JP5218923B2 - Magnesium alloy plate - Google Patents

Description

  The present invention relates to a magnesium alloy plate. In particular, it relates to a magnesium alloy plate excellent in press workability.

  Magnesium alloys are attracting attention as lightweight structural materials because they are low density metals and have high specific strength and specific rigidity. Among them, the wrought material is expected to spread in the future because it is excellent in mechanical properties such as strength and toughness. Magnesium alloys change their properties by changing the type and amount of metal element added. In particular, alloys with a high aluminum content (for example, AZ91 in the ASTM standard) have high corrosion resistance and strength, and demand for wrought materials. Is also big. However, the magnesium alloy has poor plastic workability at room temperature due to the crystal structure of the close-packed hexagonal crystal. For example, the plate material is pressed by raising the plate material temperature to 200 to 300 ° C. For this reason, development of a magnesium alloy sheet capable of stable processing at as low a temperature as possible is desired.

  By the way, various methods can be used for manufacturing the magnesium alloy plate. For example, in die casting or thixo molding, it is difficult to manufacture a thin alloy plate. When a plate is obtained, there are problems such that a large amount of crystallized matter is generated in the plate, the crystal grain size becomes large, and the surface becomes rough. In particular, a magnesium alloy with a high Al content is likely to cause crystallization and segregation during casting. Even after heat treatment and rolling after casting, the crystallization and segregation within the finally obtained alloy plate. Remains and becomes the starting point of fracture during press working.

  Further, as a typical method for producing a conventional magnesium alloy sheet, it is known that a magnesium alloy material sheet is preheated to 300 ° C. or higher and rolled with a rolling roll at room temperature, and this preheating and rolling are repeated.

  Furthermore, as a technique for obtaining a magnesium alloy plate having fine crystal grains for the purpose of improving plastic workability, a method described in Patent Document 1 is known. In this method, rolling is performed by setting the surface temperature of the rolling roll to 80 to 230 ° C and the surface temperature of the magnesium alloy base plate to 250 to 350 ° C.

  In addition, methods described in Patent Documents 2 to 5 are known as techniques for improving the plastic workability of a magnesium alloy plate.

Japanese Patent Laying-Open No. 2005-2378 JP 2003-27173 A JP 2005-29871 A JP 2001-294966 A JP 2004-346351 A

  However, in the method of repeating preheating of a material plate at 300 ° C. or higher and rolling with a rolling roll at room temperature, the crystal grains of the magnesium alloy are coarsened during preheating, and the plastic workability of the obtained magnesium alloy plate is inferior.

  On the other hand, in the method described in Patent Document 1, rolling is performed with the surface temperature of the magnesium alloy plate being 250 to 350 ° C., and when rolling is performed for a plurality of passes under these conditions, an alloy made by rolling one pass before The processing distortion of the plate is eliminated. Therefore, processing strain is not accumulated at the final plate thickness, and the crystal grains of the magnesium alloy plate may not be sufficiently refined. As a result, the plastic workability of the obtained magnesium alloy sheet may not be sufficiently improved.

  In patent document 2, the manufacturing method of the magnesium alloy thin plate containing AZ91 is disclosed. However, the specific mechanical strength characteristic value and press formability of the magnesium alloy sheet are not specified.

In Patent Document 3, an AZ91 alloy plate material is disclosed. According to Patent Document 3, superplasticity was exhibited under the conditions of 300 ° C. and a strain rate of 0.01 (s ⁻¹ ) or less in an example of a tensile test, and 200% elongation was recorded. However, the plastic workability and the tensile properties at the temperature (250 ° C. or lower) when the plate material is actually press-molded are not specified, and the examples of press forming are not described.

  Also, Patent Document 4 and Patent Document 5 do not show specific numerical values for tensile properties.

  Further, the above cited references 1 to 5 do not describe the improvement of plastic workability, particularly press workability, by reducing the amount of crystallized matter and segregation in the magnesium alloy generated during casting. .

  Therefore, one of the objects of the present invention is to provide a magnesium alloy plate excellent in plastic workability such as press working.

  Furthermore, another object of the present invention is to provide a magnesium alloy plate excellent in press workability having good strength and elongation characteristics using a twin roll casting material.

  The magnesium alloy sheet of the present invention is obtained by rolling a magnesium alloy material sheet containing 8.5 to 10.0% by mass of aluminum (Al) and 0.5 to 1.5% by mass of zinc with a rolling roll. The magnesium alloy plate is characterized in that the length in the thickness direction of segregation existing in the center line in the thickness direction of the magnesium alloy plate is 20 μm or less.

  The magnesium alloy sheet of the present invention has high plastic workability and can effectively reduce the occurrence of cracks during processing.

  Hereinafter, the present invention will be described in more detail.

  The magnesium alloy plate of the present invention is typically obtained by preparing a magnesium alloy material plate that has undergone twin-roll casting, roughly rolling the material plate, and then finish rolling. At that time, at least finish rolling is controlled rolling under the following conditions. Control rolling may be performed in the entire range of the rolling process performed after casting.

(Surface temperature Tr of rolling roll during controlled rolling)
The surface temperature Tr of the rolling roll is 150 to 180 ° C. If it is less than 150 ° C., if the rolling reduction / pass is increased, fine cracks of crocodile leather may occur in the direction perpendicular to the traveling direction of the material plate when the material plate is rolled. If the temperature exceeds 180 ° C, the distortion of the material plate accumulated during the rolling process will be eliminated by recrystallization of the alloy crystal grains during the rolling process. Difficult to do.

  In order to control the surface temperature of the rolling roll, a method of arranging a heating element such as a heater inside the rolling roll, a method of blowing warm air on the surface of the rolling roll, or the like can be used.

(Surface temperature Tb of material plate during controlled rolling)
The surface temperature Tb (° C.) of the magnesium alloy material plate immediately before insertion into the rolling roll satisfies the following formula.
8.33 × M + 135 ≦ Tb ≦ 8.33 × M + 165
However, 1.0 ≦ M ≦ 10.0

  That is, the lower limit of the surface temperature Tb is about 140 ° C., and the upper limit is about 248 ° C. This temperature Tb depends on the Al content M (mass%) in the magnesium alloy. Specifically, the temperature Tb may be set to about 160 to 190 ° C. in the case of AZ31 according to the ASTM standard and to about 210 to 247 ° C. in the case of AZ91. Below the lower limit temperature of each composition, as in the case where the surface temperature of the rolling roll is low, fine crocodile leather-like cracks may occur in the direction orthogonal to the direction of travel of the blank. Also, if the upper limit temperature of each composition is exceeded, during the rolling process, the strain of the material plate accumulated by the previous rolling will be eliminated by recrystallization of the alloy crystal grains, and the amount of processing strain will be reduced. It is difficult to miniaturize.

  Even if the surface temperature Tb of the material plate is within the above specified range, for example, if the surface temperature of the rolling roll is room temperature, the temperature decreases when the material plate contacts the roll, and cracks occur on the surface of the material plate. By defining not only the temperature of the surface of the rolling roll but also the surface temperature of the material plate, this crack can be effectively suppressed.

(Controlled rolling reduction)
The total rolling reduction of the controlled rolling is preferably 10 to 75%. The total rolling reduction is expressed by (sheet thickness before performing controlled rolling−sheet thickness after controlled rolling) / sheet thickness before performing controlled rolling × 100. When the total rolling reduction is less than 10%, the processing strain to be processed is small and the effect of refining crystal grains is small. On the other hand, if it exceeds 75%, the processing strain near the surface to be processed increases and cracks may occur. For example, when the final plate thickness is 0.5 mm, controlled rolling may be performed on a plate material of 0.56 to 2.0 mm. A more preferable range of the total rolling reduction of the controlled rolling is 20% or more and 50% or less.

  Further, the rolling reduction / pass (average rolling reduction per pass) of controlled rolling is preferably about 5 to 20%. If the rolling reduction / pass is too low, it is difficult to perform efficient rolling. Conversely, if the rolling reduction / pass is too high, defects such as cracks are likely to occur in the rolling target.

(Other rolling conditions)
It is preferable that the above-described controlled rolling is performed in a plurality of passes, and at least one of the plurality of passes is performed with the rolling direction reversed with respect to the other passes. By reversing the rolling direction, compared to the case of rolling only in the same direction, it becomes easier for processing distortion to easily enter the rolling target, and the variation in crystal grain size after the final heat treatment usually performed after controlled rolling can be reduced. .

  As described above, the rolling of the material sheet usually includes rough rolling and finish rolling. In that case, at least finish rolling is the controlled rolling. Considering further improvement in plastic workability, it is preferable to perform controlled rolling over the entire range of the rolling process, but finish rolling is most involved in suppressing the coarsening of the crystal grain size of the finally obtained magnesium alloy sheet. Therefore, this finish rolling is controlled rolling.

  In other words, rough rolling other than finish rolling is not restricted by the rolling conditions of controlled rolling. In particular, there is no particular limitation on the surface temperature of the raw material sheet that is roughly rolled. What is necessary is just to select the conditions which can make the crystal grain diameter of an alloy plate small as much as possible by adjusting the surface temperature and rolling reduction of the raw material board rough-rolled. For example, if the material plate thickness before rolling is 4.0 mm and the final plate thickness is 0.5 mm, rough rolling is performed from the material plate to a plate thickness of 0.56 to 2.0 mm, and the subsequent rolling is regarded as finish rolling. It ’s fine.

  In particular, the surface temperature of the rolling roll in this rough rolling is set to a temperature of 180 ° C. or higher, and rough rolling is performed by increasing the rolling reduction / pass, so that it can be expected to increase the processing efficiency in the rough rolling. In that case, for example, the rolling reduction / pass is preferably 20% or more and 40% or less. However, even when this temperature is 180 ° C. or higher, the roll surface temperature is preferably about 250 ° C. or lower in order to suppress recrystallization of alloy crystal grains.

  In addition, in the rough rolling process, if the surface temperature Tb of the blank sheet immediately before being inserted into the rolling roll is 300 ° C. or higher and the surface temperature of the rolling roll is 180 ° C. or higher, the surface state of the plate after rough rolling can be improved. It is preferable that no edge cracking occurs. If the plate surface temperature is 300 ° C. or less and the roll surface temperature is less than 180 ° C., the rolling reduction cannot be increased, so that the processing efficiency in the rough rolling process is deteriorated. Here, the upper limit of the plate surface temperature is not particularly limited, but if it is set to a high temperature, the surface state of the plate material after rough rolling may be deteriorated. Further, the upper limit of the surface temperature of the roll during rough rolling is not particularly limited, but the roll itself is liable to be damaged by thermal fatigue at a high temperature.

  If the rolling reduction per pass of rough rolling performed in the temperature range as described above is 20% or more and 40% or less, variation in crystal grains in the magnesium alloy sheet subjected to finish rolling after rough rolling can be reduced. preferable. If the rolling reduction per pass during rough rolling is less than 20%, the effect of reducing variation in crystal grains after rolling is poor, and if it exceeds 40%, edge cracking occurs at the end of the magnesium alloy sheet during rolling. To do. In addition, the number of rolling operations (the number of passes) performed at a rolling reduction in this range is less effective in one pass, so it is preferable to perform at least two passes.

  In the rolling of the casting material plate (initial rough rolling), the temperature of the material plate is increased, and the reduction rate is increased within the above rolling reduction range. In the rough rolling immediately before finish rolling, the temperature of the material plate is increased. Is preferably about 300 ° C. and the rolling reduction is about 20%.

  By rough rolling under the above conditions, it is possible to further improve the plastic workability of the magnesium alloy sheet obtained by finish rolling following this rough rolling. Specifically, the surface state of the alloy plate can be improved, the occurrence of edge cracking can be suppressed, and the variation in crystal grain size in the alloy plate can be reduced. Moreover, the amount of segregation in the magnesium alloy sheet can be reduced.

(Material board)
The material plate to be rolled may be a magnesium alloy containing Al, and other composition elements are not particularly limited. For example, a wide variety of materials such as AZ, AM, and AS in the ASTM standard can be suitably used.

  Moreover, the method of obtaining magnesium alloy raw material board itself is not specifically limited. For example, a raw material plate obtained by an ingot casting method, an extrusion method, a twin roll casting method, or the like can be used.

  The material plate by the ingot casting method is obtained, for example, by casting an ingot having a thickness of about 150 to 300 mm, cutting the surface of the ingot, and hot rolling the obtained cutting material. The ingot casting method is suitable for mass production and can obtain a material plate at low cost.

  The material plate by the extrusion method is obtained by casting a billet having a diameter of about 300 mm, for example, reheating the obtained billet, and extruding the billet. In the extrusion method, the billet is strongly compressed at the time of extrusion, so that crystal precipitates in the billet that are likely to become starting points such as cracks during subsequent rolling of the material plate or plastic processing of the rolled material can be pulverized to some extent.

  The material plate by the twin roll casting method is obtained by supplying molten metal from the entrance side between a pair of rolls with the outer peripheral surfaces facing each other, and sending out the solidified material plate as a thin plate from the exit side.

  Among the material plates obtained from these three methods, it is preferable to use a material plate by a twin roll casting method. In the twin roll casting method, rapid solidification using twin rolls is possible, and the resulting material plate has few internal defects such as oxides and segregation. In particular, after the final thickness of the rolled sheet is 1.2 mm or less, it is possible to eliminate defects that adversely affect the subsequent plastic working such as press working. More specifically, crystal precipitates having a particle size of 10 μm or more do not remain in the rolled sheet. Moreover, a raw material plate with few crystal precipitates can be obtained irrespective of alloy compositions, such as AZ31 and AZ91. Moreover, since a thin plate can be obtained even with a difficult-to-process material, the number of subsequent rolling steps of the material plate can be reduced and the cost can be reduced.

(Other processing conditions)
As other processing conditions, a solution treatment may be performed on the material plate before rolling as necessary. The conditions for the solution treatment are, for example, about 380 to 420 ° C. × 60 minutes to 600 minutes, preferably about 390 to 410 ° C. × 360 to 600 minutes. By performing the solution treatment in this way, segregation can be reduced. In particular, in the case of a magnesium alloy corresponding to AZ91 having a high Al content, it is preferable to perform the solution treatment for a long time.

  Moreover, you may perform strain relief annealing during a rolling process (regardless of whether it is controlled rolling) as needed. The strain relief annealing is preferably performed between some passes in the rolling process. It is preferable to select how many times this strain relief annealing is performed at which stage of the rolling process in consideration of the amount of strain accumulated in the magnesium alloy sheet. By performing this strain relief annealing, rolling of subsequent passes is performed more smoothly. The strain relief annealing conditions are, for example, about 250 to 350 ° C. × 20 minutes to 60 minutes.

Furthermore, it is also desirable to subject the rolled material after all the rolling processes to final annealing. Since the crystallographic structure of the magnesium alloy sheet after finish rolling sufficiently accumulates processing strain, it is recrystallized in a fine state when final annealing is performed. That is, even if the alloy plate is subjected to final annealing to eliminate strain, it has a fine recrystallized structure and is therefore maintained in a high strength state. In addition, by recrystallizing the structure of the alloy plate in advance, when the plastic working is performed under a temperature condition of about 250 ° C., the crystal grains of the structure of the alloy plate are coarsened before and after the plastic working. The crystal structure does not change greatly. Therefore, in the magnesium alloy plate subjected to the final annealing, the strength of the portion plastically deformed during the plastic working is improved by work hardening, and the strength of the portion not plastically deformed can maintain the strength before the processing. This final annealing condition is about 200 to 350 ° C. × 10 to 60 minutes. Specifically, when the Al content in the magnesium alloy is 2.5 to 3.5% and the zinc content is 0.5 to 1.5%, it is 10 to 30 minutes at 220 to 260 ° C. When the Al content in the magnesium alloy is 8.5 to 10.0% and the zinc content is 0.5 to 1.5%, the final annealing is performed at 300 to 340 ° C. for 10 to 30 minutes. good.

(About centerline segregation)
A plate produced from a twin roll cast material is segregated at the center of the plate thickness during casting. In the case of a magnesium alloy containing Al, the segregating substance is an intermetallic compound mainly composed of Mg ₁₇ Al ₁₂ , and an alloy having a higher impurity content in the magnesium alloy is more likely to be generated. Taking an ASTM standard AZ-based alloy as an example, the amount of segregation after casting is larger in AZ91 having an Al content of about 9% by mass than in AZ31 having about 3% by mass. Even in the case of AZ91 having a large amount of segregation, the length of segregation in the thickness direction in the magnesium alloy sheet is 20 μm or less by performing the roughing process and solution treatment before finish rolling as described above under appropriate conditions. Can be dispersed. Here, “dispersing the segregation” means dividing the linear segregation in the thickness direction or in the length direction, and the length in the thickness direction of the segregation that does not hinder the press working. Is approximately 20 μm or less. The length in the thickness direction of the segregation is preferably further smaller than 20 μm, and it is assumed that the strength characteristics are further improved when the maximum segregation length is smaller than the crystal grain size of the base material.

(Mechanical properties of magnesium alloy sheet)
When manufacturing a magnesium alloy sheet, if the strain is accumulated in the rolling process and this strain is not removed by heat treatment, the tensile strength can be easily set to 360 MPa. However, in that case, it is difficult to increase the elongation of the alloy plate to 10% or more. Specifically, when the elongation at break at room temperature is less than 15%, the plastic workability is poor, and at temperatures as low as 250 ° C. or lower, damage such as cracks and cracks occurs during press molding. On the other hand, if the breaking elongation at room temperature of the magnesium alloy plate is 15% or more, the breaking elongation at 250 ° C. of this alloy plate is 100% or more, and the surface of the magnesium alloy plate is damaged such as cracks and cracks during press forming. Almost never occurs. The above-described method for producing a magnesium alloy plate is also effective in producing a magnesium alloy plate having the above mechanical characteristics. In particular, a magnesium alloy having a high Al content M of 8.5 to 10.0% by mass (further, containing 0.5 to 1.5% by mass of zinc) has a tensile strength of 360 MPa or more at room temperature. A magnesium alloy plate having a strength of 270 MPa or more and a breaking elongation of 15% or more can be produced. Moreover, according to the manufacturing method of the magnesium alloy plate illustrated above, it can also be set as the magnesium alloy plate whose yield ratio is 75% or more.

  The plastic processing of the magnesium alloy plate is preferably performed in a temperature range in which the structure of the alloy plate is recrystallized during the plastic processing and the mechanical properties of the alloy plate are not significantly changed. For example, in the case of a magnesium alloy plate containing 1.0 to 10.0% by weight of Al, it is preferable to perform plastic working at a temperature of about 250 ° C. or lower. Here, according to the magnesium alloy sheet manufacturing method exemplified above, the magnesium alloy sheet having an Al content M of 8.5 to 10.0% by mass and a zinc content of 0.5 to 1.5% by mass. The tensile strength at 200 ° C. can be 120 MPa or more, the breaking elongation can be 80% or more, the tensile strength at 250 ° C. can be 90 MPa or more, and the breaking elongation can be 100% or more. Is suitable. Moreover, according to the magnesium alloy plate manufacturing method exemplified above, the tensile strength at 250 ° C. of the magnesium alloy plate corresponding to AZ31 can be 60 MPa or more and the elongation at break can be 120% or more.

According to the method exemplified above, the following effects can be obtained.
According to the method exemplified above, by specifying the temperature of the blank sheet and the temperature of the rolling roll at the time of rolling, it is possible to perform rolling in a range in which the crystal grains of the magnesium alloy are not recrystallized. Thereby, it is possible to perform rolling that suppresses the coarsening of the crystal grains of the alloy and hardly causes cracks on the surface of the material plate. Further, it is possible to reduce the amount of segregation in the central portion of the material plate, and to reduce the variation in crystal grain size.

  In particular, when a material plate obtained by a twin roll casting method is rolled, there are few crystal precipitates that are the starting points of cracks and the like, and plastic working can be performed with little or no cracks.

The magnesium alloy sheet of the present invention has the following characteristics.
Since the magnesium alloy sheet of the present invention is composed of fine crystal grains, it has very good plastic workability.

  The magnesium alloy sheet of the present invention satisfies the tensile strength of 360 MPa or more, the yield strength of 270 MPa or more, and the elongation at break of 15% or more at the same time.

Embodiments of the present invention will be described below.
(Test Example 1)
A magnesium alloy material plate having a composition equivalent to AZ31 containing Mg-3.0% Al-1.0% Zn (all by mass%) and having a thickness of 4 mm obtained by a twin roll continuous casting method is prepared. This material plate is roughly rolled to a thickness of 1 mm to obtain a roughly rolled plate having an average crystal grain size of 6.5 μm. Rough rolling was performed by preheating the material plate to 250 to 350 ° C. and rolling the material plate with a rolling roll at room temperature. The average crystal grain size was determined using a calculation formula described in JIS G 0551. Next, this rough rolled sheet is finish-rolled to a thickness of 0.5 mm under various different conditions. Then, a final heat treatment was performed on the finished rolled material at 250 ° C. for 30 minutes, and a disk having a diameter of 92 mm was cut out from the heat treated material to obtain a sample for evaluation.

  Next, the observation surface of each sample was buffed (diamond abrasive grains # 200), and then subjected to an etching treatment, and the structure was observed and the average crystal grain size was measured in a 400 × field of view of an optical microscope.

Furthermore, these samples were drawn and formed under the following conditions using a cylindrical punch and a die having a cylindrical hole into which the punch fits.
Mold setting temperature: 200 ℃
Punch diameter: 40.0 mm (tip R: Rp = 4 mm)
Die hole diameter: 42.5 mm (shoulder R: Rd = 4 mm)
Clearance: 1.25mm
Molding speed: 2.0 mm / min Drawing ratio: 2.3

  Here, Rp is a radius of a curve constituting the outer peripheral edge of the punch in the longitudinal section of the punch tip, and Rd is a radius of a curve constituting the die hole opening in the longitudinal section of the die. The drawing ratio is the diameter of the sample / the diameter of the punch.

Table 1 summarizes the finish rolling conditions and the test results. Each notation in this table has the following significance.
Sheet temperature: Surface temperature of the raw material plate immediately before finish rolling Roll temperature: Surface temperature of rolling roll for finish rolling Rolling direction: “Constant” indicates that all passes were rolled in the same direction, “R” for each pass Shows that the rolling direction is reversed.
1-pass average rolling reduction: Total rolling reduction (50%) / number of passes in rolling from 1 mm to 0.5 mm in thickness Thickness of the surface of the rolled material: No cracks or wrinkles in the rolled material, slightly crocodile leather-like cracking △ indicates that a crack occurred and x indicates a crack occurred.
Edge cracking: “O” indicates that there is no crack at the side edge of the rolled material, “Δ” indicates that there is only a very small crack, and “X” indicates that there is a crack.
Drawing property: “O” indicates that there are no cracks at the corners of the processed product, “Δ” indicates that there are no cracks but wrinkles are generated, and “X” indicates that there is a crack or a fracture.

  As is apparent from this table, it can be seen that all the samples in which the finish rolling is controlled rolling described above have a small average particle diameter, no edge cracks or fine cracks on the surface, and excellent drawability. In addition, the size of the crystal precipitate of the sample according to the present invention was 5 μm or less.

(Test Example 2)
Next, a material plate having the same thickness of 4 mm as the material plate used in Test Example 1 is prepared, and this material plate is roughly rolled to a predetermined thickness to obtain rough rolled plates having different thicknesses. This rough rolling was also performed by preheating the material plate to 250 to 350 ° C. and rolling the material plate with a rolling roll at room temperature. The rough rolled plate was finish-rolled at different total reduction ratios to a final thickness of 0.5 mm to obtain a finished rolled material. In the finish rolling, the surface temperature of the rough rolled plate immediately before the finish rolling was set to 160 to 190 ° C, and the surface temperature of the finish rolling roll at that time was controlled in the range of 150 to 180 ° C. Next, similarly to Test Example 1, this finished rolled material was heat-treated at 250 ° C. for 30 minutes to obtain a sample for evaluation.

  For these samples, the average crystal grain size was measured, the plate surface condition was evaluated, and the edge cracks were evaluated in the same manner as in Test Example 1, and the overall evaluation of these evaluation results was further performed. Table 2 shows the reduction ratio / pass and the total reduction ratio and the evaluation results in finish rolling. The meanings of “plate surface state” and “edge crack” in this table are the same as the same terms in Test Example 1. The “total rolling reduction” is the total rolling reduction in finish rolling from the plate thickness of the rough rolled material to the final plate thickness, that is, the total rolling reduction in rolling with the surface temperature of the plate set to 160 to 190 ° C. However, no. The numerical values described in parentheses in 2-1 indicate that the finish rolling was performed with the surface temperature of the rough rolled sheet set at 220 ° C.

  As is apparent from this table, it can be seen that samples having a total rolling reduction of 10 to 75% have excellent results in comprehensive evaluation.

(Test Example 3-1)
A 4 mm-thick magnesium alloy material plate having a composition equivalent to AZ91 containing Mg-9.0% Al-1.0% Zn (all by mass) is prepared. This material plate is roughly rolled to a predetermined thickness of 1 mm to obtain a roughly rolled plate having an average crystal grain size of 6.8 μm. Rough rolling was performed by preheating the material plate to 300 to 380 ° C. and rolling the material plate with a rolling roll at room temperature. The average crystal grain size was determined using a calculation formula described in JIS G 0551. Next, this rough rolled sheet is finish-rolled to a thickness of 0.5 mm under various different conditions. Then, a final heat treatment was performed on the finished rolled material at 320 ° C. for 30 minutes, and a disk having a diameter of 92 mm was cut out from the heat treated material to obtain a sample for evaluation.

  Next, the observation surface of each sample was buffed (diamond abrasive grains # 200), and then subjected to an etching treatment, and the structure was observed and the average crystal grain size was measured in a 400 × field of view of an optical microscope.

  Further, these samples were drawn and formed under the same conditions as in Test Example 1 except that the die set temperature was set to 250 ° C. using a cylindrical punch and a die having a cylindrical hole into which the punch was fitted. did. Table 3 summarizes the finish rolling conditions and the test results. The meaning of each notation in this table is the same as in Test Example 1.

(Test Example 3-2)
Moreover, the influence of the temperature of a raw material board at the time of finish rolling, roll temperature, etc. was tested like the test example 3-1, using the magnesium alloy raw material board from which Al content differs from the test example 3-1. Manufacturing conditions other than finish rolling and a method for evaluating a magnesium alloy plate are the same as in Test Example 3-1. The magnesium alloy material plate had an Al content of 9.8% by mass and a Zn content of 1.0% by mass. Table 4 summarizes the finish rolling conditions and the test results.

  As is apparent from Tables 3 and 4, all the samples in which the finish rolling is controlled rolling described above have a small average particle size, no edge cracks or fine cracks on the surface, and excellent drawability. Recognize.

(Test Example 4-1)
Next, a material plate having the same thickness of 4 mm as the material plate used in Test Example 3-1 is prepared, and this material plate is roughly rolled to a predetermined thickness to obtain rough rolled plates having different thicknesses. This rough rolling was also performed by preheating the material plate to 300 to 380 ° C. and rolling the material plate with a rolling roll at room temperature. The rough rolled plate was finish-rolled at different total reduction ratios to a final thickness of 0.5 mm to obtain a finished rolled material. In the finish rolling, the surface temperature of the rough rolled plate immediately before the finish rolling was set to 210 to 240 ° C, and the surface temperature of the finish rolling roll at that time was controlled in the range of 150 to 180 ° C. Next, similarly to Test Example 3-1, this finished rolled material was heat-treated at 320 ° C. for 30 minutes to obtain an evaluation sample.

  For these samples, the average crystal grain size was measured, the plate surface condition was evaluated, and the edge cracks were evaluated in the same manner as in Test Example 3-1, and the overall evaluation of these evaluation results was further performed. Table 5 shows the reduction ratio / pass and the total reduction ratio and the evaluation results in finish rolling. The meanings of “plate surface state” and “edge crack” in this table are the same as the same terms in Test Example 1. The “total rolling reduction” is the total rolling reduction in finish rolling from the plate thickness to the final plate thickness of the rough rolled material, that is, the total rolling reduction in rolling with the surface temperature of the plate being 210 to 240 ° C. However, no. The numerical values described in parentheses in 4-1 indicate that the finish rolling was performed with the surface temperature of the rough rolled sheet set at 270 ° C.

(Test Example 4-2)
Moreover, the influence of the average rolling reduction per one pass at the time of finish rolling and a total rolling reduction was tested similarly to Test Example 4-1, using the magnesium alloy raw material board from which Al content differs from Test Example 4-1. did. Manufacturing conditions other than finish rolling and a method for evaluating a magnesium alloy sheet are the same as in Test Example 4-1. The magnesium alloy material plate had an Al content of 9.8% by mass and a Zn content of 1.0% by mass. Table 6 summarizes the finish rolling conditions and the test results.

  As is clear from Tables 5 and 6, it can be seen that samples having a total rolling reduction of 10 to 75% have excellent results in comprehensive evaluation.

(Summary of Test Example 1 to Test Example 4)
From the results of Test Example 1 to Test Example 4 above, when the Al content in the magnesium alloy constituting the material plate is M (mass%), the surface temperature Tb (° C.) of the material plate immediately before insertion into the rolling roll. ) And M are organized in a graph. As a result, if the controlled rolling is performed so that the surface temperature Tb of the material plate satisfies the following formula and the surface temperature Tr of the rolling roll is 150 to 180 ° C., the crystal grain size is refined and the plastic workability is excellent. It was found that a magnesium alloy plate could be obtained.
8.33 × M + 135 ≦ Tb ≦ 8.33 × M + 165
However, 1.0 ≦ M ≦ 10.0

(Test Example 5)
Furthermore, a magnesium alloy plate (AZ31 equivalent material) was manufactured by changing the manufacturing method and rolling conditions of the material plate. Each of the manufacturing method of a raw material board and rolling conditions is as follows.

<Production method of material plate>
A1: A material plate having a thickness of 4 mm is obtained by twin-roll continuous casting.
A2: An ingot having a thickness of about 200 mm is cast, the surface of the ingot is cut, and the obtained cutting material is hot-rolled to obtain a material plate having a thickness of 4 mm.

<Rolling method>
B1: In rough rolling (sheet thickness 4 mm → 1 mm), the raw material plate is preheated to 250 to 350 ° C. and rolled with a normal temperature rolling roll, and in finish rolling (sheet thickness 1 mm → 0.5 mm), the surface temperature of the rolling roll is 150. Control rolling is performed with the surface temperature of the rough rolled plate immediately before insertion into the rolling roll at 160 to 190 ° C.
B2: The raw material plate is preheated to 300 to 400 ° C. by rolling in all passes (plate thickness 4 mm → 0.5 mm) and rolled with a rolling roll at room temperature.

  The magnesium alloy sheet was rolled in the combination shown in Table 7 under the above conditions, and the final heat treatment was performed on the rolled sheet at 250 ° C. for 30 minutes. The surface condition and edge crack were evaluated, and a comprehensive evaluation of each evaluation was made. The results are also shown in Table 7. The overall evaluation in this table is indicated by ◎, ○, △ in order from the best.

  As is apparent from this result, it is understood that a magnesium alloy sheet having particularly excellent plastic workability can be obtained by performing a predetermined controlled rolling using a material sheet obtained by twin roll casting.

(Test Example 6)
A magnesium alloy material plate having a composition equivalent to AZ31 containing Mg-3.0% Al-1.0% Zn (all by mass%) and having a thickness of 4 mm obtained by a twin roll continuous casting method is prepared. This material plate is roughly rolled to a thickness of 1 mm under different conditions to obtain a plurality of coarsely rolled plates. Next, the plurality of rough rolled plates were finish-rolled under the same conditions until a final plate thickness of 0.5 mm was obtained to obtain a magnesium alloy plate. The finish rolling was carried out by controlling the surface temperature of the rough rolled plate immediately before the finish rolling in the range of 160 to 190 ° C and the surface temperature of the finish rolling roll in the range of 150 to 180 ° C. Also, the rolling reduction per pass at that time was set to 15%. Then, the magnesium alloy plate obtained by finish rolling was heat-treated at 250 ° C. for 30 minutes to obtain a sample for evaluation. For these samples, the average crystal grain size was measured, the plate surface condition was evaluated, and the edge crack was evaluated in the same manner as in Test Example 1.

Table 8 summarizes the rough rolling conditions and the test results. Each notation in this table has the following significance.
Sheet temperature: Surface temperature of raw material plate just before rough rolling Roll temperature: Surface temperature of rolling roll for rough rolling Rolling ratio / pass: Rolling ratio in rolling from 4 mm to 1.0 mm in thickness / pass plate surface state; The one without cracks and wrinkles is marked with ◯, the one with a slight crocodile leather-like crack is marked with △, and the one with crack is marked with x.
Further, the average crystal grain size was determined using a calculation formula described in JIS G 0551.

(Test Example 7-1)
A 4 mm-thick magnesium alloy material plate having a composition equivalent to AZ91 containing Mg-9.0% Al-1.0% Zn (all by mass) is prepared. This material plate is roughly rolled to a thickness of 1 mm under different conditions to obtain a plurality of coarsely rolled plates. Next, the plurality of rough rolled plates were finish-rolled under the same conditions until a final plate thickness of 0.5 mm was obtained to obtain a magnesium alloy plate. Finish rolling was performed by controlling the surface temperature of the rough rolled sheet immediately before the finish rolling to 210 to 240 ° C. and the surface temperature of the finish rolling roll to 150 to 180 ° C. In addition, the rolling reduction per pass at that time was set to 15%. And the magnesium alloy plate obtained by finish rolling was heat-treated at 320 ° C. for 30 minutes to obtain a sample for evaluation. For these samples, the average crystal grain size was measured, the plate surface condition was evaluated, and the edge cracks were evaluated in the same manner as in Test Example 6. Further, comprehensive evaluation was performed based on these evaluation results.

  Table 9 summarizes the rough rolling conditions and the test results. The significance of each notation in this table is the same as in Test Example 6.

(Test Example 7-2)
Moreover, the influence of the temperature of a raw material board at the time of rough rolling, roll temperature, etc. was tested like the test example 3-1, using the magnesium alloy raw material board from which Al content differs from the test example 7-1. Manufacturing conditions other than rough rolling and a method for evaluating a magnesium alloy plate are the same as in Test Example 7-1. The magnesium alloy material plate had an Al content of 9.8% by mass and a Zn content of 1.0% by mass. Table 10 summarizes the finish rolling conditions and the test results.

(Test Example 8)
The same AZ31 material plate (thickness 4 mm) as the material plate used in Test Example 6 was prepared. This material plate was roughly rolled to a thickness of 1 mm under different conditions to obtain a plurality of coarsely rolled plates. Then, the plurality of rough rolled plates were finish-rolled under the same conditions until a final plate thickness of 0.5 mm was obtained to obtain a magnesium alloy plate.

  Here, the rough rolling was performed by controlling the surface temperature of the rough rolled plate immediately before the rough rolling to 350 ° C. and the surface temperature of the rough rolling roll to 200 to 230 ° C. And the rolling reduction per pass was changed in the case of this rough rolling. On the other hand, in the finish rolling, the surface temperature of the rough rolled plate immediately before the finish rolling is controlled in the range of 160 to 190 ° C., and the surface temperature of the finish rolling roll is controlled in the range of 150 to 180 ° C., and the reduction per pass in the finish rolling is performed. The rate was set to 15%.

Next, similarly to Test Example 1, this finished rolled material was heat-treated at 250 ° C. for 30 minutes to obtain a sample for evaluation. For these samples, in the same manner as in Test Example 6, measurement of the average crystal grain size, evaluation of the plate surface condition, evaluation of edge cracks, evaluation of particle size variation, and further comprehensive evaluation of each of these evaluation results Went. Table 11 shows the number of rolling and the evaluation results of rolling reduction of 20% to 40% per pass in rough rolling. The meanings of “plate surface state” and “edge crack” in this table are the same as in Test Example 6. “Rough rolling number of 20-40% rolling reduction” indicates the number of times of rough rolling in which the rolling reduction rate in one rough rolling was 20-40%, and “maximum rolling reduction / pass” is plural. The maximum rolling reduction ratio of the rough rolling of the pass is shown. The significance of the particle size variation is shown below.
Large ... maximum particle size / minimum particle size ≧ 2, medium ... 2 ≧ maximum particle size / minimum particle size ≧ 1.5
Small ... maximum particle size / minimum particle size ≦ 1.5

(Test Example 9-1)
The same AZ91 material plate (thickness 4 mm) as the material plate used in Test Example 7-1 was prepared. This material plate was roughly rolled to a thickness of 1 mm under different conditions to obtain a rough rolled plate. The rough rolled plate was finish-rolled under the same conditions until a final plate thickness of 0.5 mm was obtained to obtain a magnesium alloy plate.

  Here, the rough rolling is performed by setting the surface temperature of the plate immediately before the rough rolling to 350 ° C., and controlling the surface temperature of the finish rolling roll in the range of 200 to 230 ° C. to change the rolling reduction per pass. It was. On the other hand, the finish rolling was performed by controlling the surface temperature of the rough rolled plate immediately before the finish rolling to 210 to 240 ° C. and the surface temperature of the finish rolling roll to 150 to 180 ° C. In addition, the rolling reduction per pass at that time was set to 15%.

  Next, this finished rolled material was also heat-treated at 320 ° C. for 30 minutes in the same manner as in Test Example 7-1 to obtain an evaluation sample. For these samples, the average crystal grain size was measured, the plate surface condition was evaluated, the edge cracks were evaluated, and the dispersion was evaluated in the same manner as in Test Example 6, and the overall evaluation of these evaluation results was performed.

  Table 12 shows the number of rolling and the evaluation results of rolling reduction of 20% to 40% per pass in rough rolling. The meanings of “plate surface state”, “edge crack”, and “particle size variation” in this table are the same as the same terms in Test Example 8.

(Test Example 9-2)
Moreover, the influence of the temperature of a raw material board at the time of rough rolling, roll temperature, etc. was tested similarly to Test Example 9-1 using the magnesium alloy raw material board from which content of Al differs from Test Example 9-1. Manufacturing conditions other than rough rolling and a method for evaluating a magnesium alloy plate are the same as in Test Example 9-1. The magnesium alloy material plate had an Al content of 9.8% by mass and a Zn content of 1.0% by mass. Table 13 summarizes the finish rolling conditions and the test results.

(Summary of Test Example 6 to Test Example 9)
From the results of Test Example 6 to Test Example 9 described above, by carrying out rough rolling under appropriate conditions, the variation in the crystal grain size of the finally obtained magnesium alloy plate is small, such as defects on the plate surface and edge cracks. It was found that a magnesium alloy sheet excellent in plastic workability without the above-mentioned defects can be obtained.

(Test Example 10)
Magnesium alloy material plate (thickness 4) having a Mg-9.0% Al-1.0% Zn composition (all mass%) and a Mg-9.8% Al-1.0% Zn composition (all mass%) 0.0 mm) was obtained by twin roll continuous casting. The center line segregation generated in the magnesium alloy material plate obtained at this time had a maximum width of 50 μm in the thickness direction of the plate material. Such a magnesium alloy material plate was processed under the following three conditions and then subjected to rolling.
About Mg-9.0% Al-1.0% Zn composition (all mass%) 10-1 ... No solution treatment 10-2 ... 405 ° C. × 1 hour (solution treatment)
10-3 ... 405 ° C. × 10 hours (solution treatment)
About Mg-9.8% Al-1.0% Zn composition (all mass%) 10-4 ... No solution treatment 10-5 ... 405 ° C. × 1 hour (solution treatment)
10-6 ... 405 ° C. × 10 hours (solution treatment)

The magnesium alloy plate obtained by performing the above treatment was rolled to a thickness of 0.6 mm under the following conditions, and heat treated under appropriate conditions to obtain a plate material having an average crystal grain size of 5.0 μm. .
<Rough rolling 4.0 mm to 1.0 mm>
Roll surface temperature: 200 ° C
Plate heating temperature: 330-360 ° C
Rolling rate per pass: 20-25%
<Finish rolling 1.0 mm to 0.6 mm>
Roll surface temperature: 180 ° C
Plate heating temperature: 230 ° C
Rolling rate per pass: 10-15%
<Heat treatment>
Annealing at 320 ° C for 30 minutes

Next, a sample for tensile test of JIS 13B was produced from this plate material, and a tensile test was performed at a strain rate of 1.4 × 10 −3 (s ⁻¹ ) in a room temperature environment. Further, the alloy structure of the cross section of the 0.6 mm plate material was observed, and the amount of centerline segregation (maximum width in the thickness direction) was measured. The method and significance of each test are as follows.
Tensile strength = Load at break / (Thickness of test piece x width)
Yield strength = Measured at 0.2% yield strength Yield ratio = Yield strength / Tensile strength Elongation at break = (Distance between gauge points-50 mm when the fracture ends are butted together) / 50 mm * 1
* 1 Measured by a so-called butt method, which is obtained from a distance (50 mm) between two gauge points set in advance before the test and a distance between the gauge points when the fractured ends of the samples fractured after the test are butted.
The results are shown in Table 14.

  As shown in Table 14, the width of the center line segregation in the thickness direction is reduced by solution treatment of the magnesium alloy material plate produced by the twin roll continuous casting method, and a magnesium alloy plate having excellent mechanical properties is obtained. It was confirmed that it was obtained. In particular, in a magnesium alloy having a high Al content including a magnesium alloy equivalent to AZ91, a magnesium alloy sheet having more excellent mechanical characteristics can be obtained by performing solution treatment for a long time.

(Test Example 11)
Magnesium alloy material plate having Mg-9.0% Al-1.0% Zn composition (all mass%) equivalent to AZ91 and Mg-9.8% Al-1.0% Zn composition (all mass%) (Thickness 4.0 mm) was obtained by twin roll continuous casting. The magnesium alloy material plates obtained by subjecting these material plates to a solution treatment at 405 ° C. for 10 hours were rolled to a thickness of 0.6 mm under the following conditions to obtain magnesium alloy plates. The center line segregation generated in the magnesium alloy plate obtained at this time was 20 μm at the maximum in the thickness direction of the plate material.
<Rough rolling 4.0 mm to 1.0 mm>
Roll surface temperature: 200 ° C
Plate heating temperature: 330-360 ° C
Rolling rate per pass: 20-25%
<Finish rolling 1.0 mm to 0.6 mm>
Roll surface temperature: 180 ° C
Plate heating temperature: 230 ° C
Rolling rate per pass: 10-15%

The magnesium alloy plate obtained by rolling under the above conditions was treated under the following three conditions to obtain a plate for evaluation.
<Heat treatment>
(1) No heat treatment after rolling (2) Annealing at 230 ° C for 1 minute (3) Annealing at 320 ° C for 30 minutes

Next, a sample for tensile test of JIS 13B was prepared from this plate material, and strain rate was 1.4 × 10 −3 (s ⁻¹ ) in four temperature environments (room temperature, 150 ° C., 200 ° C., 250 ° C.). A tensile test was performed. Moreover, the alloy structure before and after the tensile test of the cross-section of a 0.6 mm plate material was observed. The meaning of each test method and term is the same as that in Test Example 10, and thus the description thereof is omitted.
The results of this test are shown in Tables 15 and 16. Table 15 shows the test results with a magnesium alloy plate having a Mg-9.0% Al-1.0% Zn composition, and Table 16 shows magnesium having a Mg-9.8% Al-1.0% Zn composition. The test result in an alloy plate is shown.

<Structure of magnesium alloy plate before pressing>
As shown in Tables 15 and 16, in the plate material (11-9 to 11-12 or 11-21 to 11-24) annealed at 320 ° C. for 30 minutes, the strain accumulated in the magnesium alloy plate by rolling disappears. And completely recrystallized. On the other hand, in the plate material (11-5 to 11-8 or 11-17 to 11-20) annealed at 230 ° C. for 1 minute, some distortion of crystal grains due to rolling remains. Moreover, the distortion | strain of the crystal grain by rolling processing remains in the board | plate material (11-1 to 11-4 or 11-13 to 11-16) which did not heat-process.

<Structure of magnesium alloy sheet after plastic deformation>
In a plate material that has been annealed at 320 ° C. for 30 minutes and is completely recrystallized, the crystal grains in the structure of the plate material are not coarsened by the temperature rise (250 ° C. or less) during tensile processing, and the average crystal grains before and after processing There was almost no difference in diameter. Accordingly, it is presumed that, in the portion of the plate material that is deformed during the tensile processing, the processing strain is accumulated and the hardness and strength are improved, and in the portion that is not deformed, the hardness and strength are not changed. On the other hand, in the plate material in which the processing strain due to rolling remained (no annealing or annealing at 230 ° C. for 1 minute), the metal structure was recrystallized due to the temperature rise during the tensile processing, and the strength and hardness decreased. And before and after processing, the strength decreased in the undeformed portion, and the strength decreased or improved in the deformed portion depending on the degree of temperature rise during processing. As described above, if there is a portion where the strength and hardness of the magnesium alloy plate are lowered before and after processing, a magnesium alloy product having desired mechanical properties cannot be stably produced.

<High temperature tensile properties>
The plate material annealed at 320 ° C. for 30 minutes had high tensile strength, yield strength, and elongation at break at room temperature, and stably exhibited high elongation at break at 200 ° C. and 250 ° C. On the other hand, some of the plate materials that have left the processing strain exhibit an abnormally high elongation at break at 200 ° C. and 250 ° C. (superplastic phenomenon), but there are very few plate materials that exhibit such a superplastic phenomenon. The plate material had low elongation at break, and damage such as cracks and cracks occurred during plastic working. Thus, if there is a large variation in the breaking elongation of the plate material, the quality of the product will not be stable when the magnesium alloy plate is subjected to plastic working to produce the product.

  Based on the above results, it is expected that the plate material with processing strain will have stable work formability because the metal structure changes due to temperature rise and deformation during plastic processing at high temperatures, and the degree of this change is unstable. Can not. On the other hand, a plate material with a completely recrystallized metal structure is unlikely to change in the metal structure before and after processing, so that the plastic workability is stabilized and the mechanical properties of the deformed part are improved and deformed. It is presumed that the mechanical properties before processing are maintained even in the absence. Therefore, the plate material that has eliminated the processing strain accumulated during rolling has stable mechanical properties even when subjected to strong processing such as press forming, and is therefore suitable for the manufacture of casing products manufactured by press forming or the like. Yes.

(Test Example 12)
Next, casting, rough rolling, and finish rolling were performed under the conditions described in Test Example 11, and a magnesium alloy sheet having a thickness of 0.6 mm (Mg-9.0% Al-1.0% Zn, and Mg-9). .8% Al-1.0% Zn). Then, the magnesium alloy plate after finish rolling was annealed at 320 ° C. for 30 minutes to prepare a sample for evaluation, and a bending test was performed using this sample. The bending test was a so-called three-point bending test in which each sample was supported at two points and bending pressure was applied to the sample with a bending tool (punch) from the direction opposite to the supporting points. The conditions for the bending test are shown below.
<Test conditions>
Sample dimensions: 20mm wide, 120mm long, 0.6mm thick
Test temperature: 25 ° C (room temperature), 200 ° C, 250 ° C
Punch tip angle ... 30 °
Punch radius (= bending radius of sample) ... 0.5mm, 1.0mm, 2.0mm
Distance between fulcrums ... 30mm
Punch indentation depth ... 40mm
Punch pushing speed: 1.0 m / min, 5.0 m / min

A test was conducted under the above conditions, and the surface state and the amount of springback of the bending radius portion of the sample were examined. In addition, the samples were comprehensively evaluated based on the surface condition and the amount of springback. Spring back refers to a phenomenon in which deformation generated in a plate-like sample due to a load applied by a punch returns after the load by the punch is released. That is, when the amount of springback of the sample is large, it can be determined that the deformability is bad, and when it is small, the deformability is good. Therefore, the ease of processing of the sample can be determined by examining the springback amount. The evaluation criteria for the surface condition and the springback amount are as follows.
<Surface condition evaluation criteria>
When there is no crack ... ○
When a minute crack occurs but it does not break ... △
When it breaks… ×
<Evaluation criteria for springback>
The evaluation criteria for springback is (the angle formed by the plane sandwiching the bending radius portion of the sample when a load is applied by a punch) − (the angle formed by the plane sandwiching the bending radius portion when the load is removed) − evaluated.
When there is a difference of 45 ° or more… Springback Large When there is a difference of 10 ° or more and less than 45 °… Springback Medium When there is a difference of less than 10 °… Springback Small <Comprehensive evaluation>
In the case of surface condition x ... comprehensive evaluation x
When the surface condition is ○ and the spring back is small… Overall evaluation ○
Other than above ... Comprehensive evaluation

Also, a bending characteristic value was defined as an index indicating the degree of processing. The bending characteristic value is expressed by the bending radius (mm) of the sample / the thickness (mm) of the sample. Here, as the bending radius of the sample is smaller, local pressure acts on the bending radius portion, so that the sample is more likely to be damaged such as cracks. The thicker the sample is, the worse the moldability of the sample is. Damage is likely to occur. Accordingly, the smaller the bending characteristic value represented by the above formula, the stronger the severer the machining conditions.
Tables 17 and 18 show the surface state, springback, bending characteristic values, and comprehensive evaluation results described above. Table 17 shows the test results with a magnesium alloy plate having an Mg-9.0% Al-1.0% Zn composition, and Table 18 shows magnesium having an Mg-9.8% Al-1.0% Zn composition. The test result in an alloy plate is shown.

  As shown in Table 17, a sample of Mg-9.0% Al-1.0% Zn was subjected to a bending test at room temperature (25 ° C.) with a bending radius of 2.0 mm, that is, a loose processing condition (bending characteristics). Only in the case of value 3.33), the surface condition of the sample was evaluated as ○ (see Sample Nos. 12-5 and 12-6). At room temperature, the springback was large and the moldability was poor regardless of the bending radius and processing speed (see Sample Nos. 12-1 to 12-6). On the other hand, when the bending test was performed at a temperature of 200 ° C. or higher, the spring back was small regardless of the bending radius and the processing speed, and the surface state was good (see Sample Nos. 12-7 to 12-18).

  On the other hand, as shown in Table 18, the Mg-9.8% Al-1.0% Zn sample showed exactly the same result as the Mg-9.0% Al-1.0% Zn sample. Specifically, in the bending test at room temperature, the moldability was poor (see Sample Nos. 12-19 to 12-24), and the moldability was good at 200 ° C. or higher (see 12-25 to 12-36). .

(Test Example 13)
Casting, rough rolling, and finish rolling were performed under the conditions described in Test Examples 11 and 12, and a magnesium alloy plate having a thickness of 0.6 mm (Mg-9.0% Al-1.0% Zn and Mg-9. 8% Al-1.0% Zn) was produced. Next, this magnesium alloy plate was treated under the following two conditions to produce a sample for evaluation. A press test was carried out using the sample for evaluation, and the surface state of the sample after pressing was examined.
<Heat treatment>
(1) No heat treatment after rolling (2) Annealing at 320 ° C. for 30 minutes <Conditions for press test>
The sample was pressed with a servo press. The pressing was performed by placing a sample on a lower mold having a rectangular parallelepiped concave portion so as to cover the concave portion and pressing the rectangular parallelepiped upper die. The upper mold has a rectangular parallelepiped shape of 60 mm × 90 mm, and four corners contacting the sample are rounded, and each corner has a constant bending radius. In addition, a heater and a thermocouple were embedded in the upper die and the lower die so that the temperature conditions during pressing could be adjusted to a desired temperature.
<Test conditions>
Bending radius of upper mold: 0.5mm, 2.0mm
Test temperature: 200 ° C, 250 ° C
Processing speed: 0.8 m / min, 1.7 m / min, 3.4 m / min, 5.0 m / min

  Press working was performed under the above conditions, and the surface state of the bending radius portion of the sample after pressing was examined. The results are shown in Tables 19 and 20. Table 19 shows the test results with a magnesium alloy plate having a Mg-9.0% Al-1.0% Zn composition, and Table 20 shows magnesium having a Mg-9.8% Al-1.0% Zn composition. The test result in an alloy plate is shown. Here, the significance of the surface state is the same as in Test Example 12, and the bending characteristic value is obtained from the bending radius of the upper die / the thickness of the sample.

  As shown in Table 19, among the samples having the composition of Mg-9.0% Al-1.0% Zn, the sample not subjected to the heat treatment after finish rolling had a temperature of the sample at the time of pressing of 200 ° C. In the case, cracks or cracks occurred on the surface. In particular, when a strong working with a bending characteristic value of 0.83 was performed, cracks occurred on the surface. Further, the sample was cracked or cracked on the surface of the sample when subjected to strong processing (bending characteristic value 0.83) even in a 250 ° C. press test. On the other hand, the sample that has been annealed at 320 ° C. for 30 minutes after finish rolling has a low processing speed when the temperature of the sample at the time of pressing is 200 ° C. (see Sample Nos. 13-9 and 13-10) When the bending characteristic value was 3.33 (see Sample Nos. 13-10, 13-12, 13-14, 13-16), the surface condition was good. Further, the samples subjected to the annealing had a good surface condition at 250 ° C. regardless of the bending characteristic value and the processing speed.

  Further, as shown in Table 20, the test result of the Mg-9.8% Al-1.0% Zn sample was almost the same as the test result of Mg-9.0% Al-1.0% Zn. It was. That is, the surface condition after pressing was better in the sample that was annealed at 320 ° C. for 30 minutes than in the sample that was not annealed. Furthermore, the higher the temperature during pressing, the better the surface condition of the sample after pressing. In particular, when an annealed magnesium alloy sheet is pressed under the condition of 250 ° C., the press formability is good even when strong processing (bending characteristic value 0.83) is performed at a processing speed of 5.0 m / min. It became clear.

(Summary of Test Examples 11 to 13)
As described above, from the results of Test Examples 11 to 13, it was revealed that the formability is stabilized by heat-treating the rolled magnesium alloy sheet at an appropriate temperature to recrystallize the structure of the alloy sheet. The reason why the formability is stabilized is presumed that the metal structure is recrystallized before the plastic working, and therefore the metal structure does not change greatly due to the temperature rise during the plastic working (including press working).

  The magnesium alloy sheet of the present invention can be suitably used as an alloy material that is lightweight and requires high mechanical properties.

Claims (6)

A magnesium alloy plate obtained by rolling a magnesium alloy material plate containing 8.5 to 10.0% by mass of aluminum (Al) and 0.5 to 1.5% by mass of zinc with a rolling roll. ,
A magnesium alloy plate characterized in that the length in the thickness direction of segregation existing at the center line in the thickness direction of the magnesium alloy plate is 20 μm or less.   The magnesium alloy sheet according to claim 1, wherein the tensile strength at room temperature is 360 MPa or more, the yield strength is 270 MPa or more, and the elongation at break is 15% or more.   The magnesium alloy sheet according to claim 1 or 2, wherein a yield ratio is 75% or more.   Magnesium according to any one of claims 1 to 3, wherein the tensile strength at 200 ° C is 120 MPa or more, the elongation at break is 80% or more, the tensile strength at 250 ° C is 90 MPa or more, and the elongation at break is 100% or more. Alloy plate.   When the bending property value (bending radius R / sheet thickness t) is 200 ° C. or higher and bending is performed at a temperature of 1.0 or lower, the surface is not damaged such as cracks or cracks. Item 5. The magnesium alloy sheet according to any one of Items 1 to 4.   When the press working is performed at a temperature of 200 ° C. or more under a condition that the bending characteristic value (bending radius R / sheet thickness t) is 1.0 or less, the surface is not damaged such as cracks or cracks. Item 6. The magnesium alloy sheet according to any one of Items 1 to 5.