JP2015004134A - Magnesium alloy sheet, magnesium alloy member and method for producing magnesium alloy sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnesium alloy sheet excellent in impact resistance at a low temperature, a magnesium alloy member using the sheet and a method for producing a magnesium alloy sheet.SOLUTION: The magnesium alloy sheet is made of a magnesium alloy containing Al and Mn. When a region from the surface to 30% of the thickness of the sheet in a thickness direction of the sheet is defined as a surface region and an arbitrary small region of 50 μmis taken from the surface region, the small region includes 15 pieces or less of crystallized products containing both Al and Mn. The particle of each crystallized product has a maximum diameter of 0.1 μm or more and 1 μm or less and a mass ratio of Al to Mn (Al/Mn) of 2 or more and 5 or less. The magnesium alloy sheet is excellent in impact resistance because the crystallized products which cause cracks or the like are small and little and excellent in mechanical characteristics even under a low temperature environment.

Description

  The present invention relates to a magnesium alloy plate suitable for materials such as a housing and various parts, a magnesium alloy member using the alloy plate, and a method for manufacturing the magnesium alloy plate. In particular, the present invention relates to a magnesium alloy plate and a magnesium alloy member that are excellent in impact resistance at low temperatures.

  Magnesium alloys containing various additive elements in magnesium have been used as materials for casings of portable electronic devices such as mobile phones and notebook PCs and members of automobile parts.

  Magnesium alloys have a hexagonal crystal structure (hcp structure) and are therefore poor in plastic workability at room temperature. Therefore, magnesium alloy members such as the above-mentioned cases are mainly cast materials by die casting or thixomolding. . Recently, it has been studied to press the plate made of AZ31 alloy in the ASTM standard to form the casing. Patent Document 1 proposes a rolled plate made of an alloy equivalent to the AZ91 alloy in the ASTM standard and having excellent press workability.

JP 2007-098470 A

  Magnesium alloys are lightweight and excellent in specific strength and specific rigidity, so that they are desired to be used not only in a normal temperature environment of about 0 to 30 ° C. but also in a cold region or a freezing warehouse where the temperature is below freezing. However, the mechanical properties of magnesium alloys in such a low temperature environment have not been sufficiently studied.

  Magnesium alloy castings are inferior in strength to magnesium alloy rolled materials and press-formed members. Further, as a result of investigations by the present inventors, the AZ31 alloy press member also has insufficient strength in a low-temperature environment and is inferior in impact resistance.

  On the other hand, a rolled plate made of AZ91 alloy as described in Patent Document 1 and a pressed member obtained by pressing the rolled plate have higher strength than a plate made of AZ31 alloy or a pressed member made of AZ31 alloy. However, as a result of investigations by the present inventors, even a rolled plate made of AZ91 alloy and a member obtained by subjecting this rolled plate to plastic working such as press working have sufficient impact resistance characteristics in a low temperature environment. I got the knowledge that it may not be.

  Accordingly, one of the objects of the present invention is to provide a magnesium alloy member having excellent impact resistance even in a low temperature environment, and a magnesium alloy plate suitable for the material of this member. Another object of the present invention is to provide a method for producing the magnesium alloy sheet of the present invention.

  The inventors have prepared a magnesium alloy plate under various conditions, and subjected the plastic plate such as press working to the obtained plate to produce a magnesium alloy member. The magnesium alloy plate and member are subjected to a low temperature environment. The impact resistance (dentation resistance) and mechanical properties of the steel were investigated. As a result, it was found that the magnesium alloy plate which was difficult to be dented had a small amount of crystallized substances having a specific composition. In addition, the magnesium alloy member obtained by using a small magnesium alloy plate with a small specific composition is difficult to dent, and this member has a small and small amount of crystallized specific composition as well as the material plate. , And got the knowledge. In manufacturing the magnesium alloy sheet as described above, the maximum diameter and the number of the crystallized substances are controlled, that is, the number of crystallized substances and coarse crystallized substances are reduced under specific conditions. The knowledge that it was preferable to cast and to roll the obtained cast plate was obtained. The present invention is based on the above findings.

The magnesium alloy plate of the present invention is made of a magnesium alloy containing Al and Mn, and in the thickness direction of the magnesium alloy plate, the surface from the surface of the alloy plate to 30% of the thickness of the alloy plate is surfaced. When an arbitrary small region of 50 μm ² is taken from this surface region, a crystallized product containing both Al and Mn and having a maximum diameter of 0.1 μm or more and 1 μm or less with respect to this small region Is 15 or less. The crystallized particles have a mass ratio of Al to Mn: Al / Mn of 2 or more and 5 or less.

The magnesium alloy plate of the present invention having the above specific structure can be produced, for example, by the following production method of the present invention. The manufacturing method of the magnesium alloy plate of this invention comprises the following casting processes and rolling processes.
Casting process: A process of casting a magnesium alloy containing Al and Mn into a plate shape.
Rolling step: A step of rolling the cast plate obtained by the casting step.
In particular, the casting is performed by a twin roll continuous casting method. The casting is performed so that the roll temperature is 100 ° C. or less and the thickness of the cast plate obtained by the casting is 5 mm or less.

The magnesium alloy member of the present invention is formed by subjecting the magnesium alloy plate of the present invention to plastic working such as press working. This alloy member also has the same structure as the magnesium alloy plate of the present invention, that is, 15 crystallized particles having the specific size and composition when an arbitrary small region of 50 μm ² is taken from the surface region. It has the following organization.

  In continuous casting methods such as twin-roll continuous casting that can be rapidly solidified, oxides and segregation can be reduced, and the formation of coarse crystals can be reduced, resulting in fine crystals. Can do. In particular, in the production method of the present invention, by setting the roll temperature and the thickness of the cast plate within the specific range, the cooling rate can be sufficiently increased, so that the generation of the crystallized product itself can be reduced. Therefore, the structure of the region on the surface side that is particularly susceptible to impact in the plate-like material can be made a structure in which minute crystallized substances are slightly present. In addition, since the amount of crystallized matter is small and small, there is little decrease in the amount of solid solution Al in the parent phase due to the crystallization of coarse or large amount of crystallized material. It is thought that there is little decrease in reinforcement. Furthermore, a cast plate having a fine structure with a small average crystal grain size is obtained by rapid solidification. Such a cast plate is excellent in plastic workability such as rolling because there are few coarse crystallized materials starting from cracks and deformation, and rolling can improve strength and elongation. it can.

  Therefore, the alloy plate of the present invention obtained by the above production method has reduced coarse crystallized substances and few crystallized substances themselves. It is reduced and has a structure in which fine crystallized substances are slightly present, preferably a structure in which crystallized substances are not substantially present, so that cracks and cracks are not easily generated even when subjected to an impact such as dropping. In addition, since the crystallized product itself is small as described above, it is possible to suppress a decrease in the amount of solid solution Al, and it is possible to maintain high strength because Al is sufficiently dissolved, The strength can be further increased by rolling. Therefore, the alloy plate of the present invention is not easily dented even when subjected to an impact, and is excellent in impact resistance not only at room temperature (about 20 ° C.) but also in a low temperature environment of less than 0 ° C. In addition, the alloy plate of the present invention having the above specific structure is excellent in plastic workability and can be easily subjected to press working, etc., and the obtained alloy member of the present invention is also particularly similar to the alloy plate of the present invention. In the region on the surface side that is susceptible to impact, the crystallized material is small and has a small structure. Therefore, the alloy member of the present invention also has high mechanical properties such as strength and elongation even in a low temperature environment, and is excellent in impact resistance.

The present invention will be described in detail below.
"composition"
Examples of the magnesium alloy plate of the present invention and the magnesium alloy constituting the magnesium alloy member of the present invention include those having various compositions containing at least Al and Mn as additive elements (remainder: Mg and impurities). Examples of the additive element other than Al and Mn include one or more elements selected from Zn, Si, Ca, Sr, Y, Cu, Ag, Ce, Zr, and rare earth elements (excluding Y). In particular, Al is preferably contained in an amount of 5% by mass to 12% by mass and Mn is preferably contained in an amount of 0.1% by mass to 2.0% by mass. By containing Al and Mn in the above ranges, mechanical properties such as strength and elongation are excellent, and corrosion resistance is also excellent. However, when there is too much content of the said element, the fall of plastic workability will be caused. The content of additive elements other than Al and Mn is Zn: 0.2 to 7.0 mass%, Si: 0.2 to 1.0 mass%, Ca: 0.2 to 6.0 mass%, Sr: 0.2 to 7.0 mass%, Y: 1.0 to 6.0 mass% %, Cu: 0.2-3.0 mass%, Ag: 0.5-3.0 mass%, Ce: 0.05-1.0 mass%, Zr: 0.1-1.0 mass%, RE (rare earth element (excluding Y)): 1.0-3.5 mass% Is mentioned. By containing these elements in addition to Al and Mn, the mechanical properties can be further enhanced. As a composition of an alloy containing Al and Mn and one or more of these elements in the above range, for example, an AZ-based alloy in the ASTM standard (Mg-Al-Zn-based alloy, Zn: 0.2 to 1.5 mass%), Examples thereof include AM alloys (Mg—Al—Mn alloys, Mn: 0.15 to 0.5 mass%). In particular, the higher the Al content (hereinafter referred to as the Al content), the better the mechanical properties and the corrosion resistance, and the more preferable the Al content is 5.8 mass% to 10 mass%. Examples of magnesium alloys having an Al amount of 5.8 to 10% by mass include, for example, AZ61 alloy, AZ80 alloy, AZ81 alloy, AZ91 alloy, and Mg-Al-Mn alloy for the Mg-Al-Zn alloy, AM60 alloy, and AM100 alloy. Etc. is a suitable composition. In particular, the AZ91 alloy having an Al content of 8.3 to 9.5% by mass is further excellent in mechanical properties such as corrosion resistance, strength, and plastic deformation resistance compared to other Mg-Al alloys.

<< Forms of Magnesium Alloy Plate and Magnesium Alloy Member >>
The alloy plate of the present invention has a pair of opposing one surface and the other surface, and these two surfaces are typically in a parallel relationship, and are usually in a front / back relationship in the scene of use. These one and other surfaces may be flat or curved. The distance between the one surface and the other surface is the thickness of the magnesium alloy plate. Since the alloy plate of the present invention is obtained by rolling a cast plate having a thickness of 5 mm or less as described above, the thickness of the alloy plate of the present invention is less than 5 mm. In particular, the alloy plate of the present invention is subjected to plastic working such as press work, and is used as a material for thin and lightweight housings and various members, so the thickness of the alloy plate is about 0.3 mm to 3 mm, In particular, the thickness is preferably 0.5 mm or more and 2.0 mm or less, and the thicker in the range, the better the strength, and the thinner, the more suitable for a thin and light housing. It is preferable to select the thickness of the finally obtained magnesium alloy plate by adjusting the casting conditions and rolling conditions according to the desired application.

The alloy member of the present invention has various shapes obtained by subjecting the magnesium alloy plate to plastic working such as press working, for example, a bottom portion and a side wall portion standing from the bottom portion] -like material or box-like material Is representative. In such a magnesium alloy member, the thickness of the flat portion where the deformation due to plastic working such as press working is not substantially performed is substantially the same as the thickness of the magnesium alloy plate used as the material, and is almost the same. Have an organization. That is, in the surface region, the maximum diameter: 0.1 to 1 μm of Al—Mn crystallized material satisfies 15 or less / 50 μm ² .

  The alloy plate of the present invention includes, in addition to a rolled plate obtained by rolling a cast material, a processed plate obtained by further subjecting the rolled plate to heat treatment, leveler processing, polishing processing, and the like. The alloy member of the present invention includes not only those in which the alloy plate is subjected to plastic processing such as press processing, but also those in which heat treatment or polishing processing is performed after plastic processing. The rolled plate, the treated plate, and the alloy member may further include an anticorrosive treatment layer or a coating layer.

《Mechanical properties》
The alloy plate and the alloy member of the present invention are excellent in mechanical properties such as strength and elongation even under a low temperature environment as described above, and are not easily dented when subjected to an impact such as dropping. For example, in a tensile test at −30 ° C., a flat portion where deformation (e.g., deformation due to drawing) or the like accompanying plastic working such as press working is not substantially performed on the alloy plate or alloy member of the present invention ( The part (substantially similar to the material plate) has a tensile strength of 350 MPa or more, a 0.2% proof stress: 280 MPa or more, and an elongation of 2% or more.

《Organization》
<Crystallized product>
The alloy plate of the present invention has a structure in which a coarse crystallized substance is not substantially present and a minute crystallized substance is slightly present when an arbitrary small region is taken from the region on the surface side. Have More specifically, in the thickness direction of the alloy plate, a region from the surface of the alloy plate to 30% of the thickness of the alloy plate is defined as a surface region, and 50 μm ² arbitrarily selected from the surface region. Take a small area and measure the particle size of all the crystals present in one small area. When the maximum diameter of each crystallized product is measured, there are 15 or less fine crystallized products having a maximum diameter of 0.1 μm or more and 1 μm or less for one small region. More preferably, only a crystallized substance having a maximum diameter of 0.5 μm or less exists. If there is a coarse crystallized product exceeding 1 μm, the coarse crystallized product can become a starting point of cracking when subjected to an impact such as dropping, so that cracking and cracking are likely to occur, and the impact resistance is low. In addition, even if the maximum diameter is 1 μm or less, if there are more than 15 for 50 μm ² , the number of cracks and the starting point of cracks will increase, leading to a decrease in strength and low impact resistance. . The smaller the number of crystallized particles having a maximum diameter of 0.1 to 1 μm, the better the impact resistance, and 10 or less is more preferable, and ideally 0 is desirable. The crystallized product contains both Al and Mn. Details of the method for measuring the maximum diameter will be described later. In the present invention, the presence of an extremely fine crystallized product that is unlikely to cause cracking, that is, a crystallized product having a maximum diameter of less than 0.1 μm is allowed, but the crystallized product exists as described above. It is preferable not to.

<Average crystal grain size>
Examples of the alloy plate of the present invention include those having a small average crystal grain size and a fine structure of 20 μm or less. As described above, a cast plate having a fine structure can be obtained by performing continuous casting under specific conditions, and by rolling the cast plate, a rolled plate having the fine structure can be obtained. The alloy plate of the present invention having such a fine structure is excellent in mechanical properties such as strength and elongation, and can improve impact resistance even in a low temperature environment. In addition, the magnesium alloy plate having the above-mentioned fine structure and the alloy member of the present invention obtained by using a processed plate obtained by subjecting this rolled plate to a leveler treatment or the like also have a fine structure with an average crystal grain size of 20 μm or less. It has excellent impact resistance. A more preferable average crystal grain size is 0.1 μm or more and 10 μm or less.

[Production method]
"casting"
In the production method of the present invention, a twin roll continuous casting method is used. In this casting, the temperature of the roll used for the mold is set to 100 ° C. or less, and the thickness of the cast plate obtained is set to 5 mm or less. In this way, by reducing the thickness of the cast plate and lowering the roll temperature, it is possible to suppress the generation of crystallized material as described above by rapid solidification, and to make a cast plate with small and few crystallized products. . In order to set the roll temperature to 100 ° C. or lower, it is possible to use a roll capable of forced cooling such as water cooling. The lower the roll temperature and the thinner the cast plate, the faster the cooling rate, and the generation of crystallized substances can be suppressed. Therefore, the roll temperature is more preferably 60 ° C. or less, and the thickness of the cast plate is more preferably 4.0 mm or less. This casting process (including the cooling process) is preferably performed in an inert gas atmosphere in order to prevent oxidation of the magnesium alloy.

"rolling"
The rolling conditions include, for example, a heating temperature of the material: 200 to 400 ° C., a heating temperature of the rolling roll: 150 to 300 ° C., and a rolling reduction per pass: 5 to 50%, and a plurality of rolling conditions can be obtained. A pass is recommended. Control rolling described in Patent Document 1 may be used. By rolling the cast material, not a cast metal structure but a rolled structure can be obtained. Also, by rolling, it is easy to obtain a microstructure with an average crystal grain size of 20 μm or less, and it reduces surface defects by reducing internal defects such as segregation and shrinkage cavities (pores) and surface defects during casting. An excellent rolled sheet can be obtained. When the final heat treatment is performed after the final rolling to obtain a fine recrystallized structure having an average crystal grain size of 20 μm or less, the strength and corrosion resistance of the obtained rolled sheet can be further improved.

《Plastic processing》
The alloy member of the present invention is made of plastic such as press processing (including punching), deep drawing, forging, blow processing, and bending so that the rolled sheet (including those subjected to heat treatment and the like) has a desired shape. Obtained by processing. When this plastic working is performed at a temperature of 200 to 280 ° C., it is possible to reduce that the rolled plate has a coarse recrystallized structure and to reduce deterioration of mechanical properties and corrosion resistance. After the plastic working, heat treatment or anticorrosion treatment may be applied, or a coating layer may be formed.

  The magnesium alloy plate of the present invention and the magnesium alloy member of the present invention are excellent in impact resistance under a low temperature environment. The manufacturing method of the magnesium alloy plate of the present invention can manufacture the magnesium alloy plate of the present invention.

FIG. 1 is a schematic explanatory view for explaining an impact test.

Embodiments of the present invention will be described below.
[Test Example 1]
Using a magnesium alloy ingot shown in Table 1 (all commercially available) to produce a magnesium alloy plate and magnesium alloy member (housing) under various conditions, the structure observation of the obtained magnesium alloy plate and magnesium alloy member, Tensile tests (low temperature) and impact tests (low temperature) were conducted. The production conditions are as follows.

(Condition A: Twin roll casting → Rolling)
A magnesium alloy ingot is heated to 700 ° C. in an inert atmosphere to produce a molten metal, and a cast plate having a thickness of 4.0 mm (<5 mm) is produced by the twin roll continuous casting method in the inert atmosphere using the molten metal. A plurality of are produced. This casting is performed while cooling the roll so that the roll temperature becomes 60 ° C. (<100 ° C.). Using each of the obtained cast plates as the raw material, the heating temperature of the raw material: 200 to 400 ° C, the heating temperature of the rolling roll: 150 to 300 ° C, the rolling reduction per pass: 5 to 50%, the thickness of the raw material Rolling is performed a plurality of times until the thickness reaches 0.6 mm to produce a rolled sheet. The obtained rolled plate (magnesium alloy plate) is used as a sample (plate). Further, the obtained rolled plate is subjected to a corner drawing process at a heating temperature of 250 ° C. to produce a cross-sectional [shaped box-shaped body, and this box-shaped body (magnesium alloy member) is used as a sample (housing). .

  After the casting, a heat treatment (solution treatment) or an aging treatment for homogenizing the composition may be performed, an intermediate heat treatment may be performed during the rolling, or a final heat treatment may be performed after the final rolling. Further, the rolled plate may be subjected to leveler processing or polishing processing, and the flatness may be improved by correction, or the surface may be smoothed by polishing. These points are the same for Test Example 2 described later.

(Condition B: Die-cast)
It is a commercially available die-cast product (cross-section [shaped box-like body, bottom surface thickness: 0.6 mm).
(Condition C: Commercial board)
A plate (thickness: 0.6 mm) made of a commercially available AZ31 alloy.
(Condition D: Commercially available housing)
A cross-section [shaped box-shaped body (thickness of bottom surface portion: 0.6 mm) obtained by subjecting a plate made of AZ31 alloy (thickness: 0.6 mm) to a corner drawing (commercially available product).

<< Organizational observation >>
About each obtained sample, the metal structure was observed as follows and the crystallization thing was investigated. In the sample (plate), the sample is cut in the plate thickness direction, and the cross section is observed with a transmission electron microscope (20,000 times). In this observation imaging, the area from the surface of the sample (plate) to 30% (0.6 mm x 30% = 0.18 mm) of the thickness of the sample (plate) in the thickness direction of the sample (plate) And From this surface region, five arbitrary 50 μm ² small regions are selected, and the sizes of all the crystallized substances existing in each small region are measured. The determination of the crystallized product is performed based on the composition. After the above section is mirror-polished, the composition of particles present in the section is determined using, for example, qualitative analysis represented by EDX and semi-quantitative analysis, and particles containing Al and Mn are crystallized. In addition, when the ratio Al / Mn between the mass of Al and the mass of Mn was measured for each crystallized particle containing Al and Mn, both of sample Nos. 1-1 and 1-2 had Al / Mn = 2. It was ~ 5. And, for each crystallized particle in the cross section, draw a straight line parallel to the cross section, the maximum value of the length across each straight line in each particle is the maximum diameter of the particle, the maximum diameter is 0.1μm or more and 1μm or less The number of crystallized substances having a size of 1 is defined as the number of crystallized substances in the small region, and the average of the five small regions is defined as the number of crystallized materials in this sample / 50 μm ² . In the sample (housing), cut the bottom surface part, which is a flat part without drawing deformation in the sample, in the plate thickness direction, and observe the cross section in the same manner as the sample (plate), the number of crystallized substances / 50 μm Measure ² However, when a coarse crystallized product whose maximum diameter exceeds 5 μm or more is observed in the above observation imaging, the area of the small region is set to 200 μm ² , and the maximum diameter of the crystallized material existing in this 200 μm ² and the crystal distillate to measure the number / 200μm ² of. In addition, as long as each said small area satisfy | fills each said area, although a shape will not be ask | required in particular, a rectangular shape (typically square) etc. are easy to utilize. Table 1 shows the measurement results.

<Tensile test (low temperature)>
JIS 13B plate specimens (JIS Z 2201 (1998)) were prepared from each sample (thickness: 0.6 mm), and a tensile test was performed based on the metal material tensile test method of JIS Z 2241 (1998). It was. Here, for the sample (plate), the gauge distance GL = 50 mm, for the sample (housing), the gauge distance GL = 15 mm, and for all the samples, the test temperature: -30 ° C and the tensile speed: 5 mm / min Tensile tests were conducted to measure tensile strength (MPa), 0.2% yield strength (MPa), and elongation (%) (number of evaluations: n = 1). The results are shown in Table 1. In the sample (housing), the test piece for the tensile test and the test piece for the impact test described later are manufactured by cutting out from the bottom surface portion, which is a flat portion that is not accompanied by drawing deformation in the sample.

《Shock test (low temperature)》
A 30 mm × 30 mm plate piece is cut out from each sample, and the cut plate piece is used as a test piece. In this test, as shown in FIG. 1, a support base 20 having a circular hole 21 with a diameter d = 20 mm on a horizontal surface was prepared. The depth of the circular hole 21 was set such that a cylindrical rod 10 described later can be sufficiently inserted. The test piece 1 is arranged so as to close the circular hole 21, and in this state, a weight of 100 g, a tip r = 5 mm, a ceramic cylindrical rod 10 is placed at a point 200 mm from the test piece 1 with its central axis. The circular hole 21 was arranged so as to be coaxial with the central axis. Then, the cylindrical bar 10 is freely dropped from the above arrangement point (height 200 mm) toward the test piece 1, and then the dent amount of the test piece 1 is measured. The dent amount (mm) was a straight line connecting both opposing sides of the test piece 1, and the distance from this straight line to the most recessed part was measured using a point micrometer. This impact test was performed in a low temperature environment of −30 ° C. The results are shown in Table 1. If the dent amount is 0.5 mm or less, ○, and more than 0.5 mm are indicated as ×, and if the dent amount cannot be measured due to cracking, it is indicated as `` crack '', and if a crack (crack) occurs, `` crack '' It shows. Note that when the thickness of four arbitrary locations on the 30 mm × 30 mm test piece prepared in the sample (housing) was measured, all the locations were equal to the thickness of the material plate (thickness 0.6 mm). (Test specimen thickness: 0.6 mm).

As shown in Table 1, magnesium alloy plates and magnesium alloy members with a maximum diameter of 0.1 μm or more and 15 μm or less of Al-Mn crystallized materials are the same for any 50 μm ² selected from the surface region. Compared to cast and wrought materials (AZ31 alloy) with a composition, the amount of dents is small even in a low temperature environment such as -30 ° C., and the impact resistance is excellent. The reason for this is considered to be due to excellent mechanical properties such as tensile strength and elongation even in a low temperature environment. In particular, in this test, the sample Nos. 1-1 and 1-2 having excellent impact resistance have only a crystallized substance having a maximum diameter of 0.5 μm or less. In Sample Nos. 1-1 and 1-2 having excellent impact resistance, no Al-Mn crystallized material having a maximum diameter of more than 1 μm was observed, and at least the surface region was substantially absent. it is conceivable that. On the other hand, a sample of a commercial product that is not manufactured under specific casting conditions has a coarse crystallized substance in the surface region, and the presence of such a coarse crystallized substance causes cracks and the like. It is thought that it became easy to occur. Furthermore, by performing plastic working such as press working on a magnesium alloy plate having 15 or less Al-Mn crystallized crystals having a maximum diameter of 0.1 μm or more and 1 μm or less for any 50 μm ² selected from the surface region, It turns out that the magnesium alloy member excellent in impact resistance is obtained.

[Test Example 2]
Using a magnesium alloy ingot shown in Table 2 (all commercially available) to produce a magnesium alloy plate and magnesium alloy member (housing) under various conditions, the structure observation of the obtained magnesium alloy plate and magnesium alloy member, An impact test (low temperature) was conducted in the same manner as in Test Example 1. The results are shown in Table 2.

  The production condition “casting → rolling” is performed by casting by a twin roll continuous casting method, and the roll temperature and the thickness of the cast plate are as shown in Table 2. The rolling conditions are the same as in Test Example 1. However, in this test, the heating time and rolling speed of the material, and the cooling rate during rolling so that the total time during which the material is maintained in the temperature range of 150 ° C. to 250 ° C. is 45 minutes or 90 minutes. Etc. are adjusted. In Test Example 1, the total time is about 60 minutes. In Table 2, the shape “plate” indicates that the sample is a rolled plate (magnesium alloy plate), and the “housing” is the sample prepared from this rolled plate under the same conditions as in Test Example 1. Indicates a box-shaped body (magnesium alloy member).

  In the production conditions, “Condition B”, “Condition C”, and “Condition D” are the same as Condition B (die-cast), Condition C (commercial plate), and Condition D (commercial housing) in Test Example 1. The production condition “extrusion → rolling” is a commercially available extrudate, and this extrudate is rolled under the same conditions as described above for “casting → rolling”, and the resulting rolled plate is used as a sample (plate). A box-shaped body produced from this rolled plate under the same conditions as in the above-described “casting → rolling” is used as a sample (housing).

As shown in Table 2, by rolling to a cast plate cast with a roll temperature of 100 ° C. or less and a cast plate thickness of 5 mm or less in a twin roll continuous casting method, an arbitrary 50 μm ² selected from the surface region On the other hand, it can be seen that a magnesium alloy plate or a magnesium alloy member having 15 or less Al-Mn crystals having a maximum diameter of 0.1 μm or more and 1 μm or less can be obtained. On the other hand, it can be seen that there is a coarse crystallized product if not produced under the above specific casting conditions. Similarly to Test Example 1, a magnesium alloy plate or magnesium alloy member having 15 or less Al-Mn crystallized crystals having a maximum diameter of 0.1 μm or more and 1 μm or less with respect to an arbitrary 50 μm ² selected from the surface region is It can be seen that it has excellent impact resistance even in a low temperature environment such as -30 ° C. In addition, when Al / Mn of each crystallized particle was measured for sample Nos. 2-1 to 2-6, all samples had Al / Mn = 2 to 5.

  Furthermore, from this test, (1) when the thickness of the cast material to be produced is the same, the lower the roll temperature, the more the crystallization can be reduced. (2) When the roll temperature is the same, the thickness of the cast material to be produced is It can be said that the thinner it is, the more crystallized substances can be reduced.

  The above-described embodiment can be appropriately changed without departing from the gist of the present invention, and is not limited to the above-described configuration. For example, the composition of the magnesium alloy, the plate thickness after casting and after rolling, the roll temperature during casting, and the like may be appropriately changed. Moreover, you may provide an anticorrosion process and a coating layer in the obtained rolled plate and the member which gave the press work.

  Since the magnesium alloy member of the present invention is excellent in impact resistance under a low temperature environment, it can be suitably used for various cases and parts used in a low temperature environment. The magnesium alloy plate of the present invention can be suitably used as a constituent material for the magnesium alloy member of the present invention. The manufacturing method of this invention magnesium alloy plate can be utilized suitably for manufacture of this invention magnesium alloy plate.

  1 Specimen 10 Cylindrical bar 20 Support base 21 Circular hole

Claims (5)

A magnesium alloy plate made of a magnesium alloy containing Al and Mn,
In the thickness direction of the magnesium alloy plate, a region from the surface of the alloy plate to 30% of the thickness of the alloy plate is defined as a surface region, and when an arbitrary small region of 50 μm ² is taken from this surface region, Al And a crystallized substance containing both Mn and 15 or less particles having a maximum diameter of 0.1 μm or more and 1 μm or less,
The crystallized particles have a mass ratio of Al to Mn: Al / Mn of 2 or more and 5 or less.   2. The magnesium alloy plate according to claim 1, wherein the magnesium alloy contains 5% by mass to 12% by mass of Al and 0.1% by mass to 2.0% by mass of Mn.   The magnesium alloy further includes one or more elements selected from Zn, Si, Ca, Sr, Y, Cu, Ag, Ce, Zr and rare earth elements (excluding Y). The magnesium alloy plate according to 1 or 2.   A magnesium alloy member obtained by subjecting the magnesium alloy plate according to any one of claims 1 to 3 to plastic working. A casting process for casting a magnesium alloy containing Al and Mn into a plate shape;
A rolling process for rolling the cast plate obtained by the casting process,
The method for producing a magnesium alloy plate, wherein the casting is performed by a twin-roll continuous casting method, the roll temperature is 100 ° C. or less, and the thickness of the cast plate is 5 mm or less.

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