientation is inclined by 45 ° are indicated by two-dot chain line circles.

As shown in fig. 8, in the magnesium alloy sheet material of sample No. 1, between the two-dot chain line of the point 82 inclined at 25 ° and the two-dot chain line of the point 83 inclined at 45 °, there is a region having a relative strength of 2.0 or more and less than 4.0 in most regions in the circumferential direction therebetween. Further, between the two-dot chain line of the point 82 inclined at 25 ° and the two-dot chain line of the point 83 inclined at 45 °, there is a region in which the relative strength in the rolling direction is 4.0 or more and less than 5.7. The region having a relative intensity of 4.0 or more and less than 5.7 is a vertically long region indicated by the most intense gray color in the vicinity of the 25 ° oblique spot 82 on the left side of the sheet of fig. 8, and is a circular region indicated by the most intense gray color in the region overlapping the 25 ° oblique spot 82 on the right side of the sheet of fig. 8. The size of the region having a relative intensity of 4.0 or more and less than 5.7 is very small. Further, there is substantially no region having a relative strength of 2.8 or more inside the two-dot chain line of the point 81 inclined by 10 °, and a region having a relative strength of less than 1.0 and a region having a relative strength of 1.0 or more and 1.4 or less account for a majority of the region.

As shown in fig. 8, in the magnesium alloy sheet material of sample No. 1, the total angle occupied by the region having a relative strength of 2.0 or more and less than 5.7 between the point 82 inclined at 25 ° and the point 83 inclined at 45 °.

The method of finding the total angle will be described with reference to fig. 10. Fig. 10 is a diagram for explaining the above-described method of determining the total angle. Therefore, for convenience of explanation, fig. 10 shows an area surrounded by the contour lines 901 having a relative intensity of 2.0 and an area surrounded by the contour lines 902 having a relative intensity of 5.7 in a simplified manner, and does not match the polar point diagrams shown in fig. 8 and 9.

The total angle is obtained from the sum of the first rotation angles θ 1. The first rotation angle θ 1 is an angle between the first straight line 911 and the first straight line 912. When a region surrounded by the contour lines 902 having a relative intensity of 5.7 exists in a region surrounded by the contour lines 901 having a relative intensity of 2.0, which will be described later, the total angle is a value obtained by subtracting the total of the second rotation angles θ 2 from the total of the first rotation angles θ 1. The second rotation angle θ 2 is an angle between the second straight line 921 and the second straight line 922.

The first straight line 911 is a straight line passing through a point located on the outermost side in the circumferential direction of the pole point diagram and the center of the pole point diagram in an area surrounded by a contour line 901 having a relative intensity of 2.0 between the point 82 inclined at 25 ° and the point 83 inclined at 45 °. The first straight line 912 is a straight line passing through a point located on the other side in the circumferential direction of the pole point diagram and the center of the pole point diagram in an area surrounded by a contour line 901 having a relative intensity of 2.0 between the point 82 inclined at 25 ° and the point 83 inclined at 45 °. The area surrounded by the contour line 901 having a relative intensity of 2.0 is located between the first line 911 and the first line 912.

The second straight line 921 is a straight line passing through a point located on the most side in the circumferential direction of the pole point diagram and the center of the pole point diagram in an area surrounded by the contour line 902 having a relative intensity of 5.7 between the point 82 inclined at 25 ° and the point 83 inclined at 45 °. The second straight line 922 is a straight line passing through a point located on the other side in the circumferential direction of the pole point diagram and the center of the pole point diagram in an area surrounded by contour lines 902 having a relative intensity of 5.7 between the 25 ° oblique point 82 and the 45 ° oblique point 83. The area enclosed by the contour line 902 with a relative intensity of 5.7 is located between the second line 921 and the second line 922.

When a plurality of regions surrounded by the contour lines 901 having a relative intensity of 2.0 are dispersed between the point 82 inclined at 25 ° and the point 83 inclined at 45 °, the first rotation angle θ 1 is obtained for each region surrounded by the contour lines 901 having a relative intensity of 2.0. Similarly, when a plurality of regions surrounded by the contour lines 902 having a relative intensity of 5.7 are dispersed between the point 82 inclined by 25 ° and the point 83 inclined by 45 °, the second rotation angle θ 2 is obtained for each region surrounded by the contour lines 902 having a relative intensity of 5.7.

In the polar diagram, a total angle occupied by the regions having the relative intensity of 2.0 or more and less than 5.7 is set to 360 ° while including the region having the relative intensity of 2.0 between the 25 ° point 82 and the 45 ° point 83, but not including the end of the contour line 901 having the relative intensity of 2.0 and not including the region having the relative intensity of 5.7.

As described above, in the magnesium alloy sheet material of sample No. 1, the crystal orientation of the bottom surface is inclined at 25 ° or more and 45 ° or less with respect to the sheet surface in many cases, and there is almost no crystal whose crystal orientation of the bottom surface is inclined at 0 ° or more and 10 ° or less with respect to the sheet surface. In the magnesium alloy sheet material of sample No. 1, the crystal orientation of the bottom surface is inclined at 25 ° or more and 45 ° or less with respect to the sheet surface, and exists substantially uniformly in the rolling direction, the sheet width direction, and the direction between the rolling direction and the sheet width direction. Therefore, as described above, the magnesium alloy sheet material of result sample No. 1 is considered to satisfy all of the above four requirements. That is, as shown by the high Elichsen values, the magnesium alloy sheet material of sample No. 1 is considered to have not only excellent plastic workability at room temperature but also small anisotropy of strength.

Although the pole point diagrams of the bottom surfaces of the magnesium alloy sheet materials of sample nos. 4 to 9 and 12 to 14 are not shown, it is considered that the pole point diagrams of the magnesium alloy sheet materials of these samples are also the same as the pole point diagram of the magnesium alloy sheet material of sample No. 1 shown in fig. 8. The reason for this is that the magnesium alloy sheet materials of these samples satisfy all four requirements as described above in the same manner as sample No. 1.

As shown in fig. 9, in the magnesium alloy sheet material of sample No. 11, between the two-dot chain line of the spot 82 inclined at 25 ° and the two-dot chain line of the spot 83 inclined at 45 °, there is a region having a relative strength of 2.8 or more and less than 4.0 in the region therebetween in the sheet width direction. Further, outside point 83 inclined at 45 °, there are regions having a relative strength of 4.0 or more and less than 5.7 in the regions on both sides in the plate width direction. The region having a relative intensity of 4.0 or more and less than 5.7 is a circular region indicated by the most intense gray outside spot 83 inclined at 45 ° on the upper side of the sheet of fig. 9, and is a circular region indicated by the most intense gray outside spot 83 inclined at 45 ° on the lower side of the sheet of fig. 9. Further, a region having a relative strength of 1.0 or more and less than 1.4 exists substantially over the entire region inside the two-dot chain line of the point 81 inclined by 10 °. Between point 82 inclined by 25 ° and point 83 inclined by 45 °, the total angle occupied by the region having a relative intensity of 2.0 or more and less than 5.7 is 119 °.

In the magnesium alloy sheet material of sample No. 11, the ratio of the number of crystals existing in the sheet width direction, which have crystal orientations of the bottom face inclined at more than 45 ° with respect to the sheet surface, and crystals inclined at 25 ° to 45 ° is very high. Therefore, it is considered that the magnesium alloy sheet material of result sample No. 11 does not satisfy the requirements of 0.9. ltoreq. mL/mC <1.3 and 0.9. ltoreq. mL/mD <1.3 as described above. That is, it is considered that the strength anisotropy of the magnesium alloy sheet material of sample No. 11 is large.

The present invention is not limited to these examples, but is intended to be represented by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

Description of the symbols

1 magnesium alloy sheet material

10 press-formed body

11 crystal inclined at 0 DEG to 10 DEG inclusive

12 crystal inclined at 25 DEG to 45 DEG inclusive

21 width direction of the board

22 in the direction of plate thickness

23 orthogonal direction

24 direction of inclination

25 direction of rolling

30 twin roll casting apparatus

31 melting furnace

32 delivery pipe

33 holding furnace

34 supply part

35 liquid filling opening

36 roller

41 melt

42 casting material

50 calendering device

51 calendering roll

61 treatment Material

62 calendering the material

71. 72 temperature curve

81 inclined by 10 deg

82 at 25 deg. inclination

83 inclined at 45 DEG

901 contour line with relative intensity of 2.0

902 relative intensity of 5.7 contour line

911. 912 first straight line

921. 922 second straight line

Theta 1 first rotation angle

Theta 2 second rotation angle

RD calendering direction

TD sheet width direction

Claims

1. A magnesium alloy sheet material comprising a magnesium-based alloy, wherein,

the magnesium-based alloy has:

a composition containing 2.0 mass% or more and less than 4.5 mass% of Al; and

the following organization: when the crystal orientation is measured by the EBSD method, wherein fa represents the proportion of the number of pixels in which the crystal orientation of the bottom surface among all the pixels in one field of view is inclined by 0 DEG to 10 DEG with respect to the plate surface, fb represents the proportion of the number of pixels in which the crystal orientation is inclined by 25 DEG to 45 DEG with respect to the plate surface, mL represents the Schmidt factor of bottom surface slip in which the direction orthogonal to both the plate width direction and the plate thickness direction is the stretching direction, mC represents the Schmidt factor of bottom surface slip in which the plate width direction is the stretching direction, and mD represents the Schmidt factor of bottom surface slip in which the direction inclined by 45 DEG with respect to both the orthogonal direction and the plate width direction is the stretching direction, fb/fa satisfies 10 or more, and mL/mC and mL/mD satisfy 0.9 or more and less than 1.3, and a maximum value of the relative strength of the crystal orientation of the bottom surface satisfies 5.2 or less.

2. The magnesium alloy sheet material according to claim 1, wherein the average grain diameter of the structure measured by the EBSD method is 2 μm or more and 7 μm or less.

3. The magnesium alloy sheet material according to claim 1 or claim 2, wherein fa is 2 or less.

4. A magnesium alloy sheet material as claimed in any one of claims 1 to 3, wherein when α represents the 0.2% yield strength in the orthogonal direction and β represents the 0.2% yield strength in the sheet width direction, α and β are 140MPa or more and the difference between α and β is 15MPa or less.

5. A magnesium alloy sheet material as claimed in any one of claims 1 to 4, wherein the Erichsen value at normal temperature is 8.5mm or more.

6. A magnesium alloy sheet material as claimed in any one of claims 1 to 5, wherein said composition further contains 0.01 mass% or more and 2.0 mass% or less of Zn.

7. The magnesium alloy sheet according to any one of claims 1 to 6,

the composition further contains at least one element selected from the group consisting of Ca, Sr, Sn, Zr and rare earth elements,

8. A magnesium alloy sheet material as claimed in any one of claims 1 to 7, wherein said composition further contains 0.1 mass% or more and 1.0 mass% or less of Mn.

9. A press-formed body comprising the magnesium alloy sheet material according to any one of claims 1 to 8.

10. A method for manufacturing a magnesium alloy sheet material, the method comprising:

a step of subjecting the rolled material to a second heat treatment, wherein

In the step of producing the casting material, the casting material is heated,

the thickness of the cast material is 2mm to 6mm,

the first heat treatment is performed by heating the casting material to 460 ℃ or higher and 510 ℃ or lower,

in the step of producing the rolled material described above,

heating the preheating temperature of the treatment material and the temperature of the reduction rolls to 170 ℃ or higher and 270 ℃ or lower,

the specific conditions are as follows:

the temperature of the plate immediately after the plate comes out of the calendering rolls in each pass is lower than the recrystallization temperature of the magnesium-based alloy,

the reduction ratio from the k-th pass to the n-th pass is 40% or more,

k is an integer of 1 or more and n-1 or less,