JP2023002015A - Magnesium alloy sheet - Google Patents

Abstract

To provide a magnesium alloy sheet excellent in the balance of strength and ductility.SOLUTION: A magnesium alloy sheet is made of a magnesium alloy. The magnesium alloy contains zinc of between 0.5 mass% and 2.0 mass% inclusive and calcium of between 0.05 mass% and 0.3 mass% inclusive, and the balance of magnesium and inevitable impurities. The crystal orientation of the bottom face in the rolling direction has an average strength of 2.50 or more and 4.00 or less in the pole figure of the bottom face of the crystal of the magnesium alloy. The average strength in the rolling direction is an average value of the average strength of the crystal orientation of the bottom face in a first region and the average strength of the crystal orientation of the bottom face in a second region. The first region is a region enclosed by the range of an angle of 0° ±30° in the circumferential direction and the range of an angle from 5° to 25° in the radial direction, whereas the second region is a region enclosed by the range of an angle of 180° ±30° in the circumferential direction and the range of an angle from 5° to 25° in the radial direction.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to magnesium alloy sheets.

Patent Document 1 discloses a magnesium alloy plate made of a magnesium alloy containing calcium and zinc. This magnesium alloy sheet has a structure in which the crystal orientation of the (0002) plane is inclined by 10° or more and 70° or less with respect to the plate surface, and three or more peaks with a pole density of 2.5 or more are present.

JP 2018-80363 A

Development of a magnesium alloy sheet with an excellent balance between strength and ductility is desired.

Magnesium alloy crystals have a close-packed hexagonal crystal structure. Generally, in a magnesium alloy plate, the bottom surface of the magnesium alloy crystal tends to become parallel to the plate surface due to rolling. Therefore, the proportion of crystals in which the crystal orientation of the bottom surface of the crystal is inclined with respect to the plate surface is small. As the ratio of crystals tilted with respect to the plate surface decreases, the strength of the magnesium alloy plate increases, but the ductility of the magnesium alloy plate decreases. Such a magnesium alloy sheet is inferior in plastic workability.

In Patent Document 1, the structure of the magnesium alloy plate is controlled so that the (0002) plane has a specific orientation by heat-treating the rolled plate. Although the magnesium alloy sheet of Patent Document 1 is said to be excellent in plastic workability, there is room for improvement in terms of strength.

One object of the present disclosure is to provide a magnesium alloy sheet having an excellent balance between strength and ductility.

The magnesium alloy pressure plate of the present disclosure is
A magnesium alloy plate made of a magnesium alloy,
The magnesium alloy is
0.5% by mass or more and 2.0% by mass or less of zinc;
0.05% by mass or more and 0.3% by mass or less of calcium,
having a composition in which the balance is magnesium and unavoidable impurities,
In the pole figure of the bottom surface of the magnesium alloy crystal, the average strength of the crystal orientation of the bottom surface in the rolling direction is 2.50 or more and 4.00 or less,
The average strength in the rolling direction is the average value of the average strength of the crystal orientation of the bottom surface in the first region of the pole figure and the average strength of the crystal orientation of the bottom surface in the second region of the pole figure,
The first region is a region surrounded by a circumferential angle of 0°±30° in the pole figure and a radial angle of 5° to 25° in the pole figure. ,
The second region is a region surrounded by an angle of 180° ± 30° in the circumferential direction and an angle of 5° to 25° in the radial direction,
The angle in the circumferential direction is an angle expressed in the range of 0° to 360° counterclockwise from the rolling direction, with the rolling direction being 0°,
The angle in the radial direction is an angle expressed in the range of 0° to 90°, with the center of the pole figure being 0° and the outer circumference of the pole figure being 90°.

The magnesium alloy sheet of the present disclosure has an excellent balance between strength and ductility.

FIG. 1 is a schematic perspective view of a magnesium alloy plate according to an embodiment. FIG. 2 is a schematic perspective view of the crystal of the magnesium alloy plate according to the embodiment. FIG. 3 is a diagram showing an example of a pole figure of the bottom surface of the crystal in the magnesium alloy plate according to the embodiment. FIG. 4 is a diagram explaining a pole figure of the bottom surface of the crystal in the magnesium alloy plate according to the embodiment. FIG. 5 is a diagram explaining the KAM value in the magnesium alloy plate according to the embodiment. FIG. 6 shows sample no. 1 is a pole figure of the bottom surface of a crystal in the magnesium alloy plate of 1-1. FIG. 7 shows sample no. It is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of 1-2. FIG. 8 shows sample no. It is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of 1-3. FIG. 9 shows sample no. It is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of No. 1-4. FIG. 10 shows sample no. 1-11 is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of No. 1-11. FIG. 11 shows sample no. 1-12 is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of No. 1-12. FIG. 12 shows sample no. 1-13 is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of No. 1-13. FIG. 13 shows sample no. 1-14 is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of No. 1-14. FIG. 14 shows sample no. 1-15 is a pole figure of the bottom surface of the crystal in the magnesium alloy plate of No. 1-15.

<<Description of Embodiments of the Present Disclosure>>
First, the embodiments of the present disclosure are listed and described.

(1) A magnesium alloy plate according to an embodiment of the present disclosure is
A magnesium alloy plate made of a magnesium alloy,
The magnesium alloy is
0.5% by mass or more and 2.0% by mass or less of zinc;
0.05% by mass or more and 0.3% by mass or less of calcium,
having a composition in which the balance is magnesium and unavoidable impurities,
In the pole figure of the bottom surface of the magnesium alloy crystal, the average strength of the crystal orientation of the bottom surface in the rolling direction is 2.50 or more and 4.00 or less,
The average strength in the rolling direction is the average value of the average strength of the crystal orientation of the bottom surface in the first region of the pole figure and the average strength of the crystal orientation of the bottom surface in the second region of the pole figure,
The first region is a region surrounded by a circumferential angle of 0°±30° in the pole figure and a radial angle of 5° to 25° in the pole figure. ,
The second region is a region surrounded by an angle of 180° ± 30° in the circumferential direction and an angle of 5° to 25° in the radial direction,
The angle in the circumferential direction is an angle expressed in the range of 0° to 360° counterclockwise from the rolling direction, with the rolling direction being 0°,
The angle in the radial direction is an angle expressed in the range of 0° to 90°, with the center of the pole figure being 0° and the outer circumference of the pole figure being 90°.

The magnesium alloy sheet of the present disclosure has an excellent balance between strength and ductility. The magnesium alloy sheet of the present disclosure includes crystals in which the crystal orientation of the bottom surface is tilted at a specific angle with respect to the plate surface by the average strength of the crystal orientation of the bottom surface in the rolling direction being within a specific range. . When the average strength in the rolling direction is 2.50 or more, the strength of the magnesium alloy sheet can be increased. When the average strength in the rolling direction is 4.00 or less, the ductility of the magnesium alloy sheet can be ensured. Therefore, the magnesium alloy sheet of the present disclosure can achieve both strength and ductility in a well-balanced manner.

(2) As one form of the magnesium alloy plate of the present disclosure,
The maximum intensity of the crystal orientation of the bottom surface may be 4.5 or more and 6.5 or less.

The said form is easy to make intensity|strength and ductility compatible more. When the maximum strength is 4.5 or more, the strength of the magnesium alloy sheet can be easily increased. When the maximum strength is 6.5 or less, it is easier to ensure the ductility of the magnesium alloy sheet.

(3) As one form of the magnesium alloy plate of the present disclosure,
A ratio of the average strength in the rolling direction to the average strength of the crystal orientation of the bottom surface in the width direction of the pole figure may be 0.80 or more and 1.20 or less.
The average intensity in the plate width direction is the average value of the average intensity of the crystal orientation of the bottom surface in the third region of the pole figure and the average intensity of the crystal orientation of the bottom surface in the fourth region of the pole figure. ,
The third region is a region surrounded by an angle of 90° ± 10° in the circumferential direction and an angle of 30° to 70° in the radial direction,
The fourth region is a region surrounded by an angle of 270° ± 10° in the circumferential direction and an angle of 30° to 70° in the radial direction,
The plate width direction is a direction orthogonal to both the plate thickness direction and the rolling direction.

The above morphology has a good balance between strength and ductility. When the ratio of the average strength in the rolling direction to the average strength in the sheet width direction is within a specific range, the crystal orientation of the bottom surface is tilted in the rolling direction and the crystal orientation of the bottom surface is tilted in the width direction. including in a balanced manner.

(4) As one form of the magnesium alloy plate of the present disclosure,
The KAM value of the crystal grains of the magnesium alloy may be 0.4° or more and 1.1° or less.

The said form is easy to make intensity|strength and ductility compatible more. A KAM value of 0.4° or more makes it easier to increase the strength of the magnesium alloy plate. A KAM value of 1.1° or less makes it easier to increase the ductility of the magnesium alloy sheet.

(5) As one form of the magnesium alloy plate of the present disclosure,
The 0.2% proof stress in the rolling direction is 190 MPa or more,
The elongation in the rolling direction may be 20% or more.

The above form has a high 0.2% proof stress and a large elongation.

(6) As one form of the magnesium alloy plate of the present disclosure,
The average value of the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the plate width direction orthogonal to both the plate thickness direction and the rolling direction is 150 MPa or more,
An average value of the elongation in the rolling direction and the elongation in the plate width direction may be 18% or more.

The above form has a high 0.2% proof stress and a large elongation.

(7) As one form of the magnesium alloy plate of the present disclosure,
A difference between the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the plate width direction orthogonal to both the thickness direction and the rolling direction may be 50 MPa or more.

The said form is easy to make intensity|strength and ductility compatible more. Since one of the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the width direction is high, sufficient strength is obtained. Ductility improves because the other 0.2% proof stress is low.

(8) As one form of the magnesium alloy plate of the present disclosure,
The 0.2% proof stress in the rolling direction is 190 MPa or more,
The Erichsen value may be 4.5 mm or more.

The above form has high strength and excellent plastic workability.

(9) As one form of the magnesium alloy plate of the present disclosure,
The thermal conductivity may be 120 W/m·K or more.

The said form is excellent in thermal conductivity.

<<Details of the embodiment of the present disclosure>>
Details of embodiments of the present disclosure are described below. The same reference numerals in the drawings indicate the same names.

<<Embodiment>>
[Magnesium alloy plate]
A magnesium alloy plate 1 according to an embodiment will be described with reference to FIGS. 1 and 2. FIG. The magnesium alloy plate 1 is a plate material made of a magnesium alloy. The plate is a minimum rectangle that includes the outline of the magnesium alloy plate 1 when the plate surface 1f of the magnesium alloy plate 1 is viewed from above, and the length of the short side of the rectangle is equal to the thickness of the magnesium alloy plate 1. 10 times or more. The plate surface 1f is a surface orthogonal to the plate thickness direction ND shown in FIG. One of the features of the magnesium alloy plate 1 is that it has a specific composition and specific structure. A detailed description will be given below.

The magnesium alloy plate 1 of the embodiment is a rolled plate. The magnesium alloy plate 1 is rolled during the manufacturing process. In the magnesium alloy sheet 1, the rolling direction is the direction in which the sheet material is conveyed during rolling. Generally, the rolling direction can be determined as follows. If the magnesium alloy plate 1 is long like a coil material, the longitudinal direction of the magnesium alloy plate 1 is the rolling direction. In the case of the magnesium alloy sheet 1 cut into an appropriate shape and size, the longitudinal direction of the elongated crystal grains is the rolling direction in the cross section perpendicular to the sheet thickness direction. When the magnesium alloy plate 1 shown in FIG. 1 is viewed in plan from the plate thickness direction ND, and the longitudinal direction of the magnesium alloy plate 1 is the rolling direction RD, the plate width direction TD corresponds to both the plate thickness direction ND and the rolling direction RD. is the direction orthogonal to That is, each of the rolling direction RD and the strip width direction TD is orthogonal to the strip thickness direction ND. The plate width direction TD is orthogonal to the rolling direction RD.

[composition]
The magnesium alloy forming the magnesium alloy plate 1 contains the largest amount of magnesium (Mg). The content of Mg in the magnesium alloy is, for example, 92% by mass or more. The Mg content may also be 95% by mass or more, particularly 97% by mass or more. The magnesium alloy contains zinc (Zn) and calcium (Ca) as additive elements. The magnesium alloy may further contain rare earth elements. Magnesium alloys are allowed to contain unavoidable impurities in addition to the above elements.

(Zn)
Zn contributes to improving the strength of the magnesium alloy plate 1 . Examples of the strength of the magnesium alloy plate 1 include 0.2% proof stress and tensile strength. The content of Zn is 0.5% by mass or more and 2.0% by mass or less.

When the Zn content is 0.5% by mass or more, the strength of the magnesium alloy plate 1 can be easily improved. As the Zn content increases, the strength of the magnesium alloy plate 1 tends to increase. From the viewpoint of increasing the strength of the magnesium alloy plate 1, the Zn content is preferably 0.6% by mass or more, 0.8% by mass or more, and 1.0% by mass or more. The Zn content is particularly preferably 1.2% by mass or more and 1.4% by mass or more.

When the Zn content is 2.0% by mass or less, it is easy to reduce the weight of the magnesium alloy plate 1 . When the Zn content is 2.0% by mass or less, it is easy to improve the thermal conductivity of the magnesium alloy plate 1 . The smaller the Zn content, the smaller the solid solution amount of Zn. Therefore, a decrease in thermal conductivity due to solid solution of Zn can be suppressed. From the viewpoint of reducing the weight of the magnesium alloy plate 1 and improving the thermal conductivity, the Zn content is preferably less than 2.0% by mass and 1.9% by mass or less. The Zn content is particularly preferably 1.8% by mass or less.

The Zn content is, for example, preferably 0.6% by mass or more and less than 2.0% by mass, and more preferably 1.2% by mass or more and 1.8% by mass or less.

(Ca)
Ca contributes to improving the strength of the magnesium alloy plate 1 . The content of Ca is 0.05% by mass or more and 0.3% by mass or less.

When the Ca content is 0.05% by mass or more, the strength and corrosion resistance of the magnesium alloy plate 1 are easily improved. As the Ca content increases, the strength and corrosion resistance of the magnesium alloy plate 1 tend to increase. The Ca content is preferably 0.06% by mass or more, particularly 0.08% by mass or more.

When the Ca content is 0.3% by mass or less, it is easy to improve the rolling workability in the manufacturing process of the magnesium alloy plate 1 . The smaller the Ca content, the higher the rolling workability of the magnesium alloy sheet 1 tends to be. The Ca content is preferably 0.2% by mass or less, particularly 0.15% by mass or less.

The content of Ca is, for example, preferably 0.06% by mass or more and 0.2% by mass or less, more preferably 0.08% by mass or more and 0.15% by mass or less.

(rare earth elements)
A rare earth element contributes to improving the strength of the magnesium alloy plate 1 . The rare earth element is at least one element selected from the group consisting of Group 3 elements of the periodic table, namely scandium (Sc), yttrium (Y), lanthanides and actinides. The content of rare earth elements is, for example, 0.01% by mass or more and 2.0% by mass or less. When multiple types of rare earth elements are included, the content of rare earth elements is the total content of all rare earth elements.

If the rare earth element content is 0.01% by mass or more, the strength of the magnesium alloy plate 1 can be easily improved. The content of the rare earth element is preferably 0.05% by mass or more, particularly 0.15% by mass or more. If the content of the rare earth element is 2.0% by mass or less, it is easy to reduce the weight of the magnesium alloy plate 1 and improve the thermal conductivity of the magnesium alloy plate 1 . The content of rare earth elements is preferably 1.6% by mass or less, particularly 1.2% by mass or less.

The content of the rare earth element is, for example, preferably 0.05% by mass or more and 1.6% by mass or less, more preferably 0.15% by mass or more and 1.2% by mass or less.

(Inevitable impurities)
The types of inevitable impurities are not particularly limited. Examples of inevitable impurities include aluminum (Al), iron (Fe), and silicon (Si). The content of unavoidable impurities is practically 1% by mass or less. The content of unavoidable impurities is preferably 0.5% by mass or less, particularly 0.2% by mass or less. When a plurality of elements are included as inevitable impurities, the content of the inevitable impurities is the total content. The content of Al is practically 0.4% by mass or less. The Al content is preferably 0.3% by mass or less, particularly 0.2% by mass or less. The Fe content is practically 0.01% by mass or less. The Fe content is preferably 0.009% by mass or less, particularly 0.008% by mass or less. The Si content is practically 0.3% by mass or less. The Si content is preferably 0.2% by mass or less, particularly 0.1% by mass or less.

The composition of the magnesium alloy can be determined by, for example, ICP emission spectrometry (Inductively Coupled Plasma Optical Emission Spectrometry).

[Organization]
The structure of the magnesium alloy plate 1 includes magnesium alloy crystals 10, as shown in FIG. The magnesium alloy crystal 10 is a close-packed hexagonal crystal. The crystal 11 in FIG. 2 exemplifies a crystal in which the crystal orientation of the bottom surface 15 of the crystal 11 is inclined with respect to the plate surface 1f. The crystal 12 in FIG. 2 exemplifies a crystal in which the crystal orientation of the bottom surface 15 of the crystal 12 is parallel to the plate surface 1f. Bottom surface 15 is the (0001) plane of crystal 10 . The (0001) plane is a hexagonal plane in the hexagonal crystal schematically shown in FIG. In FIG. 2, the (0001) plane, which is the bottom surface 15, is hatched for convenience of explanation.

The magnesium alloy crystal 10 forming the magnesium alloy plate 1 has an average strength IR of the crystal orientation of the bottom surface 15 in the rolling direction _satisfying a specific range. The strength of the crystal orientation of the bottom surface 15 is obtained from the pole figure of the bottom surface. First, the pole figures will be described with reference to FIGS. 3 and 4. FIG.

<Pole figure>
A pole figure 70 in FIG. 3 shows an example of a pole figure of the bottom surface of the crystal in the magnesium alloy plate 1 . The pole figure 70 is obtained by measuring the crystal orientation of the bottom surface of the crystal by the EBSD (Electron Back Scattered Diffraction Pattern) method. The pole figure 70 is a stereographic projection of the crystal orientation distribution of the bottom surface of the crystal. In the pole figure 70, the intensity of the crystal orientation of the basal plane is represented by contour lines. The intensity of crystal orientation is an index that indicates the degree of clustering of crystal orientations relative to random crystal orientations. The higher the strength of the crystal orientation, the more crystals are oriented in that crystal orientation.

As shown in FIG. 4, in the pole figure 70, the angle α in the circumferential direction C and the angle β in the radial direction R are taken. The angle α is an angle expressed in the range of 0° to 360° counterclockwise from the RD direction, with the RD direction on the right side of the pole figure 70 being 0°. The TD direction is the direction rotated counterclockwise by 90° and 270° from the RD direction. That is, the directions of angles α=90° and α=270° are defined as TD directions. In the pole figures 70 of FIGS. 3 and 4, the left-right direction on the paper surface passing through the center of the pole figure 70 is the RD direction, and the up-down direction on the paper surface passing through the center of the pole figure 70 is the TD direction. The RD direction is the rolling direction. The TD direction is the sheet width direction orthogonal to the RD direction. The angle β is an angle expressed in a range of 0° to 90°, with the center of the pole figure 70 being 0° and the outer circumference of the pole figure being 90°. The central axis of the pole figure 70 extends along the plate thickness direction.

<Strength of Crystal Orientation at the Bottom>
(Average strength in rolling direction)
The average strength IR of the crystal orientation of the bottom surface in the rolling direction, that is, the _RD direction is 2.50 or more and 4.00 or less. The average intensity I _R is the average intensity I _R1 of the crystal orientation of the _basal plane in the first region _AR 1 of the pole figure 70 shown in FIG _. is the average value of The first area _AR1 is an area surrounded by an angle α in the range of 0°±30° and an angle β in the range of 5° to 25°. The range of the angle α of the first region _AR1 is a range of 60°, which is the sum of the range of 0° to 30° and the range of 330° to 360°. The second area _AR2 is an area surrounded by an angle α in the range of 180°±30° and an angle β in the range of 5° to 25°. The range of the angle α of the second region _AR2 is 60° from 150° to 210°.

The magnesium alloy sheet 1 having an average strength I _R of 2.50 or more and 4.00 or less contains crystals in a specific range in which the crystal orientation of the bottom surface is tilted in the rolling direction with respect to the sheet surface 1f. When the average strength IR is _2.50 or more, the strength of the magnesium alloy plate 1 can be increased. When the average strength IR is 4.00 or less, the _ductility of the magnesium alloy sheet 1 can be ensured. Therefore, both strength and ductility of the magnesium alloy plate 1 can be achieved in a well-balanced manner. The average intensity IR is preferably _2.70 or more and 3.50 or less.

(Average strength in sheet width direction)
The average intensity I _T of the crystal orientation of the bottom surface in the plate width direction, ie, the TD direction, is preferably 2.80 or more and 4.00 or less, for example. The average intensity I _T is the average intensity I _T1 of the basal crystal orientation in the third region A _T1 of the pole figure 70 shown in FIG. 4 and the average intensity I _T2 of the basal crystal orientation in the fourth region A _T2 of the pole figure 70 is the average value of The third area _AT1 is an area surrounded by an angle α in the range of 90°±10° and an angle β in the range of 30° to 70°. The range of the angle α of the third region _AT1 is 20° in the range from 80° to 100°. The fourth area _AT2 is an area surrounded by an angle α in the range of 270°±10° and an angle β in the range of 30° to 70°. The range of the angle α of the fourth area _AT2 is 20° in the range from 260° to 280°.

The magnesium alloy sheet 1 having an average strength I _T of 2.80 or more and 4.00 or less contains crystals in a specific range in which the crystal orientation of the bottom surface is inclined in the sheet width direction with respect to the sheet surface 1f. When the average strength I _T is 2.80 or more, the ductility of the magnesium alloy sheet 1 can be easily increased. When the average strength I _T is 4.00 or less, the strength of the magnesium alloy plate 1 can be easily secured. Therefore, it is easier to achieve both strength and ductility of the magnesium alloy plate 1 . The average intensity I _T is preferably 2.90 or more and 3.50 or less.

(Ratio of average strength in rolling direction to average strength in sheet width direction)
The ratio I _R /I _T between the average intensity I _R and the average intensity I _T is preferably 0.80 or more and 1.20 or less, for example. When the ratio I _R /I _T is within the above range, the crystal includes a crystal having a bottom crystal orientation inclined to the rolling direction and a crystal having a bottom crystal orientation inclined to the sheet width direction in a well-balanced manner. As a result, the magnesium alloy plate 1 has a good balance between strength and ductility. The ratio I _R /I _T is preferably 0.90 or more and 1.10 or less.

(maximum strength)
The maximum intensity Imax of the crystal orientation of the bottom surface is preferably 4.5 or more and 6.5 or less, for example. The magnesium alloy plate 1 having a maximum strength Imax of 4.5 or more and 6.5 or less contains crystals in a specific range in which the crystal orientation of the bottom surface is inclined with respect to the plate surface 1f. When the maximum strength Imax is 4.5 or more, the strength of the magnesium alloy plate 1 can be easily increased. When the maximum strength Imax is 6.5 or less, it is easier to ensure the ductility of the magnesium alloy plate 1 . Therefore, it is easier to achieve both strength and ductility of the magnesium alloy plate 1 . The maximum intensity Imax is more preferably 4.6 or more and 6.0 or less.

<KAM value>
Further, the magnesium alloy plate 1 preferably has a KAM (Kernel Average Misorientation) value of the magnesium alloy crystal grains of 0.4° or more and 1.1° or less. The KAM value is the average value of crystal misorientation between a measurement point and its adjacent measurement points. A larger KAM value indicates a larger strain in the crystal grains. That is, the larger the KAM value, the more strain is introduced, so the strength increases but the ductility decreases. On the other hand, when the KAM value is small, the strain is small, so the ductility is improved, but the strength is reduced. When the KAM value is 0.4° or more, the strength of the magnesium alloy plate 1 can be easily increased. A KAM value of 1.1° or less makes it easier to increase the ductility of the magnesium alloy sheet. Therefore, it is easier to achieve both strength and ductility of the magnesium alloy plate 1 .

The KAM value can be obtained by measuring the crystal orientation difference between adjacent measurement points obtained by the EBSD method. As shown in FIG. 5, with one pixel Pm as a measurement point, all orientation differences between the pixel Pm and six pixels P1, P2, P3, P4, P5, and P6 adjacent to the pixel Pm are obtained. Calculate the mean value of the orientation difference of six adjacent points. At this time, among the six adjacent points, the point with the misorientation larger than an arbitrary upper limit value is regarded as a grain boundary and excluded from the calculation of the average value. That is, the average value of the orientation differences at points where the orientation difference is equal to or less than an arbitrary upper limit value among the six adjacent points is calculated. Let this average value be the KAM value of the pixel Pm. For example, the orientation difference between pixel Pm and pixel P1 is 2.6°, the orientation difference between pixel Pm and pixel P2 is 2.4°, the orientation difference between pixel Pm and pixel P3 is 1.1°, and the orientation difference between pixel Pm and pixel Pm is 2.4°. Assume that the orientation difference with the pixel P4 is 1.3°. Also, assume that the orientation difference between the pixel Pm and the pixel P5 is 41.2°, and the orientation difference between the pixel Pm and the pixel P6 is 35.6°. When the upper limit of the misorientation is set to 5°, the grain boundaries between the pixel Pm and the pixel P5 and between the pixel Pm and the pixel P6 are regarded as grain boundaries. In this case, the KAM value of pixel Pm is (2.6°+2.4°+1.1°+1.3°)/4=1.85°. Then, similar calculations are performed for all pixels, and the average value of the calculated KAM values is taken as the KAM value of the magnesium alloy plate 1 . However, out of all the pixels, the pixels located on the outer edge are excluded from the calculation because they are not surrounded by other pixels.

[Characteristic]
Magnesium alloy plate 1 preferably has the following properties. In the following description, the plate width direction is a direction orthogonal to both the plate thickness direction and the rolling direction.

(0.2% proof stress)
The 0.2% proof stress in the rolling direction is, for example, 190 MPa or more, preferably 200 MPa or more. The 0.2% yield strength in the plate width direction is, for example, 125 MPa or more, preferably 130 MPa or more. Magnesium alloy plate 1 having a high 0.2% yield strength is excellent in strength. The upper limit of the 0.2% yield strength in the rolling direction is practically about 300 MPa. That is, the 0.2% yield strength in the rolling direction is preferably 190 MPa or more and 300 MPa or less, more preferably 200 MPa or more and 300 MPa or less. The upper limit of the 0.2% yield strength in the sheet width direction is practically about 200 MPa. That is, the 0.2% yield strength in the sheet width direction is preferably 125 MPa or more and 200 MPa or less, more preferably 130 MPa or more and 200 MPa or less.

The average value of the 0.2% yield strength in the rolling direction and the 0.2% yield strength in the sheet width direction is, for example, 150 MPa or more, preferably 160 MPa or more. This magnesium alloy plate 1 is excellent in strength. The upper limit of the average value of 0.2% yield strength is practically about 250 MPa. That is, the average value of the 0.2% yield strength is preferably 150 MPa or more and 250 MPa or less, more preferably 160 MPa or more and 250 MPa or less.

The difference between the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the width direction is, for example, 50 MPa or more, preferably 60 MPa or more. The above difference is an absolute value. When the difference in the 0.2% proof stress is 50 MPa or more, both strength and ductility of the magnesium alloy plate 1 can be achieved. This magnesium alloy sheet 1 has sufficient strength because one of the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the plate width direction is high. The magnesium alloy sheet 1 has improved ductility because the other of the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the width direction is low. The upper limit of the difference in 0.2% proof stress is practically about 110 MPa, and further about 100 MPa. That is, the difference in 0.2% yield strength is preferably 50 MPa or more and 110 MPa or less, more preferably 60 MPa or more and 100 MPa or less.

(stretch)
The elongation in the rolling direction is, for example, preferably 20% or more, more preferably 21% or more. The elongation in the sheet width direction is, for example, 22% or more, preferably 24% or more. Magnesium alloy plate 1 having a large elongation is excellent in ductility. The upper limit of the elongation in the rolling direction is practically about 30%. That is, the elongation in the rolling direction is preferably 20% or more and 30% or less, more preferably 21% or more and 30% or less. The upper limit of the elongation in the sheet width direction is practically about 40%. That is, the elongation in the sheet width direction is preferably 22% or more and 40% or less, more preferably 24% or more and 40% or less. The above elongation is breaking elongation.

The average value of the elongation in the rolling direction and the elongation in the sheet width direction is, for example, 18% or more, preferably 20% or more, and particularly preferably 22% or more. This magnesium alloy plate 1 is excellent in ductility. The upper limit of the above average elongation is practically about 35%. That is, the average elongation is preferably 18% or more and 35% or less, more preferably 20% or more and 35% or less, particularly 22% or more and 35% or less.

(Tensile strength)
The tensile strength in the rolling direction is, for example, 260 MPa or more, preferably 265 MPa or more. The tensile strength in the plate width direction is, for example, preferably 235 MPa or more, more preferably 238 MPa or more. Magnesium alloy plate 1 having high tensile strength is excellent in strength. The upper limit of the tensile strength in the rolling direction is practically about 320 MPa. That is, the tensile strength in the rolling direction is preferably 260 MPa or more and 320 MPa or less, more preferably 265 MPa or more and 320 MPa or less. The upper limit of the tensile strength in the sheet width direction is practically about 300 MPa. That is, the tensile strength in the sheet width direction is preferably 235 MPa or more and 300 MPa or less, more preferably 265 MPa or more and 300 MPa or less.

The average value of the tensile strength in the rolling direction and the tensile strength in the plate width direction is, for example, 245 MPa or more, preferably 255 MPa or more. This magnesium alloy plate 1 is excellent in strength. The upper limit of the above average tensile strength is practically about 300 MPa. That is, the average tensile strength is preferably 245 MPa or more and 300 MPa or less, more preferably 255 MPa or more and 300 MPa or less.

The 0.2% yield strength, elongation, and tensile strength can be measured according to "Metal Material Tensile Test Method JIS Z 2241 (2011)". 0.2% yield strength, elongation, and tensile strength are measured at room temperature. Room temperature is 20°C ± 15°C.

(Erichsen value)
The Erichsen value is, for example, 4.5 mm or more, preferably 5.0 mm. When the Erichsen value is 4.5 mm or more, the plastic workability is excellent. The upper limit of the Erichsen value is practically about 10 mm. That is, the Erichsen value is preferably 4.5 mm or more and 10 mm or less, more preferably 5.0 or more and 10 mm or less.

The Erichsen value can be measured according to "Erichsen tester JIS B 7729 (2005)" and "Erichsen test method JIS Z 2247 (2006)". Erichsen values are measured at room temperature.

(Thermal conductivity)
The thermal conductivity is preferably 120 W/m·K or more, for example. The thermal conductivity is 120 W/m·K or more, so that the thermal conductivity is excellent. The higher the thermal conductivity, the better, and there is no particular upper limit for the thermal conductivity. The upper limit of thermal conductivity is, for example, 150 W/m·K.

Thermal conductivity can be measured by the AC method.

From the viewpoint of the balance between strength and ductility, the magnesium alloy plate 1 preferably satisfies at least one of the following four properties.

The first characteristic is that the 0.2% proof stress in the rolling direction is 190 MPa or more and the elongation in the rolling direction is 20% or more. This magnesium alloy plate 1 has a high 0.2% proof stress and a large elongation. Therefore, this magnesium alloy plate 1 has an excellent balance between strength and ductility.

The second characteristic is that the average value of the 0.2% yield strength in the rolling direction and the 0.2% yield strength in the sheet width direction is 150 MPa or more, and the average value of the elongation in the rolling direction and the elongation in the sheet width direction. is 18% or more. This magnesium alloy plate 1 has a high 0.2% proof stress and a large elongation. Therefore, this magnesium alloy plate 1 has an excellent balance between strength and ductility.

The third characteristic is that the difference between the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the plate width direction is 50 MPa or more. The above difference is an absolute value. This magnesium alloy plate 1 can achieve both strength and ductility. Since one of the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the width direction is high, sufficient strength is obtained. Ductility improves because the other 0.2% proof stress is low.

The fourth characteristic is that the 0.2% proof stress in the rolling direction is 190 MPa or more and the Erichsen value is 4.5 mm or more. This magnesium alloy plate 1 has high strength and excellent plastic workability.

More preferably, the magnesium alloy plate 1 satisfies two or more of the four properties described above. The magnesium alloy plate 1 preferably satisfies all of the above four characteristics.

[thickness]
The thickness of the magnesium alloy plate 1 can be appropriately selected depending on the application. The thickness of the magnesium alloy plate 1 is, for example, 0.4 mm or more and less than 2.0 mm.

The thickness of the magnesium alloy plate 1 can be obtained as follows. A test piece having a predetermined size is taken from the magnesium alloy plate 1 . The predetermined size is, for example, a length of 300 mm or more and 600 mm or less and a width of 200 mm or more and 350 mm or less. At least 10 measurement points are taken from the specimen. For example, the test piece is divided lengthwise into 10 or more small areas, and measurement points are taken from each small area. Let the value which averaged the thickness in each measurement point be thickness.

[Production method]
The magnesium alloy plate 1 of the present embodiment can be manufactured by the method for manufacturing a magnesium alloy plate described below. A method for manufacturing a magnesium alloy plate includes, for example, a casting process, a heat treatment process, and a rolling process. In this magnesium alloy sheet manufacturing method, the heat treatment process is not performed after the rolling process. Each step will be described in order below.

(Casting process)
A casting process is a process of producing a cast plate made of a magnesium alloy. A magnesium alloy has a specific composition as described above. A cast plate is produced by casting a molten magnesium alloy. Casting methods include, for example, continuous casting and gravity casting. As a continuous casting method, for example, there is a twin roll method. The twin roll method is a method in which molten metal is supplied between a pair of rolls, which are movable molds, and brought into contact with the rolls to rapidly solidify the molten metal. By rapidly cooling and solidifying the molten metal, it is easy to produce a cast plate with few internal defects such as shrinkage cavities, pores, and segregation. Further, by rapidly cooling and solidifying the molten metal, the crystal grains of the magnesium alloy become smaller, so that a fine crystal structure can be obtained.

The cooling rate during casting is preferably 100° C./second or more, for example. From the viewpoint of refining the crystal grains of the magnesium alloy, the cooling rate is preferably 200° C./second or more and 500° C./second or more. The upper limit of the cooling rate is practically 2000° C./s or less.

The thickness of the cast plate is, for example, 2 mm or more and 6 mm or less. The thickness of the cast plate is preferably 2.5 mm or more and 5.5 mm or less, more preferably 3 mm or more and 5 mm or less.

(Heat treatment process)
The heat treatment step is a step of heat-treating the cast plate to produce a treated plate. The heat treatment is performed, for example, in a continuous heat treatment furnace, a batch heat treatment furnace, or the like. This heat treatment is a homogenization treatment. In the heat treatment step, it is preferable to set the temperature of the cast plate to 350° C. or higher and 400° C. or lower. By setting the temperature of the cast plate to 350° C. or higher, the elements that are not dissolved in the magnesium alloy are easily dissolved sufficiently. By setting the temperature of the cast plate to 400° C. or less, the temperature of the cast plate is not excessively high, and discoloration due to excessive oxidation can be easily suppressed. Also, if the temperature of the cast plate is 400° C. or less, it is easy to produce a treated plate with excellent surface properties and few defects caused by melting of intermetallic compounds. The temperature of the cast plate is preferably 380° C. or higher and 400° C. or lower, more preferably 390° C. or higher and 400° C. or lower.

(rolling process)
The rolling step is a step of rolling the treated plate to produce a rolled plate. The rolling process may be either reverse rolling or tandem rolling. The rolling process uses, for example, a pair of rolling rolls that are arranged vertically facing each other. In the rolling process, the treated plate is rolled by passing the treated plate between a pair of rolling rolls. Each rolling roll has the same diameter as each other. The rotation axis of the rolling rolls is not eccentric and is located in the center of the rolling rolls. The rotation speed of each rolling roll is the same.

The rolling process is performed in a plurality of passes so that the thickness of the rolled sheet becomes a predetermined thickness. The rolling reduction D per pass is preferably 10% or more and 35% or less, for example. The rolling reduction D per pass is obtained as {(t ₂ −t ₁ )/t ₂ }×100. t2 is the plate thickness before rolling in _each pass. t1 is the strip thickness after rolling in _each pass. The rolling reduction of each pass may be the same or may be different within the above range. The rolling reduction D per pass is preferably 20% or more and 35% or less, more preferably 25% or more and 32% or less.

The total rolling reduction Dt from the first pass to the final pass is preferably, for example, 50% or more and 95% or less. The total rolling reduction Dt is obtained as {(t _b −t _a )/t _b }×100. _tb is the thickness of the treated plate before the start of rolling. This thickness is called the initial plate thickness. The initial plate thickness is substantially the same as the cast plate thickness. t _a is the thickness of the rolled plate after the rolling is finished. This thickness is called the final plate thickness. The total rolling reduction Dt is preferably 60% or more and 95% or less, more preferably 70% or more and 95% or less.

The rolling process is carried out in a state in which a treated plate provided between a pair of rolling rolls is set to a specific temperature and the pair of rolling rolls is set to a specific temperature. The temperature of the treated plate and the temperature of the rolling rolls are respectively 150° C. or higher and 300° C. or lower. The temperature of the treated plate refers to the surface temperature of the plate just before the treated plate is passed through the rolling rolls in each pass. The term "immediately before passing through the rolling rolls" refers to a point on the surface of the widthwise center of the plate material which is 200 mm or more and 500 mm or less away from directly below the rolling rolls in the direction opposite to the rolling direction. The temperature of the pressure roll means the temperature of the surface of the pressure roll.

By setting the temperature of the treated plate and the temperature of the rolling rolls to 150° C. or higher, rolling can be easily performed. By setting the temperature of the treated plate and the temperature of the rolling rolls to 300° C. or less, it is easy to suppress coarsening of the crystal grains of the magnesium alloy. The temperature of the treated plate and the temperature of the rolling rolls are preferably 200° C. or higher and 290° C. or lower, and 220° C. or higher and 260° C. or lower. The temperature of the treated plate and the temperature of the rolling rolls may be the same or different. If the temperature of the treated plate and the temperature of the rolling rolls are the same, the temperature of the plate does not change during rolling, and it is easy to produce a rolled plate having a homogeneous structure over the entire length.

Rolling is performed under specific conditions at least in the final pass among a plurality of passes. Rolling may be performed under specific conditions in passes other than the final pass. It is preferable to perform rolling under specific conditions in all passes including the final pass.

The specific conditions are to set the rolling temperature to 230° C. or higher. Rolling temperature refers to the surface temperature of the sheet immediately after it leaves the rolling rolls in each pass. The term "immediately after coming out of the rolling rolls" refers to a point on the surface of the center in the width direction of the plate material that is 200 mm or more and 500 mm or less away in the rolling direction from directly under the rolling rolls. The rolling temperature is preferably 235° C. or higher and 240° C. or higher.

<Other processes>
A straightening process may be performed after the rolling process. The straightening step is a step of straightening the rolled plate. In the straightening process, bending of the rolled plate is removed by passing the rolled plate through leveler rolls. The straightening of the rolled plate is performed in a state in which recrystallization does not occur in the magnesium alloy forming the rolled plate. Specifically, the straightening of the rolled plate is performed by setting the temperature of the rolled plate to, for example, 180° C. or higher and lower than 250° C., further 200° C. or higher and 240° C. or lower, and the treatment time at that temperature is 0.5 minutes or longer and 3 minutes or shorter. Furthermore, it is preferable to set the time to 1 minute or more and 2 minutes or less.

In the steps subsequent to the rolling step, the rolled sheet is not subjected to heat treatment that causes recrystallization of the magnesium alloy. Annealing treatment is mentioned as a specific heat treatment. In the annealing treatment, the rolled plate is annealed, for example, at 250° C. or higher for 1 hour or longer. Therefore, in this embodiment, annealing treatment is not performed after the rolling process.

[Use]
The magnesium alloy plate 1 can be used as a constituent member of transportation equipment, a constituent member of electric/electronic equipment, and the like. Transportation equipment includes, for example, automobiles, aircraft, and railroads. Electrical and electronic devices are, for example, mobile phones and laptop computers. In particular, the magnesium alloy plate 1 can be suitably used as a material for pressed products. A press-formed product is obtained by bending the magnesium alloy plate 1 and press-forming it by drawing or the like. Bending is a process of bending the magnesium alloy plate 1 into a predetermined shape. Drawing is a process of forming the magnesium alloy plate 1 into a predetermined container shape.

[Test Example 1]
A sample of a magnesium alloy plate was produced. The produced magnesium alloy plate was evaluated.

(Preparation of sample)
Magnesium alloy plate samples were produced through a casting process, a heat treatment process, and a rolling process in the same manner as in the manufacturing method of the magnesium alloy plate described above. The produced magnesium alloy plate is a rolled plate.

(Casting process)
In the casting process, a cast plate made of a magnesium alloy was produced. The cast plate was produced by continuous casting by the twin roll method using a twin roll continuous casting apparatus. The cooling rate during casting is 1000° C./second or more. In this test example, molten metals of magnesium alloys with different compositions were cast to produce cast plates with different magnesium alloy compositions.

The thickness of the cast plate was 4.0 mm or 4.2 mm. The width of the cast plate was 410 mm. The length of the cast plate was 20 m or longer.

(Heat treatment process)
In the rolling process, the cast plate was heat-treated to produce a treated plate. In the heat treatment, the cast plate was heated so that the temperature of the cast plate reached 400°C, and the cast plate was held at 400°C for 5 hours.

(rolling process)
In the rolling step, the treated plate was rolled to produce a rolled plate. The rolling process was performed by passing the treated plate between the rolling rolls using a rolling device having a pair of rolling rolls per pass. A pair of rolling rolls are arranged facing each other vertically. Each rolling roll has the same diameter as each other. The rotation axis of each rolling roll is not eccentric and is located at the center of the rolling roll. The rotation speed of each rolling roll was the same.

Multiple passes of rolling were performed. Different rolling conditions were used for each sample. However, No. 1-13 to No. For samples No. 1-15. The same rolling conditions as 1-1 were used. Tables 1 and 2 show the rolling conditions for each sample.

No. 1-1, No. 1-2, No. 1-4 and No. 1-11 used a treated plate obtained by heat-treating a cast plate having a thickness of 4.0 mm. No. 1-3 and No. 1-12 used a treated plate obtained by heat-treating a cast plate with a thickness of 4.2 mm. No. 1-1 to No. 1-3, and No. 1-12 to No. 1-15 was rolled in 5 passes. No. 1-4 performed 7-pass rolling. No. 1-11 was subjected to 6-pass rolling. Table 1 shows the rolling reduction D in each pass and the total rolling reduction Dt. In Table 1, "initial plate thickness" is the thickness of the treated plate before starting rolling. The thickness of the treated plate is the same as the thickness of the cast plate. "Final sheet thickness" is the thickness of the rolled sheet after completion of rolling.

In the rolling process, the rolling temperature was controlled in each rolling of multiple passes. The rolling temperature is the surface temperature of the plate immediately after it leaves the rolling rolls, as described above. Table 2 shows the rolling temperature in each pass. The rolling temperature in each pass was controlled by controlling the temperature of the rolling rolls in each pass and the temperature of the treated plate in each pass. The temperature of the rolling rolls in each pass and the temperature of the treated plate in each pass were set so as to be the rolling temperatures shown in Table 2. The temperature of the rolling rolls in each pass and the temperature of the treated plate in each pass do not necessarily match the rolling temperatures shown in Table 2. For controlling the rolling temperature, for example, the temperature of the treated plate in each pass may be set higher than the rolling temperature, and the temperature of the rolls in each pass may be set lower than the rolling temperature. Also, in controlling the rolling temperature, for example, the temperature of the treated plate in each pass and the temperature of the rolling rolls in each pass may be set higher than the rolling temperature. Even if the temperature of the treated plate in each pass is set higher than the rolling temperature, the temperature of the plate may drop before it contacts the rolling rolls. In this test example, the plate was heated between each pass. The heating time was 30 minutes.

No. 1-1 to No. In 1-4, the rolling temperature was set to 230° C. or higher in all passes including the final pass. No. 1-11 and No. 1-12 set the rolling temperature in the final pass to less than 230°C.

No. 1-13 to No. 1-15 was annealed after the rolling process. In Table 2, when the column of "annealing treatment (yes/no)" is "yes", it indicates that the rolled sheet was annealed. Moreover, in the case of "None", it indicates that the rolled plate was not annealed. No. 1-13 annealed the rolled plate at 250° C. for 1 hour. No. 1-14 annealed the rolled plate at 300° C. for 1 hour. No. 1-15 annealed the rolled plate at 350° C. for 1 hour. No. 1-1 to No. 1-4, No. 1-11 and No. In No. 1-12, no heat treatment including annealing was performed after the rolling process.

(composition)
Table 3 shows the composition of the magnesium alloy constituting the magnesium alloy plate of each sample. The composition of the magnesium alloy was determined by ICP emission spectrometry. The content of each element shown in Table 3 is a value when the total content of the elements contained in the magnesium alloy is 100% by mass. No. 1-1 composition and No. 1-13 to No. The composition is the same as that of each of 1-15. No. 1-3 composition and No. The composition is the same as that of 1-12.

(organization)
As a structural analysis of the magnesium alloy plate of each sample, the crystal orientation distribution of the bottom surface of the magnesium alloy crystal was examined. The crystal orientation distribution of the bottom surface was measured as follows.

A first measurement piece for structural analysis was produced from the magnesium alloy plate of each sample.

Prior to polishing, the first measurement piece was fixed to a polishing jig so that the cross section perpendicular to the plate width direction was the polished surface. The polishing jig was attached to an IS-POLISHER manufactured by Ikegami Seiki Co., Ltd., and surface polishing, intermediate polishing, and final polishing were performed on the first measurement piece in this order. Abrasive paper containing silicon carbide as abrasive grains was used for surface polishing. Three types of abrasive paper were used, #400, #1200, and #2000. The intermediate polishing used aluminum oxide with a particle size of 0.3 μm as an abrasive. In the final polishing, silicon dioxide with a particle size of 0.04 μm was used as an abrasive. After final polishing, the surface was washed with ethanol to obtain a first measurement piece for tissue analysis.

Each first measurement piece was fixed to a sample stage for EBSD measurement. At that time, it was attached so that the rolling direction coincided with the horizontal direction of the attachment surface of the sample table. At this time, the error between the rolling direction and the horizontal direction of the mounting surface of the sample stage is approximately 0.5° or less. The sample stage on which the first measurement piece was fixed was inserted into an FE-SEM (Field Emission Scanning Electron Microscope). JSM-7000F manufactured by JEOL Ltd. was used as the FE-SEM apparatus. The sample chamber of the FE-SEM was evacuated. The measurement conditions were room temperature and an acceleration voltage of 10 kV.

One observation field of view is taken from the cross section of each first measurement piece. The size of the observation field was set so that the length in the plate thickness direction was from the plate surface to the plate thickness center, and the length along the rolling direction was 180 μm or more.

The crystal orientation in each observation field of each first measurement piece was measured by the EBSD method. Using OIM Analysis (Version 8.5) manufactured by TSL Solutions Co., Ltd., the crystal orientation distribution was analyzed to obtain a pole figure. The pole figure shows the intensity distribution of the crystal orientation of the base of the crystal with contour lines. The spot diameter of the irradiated electron beam is about 0.05 μm. The scanning interval of the electron beam was set to 0.5 μm. Data points with a Confidence Index of 0.1 or higher in the above analysis software were adopted. The reliability coefficient is an index that indicates the reliability of the results of indexing/direction calculation by the EBSD method, and a reliability value coefficient of 0.1 or more indicates that 95% or more of correct indexing/direction calculation has been performed. .

Figs. 6 to 14 show the pole figures of the basal plane of crystals in the magnesium alloy plate of each sample.

(Intensity of crystal orientation of the basal plane)
From the pole figures of each sample, the above-mentioned average intensity I _R , average intensity I _T , and maximum intensity Imax were determined. Table 4 shows the results. A ratio I _R / _IT between the average intensity I _R and the average intensity I _T was obtained. The results are also shown in Table 4.

(KAM value)
Also, the KAM value of the crystal grains of the magnesium alloy in each sample was examined. The KAM value was determined as follows. The crystal orientation in each observation field of each first measurement piece was measured by the EBSD method, and the KAM value was obtained by analyzing using the analysis software described above. KAM values were calculated, as described above, for boundaries where the orientation difference between the pixel of the measurement point and the neighboring pixels was 5° or less. Then, the average value of the KAM values at all measurement points was calculated as the KAM value of the sample. Table 4 shows the results.

As shown in Table 4, No. 1-1 to No. 1-4 had an average intensity I _R within the range of 2.50 or more and 4.00 or less. Furthermore, No. 1-1 to No. 1-4, the maximum intensity Imax was within the range of 4.5 or more and 6.5 or less. No. 1-1 to No. 1-4 had a KAM value within the range of 0.4° or more and 1.1° or less. On the other hand, No. 1-11 to No. 1-15, the average intensity I _R , maximum intensity Imax, and KAM values were outside the above ranges.

(mechanical properties)
The mechanical properties of the magnesium alloy plate of each sample were evaluated. Here, 0.2% proof stress, elongation, and tensile strength were measured as mechanical properties. The elongation shall be the elongation at break. The 0.2% proof stress, elongation and tensile strength were measured in the rolling direction and the sheet width direction. 0.2% yield strength, elongation and tensile strength were measured as follows.

Two types of test pieces, a first test piece and a second test piece, were produced from the magnesium alloy plate of each sample. Each test piece is a plate-shaped piece of JIS No. 13B, and is sampled from an arbitrary portion of the magnesium alloy plate. In addition, it is preferable to remove the peripheral edge of the magnesium alloy plate and the area in the vicinity of the peripheral edge of the magnesium alloy plate so as to facilitate proper measurement. For example, each test piece is taken from an inner region at least 5 mm away from the rim. Each test piece was a small test piece with a gauge length of 50 mm and a width of 12.5 mm. The longitudinal direction of the first test piece was along the rolling direction of the magnesium alloy plate. The longitudinal direction of the second test piece was along the width direction of the magnesium alloy plate. A tensile force was applied along the longitudinal direction of each test piece at room temperature in accordance with "Metal Material Tensile Test Method JIS Z 2241:2011".

Table 5 shows the 0.2% proof stress, elongation, and tensile strength of the magnesium alloy plate of each sample. In Table 5, "RD" shown in the "Direction" column indicates the rolling direction. Also, "TD" indicates that it is in the sheet width direction. For the 0.2% yield strength, the 0.2% yield strength in the rolling direction, the 0.2% yield strength in the width direction, the average value of both 0.2% yield strengths, and the difference between both 0.2% yield strengths 5. The difference in 0.2% proof stress is shown as an absolute value. As for the elongation, Table 5 shows the elongation in the rolling direction, the elongation in the sheet width direction, and the average value of both elongations. Regarding the tensile strength, Table 5 shows the tensile strength in the rolling direction and the tensile strength in the plate width direction.

(plastic workability)
The plastic workability of the magnesium alloy plate of each sample was evaluated. Here, No. 1-1, No. 1-2, No. 1-4, No. 1-11, and No. 1-13 to No. For 1-15, the Erichsen value was measured. No. 1-3, and No. For 1-12, drawing was actually performed and drawability was evaluated.

(Erichsen value)
A square test piece was cut out from a magnesium alloy plate. The length of one side of the test piece was 90 mm. The Erichsen value was measured according to "Erichsen tester JIS B 7729 (2005)" and "Erichsen test method JIS Z 2247 (2006)". Measurements were made at room temperature. Erichsen values are shown in Table 6. No. 1-3, and No. Since the Erichsen value was not measured for 1-12, the column of "Erichsen value" is set to "-".

(Drawability)
The drawability was evaluated by subjecting the magnesium alloy sheet to cylindrical deep drawing at room temperature and visually checking for cracks. Normal temperature means that the material is not heated or cooled from the outside under room temperature, and is the same as room temperature.

A disc-shaped test piece was cut out from a magnesium alloy plate. The diameter of the test piece was 80 mm. A die provided with a punch, a die and a holder was used for cylindrical deep drawing. A punch presses the test piece. The shape of the punch is cylindrical. The punch diameter was 40 mm. That is, the drawing ratio is 2.0. The drawing ratio is the diameter of the specimen/the diameter of the punch. The bending radius of the shoulder of the punch was 5 mm. The die and holder sandwich the specimen. The die and holder have holes through which the punches are inserted. A die is mounted with a test piece. The holder supports the peripheral portion of the test piece and suppresses the occurrence of wrinkles during processing of the test piece. The die and holder have built-in heaters so that the specimen can be heated. The test piece is arranged on the end face of the die so as to block the hole of the die, and is sandwiched between the die and the holder.

The mold temperature was 250°C. The press speed was 50 mm/s. Pressing was performed immediately after placing the room temperature magnesium alloy plate in the mold. "Immediately after placing in the mold" means that the time from when the magnesium alloy sheet is set in the mold to when the pressing is started is within 10 seconds. During pressing, the press is not stopped in order to heat the magnesium alloy sheet. Pressing was performed by interposing a fluororesin sheet between the test piece and the punch and between the test piece and the die. After the cylindrical deep drawing, the presence or absence of cracks in the corner portions of the processed product was visually observed. If no cracks were observed, the drawability was evaluated as "A". If even one crack is observed, the drawability is evaluated as "B". Table 6 shows the results. No. 1-1, No. 1-2, No. 1-4, No. 1-11, and No. 1-13 to No. For 1-15, the drawability was not evaluated, so "-" is entered in the "drawability" column.

(Thermal conductivity)
The thermal conductivity of the magnesium alloy plate of each sample was measured. Thermal conductivity was determined as follows. A test piece for measurement was taken from the magnesium alloy plate of each sample. The size of the test piece was 25 mm in length, 5 mm in width, and 0.4 mm in thickness. The thermal diffusivity was measured by the optical alternating current method using a commercially available measuring device. Here, as a measuring device, a light AC method thermal diffusivity measuring device LaserPIT manufactured by Advance Riko Co., Ltd. was used. Thermal conductivity was calculated based on the measured thermal diffusivity. The thermal conductivity was determined as thermal diffusivity x specific heat capacity x density. Measurements were made at room temperature. The direction of measurement was the plate thickness direction. Thermal conductivity is shown in Table 6.

As shown in Table 5, No. 1-1 to No. 1-4 had a 0.2% yield strength of 190 MPa or more in the RD direction, that is, the rolling direction, and an elongation in the RD direction of 20% or more. Furthermore, No. 1-1 to No. 1-4 had an average value of 0.2% yield strength of 150 MPa or more and an average value of elongation of 18% or more. No. 1-1 to No. 1-4 had a difference of 50 MPa or more in 0.2% proof stress. No. 1-1 to No. 1-4 is high in strength, yet has sufficient ductility, and has an excellent balance between strength and ductility.

As shown in Table 6, No. 1-1 to No. 1-4 satisfies the Erichsen value of 4.5 mm or more, or the evaluation of drawing workability is "A". Therefore, no. 1-1 to No. 1-4 has good plastic workability.

On the other hand, No. 1-11 to No. 1-15 does not satisfy the 0.2% yield strength in the RD direction of 190 MPa or more and the elongation in the RD direction of 20% or more. No. 1-11 and No. 1-12 has a high 0.2% proof stress but a small elongation. Therefore, No. 1-11 and No. 1-12 has high strength but is deficient in ductility. No. 1-11 has an Erichsen value of less than 4.5 mm and low plastic workability. No. In 1-12, the drawing workability was evaluated as "B" and the plastic workability was low.

On the other hand, No. 1-13 to No. 1-15 has a low 0.2% proof stress but a large elongation. Therefore, No. 1-13 to No. Although 1-15 is excellent in plastic workability, it is insufficient in terms of strength.

The present invention is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all modifications within the meaning and scope of equivalents of the scope of the claims.

1 magnesium alloy plate 1f plate surface 10, 11, 12 crystal 15 bottom surface 70 pole figure A _R1 first region, A _R2 second region A _T1 third region, A _T2 fourth region Pm, P1, P2, P3, P4, P5, P6 Pixel RD Rolling direction TD Strip width direction ND Strip thickness direction C Circumferential direction, R Radial direction α, β Angle

Claims (9)

A magnesium alloy plate made of a magnesium alloy,
The magnesium alloy is
0.5% by mass or more and 2.0% by mass or less of zinc;
0.05% by mass or more and 0.3% by mass or less of calcium,
having a composition in which the balance is magnesium and unavoidable impurities,
In the pole figure of the bottom surface of the magnesium alloy crystal, the average strength of the crystal orientation of the bottom surface in the rolling direction is 2.50 or more and 4.00 or less,
The average strength in the rolling direction is the average value of the average strength of the crystal orientation of the bottom surface in the first region of the pole figure and the average strength of the crystal orientation of the bottom surface in the second region of the pole figure,
The first region is a region surrounded by a circumferential angle of 0°±30° in the pole figure and a radial angle of 5° to 25° in the pole figure. ,
The second region is a region surrounded by an angle of 180° ± 30° in the circumferential direction and an angle of 5° to 25° in the radial direction,
The angle in the circumferential direction is an angle expressed in the range of 0° to 360° counterclockwise from the rolling direction, with the rolling direction being 0°,
The angle in the radial direction is an angle expressed in the range of 0° to 90°, where the center of the pole figure is 0° and the outer circumference of the pole figure is 90°.
Magnesium alloy plate. 2. The magnesium alloy plate according to claim 1, wherein the maximum strength of the crystal orientation of said bottom surface is 4.5 or more and 6.5 or less. The ratio of the average strength in the rolling direction to the average strength of the crystal orientation of the bottom surface in the plate width direction of the pole figure is 0.80 or more and 1.20 or less,
The average intensity in the plate width direction is the average value of the average intensity of the crystal orientation of the bottom surface in the third region of the pole figure and the average intensity of the crystal orientation of the bottom surface in the fourth region of the pole figure. ,
The third region is a region surrounded by an angle of 90° ± 10° in the circumferential direction and an angle of 30° to 70° in the radial direction,
The fourth region is a region surrounded by an angle of 270° ± 10° in the circumferential direction and an angle of 30° to 70° in the radial direction,
3. The magnesium alloy sheet according to claim 1, wherein said sheet width direction is a direction orthogonal to both the sheet thickness direction and said rolling direction. The magnesium alloy sheet according to any one of claims 1 to 3, wherein the KAM value of the crystal grains of the magnesium alloy is 0.4° or more and 1.1° or less. The 0.2% proof stress in the rolling direction is 190 MPa or more,
The magnesium alloy sheet according to any one of claims 1 to 4, wherein the elongation in the rolling direction is 20% or more. The average value of the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the plate width direction orthogonal to both the plate thickness direction and the rolling direction is 150 MPa or more,
The magnesium alloy sheet according to any one of claims 1 to 5, wherein an average value of the elongation in the rolling direction and the elongation in the sheet width direction is 18% or more. The difference between the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the plate width direction orthogonal to both the plate thickness direction and the rolling direction is 50 MPa or more, The magnesium alloy plate according to any one of items 1 and 2. The 0.2% proof stress in the rolling direction is 190 MPa or more,
The magnesium alloy sheet according to any one of claims 1 to 7, having an Erichsen value of 4.5 mm or more. The magnesium alloy plate according to any one of claims 1 to 8, which has a thermal conductivity of 120 W/m·K or more.

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