WO2021210510A1 - Magnesium alloy sheet, magnesium alloy molded article, method for manufacturing magnesium alloy sheet, and method for manufacturing magnesium alloy molded article - Google Patents

Abstract

A magnesium alloy sheet composed of a magnesium alloy, wherein: the magnesium alloy has a composition containing less than 2.00 mass% of aluminum and 1.00 mass% or less of manganese, with the remainder consisting of magnesium and unavoidable impurities, and also has a structure in which crystals containing aluminum and manganese are dispersed therein; and the maximum size of the crystals is 0.20 μm to 1.50 μm inclusive.

Description

Magnesium alloy plate, magnesium alloy molded body, manufacturing method of magnesium alloy plate, and manufacturing method of magnesium alloy molded body

The present disclosure relates to a magnesium alloy plate, a magnesium alloy molded body, a method for manufacturing a magnesium alloy plate, and a method for manufacturing a magnesium alloy molded body.
This application claims priority based on PCT / JP2020 / 016797 of the international application dated April 16, 2020, and incorporates all the contents described in the international application.

Patent Document 1 discloses a magnesium alloy rolled material made of a magnesium alloy. This magnesium alloy contains aluminum, a first-class element and a second-class element, and the balance is composed of magnesium and unavoidable impurities. Aluminum is contained in an amount of 0.3% by mass or more and less than 3% by mass. The first-class element is at least one element selected from the group consisting of calcium, strontium, and lanthanoids having atomic numbers 57 to 64, which are 0.1% by mass or more and 1.5% by mass or less. The second element is at least one element selected from the group consisting of manganese, vanadium, and zirconium of 0.05% by mass or more and 1.5% by mass or less.

Patent Document 1 discloses a manufacturing method including a casting step, a pre-rolling heat treatment step, a rolling step, a post-rolling heat treatment step, and an aging heat treatment step as a method for manufacturing the magnesium alloy rolled material. The magnesium alloy rolled material obtained by this production method contains a first precipitate containing aluminum and a first-class element, and a second precipitate containing aluminum and a second-class element. Each of the first precipitate and the second precipitate is an extremely small nano-order precipitate.

JP-A-2017-78220

The magnesium alloy plate of the present disclosure is a magnesium alloy plate made of a magnesium alloy, and the magnesium alloy contains less than 2.00% by mass of aluminum and 1.00% by mass or less of manganese, and the balance is magnesium and It has a composition composed of unavoidable impurities and a structure in which crystallizations containing aluminum and manganese are dispersed, and the maximum diameter of the crystallization is 0.20 μm or more and 1.50 μm or less.

The magnesium alloy molded product of the present disclosure includes the magnesium alloy plate of the present disclosure.

The method for producing a magnesium alloy plate of the present disclosure includes a casting step of continuously casting a molten magnesium alloy by a twin roll casting method to produce a plate-shaped cast material, and rolling the cast material to produce a magnesium alloy plate. In the casting step, the magnesium alloy containing less than 2.00% by mass of aluminum and 1.00% by mass or less of manganese is prepared, and the balance is magnesium and unavoidable impurities. The cooling rate of the molten metal is set to 800 ° C./sec or more.

The method for producing a magnesium alloy molded product of the present disclosure includes a molding step of warm-molding the magnesium alloy plate obtained by the method for producing a magnesium alloy plate of the present disclosure to produce a magnesium alloy molded product. The molding temperature is 200 ° C. or higher and 300 ° C. or lower.

FIG. 1 is a flowchart showing a method for manufacturing a magnesium alloy plate according to an embodiment and a method for manufacturing a magnesium alloy molded body according to the embodiment. FIG. 2 is a graph showing the relationship between the cooling rate of the molten metal when the molten magnesium alloy is continuously cast by the double roll casting method and the maximum diameter of the crystals in the obtained magnesium alloy plate. FIG. 3 shows the sample No. 1 in Test Example 1. It is a figure which shows the micrograph which observed the cross section of the magnesium alloy plate of 1 with a tabletop microscope. FIG. 4 shows the sample No. 1 in Test Example 1. It is a figure which shows the appearance photograph which evaluated the corrosion resistance of the magnesium alloy plate of 1. FIG. 5 shows the sample No. 1 in Test Example 1. It is a figure which shows the micrograph which observed the cross section of the magnesium alloy plate of 2 with a tabletop microscope. FIG. 6 shows the sample No. 1 in Test Example 1. It is a figure which shows the appearance photograph which evaluated the corrosion resistance of the magnesium alloy plate of 2. FIG. 7 shows the sample No. 1 in Test Example 1. It is a figure which shows the micrograph which observed the cross section of the magnesium alloy plate of 3 with a tabletop microscope. FIG. 8 shows the sample No. 1 in Test Example 1. It is a figure which shows the appearance photograph which evaluated the corrosion resistance of the magnesium alloy plate of 3. FIG. 9 shows the sample No. 1 in Test Example 1. It is a figure which shows the micrograph which observed the cross section of the magnesium alloy plate of 4 with a tabletop microscope. FIG. 10 shows the sample No. 1 in Test Example 1. It is a figure which shows the appearance photograph which evaluated the corrosion resistance of the magnesium alloy plate of 4. FIG. 11 shows the sample No. 1 in Test Example 1. It is a figure which shows the micrograph which observed the cross section of the magnesium alloy plate 5 with a tabletop microscope. FIG. 12 shows the sample No. 1 in Test Example 1. It is a figure which shows the appearance photograph which evaluated the corrosion resistance of the magnesium alloy plate of 5. FIG. 13 shows the sample No. 1 in Test Example 1. It is a figure which shows the micrograph which observed the cross section of 10 magnesium alloy plates with a tabletop microscope. FIG. 14 shows the sample No. 1 in Test Example 1. It is a figure which shows the appearance photograph which evaluated the corrosion resistance of 10 magnesium alloy plates.

[Issues to be solved by this disclosure]
Aluminum contained in the magnesium alloy contributes to the improvement of corrosion resistance, but can reduce the thermal conductivity. Magnesium alloys containing aluminum contain manganese in order to prevent impurities such as iron from being mixed in during the manufacturing process. When aluminum and manganese are contained in the magnesium alloy, crystallizations containing aluminum and manganese can be produced in the matrix composed of magnesium. This crystallized material is the starting point of corrosion. In order to suppress the deterioration of corrosion resistance due to crystallization, it is desirable to increase the aluminum content. However, when the aluminum content is increased, the thermal conductivity decreases. Patent Document 1 has room for further improvement in obtaining a magnesium alloy plate having both thermal conductivity and corrosion resistance, although it is excellent in moldability.

One of the purposes of the present disclosure is to provide a magnesium alloy plate having excellent thermal conductivity and excellent corrosion resistance, and a magnesium alloy molded body. Another object of the present disclosure is to provide a method for producing a magnesium alloy plate having excellent thermal conductivity and excellent corrosion resistance, and a method for producing a magnesium alloy molded product.

[Effect of the present disclosure]
The magnesium alloy plate of the present disclosure and the magnesium alloy molded product of the present disclosure are excellent in thermal conductivity and corrosion resistance. The method for producing a magnesium alloy plate of the present disclosure can obtain a magnesium alloy plate having excellent thermal conductivity and corrosion resistance. The method for producing a magnesium alloy molded product of the present disclosure provides a magnesium alloy molded product having excellent thermal conductivity and corrosion resistance.

[Explanation of Embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.

(1) The magnesium alloy plate according to one aspect of the present disclosure is a magnesium alloy plate made of a magnesium alloy, and the magnesium alloy contains less than 2.00% by mass of aluminum and 1.00% by mass or less of manganese. The composition is composed of magnesium and unavoidable impurities in the balance, and has a structure in which crystallization containing aluminum and manganese is dispersed, and the maximum diameter of the crystallization is 0.20 μm or more and 1.50 μm or less. ..

When the content of aluminum contained in the magnesium alloy is less than 2.00% by mass, the decrease in thermal conductivity can be suppressed. By containing 1.00% by mass or less of manganese in the magnesium alloy, it is possible to prevent impurities such as iron from being mixed in during the manufacturing process. As described above, in the magnesium alloy, crystals containing aluminum and manganese can be produced in the matrix composed of magnesium. Even if the crystallized product is generated, since the maximum diameter of the crystallized product is as fine as 1.50 μm or less, the crystallized product is unlikely to be the starting point of corrosion, and a decrease in corrosion resistance can be suppressed. Since the crystallized products having a maximum diameter of 0.20 μm or more are dispersed in the matrix phase, the effect of improving the yield strength can be expected. From the above, the magnesium alloy plate of the present disclosure is excellent in thermal conductivity and corrosion resistance.

As will be described later, the crystallized product is an intermetallic compound produced in the casting process during the production of a magnesium alloy plate, and its size is usually on the micro order. On the other hand, the precipitate disclosed in Patent Document 1 is an intermetallic compound produced in the heat treatment process applied to the cast material, and the size is usually nano-order.

(2) As an example of the magnesium alloy plate of the present disclosure, there is a form in which aluminum is contained in an amount of 0.10% by mass or more.

When the content of aluminum contained in the magnesium alloy is 0.10% by mass or more, it is easy to improve the corrosion resistance.

(3) As an example of the magnesium alloy plate of the present disclosure, a form in which manganese is contained in an amount of 0.10% by mass or more can be mentioned.

When the content of manganese contained in the magnesium alloy is 0.10% by mass or more, it is easy to prevent impurities such as iron from being mixed in during the manufacturing process. By suppressing the mixing of impurities such as iron, it is easy to suppress the deterioration of corrosion resistance.

(4) As an example of the magnesium alloy plate of the present disclosure, the composition further includes a form containing 0.10% by mass or more and 1.00% by mass or less of calcium.

Since the magnesium alloy further contains calcium in the above range, it is easy to improve mechanical properties such as strength and proof stress. Further, when the magnesium alloy further contains calcium in the above range, the flame retardancy can be easily improved.

(5) As an example of the magnesium alloy plate of the present disclosure, the composition further includes a form containing 0.10% by mass or more and 2.00% by mass or less of zinc.

Since the magnesium alloy further contains zinc in the above range, it is easy to improve the mechanical properties. Further, when the magnesium alloy further contains zinc in the above range, the warm formability can be easily improved. However, when the magnesium alloy contains both calcium and zinc, the corrosion resistance tends to decrease.

(6) As an example of the magnesium alloy plate of the present disclosure, the composition further includes a form containing 0.10% by mass or more and 1.00% by mass or less of strontium.

Since the magnesium alloy further contains strontium in the above range, it is easy to improve the mechanical properties. Further, when the magnesium alloy further contains strontium in the above range, the heat resistance can be improved and the high temperature creep resistance can be improved.

(7) As an example of the magnesium alloy plate of the present disclosure, there is a form in which ^{the number density of the crystallized products is 0.010 / μm 2} or more and 0.060 / μm ^{2 or less.}

When the number density of crystallization is 0.060 / μm ² or less, there are few crystallizations that can be the starting point of corrosion, and it is easy to suppress a decrease in corrosion resistance. On the other hand, when the number density of the crystallized material is 0.010 / μm ² or more, the effect of improving the yield strength of the crystallized material can be expected.

(8) As an example of the magnesium alloy plate of the present disclosure, there is a form in which the thermal conductivity is 100 W / m · K or more.

The above form is superior in thermal conductivity to known standard alloys such as AZ91 and AZ31.

(9) As an example of the magnesium alloy plate of the present disclosure, there is a form in which the 0.2% proof stress is 200 MPa or more.

The above form has high yield strength.

(10) As an example of the magnesium alloy plate of the present disclosure, there is a form in which the half width of the X-ray diffraction peak is 0.07 ° or more and 0.40 ° or less.

The half width of the X-ray diffraction peak correlates with the strain introduced in the manufacturing process of the magnesium alloy plate. When the half width of the X-ray diffraction peak satisfies the above range, it can be said that a specific amount of strain remains in the magnesium alloy plate. When the magnesium alloy plate has a specific amount of strain, it is easy to perform warm forming on the magnesium alloy plate, and the formability by warm forming can be improved.

(11) The magnesium alloy molded product according to one aspect of the present disclosure includes the magnesium alloy plate according to any one of (1) to (10) above.

The magnesium alloy molded body of the present disclosure is excellent in thermal conductivity and corrosion resistance by containing the magnesium alloy plate of the present disclosure.

(12) The method for producing a magnesium alloy plate according to one aspect of the present disclosure includes a casting step of continuously casting a molten magnesium alloy by a twin roll casting method to produce a plate-shaped cast material, and rolling the cast material. The casting step includes a rolling step of applying the magnesium alloy plate to produce a magnesium alloy plate, and the casting step contains less than 2.00% by mass of aluminum and 1.00% by mass or less of manganese, and the balance is magnesium and unavoidable impurities. A magnesium alloy is prepared, and the cooling rate of the molten metal is set to 800 ° C./sec or more.

When the content of aluminum contained in the magnesium alloy is less than 2.00% by mass, the decrease in thermal conductivity can be suppressed. By containing 1.00% by mass or less of manganese in the magnesium alloy, it is possible to prevent impurities such as iron from being mixed in during the manufacturing process. When aluminum and manganese are contained in the magnesium alloy, crystallizations containing aluminum and manganese may be produced in the matrix composed of magnesium in the casting process. In the method for producing a magnesium alloy plate of the present disclosure, the cooling rate at the time of casting is as fast as 800 ° C./sec or more. Therefore, even if the above-mentioned crystallized product is produced in the casting process, the crystallized product is fine. Specifically, the crystallized product has a maximum diameter of 1.50 μm or less. Since the crystallized material is fine, the crystallized material is unlikely to be the starting point of corrosion in the obtained magnesium alloy plate, and the deterioration of corrosion resistance can be suppressed. From the above, the method for producing a magnesium alloy plate of the present disclosure can obtain a magnesium alloy plate having excellent thermal conductivity and corrosion resistance.

(13) As an example of the method for producing a magnesium alloy plate of the present disclosure, a heat treatment step of heat-treating the cast material to homogenize it is provided between the casting step and the rolling step. Examples thereof include a form in which the cast material heat-treated in the heat treatment step is rolled.

By providing a heat treatment process between the casting process and the rolling process, the composition of the magnesium alloy can be homogenized, and it is easy to suppress variations in characteristics.

(14) In the method for producing a magnesium alloy molded product according to one aspect of the present disclosure, the magnesium alloy plate obtained by the method for producing a magnesium alloy plate according to the above (12) or (13) is warm-formed. A molding step for producing a magnesium alloy molded body is provided, and the temperature of the warm molding is set to 200 ° C. or higher and 300 ° C. or lower.

The magnesium alloy plate obtained by the above-mentioned method for manufacturing a magnesium alloy plate has a specific amount of strain remaining due to rolling. By performing warm forming on the magnesium alloy plate in which the strain remains, the moldability by warm forming is improved. Therefore, the method for producing a magnesium alloy molded product of the present disclosure can obtain a magnesium alloy molded product which is excellent in thermal conductivity, excellent corrosion resistance, has little damage such as cracks, or is substantially nonexistent.

[Details of Embodiments of the present disclosure]
Hereinafter, the magnesium alloy plate, the magnesium alloy molded body, the method for producing the magnesium alloy plate, and the method for producing the magnesium alloy molded body according to the embodiment of the present disclosure will be specifically described.

<Magnesium alloy plate>
The magnesium alloy plate of the embodiment is a plate material made of a magnesium alloy. The magnesium alloy constituting the magnesium alloy plate contains aluminum of more than 0% by mass and less than 2.00% by mass and manganese of more than 0% by mass and less than 1.00% by mass, and the balance is composed of magnesium and unavoidable impurities. Be prepared. Further, the magnesium alloy constituting the magnesium alloy plate has a structure in which crystals containing aluminum and manganese are dispersed. Hereinafter, a detailed description will be given.

〔composition〕
The magnesium alloy constituting the magnesium alloy plate of the embodiment contains aluminum (Al) and manganese (Mn), which are solute elements soluble in magnesium (Mg), in a specific range, and also contains the largest amount of magnesium. The magnesium content is 90.00% by mass or more. The magnesium alloy can further contain calcium (Ca), zinc (Zn), strontium (Sr) and the like in a specific range.

<aluminum>
Aluminum contributes to the improvement of corrosion resistance. Aluminum mainly exists as a crystallized product together with manganese. Crystals containing aluminum and manganese are dispersed in the matrix composed of magnesium. Since the above-mentioned crystals are dispersed in the matrix phase, the effect of improving the yield strength can be expected.

The aluminum content is preferably 0.10% by mass or more. When the aluminum content is 0.10% by mass or more, the corrosion resistance can be easily improved. The content of aluminum is less than 2.00% by mass. Aluminum contributes to the improvement of corrosion resistance, but can reduce the thermal conductivity. When the aluminum content is less than 2.00% by mass, the decrease in thermal conductivity can be suppressed. The content of aluminum is 0.10% by mass or more and less than 2.00% by mass, and further 0.20% by mass or more and 1.50% by mass or less, particularly 0.25% by mass or more and 1.00% by mass or less. Can be mentioned.

<manganese>
Manganese suppresses the mixing of impurities such as iron (Fe) in the manufacturing process. By suppressing the mixing of impurities such as iron, it is easy to suppress the deterioration of corrosion resistance. As mentioned above, manganese mainly exists as a crystallized product together with aluminum.

The manganese content is preferably 0.10% by mass or more. When the manganese content is 0.10% by mass or more, it is easy to prevent impurities such as iron from being mixed in during the manufacturing process. The manganese content is 1.00% by mass or less. If the amount of manganese is too large, a large amount of crystallized products containing aluminum and manganese are likely to be produced. The above-mentioned crystallized product tends to be a starting point of corrosion and may reduce corrosion resistance. The crystallized product is preferably dispersed in the matrix in a specific range. When the manganese content is 1.00% by mass or less, it is possible to suppress excessive formation of the above-mentioned crystallized products. The manganese content may be 0.10% by mass or more and 1.00% by mass or less, further 0.20% by mass or more and 0.80% by mass or less, and particularly 0.20% by mass or more and 0.70% by mass or less. Can be mentioned.

<Calcium, zinc, strontium>
Calcium, zinc, and strontium contribute to the improvement of mechanical properties such as strength and yield strength.

Calcium also contributes to improving flame retardancy. The calcium content may be 0.10% by mass or more and 1.00% by mass or less. Further, the calcium content is 0.10% by mass or more and 0.80% by mass or less, particularly 0.10% by mass or more and 0.50% by mass or less.

Zinc also contributes to the improvement of warm moldability. The zinc content is 0.10% by mass or more and 2.00% by mass or less. Further, the zinc content is 0.10% by mass or more and 1.50% by mass or less, and in particular, 0.10% by mass or more and 1.00% by mass or less.

Strontium also contributes to the improvement of heat resistance. Strontium also contributes to the improvement of high temperature creep resistance. High-temperature creep property is a phenomenon in which a material to which a constant stress is applied in a high-temperature environment deforms with the passage of time. The content of strontium is 0.10% by mass or more and 1.00% by mass or less. Further, the content of strontium is 0.20% by mass or more and 0.80% by mass or less, particularly 0.20% by mass or more and 0.50% by mass or less.

Magnesium alloy may contain one element selected from the group consisting of calcium, zinc, and strontium. Magnesium alloys include calcium and strontium, or zinc and strontium in combination. The combination of calcium and zinc tends to reduce corrosion resistance.

<Inevitable impurities>
The unavoidable impurities are not particularly limited, and examples thereof include iron, silicon (Si), nickel (Ni), cobalt (Co), and copper (Cu). The total content of unavoidable impurities is preferably 1.00% by mass or less, more preferably 0.50% by mass or less, 0.15% by mass or less, and 0.05% by mass or less. In particular, the total content of iron, nickel, and cobalt that can hinder the improvement of corrosion resistance is preferably less than 0.05% by mass, more preferably 0.01% by mass or less.

The composition of the magnesium alloy can be confirmed by performing component analysis. For component analysis, for example, energy dispersive X-ray spectroscopy (EDX) or electron probe microanalyzer (EPMA) attached to a scanning electron microscope (SEM) can be used. Other component analysis methods include inductively coupled plasma emission spectroscopic analysis (ICP-OES) or emission spectroscopic analysis. It is preferable to use ICP-OES for component analysis.

[Organization]
The magnesium alloy constituting the magnesium alloy plate of the embodiment includes a structure containing a matrix containing magnesium as a main component and crystals dispersed in the matrix. The matrix is composed of a solid solution in which a solute element such as aluminum is dissolved in magnesium. The crystallization contains aluminum and manganese.

<particle size of crystallized material>
The crystallization is typically fine particles. Specifically, the maximum diameter of the crystallized product is 0.20 μm or more and 1.50 μm or less. As described above, the crystallized product tends to be a starting point of corrosion and can reduce the corrosion resistance. When the maximum diameter of the crystallized product is 1.50 μm or less, even if the crystallized product is generated, the crystallized product is unlikely to be the starting point of corrosion, and a decrease in corrosion resistance can be suppressed. On the other hand, when the maximum diameter of the crystallized product is 0.20 μm or more, the effect of improving the yield strength due to the dispersion of the crystallized product can be expected. Further, the maximum diameter of the crystallized product is 0.50 μm or more and 1.50 μm or less, particularly 0.80 μm or more and 1.40 μm or less, and 1.00 μm or more and 1.40 μm or less.

The average particle size of the crystallized product is 0.20 μm or more and 0.40 μm or less. When the average particle size of the crystallized product is 0.20 μm or more, the effect of improving the yield strength due to the dispersion of the crystallized product can be expected. On the other hand, when the average particle size of the crystallized product is 0.40 μm or less, even if the crystallized product is generated, the crystallized product is unlikely to be the starting point of corrosion, and a decrease in corrosion resistance can be suppressed. Further, the average particle size of the crystallized product is 0.25 μm or more and 0.38 μm or less, particularly 0.28 μm or more and 0.36 μm or less.

The maximum diameter and average particle size of the crystallized material can be determined by using an observation image acquired by a tabletop microscope on the surface or cross section of the magnesium alloy plate. The observation field of view is acquired so that the observation image contains 200 or more crystallized materials. The observation field of view may be one or more. When acquiring a plurality of observation visual fields, each observation visual field is acquired so that the total number of crystals in each observation visual field is 200 or more. When acquiring a plurality of observation visual fields, the number of observation visual fields may be 5 or more. The size of each observation field may be 80 μm × 60 μm. The observation image of each observation field is binarized to extract crystallization of 0.20 μm or more. For each of the extracted crystals, determine the equivalent circle diameter. The equivalent circle diameter is the diameter of a perfect circle having the area of the extracted crystallized material. The maximum circle-equivalent diameter of the obtained circle-equivalent diameters is defined as the maximum diameter of the crystallized material. The maximum diameter of the crystallized material in the magnesium alloy shall be the largest value among the maximum diameters of each observation field of view. Further, the average value of the obtained circle-equivalent diameter is defined as the average particle size of the crystallized product. The average particle size of the crystals in the magnesium alloy shall be the average value of the average particle size of the entire observation field.

<Number density of crystallization>
The number density of crystallization is 0.010 / μm ² or more and 0.060 / μm ² or less. When the number density of crystallization is 0.060 / μm ² or less, there are few crystallizations that can be the starting point of corrosion, and it is easy to suppress a decrease in corrosion resistance. On the other hand, when the number density of the crystallized material is 0.010 / μm ² or more, the effect of improving the yield strength of the crystallized material can be expected. Further, the number density of the crystallization is 0.012 / μm ² or more and 0.050 / μm ² or less, particularly 0.013 / μm ² or more and 0.045 / μm ² or less. The number density of the crystallization is determined by using the above-mentioned observation image acquired by a tabletop microscope. In each observation field, the number of extracted crystals in the observation field is measured. The average value obtained by dividing the number of crystallizations by the visual field area is defined as the number density of crystallizations. The number density of the crystallized matter in the magnesium alloy shall be the average value of the number density of the crystallized matter in the entire observation field.

〔Thermal conductivity〕
The thermal conductivity of the magnesium alloy plate of the embodiment is 100 W / m · K or more. When the thermal conductivity is 100 W / m · K or more, the magnesium alloy plate of the embodiment is superior in thermal conductivity to known standard alloys such as AZ91 and AZ31. The reason why the magnesium alloy plate of the embodiment is excellent in thermal conductivity is that the content of aluminum in the magnesium alloy constituting the magnesium alloy plate is small. The higher the thermal conductivity of the magnesium alloy plate, the more preferable it is, and further, it is mentioned that it is 120 W / m · K or more, particularly 130 W / m · K or more. The thermal conductivity of the magnesium alloy plate is less than 150 W / m · K. The thermal conductivity is obtained by using a commercially available measuring device and using a laser flash method or an optical alternating current method.

[Area ratio of corrosion products]
The area ratio of the corrosion product of the magnesium alloy plate of the embodiment is 7.0% or less. A corrosion product is a substance produced when the matrix is chemically or electrochemically eroded or materially deteriorated starting from a crystallized product. When the area ratio of the corrosion product is 7.0% or less, the magnesium alloy plate of the embodiment has excellent corrosion resistance. The reason why the magnesium alloy plate of the embodiment is excellent in corrosion resistance is that the maximum diameter of the crystallized product is as fine as 1.50 μm or less. The smaller the area ratio of the corrosion product of the magnesium alloy plate is, the more preferable it is, and more preferably 3.0% or less, particularly 2.0% or less.

The area ratio of corrosion products of magnesium alloy plates is determined by measurement in accordance with JIS H 0541: 2003 "Alkaline salt water corrosion test method for magnesium and magnesium alloys". The alkaline salt spray test is carried out in accordance with JIS Z 2371: 2015. The test piece shall be a flat plate, and as a typical size, the thickness shall be 3 mm or less, and the size shall be 150 mm × 70 mm. The test time is 96 hours. The surface of the test piece after the test is captured by a scanner and binarized using the image analysis software "ImageJ" to determine the area of the corrosion product. The area ratio of the corrosion product is a value obtained by dividing the area of the corrosion product by the exposed area of the test piece to be subjected to the alkaline salt spray test as a percentage.

[0.2% proof stress]
The 0.2% proof stress of the magnesium alloy plate of the embodiment is 200 MPa or more. When the 0.2% proof stress is 200 MPa or more, the magnesium alloy plate of the embodiment has a high proof stress and is unlikely to break. The reason why the magnesium alloy plate of the embodiment has a high yield strength is that crystals having a maximum diameter of 0.20 μm or more are dispersed in the matrix phase. The higher the 0.2% proof stress of the magnesium alloy plate is, the more preferable it is, and further, 210 MPa or more, particularly 220 MPa or more can be mentioned.

0.2% proof stress is measured by performing a tensile test in accordance with JIS Z 2241: 2011 "Metallic Material Tensile Test Method". The 0.2% proof stress is a value at room temperature. Room temperature is 20 ° C ± 15 ° C. The test piece shall be a JIS 13B plate-shaped piece, and shall be collected from any location on the magnesium alloy plate. It is preferable to collect the test piece excluding the peripheral edge of the magnesium alloy plate and the region in the vicinity thereof so that proper measurement can be easily performed. For example, a test piece may be collected from an inner region 5 mm or more away from the peripheral edge.

〔others〕
In the magnesium alloy plate of the embodiment, the half width of the X-ray diffraction peak is 0.07 ° or more and 0.40 ° or less. Specifically, in the magnesium alloy plate of the embodiment, the half width of the peak of the (0002) plane by X-ray diffraction using CuKαX-ray is 0.07 ° or more and 0.40 ° or less. The half width of the X-ray diffraction peak correlates with the strain introduced in the manufacturing process of the magnesium alloy plate. When the half width of the X-ray diffraction peak is large, it means that the amount of distortion of the magnesium alloy plate is large. A half-value width of 0.07 ° or more means that the magnesium alloy plate has some strain. When the magnesium alloy plate has a certain degree of distortion, it is easy to perform warm forming on the magnesium alloy plate, and the moldability by warm forming can be improved. On the other hand, when the half width is 0.40 ° or less, it can be said that excessive strain does not remain in the magnesium alloy plate. Since no excessive strain remains on the magnesium alloy plate, it is possible to suppress a decrease in room temperature ductility of the magnesium alloy plate. The half width of the X-ray diffraction peak in the magnesium alloy plate is further 0.08 ° or more and 0.30 ° or less, particularly 0.10 ° or more and 0.20 ° or less.

<Magnesium alloy molded product>
The magnesium alloy molded product of the embodiment includes the magnesium alloy plate of the above-described embodiment. The magnesium alloy molded body of the embodiment is not particularly limited as long as it is press-molded using the magnesium alloy plate of the above-described embodiment, and includes housings for electronic devices, various panels for automobiles, industrial equipment parts, and the like. Can be mentioned.

<Manufacturing method of magnesium alloy plate and manufacturing method of magnesium alloy molded product>
As shown in FIG. 1, the method for manufacturing a magnesium alloy plate of the embodiment includes a casting step 1 and a rolling step 3. The method for producing a magnesium alloy plate of the embodiment can include a heat treatment step 2 between the casting step 1 and the rolling step 3.

As shown in FIG. 1, the method for manufacturing the magnesium alloy molded product of the embodiment includes a casting step 1, a rolling step 3, and a molding step 4. The method for producing a magnesium alloy molded product of the embodiment can include a heat treatment step 2 between the casting step 1 and the rolling step 3. That is, the method for manufacturing the magnesium alloy molded body of the embodiment further includes the molding step 4 after the rolling step 3 as compared with the method for manufacturing the magnesium alloy plate of the embodiment. Hereinafter, a detailed description will be given.

[Casting process]
The casting step 1 is a step of continuously casting a molten magnesium alloy by a double roll casting method to produce a plate-shaped cast material. Magnesium alloys have the specific composition described above. The composition of the magnesium alloy constituting the molten metal is maintained during the manufacturing process. Therefore, the composition of the magnesium alloy constituting the molten metal and the composition of the magnesium alloy constituting the obtained magnesium alloy plate are the same. The double roll casting method is a kind of continuous casting method and is a casting method capable of quenching and solidifying. In the twin-roll casting method, molten metal is supplied between a pair of rolls, which are movable molds, and brought into contact with the rolls to cool and solidify the molten metal. In the casting step 1, crystals containing aluminum and manganese can be produced in the matrix composed of magnesium.

The cooling rate of the molten metal and the maximum diameter of the crystals in the obtained magnesium alloy plate are in a relationship expressed by the formula of "y = −1.492 ln (x) + 11.485". The symbol "y" is the maximum diameter of the crystallized product in the obtained magnesium alloy plate. The unit of the maximum diameter of the crystallized product is μm. The symbol "x" is the cooling rate of the molten metal. The unit of cooling rate is ° C / sec. The symbol "ln" means the natural logarithm. As shown in FIG. 2, the above calculation formula is an approximate formula obtained from the result of actually producing a magnesium alloy plate by changing the cooling rate of the molten metal and measuring the maximum diameter of the crystallized product in the obtained magnesium alloy plate. Is. In the graph shown in FIG. 2, the horizontal axis is the cooling rate and the vertical axis is the maximum diameter of the crystallized material. In the graph shown in FIG. 2, when the magnesium alloy plate is produced at each cooling rate by changing the cooling rate from the lowest to 2.5 ° C / sec, 100 ° C / sec, 450 ° C / sec, and 1000 ° C / sec. The maximum diameter of the crystallized material is indicated by a black circle. The manufacturing conditions other than the cooling rate are all the same. In the above formula, examples of the cooling rate and the maximum diameter of the crystallized product include the following. The cooling rate is 600 ° C./sec and the maximum diameter of the crystallized material is 1.9 μm. The cooling rate is 800 ° C./sec and the maximum diameter of the crystallized material is 1.5 μm. The cooling rate is 900 ° C./sec and the maximum diameter of the crystallized material is 1.3 μm. The cooling rate can be changed by adjusting the cooling conditions. Examples of the cooling conditions include the temperature and flow rate of the refrigerant flowing in the roll, the flow velocity, the thermal conductivity of the constituent materials of the roll, and the like.

From the above formula, the cooling rate of the molten metal is 800 ° C / sec or more. When the cooling rate is 800 ° C./sec or more, the crystallized product is fine. Specifically, the crystallized product has a maximum diameter of 1.5 μm or less. Since the crystallized material is fine, the crystallized material is unlikely to be the starting point of corrosion in the obtained magnesium alloy plate, and the deterioration of corrosion resistance can be suppressed. As for the cooling rate, the faster the crystallized material is, the finer the crystallized product is, and further, 900 ° C./sec or more, 950 ° C./sec or more, particularly 1000 ° C./sec or more.

[Heat treatment process]
The heat treatment step 2 is a step of subjecting the cast material obtained in the casting step to heat treatment to homogenize it. The heat treatment temperature may be 350 ° C. or higher and 450 ° C. or lower. The heat treatment temperature is the temperature of the casting material to be heated. When the heat treatment temperature is 350 ° C. or higher, the composition of the magnesium alloy can be homogenized, and variations in characteristics can be suppressed. On the other hand, when the heat treatment temperature is 450 ° C. or lower, excessive heat treatment can be suppressed. The heat treatment temperature may be further set to 370 ° C. or higher and 430 ° C. or lower, particularly 380 ° C. or higher and 420 ° C. or lower. The holding time of the heat treatment may be 1 hour or more and 24 hours or less. When the heat treatment holding time is 1 hour or more, the composition of the magnesium alloy can be homogenized, and variations in characteristics can be suppressed. On the other hand, when the heat treatment holding time is 24 hours or less, excessive heat treatment can be suppressed. The holding time of the heat treatment may be further set to 2 hours or more and 20 hours or less, particularly 3 hours or more and 10 hours or less. Examples of the heat treatment atmosphere include an atmospheric atmosphere and a nitrogen atmosphere. The heat treatment step 2 is not essential and can be omitted.

[Rolling process]
The rolling step 3 is a step of rolling the cast material to produce a magnesium alloy plate. When the heat treatment step 2 is performed, the rolling step 3 rolls the heat-treated cast material. For rolling, a rolling apparatus having rolling rolls arranged facing each other is used, and a casting material is inserted between the rolling rolls. At this time, each of the cast material and the rolling roll is heated to a specific temperature.

The heating temperature during rolling may be 200 ° C. or higher and 300 ° C. or lower for both the cast material and the rolling roll. When the heating temperature is 200 ° C. or higher, it is possible to suppress the occurrence of cracks during rolling. On the other hand, when the heating temperature is 300 ° C. or lower, excessive heating can be suppressed. The heating temperature may be further set to 220 ° C. or higher and 280 ° C. or lower, particularly 230 ° C. or higher and 270 ° C. or lower. The heating temperature of the cast material is the temperature of the cast material immediately before it comes into contact with the rolling roll. Heating of the cast material may be performed by separately providing a heating furnace. It is possible to adjust the transport distance and transport time, and control the temperature of the atmosphere so that the temperature does not drop between the time when the cast material comes into contact with the rolling roll from the heating furnace.

Rolling may be performed in one or more passes, and may be performed in multiple passes. The reduction rate per pass is 10% or more and less than 40%, and further 20% or more and 30% or less. When performing a plurality of passes, the total reduction rate may be 50% or more and 95% or less, and further 65% or more and 85% or less. The rolling reduction is an amount calculated by {(h1-h2) / h1} × 100 when the plate thicknesses of the plate materials before and after rolling are h1 and h2, respectively, and represents the degree of rolling workability.

The method for manufacturing a magnesium alloy plate of the embodiment does not include a second heat treatment step after the rolling step 3. The second heat treatment step after the rolling step 3 is a heat treatment including a post-rolling heat treatment step and an aging heat treatment step disclosed in Patent Document 1.

[Molding process]
The molding step 4 is a step of warm-forming the magnesium alloy plate obtained in the rolling step 3 to produce a magnesium alloy molded body. In warm molding, the mold is molded in a heated state. The heating temperature may be 200 ° C. or higher and 300 ° C. or lower. When the heating temperature is 200 ° C. or higher, it is possible to prevent the magnesium alloy plate from cracking during molding. On the other hand, when the heating temperature is 300 ° C. or lower, excessive heating can be suppressed. The heating temperature may be further set to 220 ° C. or higher and 280 ° C. or lower, particularly 230 ° C. or higher and 270 ° C. or lower.

<Effect>
The magnesium alloy plate and the magnesium alloy molded product of the embodiment are excellent in thermal conductivity. This is because the content of aluminum contained in the magnesium alloy is as small as less than 2.00% by mass. Further, the magnesium alloy plate and the magnesium alloy molded product of the embodiment are excellent in corrosion resistance. Even if crystallization containing aluminum and manganese is generated in the magnesium alloy, the crystallization is unlikely to be the starting point of corrosion because the maximum diameter of the crystallization is as fine as 1.50 μm or less. Is. Further, the magnesium alloy plate and the magnesium alloy molded product of the embodiment have high yield strength. This is because the above-mentioned crystals having a maximum diameter of 0.20 μm or more are dispersed in the matrix composed of magnesium. Further, the magnesium alloy plate and the magnesium alloy molded product of the embodiment are easy to be warm-molded, and the moldability by the warm-molding can be improved. This is because the magnesium alloy plate has a specific amount of strain.

In the method for producing a magnesium alloy plate of the embodiment, the cooling rate at the time of casting is set to 800 ° C./sec or more, so that even if crystals containing aluminum and magnesium are produced in the casting process, the crystals are produced. Can be finely divided. Therefore, the method for manufacturing the magnesium alloy plate of the embodiment can satisfactorily manufacture the magnesium alloy plate of the embodiment. The method for producing the magnesium alloy molded product of the embodiment is that the magnesium alloy plate of the embodiment is warm-molded to have excellent thermal conductivity, excellent corrosion resistance, and less damage such as cracks. The alloy molded body can be manufactured satisfactorily.

[Test Example 1]
A magnesium alloy plate was prepared and examined for structure, thermal conductivity, corrosion resistance, and proof stress.

<Test piece>
<< Sample No. Sample No. 1 to sample No. 5 ≫
Sample No. Sample No. 1 to sample No. Reference numeral 5 denotes a magnesium alloy plate obtained through a casting step, a heat treatment step, and a rolling step.

[Casting process]
In the casting process, molten magnesium alloy was continuously cast by a double-roll casting method to produce a plate-shaped cast material. The composition of the magnesium alloy of each sample was as follows. Sample No. Reference numeral 1 contains 0.49% by mass of aluminum and 0.24% by mass of manganese, and the balance is magnesium and unavoidable impurities. In Table 1, it is expressed as Mg-0.49% Al-0.24% Mn. Sample No. Reference numeral 2 contains 1.10% by mass of aluminum, 0.70% by mass of manganese, and 0.25% by mass of calcium, and the balance is magnesium and unavoidable impurities. In Table 1, it is expressed as Mg-1.10% Al-0.70% Mn-0.25% Ca. Sample No. 3 contains 0.48% by mass of aluminum, 0.24% by mass of manganese, and 0.11% by mass of calcium, and the balance is magnesium and unavoidable impurities. In Table 1, it is expressed as Mg-0.48% Al-0.24% Mn-0.11% Ca. Sample No. Reference numeral 4 contains 0.52% by mass of aluminum, 0.25% by mass of manganese, and 0.20% by mass of strontium, and the balance is magnesium and unavoidable impurities. In Table 1, it is expressed as Mg-0.52% Al-0.25% Mn-0.20% Sr. Sample No. Reference numeral 5 contains 0.25% by mass of aluminum, 0.18% by mass of manganese, and 0.10% by mass of zinc, and the balance is magnesium and unavoidable impurities. In Table 1, it is expressed as Mg-0.25% Al-0.18% Mn-0.10% Zn.

A known configuration can be used for the double roll continuous casting apparatus. The cooling rate in the casting process was 1000 ° C./sec. The thickness of the plate was 4 mm.

[Heat treatment process]
In the heat treatment step, the cast material obtained in the casting step was heat-treated. In the heat treatment, the cast material to be heated was heated to 400 ° C. The holding time of the heat treatment was 5 hours.

[Rolling process]
In the rolling step, the cast material heat-treated in the heat treatment step was rolled to produce a magnesium alloy plate. For rolling, a rolling apparatus equipped with rolling rolls arranged facing each other was used. A known configuration can be used for the rolling apparatus. Rolling was carried out in a state where both the cast material and the rolling roll were heated to 240 ° C. Rolling was carried out in 7 passes with a rolling reduction rate of 25% per pass. The thickness of the magnesium alloy plate was 0.6 mm.

Since the rolling process, the magnesium alloy plate has not been heat treated.

<< Sample No. 10 >>
A magnesium alloy plate made of ASTM standard AZ31 alloy was prepared. Conditions other than the composition of the magnesium alloy are described in Sample No. Sample No. 1 to sample No. It was the same as 5.

<Composition>
The composition of the magnesium alloy plate of each of the obtained samples was measured by ICP-OES. As a result, the composition of the magnesium alloy plate of each sample was almost the same as the composition of the magnesium alloy of the molten metal used in each sample.

<Organization>
The cross section of the magnesium alloy plate of each of the obtained samples was observed with a tabletop microscope, and the maximum diameter, average particle size, and number density of the crystals containing aluminum and manganese were measured. As the tabletop microscope, a Miniscope TM3030 manufactured by Hitachi High-Tech Co., Ltd. was used. First, in the observation image of the cross section of the magnesium alloy plate acquired by the tabletop microscope, five observation fields were acquired so as to include 300 or more crystallized substances. Each observation field was acquired so that the total number of crystals in each of the five observation fields was 300 or more. The observation magnification was 2000 times. The size of each observation field was 80 μm × 60 μm. Next, the observation image of each observation field of view was binarized using the image analysis software "Image J", and crystallization of 0.20 μm or more was extracted. That is, when calculating the average particle size of the crystallized material, the crystallized material having a size of less than 0.20 μm is not extracted. Then, the equivalent circle diameter was determined for each of the extracted crystals. The equivalent circle diameter is the diameter of a perfect circle having the area of the extracted crystallized material. The largest circle-equivalent diameter among the obtained circle-equivalent diameters was defined as the maximum diameter of the crystallized material. The maximum diameter of the crystallized material in the magnesium alloy was set to the largest value among the maximum diameters of each observation field of view. Further, the average value of the obtained circle-equivalent diameter was taken as the average particle size of the crystallized product. The average particle size of the crystals in the magnesium alloy was taken as the average value of the average particle size of all observation fields. Further, the number of extracted crystallized substances in the observation visual field was measured, and the average value of the values obtained by dividing the number of crystallized substances present by the visual field area was taken as the number density of the crystallized products. The number density of the crystallized matter in the magnesium alloy was taken as the average value of the number density of the crystallized matter in the entire observation field. The results are shown in Table 1.

FIG. 3 shows the sample No. This is an example of a micrograph of the cross section of the magnesium alloy plate 10 of No. 1 observed with a tabletop microscope. FIG. 5 shows the sample No. This is an example of a micrograph of the cross section of the magnesium alloy plate 10 of No. 2 observed with a tabletop microscope. FIG. 7 shows the sample No. This is an example of a micrograph of the cross section of the magnesium alloy plate 10 of No. 3 observed with a tabletop microscope. FIG. 9 shows the sample No. This is an example of a micrograph of the cross section of the magnesium alloy plate 10 of No. 4 observed with a tabletop microscope. FIG. 11 shows the sample No. This is an example of a micrograph of the cross section of the magnesium alloy plate 10 of No. 5 observed with a tabletop microscope. FIG. 13 shows the sample No. This is an example of a micrograph of the cross section of the magnesium alloy plate 10 of 10 observed with a tabletop microscope. In each of the magnesium alloy plates 10 of FIGS. 3, 5, 7, 9, 11, and 13, the region that looks gray is the matrix 11, and the region that looks white is the crystallized product 12.

<Thermal conductivity>
The thermal conductivity of the magnesium alloy plate of each of the obtained samples was measured. The thermal conductivity was determined from the thermal diffusivity obtained by collecting a test piece for measurement from the magnesium alloy plate of each sample and measuring the thermal diffusivity using a commercially available measuring device. As the measuring device, the optical AC method thermal diffusivity measuring device LaserPIT manufactured by Advance Riko Co., Ltd. was used. The size of the test piece was 5 mm × 25 mm × thickness 0.4 mm. The thermal conductivity was calculated from thermal diffusivity × specific heat capacity × density. The results are shown in Table 1.

<Corrosion resistance>
The area ratio of the corrosion products of the magnesium alloy plate of each of the obtained samples was measured. The area ratio of corrosion products was measured in accordance with JIS H 0541: 2003 “Magnesium and Magnesium Alloy Alkaline Salt Water Corrosion Test Method”. Specifically, a test piece for measurement was taken from the magnesium alloy plate of each sample, and the alkaline salt spray test specified in JIS Z 2371: 2015 was carried out for 96 hours. The test piece had a size of 150 mm × 70 mm × thickness 0.6 mm, and the outer peripheral portion and the back surface were covered with masking tape. The exposed area of the test piece to be subjected to the alkaline salt spray test was 140 mm × 60 mm. The surface of the test piece after the test was scanned with a scanner and binarized using the image analysis software "Image J" to determine the area of the corrosion product. As the scanner, DADF-AK1 manufactured by Canon Inc. was used. The area ratio of the corrosion product was a value obtained by dividing the area of the corrosion product by the above-mentioned exposed area as a percentage. The results are shown in Table 1.

FIG. 4 shows the sample No. This is an example of an external photograph of the magnesium alloy plate 10 of No. 1 after being subjected to an alkaline salt spray test. FIG. 6 shows the sample No. This is an example of an external photograph of the magnesium alloy plate 10 of No. 2 after being subjected to an alkaline salt spray test. FIG. 8 shows the sample No. This is an example of an external photograph of the magnesium alloy plate 10 of No. 3 after being subjected to an alkaline salt spray test. FIG. 10 shows the sample No. This is an example of an external photograph of the magnesium alloy plate 10 of No. 4 after being subjected to an alkaline salt spray test. FIG. 12 shows the sample No. This is an example of an external photograph of the magnesium alloy plate 10 of No. 5 after being subjected to an alkaline salt spray test. FIG. 14 shows the sample No. This is an example of an external photograph of the magnesium alloy plate 10 of No. 10 after being subjected to an alkaline salt spray test. In each of the magnesium alloy plates 10 of FIGS. 4, 6, 8, 10, 12, and 14, the region that appears black or white is the corrosion product 20.

<Yield strength>
The 0.2% proof stress of the magnesium alloy plate of each of the obtained samples was measured. The 0.2% proof stress was measured by performing a tensile test in accordance with JIS Z 2241: 2011 “Metallic Material Tensile Test Method”. The tensile test was measured along each of the rolling direction and the plate width direction of the magnesium alloy plate. The average value of the 0.2% proof stress in the rolling direction and the 0.2% proof stress in the plate width direction was taken as the 0.2% proof stress of the magnesium alloy plate. The test temperature was room temperature, 22 ° C. here. The results are shown in Table 1.

The following can be seen from Table 1. Sample No. Sample No. 1 to sample No. The magnesium alloy plate of No. 5 has a thermal conductivity of 100 W / m · K or more, particularly 115 W / m · K or more, and is excellent in thermal conductivity. Sample No. Sample No. 1 to sample No. It is considered that the reason why the magnesium alloy plate of No. 5 is excellent in thermal conductivity is that the content of aluminum contained in the magnesium alloy is as small as less than 2.00% by mass. This is because aluminum contributes to the improvement of corrosion resistance, but can reduce the thermal conductivity. In particular, sample No. 1. Sample No. Sample No. 3 to sample No. The magnesium alloy plate of No. 5 has an aluminum content of less than 1.10% by mass, particularly 0.52% by mass or less, and is further excellent in thermal conductivity.

Sample No. Sample No. 1 to sample No. The magnesium alloy plate of No. 5 has an area ratio of corrosion products of 7.0% or less and is excellent in corrosion resistance. Sample No. Sample No. 1 to sample No. It is considered that the reason why the magnesium alloy plate of No. 5 is excellent in corrosion resistance is that the maximum diameter of the crystallized product is as small as 1.50 μm or less. It is considered that the maximum diameter of the crystallized product was as small as 1.50 μm or less, so that the crystallized product could be suppressed from becoming the starting point of corrosion. Further, it is considered that the fact that the average particle size of the crystallized product was as small as 0.40 μm or less also prevented the crystallized product from becoming the starting point of corrosion. As shown in FIGS. 4, 6, 8, 10, and 12, the sample No. Sample No. 1 to sample No. The magnesium alloy plate of No. 5 showed almost no corrosion in appearance. Sample No. Sample No. 1 to sample No. As shown in FIGS. 3, 5, 7, 9, and 11, the magnesium alloy plate of No. 5 had fine crystallized substances dispersed therein.

Sample No. From sample No. 2 The magnesium alloy plate of No. 4 is more excellent in corrosion resistance because the number density of crystallized products is 0.010 / μm ² or more and 0.060 / μm ^{2 or less.} In addition, sample No. From sample No. 2 The magnesium alloy plate of No. 4 has a 0.2% proof stress of 200 MPa or more and is also excellent in proof stress when ^{the number density of crystallization is 0.010 / μm 2} or more and 0.060 / μm ^{2 or less.} Sample No. From sample No. 2 It is considered that the reason why the magnesium alloy plate of No. 4 is excellent in proof stress is that a certain number of crystallizations of 1.00 μm or more are dispersed in the matrix composed of magnesium.

On the other hand, sample No. The magnesium alloy plate of 10 has a thermal conductivity of 66 W / m · K and is inferior in thermal conductivity. Sample No. It is considered that the reason why the magnesium alloy plate of 10 is inferior in thermal conductivity is that the content of aluminum contained in the magnesium alloy is as high as 2.0% by mass or more.

Sample No. The magnesium alloy plate of 10 has an area ratio of corrosion products of 15.3% and is inferior in corrosion resistance. Actually, the sample No. As shown in FIG. 14, the magnesium alloy plate of No. 10 was found to be corroded in appearance. Sample No. It is considered that the reason why the magnesium alloy plate of No. 10 is inferior in corrosion resistance is that, as shown in FIG. 13, the maximum diameter of the crystallized product is as large as more than 1.50 μm. It is considered that the crystallized material became the starting point of corrosion because the maximum diameter of the crystallized material was as large as more than 1.50 μm. Further, it is considered that the crystallized product became the starting point of corrosion because the average particle size of the crystallized product was as large as more than 0.50 μm.

[Test Example 2]
Sample No. prepared in Test Example 1. The magnesium alloy plate of No. 2 was subjected to square drawing at a heating temperature of 240 ° C. to prepare a magnesium alloy molded body. Sample No. The recrystallization temperature of the magnesium alloy constituting the magnesium alloy plate of No. 2 is 230 ° C. Therefore, the heating temperature is the sample No. It is equal to or higher than the recrystallization temperature of the magnesium alloy in 2. The magnesium alloy molded body has a box shape including a rectangular flat plate portion and a side wall portion erected from the flat plate portion. The size of the top plate was 100 mm × 50 mm, and the height of the side wall was 10 mm. The cracked state of the obtained magnesium alloy molded product was visually confirmed. As a result, no cracks were found in the magnesium alloy molded product.

Sample No. For the magnesium alloy plate of No. 2, the half width of the peak of the (0002) plane was measured by the X-ray diffraction method (XRD). The measurement was carried out using CuKαX-ray under the following conditions. The excitation conditions were 45 kV and 40 mA. The incident optical system was Bragg-Brentano HD (BBHD). The divergence slit was 1/4 °. The divergence prevention slit was set to 1 °. The light receiving optical system was set to 4 mrad with a solar slit. The operation method was a 2θ-θ scan. The measurement range was 2θ = 30 ° to 40 °. The step width was 0.0131 °. The integration time was 148.92 sec. As a result, the sample No. The magnesium alloy plate of No. 2 had a half width of the X-ray diffraction peak of 0.11140 °. That is, the sample No. The magnesium alloy plate of No. 2 had some distortion. Sample No. It is considered that since the magnesium alloy plate of No. 2 has a certain degree of distortion, it is easy to perform warm forming on the magnesium alloy plate, and the moldability by warm forming can be improved.

For reference, sample No. The half width of the peak of the (0002) plane was measured by XRD for the magnesium alloy plate of No. 2 whose strain was removed by annealing. The measurement conditions were the same as those described above. As a result, the half-value width of the X-ray diffraction peak of the magnesium alloy plate from which the strain after annealing was removed was 0.0587 °. From this, the sample No. It can be seen that the magnesium alloy plate of No. 2 has some distortion.

Sample No. 1. Sample No. Sample No. 3 to sample No. Regarding the magnesium alloy plate of No. 5, the sample No. A magnesium alloy molded product was produced by performing square drawing in the same manner as in 2. As a result, no cracks were found in any of the magnesium alloy molded bodies. All of the magnesium alloy plates have a half-value width of the X-ray diffraction peak of 0.07 ° or more and 0.40 ° or less, and have a certain degree of distortion, so that the magnesium alloy plate can be easily warm-formed. It is considered that the moldability by warm molding could be improved.

The present invention is not limited to these examples, but is indicated by the claims and is intended to include all modifications within the meaning and scope equivalent to the claims. For example, in the test example, the composition of the magnesium alloy, the cooling rate in the casting process, the rolling conditions in the rolling process, and the like can be appropriately changed.

1 Casting process, 2 Heat treatment process, 3 Rolling process, 4 Molding process 10 Magnesium alloy plate, 11 Mother phase, 12 Crystals 20 Corrosion products

Claims (14)

1. It is a magnesium alloy plate made of magnesium alloy.
   The magnesium alloy is
   A composition containing less than 2.00% by mass of aluminum and 1.00% by mass or less of manganese, with the balance being magnesium and unavoidable impurities.
   It has a structure in which crystals containing aluminum and manganese are dispersed.
   The maximum diameter of the crystallized product is 0.20 μm or more and 1.50 μm or less.
   Magnesium alloy plate.
2. The magnesium alloy plate according to claim 1, wherein aluminum is contained in an amount of 0.10% by mass or more.
3. The magnesium alloy plate according to claim 1 or 2, wherein manganese is contained in an amount of 0.10% by mass or more.
4. The magnesium alloy plate according to any one of claims 1 to 3, further comprising 0.10% by mass or more and 1.00% by mass or less of calcium.
5. The magnesium alloy plate according to any one of claims 1 to 3, further comprising 0.10% by mass or more and 2.00% by mass or less of zinc.
6. The magnesium alloy plate according to any one of claims 1 to 5, further comprising 0.10% by mass or more and 1.00% by mass or less of strontium.
7. The magnesium alloy plate according to any one of claims 1 to 6, wherein the number density of the crystallized products is 0.010 / μm ² or more and 0.060 / μm ^{2 or less.}
8. The magnesium alloy plate according to any one of claims 1 to 7, wherein the thermal conductivity is 100 W / m · K or more.
9. The magnesium alloy plate according to any one of claims 1 to 8, wherein the 0.2% proof stress is 200 MPa or more.
10. The magnesium alloy plate according to any one of claims 1 to 9, wherein the half width of the X-ray diffraction peak is 0.07 ° or more and 0.40 ° or less.
11. The magnesium alloy plate according to any one of claims 1 to 10 is included.
    Magnesium alloy molded body.
12. A casting process in which molten magnesium alloy is continuously cast by a double-roll casting method to produce a plate-shaped casting material.
    It is provided with a rolling process for producing a magnesium alloy plate by rolling the cast material.
    In the casting process,
    Prepare the magnesium alloy containing less than 2.00% by mass of aluminum and 1.00% by mass or less of manganese, the balance of which is magnesium and unavoidable impurities.
    The cooling rate of the molten metal is set to 800 ° C./sec or more.
    Manufacturing method of magnesium alloy plate.
13. A heat treatment step of heat-treating the cast material to homogenize it is provided between the casting step and the rolling step.
    The method for producing a magnesium alloy plate according to claim 12, wherein in the rolling step, the cast material heat-treated in the heat treatment step is rolled.
14. A molding step of warm-molding the magnesium alloy plate obtained by the method for producing a magnesium alloy plate according to claim 12 or 13 to produce a magnesium alloy molded body is provided.
    The temperature of the warm molding is set to 200 ° C. or higher and 300 ° C. or lower.
    A method for manufacturing a magnesium alloy molded product.

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