WO2016059950A1 - Magnesium alloy, magnesium alloy plate, magnesium alloy member, and method for producing magnesium alloy - Google Patents

Abstract

A magnesium alloy which contains, in mass%, from 1% to 12% (inclusive) of Al and from 0.1% to 5% (inclusive) of Mn, and which is provided with a structure wherein particles of a compound containing Al and Mn are dispersed. The average particle diameter of the particles of the compound is from 0.3 μm to 1 μm (inclusive), and the area ratio of the particles of the compound is from 3.5% to 25% (inclusive).

Description

Magnesium alloy, magnesium alloy plate, magnesium alloy member, and method for producing magnesium alloy

The present invention relates to a magnesium alloy suitable for a constituent material such as a casing or various parts, a magnesium alloy plate suitable for a material of a secondary processing material (primary processed material) such as a casing or various parts, a casing, The present invention relates to a magnesium alloy member suitable for secondary processing materials such as various parts, and a method for manufacturing a magnesium alloy. In particular, the present invention relates to a magnesium alloy, a magnesium alloy plate, and a magnesium alloy member that are excellent in impact resistance, mechanical properties, plastic workability, and productivity.

Magnesium alloys that are lightweight and have excellent specific strength and specific rigidity have been used as constituent materials for various parts such as casings for portable electronic and electrical devices such as mobile phones and notebook personal computers and automobile parts.

Magnesium alloy is light and high in specific strength among metals, has excellent shock absorption, and has excellent corrosion resistance by adding various elements to active Mg (magnesium). It is preferable for the constituent materials of various parts. In particular, an Mg—Al-based alloy containing Al (aluminum) is excellent in strength and corrosion resistance among magnesium alloys, and is preferable for the above constituent materials.

Patent Document 1 discloses a magnesium alloy plate made of a magnesium alloy containing Al and Mn (manganese) and having excellent impact resistance and mechanical properties not only at room temperature but also at low temperature.
This magnesium alloy sheet is very fine and contains very little, preferably substantially, a compound containing Al and Mn (mainly crystallized product, hereinafter sometimes referred to as Al-Mn crystallized product). do not do. For this reason, this magnesium alloy sheet is hardly cracked due to coarse Al—Mn crystallized matter, and is excellent in impact resistance and mechanical properties, and also in plastic workability such as press working.

JP 2011-006754 A

マ グ ネ シ ウ ム It is desired to develop a magnesium alloy that is excellent in impact resistance, mechanical properties such as strength and proof stress, elongation, and workability of plastic working such as rolling and pressing, and also excellent in productivity.

Although the magnesium alloy sheet disclosed in Patent Document 1 is excellent in impact resistance as described above, the molten metal temperature is raised to 700 ° C. in order to reduce Al—Mn crystallized matter. Here, the Al—Mn crystallized product is theoretically generated or grown most when the temperature of the molten magnesium alloy containing Al and Mn is around 630 ° C., particularly below 630 ° C. . Therefore, by making the temperature of the molten metal sufficiently higher than 630 ° C., preferably over 690 ° C., generation and growth of Al—Mn crystallized substances can be effectively prevented. However, when the temperature of the molten metal is increased, (α) the molten metal is likely to be oxidized, resulting in a decrease in yield due to the formation and mixing of oxides. (Β) When the atmosphere is set to a high vacuum to prevent oxidation, Mg becomes High vapor pressure makes it difficult to handle the molten metal, resulting in reduced workability. (Γ) Increases energy to maintain the molten metal at a high temperature. (Δ) Thermal degradation of equipment due to the high temperature of the molten metal. It is difficult to improve productivity from the viewpoint of speed. In addition, the points (α) to (δ) may increase the cost.

Therefore, one of the objects of the present invention is to provide a magnesium alloy that is excellent in impact resistance, mechanical properties, and plastic workability and also in productivity.

Another object of the present invention is to provide a magnesium alloy sheet that is excellent in impact resistance, mechanical properties, and plastic workability, and also in productivity.

Another object of the present invention is to provide a magnesium alloy member that is excellent in impact resistance and mechanical properties and also in productivity.

Another object of the present invention is to provide a method for producing a magnesium alloy, which can produce a magnesium alloy excellent in impact resistance, mechanical properties and plastic workability with high productivity.

The magnesium alloy according to one embodiment of the present invention contains, by mass%, Al 1% or more and 12% or less, Mn 0.1% or more and 5% or less, and a structure in which particles of a compound containing Al and Mn are dispersed. The average particle size of the particles of the compound is 0.3 μm or more and 1 μm or less, and the area ratio of the particles of the compound is 3.5% or more and 25% or less.

A method for producing a magnesium alloy according to one embodiment of the present invention includes a step of continuously casting a molten magnesium alloy containing, by mass%, Al in a range of 1% to 12% and Mn in a range of 0.1% to 5%. . In this manufacturing method, the temperature of the molten metal immediately before contacting the mold is set to 630 ° C. or higher and 690 ° C. or lower, and the cooling rate of the molten metal is set to 560 ° C./second or higher.

マ グ ネ シ ウ ム The magnesium alloy described above is excellent in impact resistance, mechanical properties, plastic workability and productivity. The above magnesium alloy production method can produce a magnesium alloy excellent in impact resistance, mechanical properties, and plastic workability with high productivity.

The upper figure is a micrograph (secondary electron image) obtained by observing the cross section of the magnesium alloy plate (sample No. 1-1) of the embodiment with a scanning electron microscope (SEM), and the lower figure is the secondary electron image. It is the binarized image which converted the contrast of the. 2 is a micrograph (reflection electron image) obtained by observing a cross section of the magnesium alloy plate (Sample No. 1-1) of the embodiment with an SEM. FIG. 4 is a composition mapping by a field emission electron microanalyzer (FE-EPMA) when the acceleration voltage of the electron gun is 15 kV for the cross section of the magnesium alloy plate (Sample No. 1-1) of the embodiment, and the concentration of Mn Show the distribution. 4 is a histogram showing the Mn concentration (Mn count number), the frequency of each concentration, and the cumulative frequency created using the composition mapping by FE-EPMA (15 kV) shown in FIG. 3. The left figure shows the composition mapping by FE-EPMA when the acceleration voltage of the electron gun is 5 kV for the cross section of the magnesium alloy plate (sample No. 1-1) of the embodiment, showing the Mn concentration distribution, The figure is a micrograph (backscattered electron image) obtained by observing the same region as the region where composition mapping has been performed with an SEM. 6 is a histogram showing the Mn concentration (Mn count number), the frequency of each concentration, and the cumulative frequency created using the composition mapping by FE-EPMA (5 kV) shown in FIG. 5. It is explanatory drawing explaining the test method of an impact resistance test.

The inventors have produced a magnesium alloy under various production conditions, particularly for a magnesium alloy containing Al and Mn as a composition excellent in strength and corrosion resistance, and have impact resistance, mechanical properties, and plastic working. The structure of magnesium alloy with excellent properties was investigated. As a result, if the compound containing Al and Mn (Al-Mn crystallized product) is present in a specific range and the compound has a size in a specific range, the amount of the compound is very small. In addition, the inventors have found that it has impact resistance, mechanical properties, and plastic workability comparable to those of a magnesium alloy that does not substantially exist. In other words, if the structure is relatively fine, uniformly dispersed, and contains a certain amount, the impact resistance of the same level as a magnesium alloy with very little or substantially no compound, It can be said that it has mechanical properties and plastic workability. In addition, the magnesium alloy having such a specific structure is subjected to a specific casting process in which continuous casting is performed, the temperature of the molten metal until it contacts the mold is as low as possible, and the cooling rate is extremely high. The knowledge that it can manufacture was acquired. This manufacturing method can reduce the above-mentioned problems (α) to (δ) that may occur when the molten metal is at a high temperature, thereby reducing impact resistance, mechanical properties, plastic working. It can be said that productivity of a magnesium alloy having excellent properties can be improved. The present invention is based on these findings. First, the contents of the embodiment of the present invention will be listed and described.

(1) A magnesium alloy according to an embodiment of the present invention is composed of mass%, containing 1% to 12% Al, 0.1% to 5% Mn, and particles of a compound containing Al and Mn. Provide a distributed organization. In this magnesium alloy, the average particle size of the particles of the compound is 0.3 μm or more and 1 μm or less, and the area ratio of the particles of the compound is 3.5% or more and 25% or less.

The average particle diameter of the particles of the above compound is measured using an observation image of an optical microscope.
The area ratio of the particles of the compound is measured for the cross section of the magnesium alloy using composition mapping by FE-EPMA when the acceleration voltage of the electron gun is 5 kV or 15 kV. Details of the measurement method will be described later.

マ グ ネ シ ウ ム The above magnesium alloy has excellent strength and corrosion resistance by containing Al and Mn in a specific range. In particular, the above magnesium alloy is fine although particles of a compound containing Al and Mn are present to some extent within a specific range. For this reason, the above magnesium alloy is unlikely to be a starting point for cracks when subjected to impacts such as dropping, or plastic processing such as rolling or pressing, and mechanical properties such as strength, proof stress, and elongation. Excellent properties, impact resistance and plastic workability. In addition, it can be said that the magnesium alloy has a dispersion strengthened structure in which particles of the fine compound are dispersed. By increasing the yield strength by the dispersion strengthened structure, it is difficult to dent due to the impact. Excellent. And said magnesium alloy which has said specific composition and structure | tissue is excellent also in productivity by being able to manufacture through the specific casting process mentioned later, for example.

(2) As an example of the magnesium alloy, a form in which the maximum diameter of the particles of the compound is less than 2.5 μm can be given.

In the above form, even if there are some particles of a compound containing Al and Mn, all the particles are sufficiently small. Therefore, the above-mentioned form is less likely to cause cracks starting from coarse compound particles, and is excellent in impact resistance, mechanical properties such as strength and proof stress, elongation, and plastic workability.

(3) の 一 As an example of the magnesium alloy, there is a form in which the average crystal grain size of the magnesium alloy is 10 μm or less.

Since the crystal itself is fine, the above-described form is less likely to cause cracks starting from coarse crystal grains, and is excellent in impact resistance, mechanical properties such as strength and proof stress, elongation, and plastic workability.

(4) A magnesium alloy sheet according to an aspect of the present invention is made of the magnesium alloy according to any one of the above (1) to (3).

Since the magnesium alloy plate, which is an example of the magnesium alloy, is composed of the magnesium alloy having the specific structure described above, the mechanical properties such as impact resistance, strength, proof stress, and elongation, press working, etc. In addition to excellent workability for plastic working, it also excels in productivity. Such a magnesium alloy plate as described above can be suitably used as a material for a secondary processed material (for example, a magnesium alloy member described later) subjected to plastic processing such as press processing.

(5) A magnesium alloy member according to one aspect of the present invention is made of a magnesium alloy according to any one of the above (1) to (3), and has a plastic working portion at least partially subjected to plastic working. .

Since the magnesium alloy member, which is an example of the magnesium alloy, is composed of the magnesium alloy having the specific structure described above, it has excellent mechanical properties such as impact resistance, strength, proof stress, and elongation. Excellent productivity. The magnesium alloy member is also excellent in productivity from the viewpoint that cracks and the like are not easily generated when plastic working such as press working is performed.

(6) A method for producing a magnesium alloy according to an embodiment of the present invention is a method of continuously casting a molten magnesium alloy containing 1% to 12% Al and 0.1% to 5% Mn by mass%. A process is provided. In this manufacturing method, the temperature of the molten metal immediately before contacting the mold is set to 630 ° C. or higher and 690 ° C. or lower, and the cooling rate of the molten metal is set to 560 ° C./second or higher.

は The magnesium alloy production method described above can produce a magnesium alloy having excellent strength and corrosion resistance by using a molten magnesium alloy containing Al and Mn in a specific range. In particular, in the above-described magnesium alloy manufacturing method, the temperature of the molten metal is made lower than before, and the cooling rate is very high while maintaining a temperature at which a compound containing Al and Mn (Al-Mn crystallized product) is easily generated. By making it faster, the time during which the material in the solidification process is held at around 630 ° C. can be shortened. As a result, the above-described method for producing a magnesium alloy can generate an appropriate amount of Al-Mn crystallized material in the alloy, and suppress the growth of Al-Mn crystallized particles, so that relatively fine Al-Mn crystallized material can be produced. —Mn crystallized particles, typically Al—Mn crystallized particles having an average particle size of 1 μm or less. Further, in the above magnesium alloy manufacturing method, such fine Al—Mn crystallized particles can be uniformly dispersed.

Here, even if the temperature of the molten metal is high, if the cooling rate is slow, the Al—Mn crystallized particles grow, resulting in a structure in which coarse grains having a maximum diameter of 2.5 μm or more are unevenly distributed. This coarse grain can be a starting point for cracks and the like. In addition, since Al and Mn are contained in coarse particles, the amount of Al and Mn necessary for the fine particles cannot be secured, and the fine particles cannot be sufficiently present. It is thought that the strengthening effect cannot be obtained properly. Therefore, a magnesium alloy in which such coarse Al—Mn crystallized substances are present locally can cause a decrease in impact resistance, mechanical properties, and plastic workability. On the other hand, the above-mentioned magnesium alloy manufacturing method has improved mechanical properties such as strength and proof strength and impact resistance by dispersion strengthening of Al-Mn crystallized particles, which are usually harder than the parent phase magnesium alloy. Excellent magnesium alloy can be manufactured. In addition, since the magnesium alloy production method described above can make Al—Mn crystallized particles fine, and the fine particles are unlikely to become the starting point of cracking, etc., it has improved toughness such as elongation, impact resistance, and plastic workability. Excellent magnesium alloy can be produced.

Further, the above-described magnesium alloy manufacturing method is such that the temperature of the molten metal is relatively low, so that (α ′) the oxidation of the molten metal can be easily suppressed, and the decrease in yield due to the oxide can be reduced. (Γ ′) can reduce energy required for heat insulation of the molten metal, and (δ ′) can reduce thermal deterioration of the production equipment. In addition, the magnesium alloy production method described above is capable of mass production of magnesium alloys because continuous casting is performed, and also because it is easy to make a fine crystal structure by increasing the cooling rate, impact resistance, mechanical properties, It is easy to produce a magnesium alloy excellent in plastic workability. From these points, it can be said that the above magnesium alloy production method can produce a magnesium alloy excellent in impact resistance, mechanical properties, and plastic workability with high productivity.

[Details of the embodiment of the present invention]
Hereinafter, a magnesium alloy, a magnesium alloy plate, a magnesium alloy member, and a method for producing a magnesium alloy according to embodiments of the present invention will be described in order. Hereinafter, the unit of element content is mass%.

(Magnesium alloy, magnesium alloy plate, magnesium alloy member)
-Composition The magnesium alloy of the embodiment is characterized by having a composition containing at least both Al and Mn as additive elements. If a specific amount of a compound (Al—Mn crystallized product) containing Al and Mn having a specific size can be generated in the manufacturing process, it may contain a second additive element described later in addition to the composition containing Al and Mn. it can. In any composition, the balance is Mg and inevitable impurities, and the Mg content is more than 50%.

含有 Al content is 1% or more and 12% or less. By containing Al in this range, mechanical properties such as strength and corrosion resistance are particularly excellent. The more the Al content is in the above range, the better the strength and corrosion resistance. Therefore, the Al content can be 3% or more, 5% or more, 5.5% or more, or 7% or more. A magnesium alloy having an Al content of not less than 8.3% and not more than 9.5%, for example, an ASTM standard AZ91 alloy is compared with a magnesium alloy having an Al content of about 3%, for example, an ASTM standard AZ31 alloy. Therefore, it is further excellent in mechanical properties and corrosion resistance. On the other hand, the Al content tends to be easier to perform plastic working such as bending as the content is smaller in the above range, and can be 7% or less, and further 4% or less. Examples of the Al content that is excellent in balance between strength and workability include 5.5% to 12%. A part of Al in the alloy typically exists as a compound such as a compound containing Al and Mn, an intermetallic compound such as a compound containing Al and Mg, and the other part exists as a solid solution in Mg. .

Mn content is 0.1% or more and 5% or less. By containing Mn in this range, the corrosion resistance is excellent. The Mn content can be set to 0.15% or more because the corrosion resistance increases as the content increases in the above range. As the Mn content increases, a compound containing Al and Mn is more likely to be produced, or it is easier to grow, so that the solid solution amount of Al is reduced or coarse compound particles are likely to exist. 2% or less, 1.5% or less, and further 1% or less. If the Mn content is 0.2% or more and 0.5% or less, it is expected that the excessive production and growth of the compound can be effectively suppressed.

As the second additive element, Zn (zinc), Ca (calcium), Si (silicon), Be (beryllium), Sr (strontium), Y (yttrium), Ag (silver), Sn (tin), Zr ( Examples thereof include one or more elements selected from zirconium), Ce (cerium), Au (gold), and rare earth elements (excluding Y and Ce). Specifically, the contents of Zn are 0.2% to 7.0%, Ca is 0.2% to 6.0%, Si is 0.2% to 1.0%, and Be is 0.00%. 0001% to 0.002%, Sr is 0.2% to 7.0%, Y is 1.0% to 6.0%, Ag is 0.5% to 3.0%, Sn is 0.01% or more and 2.0% or less, Zr is 0.1% or more and 1.0% or less, Ce is 0.05% or more and 1.0% or less, and rare earth elements (excluding Y and Ce) are 1.0%. % Or less and 3.5% or less.

場合 When the second additive element is contained, the element group can contain only one element or a combination of two or more elements. When the second additive element is contained, mechanical properties such as strength and elongation (for example, Zn, Zr, etc.), high temperature strength and creep resistance (for example, Si, rare earth elements, Ag, etc.), flame retardancy (for example, , Ca, etc.) and the like are excellent, and effects such as refinement of crystals and suppression of hot cracking (eg, Zr) can be achieved. Even in the composition containing the second additive element, Al and Mn are contained in the specific range described above, and in particular, the specific size including Al and Mn is manufactured under the specific manufacturing conditions described later. And a magnesium alloy in which particles of these compounds are uniformly dispersed.

As a more specific composition of the magnesium alloy containing Al and Mn, for example, the following may be mentioned.
・ AM-based alloys (AM60 alloy, AM100 alloy, etc.) according to ASTM standards
-ASTM standard AZ alloys (AZ61 alloy, AZ80 alloy, AZ81 alloy, AZ91 alloy, etc.)

The AZ alloy contains 0.2% or more and 1.5% or less of Zn as a second additive element in addition to Al and Mn. The AZ-based alloy tends to have excellent mechanical properties such as strength and proof stress and corrosion resistance as the Al content increases, and the plastic workability tends to improve as the Al content decreases.

Structure The magnesium alloy according to the embodiment is made of a compound containing Al and Mn, and has a structure in which relatively fine particles are uniformly dispersed. A compound containing Al and Mn is a crystallized product produced mainly during casting. This crystallized product has high hardness, and once produced, it is difficult to change the size and content in the subsequent manufacturing process. Then, the magnesium alloy of embodiment controls the magnitude | size and content of the said compound (crystallized substance) by setting it as the specific casting conditions mentioned later, for example.

.. Composition of Compound Examples of the compound containing Al and Mn include an intermetallic compound containing only Al and Mn, and an intermetallic compound further containing iron (Fe) in addition to Al and Mn. Fe contained in the latter intermetallic compound is an inevitable impurity. The composition of these compounds can be confirmed by performing component analysis by, for example, energy dispersive X-ray analysis (EDX) or Auger electron spectroscopy (AES).

.. Compound size A compound containing Al and Mn exists as particles in the matrix of the magnesium alloy of the embodiment. The average particle size of the particles of this compound is 0.3 μm or more and 1 μm or less. When the average particle diameter is within this range, the compound particles function well as a structure-strengthening dispersion material and are unlikely to become a starting point of cracking, and are excellent in impact resistance, mechanical properties, and plastic workability. The average particle diameter can be 0.3 μm or more and 0.9 μm or less, and further 0.35 μm or more and 0.8 μm or less.

The maximum diameter of the compound containing Al and Mn is preferably less than 2.5 μm. Due to the absence of coarse particles of 2.5 μm or more, cracks and the like starting from such coarse particles are unlikely to occur, and the deterioration of impact resistance, mechanical properties, and plastic workability caused by these coarse particles can be suppressed. . Moreover, the fall of content of the fine grain by presence of the said coarse grain can be suppressed, and a fine grain can be included appropriately. From these things, it can be set as the magnesium alloy excellent in impact resistance, mechanical characteristics, and plastic workability. The smaller the compound is, the smaller the coarse particles that become the starting point of cracks and the like, and the fine particles tend to be appropriately present. Therefore, the maximum diameter is 2 μm or less, further 1.5 μm or less, 1.2 μm or less, further 1 μm or less Is preferred. When the average particle diameter of the compound is in the above-mentioned range and the maximum diameter of the compound is less than 2.5 μm, preferably 2 μm or less, the variation in the size of the compound is small and it can be said that the compound has a uniform size. Therefore, this form can also suppress variation in characteristics due to variation in size of the compound, and can have favorable characteristics.

-Content of compound The content of the compound containing Al and Mn takes a cross section of the magnesium alloy and is defined by the area ratio of the compound in the cross section, and is 3.5% or more and 25% or less. When the area ratio is 3.5% or more, the compound is sufficiently present in the magnesium alloy, and the dispersion strengthening effect by the particles of the compound can be favorably obtained. When the area ratio is 25% or less, the above-described compound is appropriately present, and the brittleness of the alloy due to the presence of the above-described compound is suppressed, and the corrosion resistance is decreased due to the decrease in the amount of Al solid solution. Excellent in impact resistance, mechanical properties, and plastic workability.

The area ratio is measured as follows. A cross section of the magnesium alloy is taken, and the following observation visual field (for example, a square region of 195 μm × 195 μm) is taken from this cross section, and composition mapping by FE-EPMA is performed on this observation visual field to obtain a concentration distribution of Mn. Then, it is estimated that Mn in the observation field substantially exists as a compound containing Al and Mn, and the area ratio of Mn with respect to the observation field is regarded as the area ratio of the compound containing Al and Mn. That is, the area ratio of the compound is determined using the concentration distribution of Mn by the composition mapping. A specific calculation method will be described later.

The observation field of view is selected from the surface layer region, which is a region up to 30% of the thickness of the magnesium alloy from the surface of the magnesium alloy to the inside. The reason for selecting the observation visual field from the surface layer region is that a region where a crack or the like occurs or a region which receives an impact such as a drop directly is usually considered to be the surface layer region.

The Mn concentration distribution changes depending on the acceleration voltage of the electron gun used for FE-EPMA, and the greater the acceleration voltage, the larger the amount of information to be acquired, and the higher the Mn concentration (level). That is, the size of the area ratio can be changed depending on the size of the acceleration voltage. Therefore, in measuring the area ratio, the acceleration voltage of the electron gun is set to 15 kV or less.
For example, when the electron gun acceleration voltage is 15 kV and the composition mapping is performed by FE-EPMA on the observation field of the cross section, the area ratio is 9.5% or more, more preferably 10% or more and 25% or less, and 15% or more and 24%. % Or less.
For example, when the accelerating voltage of the electron gun is 5 kV and the composition mapping by FE-EPMA is performed on the observation field of the cross section, the area ratio is 3.5% or more and 15% or less, and further 4.0% or more and 12% or less. 5.0% or more and 10% or less.

..Crystal grain size As an example of the magnesium alloy of the embodiment, a form having a fine crystal structure may be mentioned. For example, a structure satisfying an average crystal grain size of 10 μm or less can be given. If the average crystal grain size is 10 μm or less, coarse crystal grains are substantially absent, and cracks due to coarse crystal grains can be reduced. Accordingly, this form is superior in impact resistance, mechanical properties such as strength and elongation, and plastic workability. The smaller the crystal grain, the more effectively the cracks caused by the coarse crystal grain can be reduced. For example, the average crystal grain size can be 6 μm or less, particularly 4 μm or less. The lower limit of the average crystal grain size is, for example, 2 μm, and further 1 μm. In order to reduce the crystal grain size, it is effective to perform plastic working such as rolling after casting. That is, typical examples of the magnesium alloy having a fine crystal structure include a rolled plate and a pressed material obtained by pressing the rolled plate. In addition, if the cooling rate in the casting process is increased (560 ° C./second or more, further 600 ° C./second or more) or the second additive element described above is included, it is expected that the crystal grain size can be made finer. Is done.

Specification differentiated from manufacturing process Specific specifications of the magnesium alloy of the embodiment are distinguished from the manufacturing process. (1) Cast material, (2) Cast material subjected to plastic processing (primary processing) such as rolling 1 Next processed materials (rolled materials, etc.), (3) Treated materials obtained by subjecting the primary processed materials to various treatments, such as heat treatment and anticorrosion treatment (chemical conversion treatment, anodizing treatment) for polishing, straightening, distortion removal, etc. ), Decorative processing (cutting and etching such as diamond cutting and hairline, shot blasting, etc.), painting processing, and (4) plastic processing (secondary processing) such as press processing on the primary processing material and the above processing materials. Secondary processed material (magnesium alloy member of the embodiment), (5) surface treatment material (magnesium alloy member of the embodiment) obtained by subjecting the secondary processed material to surface treatment such as anticorrosion treatment, painting, and decoration processing. Cited . Primary processed materials such as rolled materials and the above-mentioned treated materials are suitable for materials of secondary processed materials such as press-worked materials because the average crystal grain size is smaller than that of cast materials and cracks are less likely to occur as described above. Available to: The primary work material is typically subjected to plastic working on the whole, and the whole can be said to be a plastic working portion. The secondary processed material has a form (for example, a press-worked material having a curved portion) in which only a part of the material is subjected to plastic working, and a form in which plastic working is performed over the entire material ( For example, a processed material bent into a cylindrical shape or the like.

-Shape As a specific shape of the magnesium alloy of the embodiment, for example, a plate material (a magnesium alloy plate of the embodiment) provided with a pair of parallel one surface and the other surface may be mentioned. The one surface and the other surface are typically flat surfaces, but can be curved by applying a process such as bending. The planar shape of the plate material is typically a rectangular shape, but can be circular or other shapes by punching or the like. When the plate material is distinguished from the above manufacturing process, (1) cast material, (2) primary processed material (rolled plate, etc.), (3) treated material, (4) secondary processed material, (5) surface treated material. Either of these can be taken. Specific examples of the shape of the secondary processed material include a cross-sectional member (a member having a plate portion) including a bottom surface portion and a side wall portion erected from the bottom surface portion.

-When the magnesium alloy of the embodiment is a plate material (magnesium alloy plate of the embodiment), or a member (magnesium alloy member of the embodiment) in which plastic working such as pressing is performed on at least a part of the plate material, The form whose thickness is 5 mm or less is mentioned. The thickness of the plate means the average distance between the one surface and the other surface. When the plate material undergoes plastic working such as rolling, that is, when it is a primary work material or a secondary work material, the thickness is likely to be uniform throughout, and the thickness is further reduced. Easy to do. For example, the form whose thickness is about 3 mm or less and also 2.5 mm or less is mentioned. The thicker the plate, the better the strength and rigidity. As the thickness of the plate material is thinner (preferably 2 mm or less, further 1.5 mm or less, and further 1.2 mm or less), a thin and light primary processed material or secondary processed material can be obtained. The lower limit of the thickness of the plate material is 0.1 mm or more, and further 0.3 mm or more. The thickness of the finally obtained plate material may be selected by adjusting casting conditions, rolling conditions, and the like according to the desired application. In addition to a form having a uniform thickness over the entire plate material or member, a form having a portion having a different thickness (for example, a form having a through-hole, a form having a groove or a protrusion) can be used.

-Characteristics The magnesium alloy of the embodiment is excellent in mechanical characteristics such as strength, yield strength, and elongation. For example, as an example of the magnesium alloy of the embodiment, at least one, preferably three, having a tensile strength (room temperature) of 270 MPa or more, a 0.2% proof stress (room temperature) of 200 MPa or more, and a breaking elongation (room temperature) of 5% or more. A form that satisfies all three conditions can be mentioned. Examples of such a form include those subjected to plastic processing such as rolling as described above, that is, primary processed materials and secondary processed materials. Although it depends on the composition and manufacturing process, the tensile strength is 280 MPa to 450 MPa and the 0.2% proof stress is 230 MPa to 350 MPa by containing 5% or more of Al or undergoing plastic processing such as rolling. The elongation at break can satisfy at least one, preferably all three, of 5% or more and 15% or less.

The magnesium alloy of the embodiment is difficult to dent when subjected to impact such as dropping. For example, when the impact resistance test described later is performed, the amount of dents is small and satisfies less than 0.63 mm. When the magnesium alloy of the embodiment has undergone plastic working such as rolling as described above, that is, when it is a primary work material or a secondary work material, the amount of dent is further reduced to 0.6 mm or less, and further to 0.55 mm. Satisfies the following:

(Manufacturing method of magnesium alloy)
The method for producing a magnesium alloy according to the embodiment includes a specific casting step in order to form a structure having a specific size and a specific amount of a compound having a specific composition called a compound containing Al and Mn. One of the features. Specifically, this casting process has three conditions: (1) continuous casting, (2) a relatively low temperature of the molten metal, and (3) a very high cooling rate of the molten metal. . Hereinafter, the casting process will be described in detail, and then the processes after casting will be described.

-Casting process-Continuous casting In the magnesium alloy manufacturing method of the embodiment, a molten magnesium alloy having a specific composition containing Al and Mn in the specific range described above is prepared and continuous casting is performed. Continuous casting is capable of rapid solidification, which can reduce oxides, segregation, etc., easily reduce the formation of coarse crystals, and control the compound containing Al and Mn to the specific size described above. easy. Specific examples of the continuous casting method include a twin roll method. The twin roll method is suitable for the production of cast plates. In the twin roll method, the cooling rate is reduced by reducing the thickness of the cast plate (preferably 5 mm or less), lowering the roll temperature (preferably 100 ° C. or less), adjusting the material of the roll, etc. Speeded up.

.. Molten metal temperature The temperature of the molten metal immediately before coming into contact with the mold is 630 ° C. or higher and 690 ° C. or lower. The reason for defining the lower limit is that when the temperature of the molten metal is lower than 630 ° C., a compound containing Al and Mn is very easily generated. The reason for defining the upper limit is that if the temperature exceeds 690 ° C., the molten metal temperature is too high, leading to a decrease in productivity. By setting the temperature of the molten metal within the above range, a compound containing Al and Mn can be satisfactorily produced during the solidification process, and an appropriate amount (the above-mentioned specific content) can be obtained. In order to sufficiently produce the compound, the temperature of the molten metal is preferably as low as possible, preferably 685 ° C. or lower, more preferably 680 ° C. or lower, and further 675 ° C. or lower. When the temperature of the molten metal is 635 ° C. or higher, further 640 ° C. or higher, and further 645 ° C. or higher, excessive formation and coarsening of the compound can be easily suppressed, and the content and size of the compound can be easily controlled. From this point, productivity is expected to be improved. Since the melting temperature tends to increase as the Al content decreases, the temperature of the molten metal is adjusted within the above range according to the composition.

The molten metal is held in facilities such as a melting furnace, a transfer rod, and a holding furnace until it comes into contact with the casting mold. If the temperature of the molten metal in the facility for holding the molten metal is made uniform, that is, a temperature selected from a range of 630 ° C. or higher and 690 ° C. or lower, temperature control is easy to perform. In addition, since this temperature range is lower than that in the prior art, it is easy to suppress thermal damage to the equipment, and the life of the equipment can be extended. From this point, improvement in productivity and cost reduction can be expected.

..Cooling rate The above-mentioned relatively low-temperature molten metal is rapidly cooled at a cooling rate of 560 ° C./second or more. By performing such rapid cooling, in the solidification process, the retention time in the vicinity of 630 ° C., which is a temperature range in which a compound containing Al and Mn is likely to be generated, is sufficiently shortened, so that excessive generation and coarsening of the compound can be achieved. It can suppress effectively and can form the structure | tissue in which the said comparatively fine said compound exists to some extent favorably. The higher the cooling rate, the better. The cooling rate can be 600 ° C./second or more, 620 ° C./second or more, and further 650 ° C./second or more. The cast material obtained by performing such rapid solidification has a dispersion strengthened structure in which at least the surface layer region is uniformly dispersed with the above-mentioned compound having the above-mentioned specific size, and the crystal has a fine structure. .

The cooling rate is calculated using DAS (dendrite arm spacing). Here, regarding the magnesium alloy, when α and β are constants based on the composition, d (μm) is DAS, and V (° C./second) is the cooling rate, the following relational expression (1) can be used.
d = α × V ^−β (1)
For example, in the ASTM standard AZ alloy, α = 35.5 and β = 0.31 in the relational expression (1), and the cooling rate V _AZ is expressed as follows, with DAS being expressed as d _AZ. .
d _AZ = 35.5 × V _AZ ^−0.31
Using test pieces of various compositions and sizes (thickness, width, etc.), the relationship between DAS and cooling rate is obtained in advance, and correlation data is created. When the cooling conditions are adjusted so that the cooling rate is achieved, the workability is excellent.

Examples of methods for realizing a cooling rate of 560 ° C./second or more include the following. (1) Lower the surface temperature of the mold (for example, 100 ° C. or lower, and further 80 ° C. or lower). For example, by using a mold capable of forced cooling such as water cooling, the surface temperature of the mold can be kept low. (2) Reduce the size of the cast material. For example, in a cast plate, the thickness is 5 mm or less, further 4.5 mm or less, and further 4 mm or less. (3) A mold made of a material having a high cooling capacity is used. For example, if a mold made of a material having high thermal conductivity is used, the cooling rate can be increased because of excellent heat dissipation.

The casting process (including the cooling process) is preferably performed in an inert gas atmosphere in order to prevent oxidation of the magnesium alloy.

-Process after casting-Rolling process When the magnesium alloy of the embodiment is used as a rolled material (typically a rolled plate), the above-mentioned cast material (typically a cast plate) is subjected to a rolling process of at least one pass. . That is, as an example of the manufacturing method of the magnesium alloy of the embodiment, the above-described casting process, and a process of rolling at least one pass on the cast material obtained by continuous casting (hereinafter sometimes referred to as a rolling process). The form provided is mentioned. At least one pass is preferably warm rolling at a rolling temperature of 200 ° C. or higher and 400 ° C. or lower. The number of passes in the rolling process, the rolling reduction per pass, the total rolling reduction, and the like can be appropriately selected so as to obtain a rolled sheet having a desired thickness. By rolling the cast material, a rolled structure (typically a recrystallized structure) can be formed instead of a cast structure. Also, by rolling, (1) a fine structure with an average crystal grain size of 20 μm or less, more preferably 10 μm or less is easily obtained, (2) internal defects such as segregation, shrinkage nests and voids (pores) during casting, surface It is also possible to expect the effect that excellent surface properties can be obtained by reducing defects and the like, and (3) the strength and corrosion resistance can be further improved by forming a fine recrystallized structure. A rolled sheet that has undergone such a rolling process has at least a surface region having a finer crystal structure and the above-mentioned specific size, and a compound containing Al and Mn is uniformly dispersed. Has a dispersion strengthened organization. After the rolling step, it can be provided with a step of performing at least one additional processing such as the above-described polishing, correction, anticorrosion treatment, painting, decoration processing, heat treatment for distortion removal and the like.

.. Secondary processing step When the magnesium alloy of the embodiment is used as a plastic processing member, plastic processing is performed on at least a part of the rolled plate (which may be subjected to additional processing such as polishing or correction). That is, as an example of the manufacturing method of the magnesium alloy of the embodiment, the above-described casting step, the above-described rolling step, and a step of performing plastic working (secondary processing) on at least a part of the material that has undergone the rolling step are provided. A form is mentioned.

Specific plastic processing (secondary processing) includes press processing (deep drawing processing, punching processing, upsetting, etc.), forging processing, bending processing, and the like. If this plastic working is warm working at a working temperature of 200 ° C. or higher and 280 ° C. or lower, the plastic workability of the material (typically, the rolled sheet) is improved and the plastic working (secondary work) can be performed with high accuracy. It is preferable. Moreover, when it is set as warm processing, it can reduce that a structure | tissue of a raw material turns into a coarse recrystallized structure, and can reduce deterioration of a mechanical characteristic or corrosion resistance. Plastic processing (secondary processing) can be performed on only a part of the material or on the whole. After the secondary processing step, there can be provided a step of performing at least one additional processing such as the above-described polishing, anticorrosion processing, coating, decoration processing, heat treatment for the purpose of distortion removal and the like.

Hereinafter, with reference to test examples, the magnesium alloy of the embodiment and the manufacturing method thereof will be described more specifically.

[Test Example 1]
Using magnesium alloys having various compositions shown in Table 1, a magnesium alloy plate under various conditions, and pressing the magnesium alloy plate to produce a pressed material, observing the structure of the obtained magnesium alloy plate, Tensile tests (room temperature), impact resistance tests (room temperature), press workability confirmation, and productivity pass / fail judgment were performed.

Content of each element shows a mass ratio (mass%).
-AZ91 shown in Table 1 is a magnesium alloy containing Al, Mn, Zn corresponding to ASTM standard AZ91 alloy. Here, 9.1% of Al, 0.16% of Mn, and 0.72% of Zn are contained.
AZX911 shown in Table 1 is a magnesium alloy containing Al, Mn, Zn corresponding to ASTM standard AZ91 alloy and further containing Ca. Here, 9.0% Al, 0.16% Mn, 0.74% Zn, and 1.0% Ca are included.
-AZ61 shown in Table 1 is a magnesium alloy containing Al, Mn, Zn corresponding to ASTM standard AZ61 alloy. Here, 6.1% Al, 0.22% Mn, and 0.70% Zn are included.
-AM60 shown in Table 1 is a magnesium alloy containing Al and Mn corresponding to ASTM standard AM60 alloy. Here, 6.2% Al and 0.20% Mn are included.

Here, through a manufacturing process of twin roll continuous casting → rolling → press processing, a cast plate (magnesium alloy plate), a rolled plate (magnesium alloy plate), and a pressed material (magnesium alloy member) were produced. Specifically, magnesium alloy ingots having various compositions shown in Table 1 are melted in an inert atmosphere to prepare a molten metal. Table 1 shows the temperature of the molten metal immediately before contact with the mold (hereinafter referred to as hot water temperature, ° C.). Here, using a facility comprising a melting furnace, a holding furnace for holding the molten metal, and a transfer unit that transfers the molten metal from the holding furnace to a mold (a pair of rolls), the temperature of the molten metal in the transfer unit is referred to as the “hot water temperature”. To do. The temperature of the molten metal in the transfer section is the set temperature of the equipment. This molten metal is brought into contact with a mold (roll) and solidified to produce a cast plate having a thickness of 5.0 mm.

Table 1 shows the cooling rate (° C./sec) in the casting process. Sample No. 1-1-No. 1-5, No. 1 1-101, no. In 1-201, the cooling rate was changed by adjusting the roll temperature, roll peripheral speed, casting speed, and the like. Sample No. 1-1-No. 1-5, No. 1 In 1-101, casting is performed using a water-cooled mold while cooling the roll so that the roll temperature is 100 ° C. or lower.

Each of the obtained cast plates is subjected to multiple passes of warm rolling to produce a rolled plate having a thickness of 0.7 mm. The conditions for warm rolling are a rolling temperature of 200 ° C. or more and 400 ° C. or less, a rolling reduction per pass of 5% or more and 20% or less, and a total rolling reduction of 86%.

Each obtained rolled plate is cut into 200 mm × 30 mm to be used as a press material. This material is subjected to press processing (square drawing), and includes a top plate portion and leg portions extending from the top plate portion. [A shaped press-work material is produced. The pressing conditions are a heating temperature of 250 ° C. and an angle R connecting the top plate and the leg is 2 mm.

The cast plate after continuous casting is subjected to a heat treatment (solution treatment) or an aging treatment for homogenizing the composition, an intermediate heat treatment during the rolling, or a final heat treatment after the final rolling. Can be. Further, the flatness can be improved by correcting the rolled plate, or the surface can be smoothed by polishing.

-Microstructure observation About the rolling plate of each obtained sample, the metal structure was observed as follows. A section (longitudinal section) is taken by cutting along a plane parallel to the thickness direction of the rolled sheet. This cross section is a CP cross section performed using a commercially available cross section polisher (CP) processing apparatus. With respect to this CP cross section, a region from the surface to 30% of the plate thickness is defined as a surface layer region (here, 0.7 mm × 0.3 = 0.21 mm), and an observation field of view is arbitrarily taken from the surface layer region. The upper diagram in FIG. For the rolled sheet of 1-1, a secondary electron image obtained by observing the selected observation field with an SEM is shown, and the following figure shows a binary image obtained by binarizing the secondary electron image. FIG. 2 shows a backscattered electron image obtained by observing a selected observation field with an SEM.

As shown in the upper diagram of FIG. 1, it can be seen that a large number of large and small grains are dispersed in a fine crystal structure. Specifically, it can be seen that there are relatively large grains (maximum length of about 0.1 μm to 1 μm) shown in light gray and relatively small grains shown in white. When component analysis of these grains was performed, relatively large grains (light gray) are compounds containing Al and Mg (β phase, mainly precipitates), and grains smaller than the β phase (white) are It is a compound containing Al and Mn (Al-Mn crystallized product). When the contrast is converted as shown in the lower diagram of FIG. 1 so that the existence state of the white grains can be easily grasped, it can be seen that the white grains are uniformly dispersed in the crystal structure. It can also be seen that white grains are present to some extent although they are smaller than the β phase and less in amount than the β phase. This point can also be grasped from FIG. Also in the SEM reflected electron image shown in FIG. 2, there are light gray particles and white particles, white particles are smaller than light gray particles and less in amount than light gray particles, but are present to some extent. I understand that. From these facts, sample no. The rolled plate 1-1 has a relatively small amount of a compound containing Al and Mn (Al—Mn crystallized product), but it is present in a certain amount and is uniformly dispersed. I understand. Sample No. 1-2 to No. The rolled plate of 1-5 is also sample no. A structure similar to that of the rolled sheet 1-1, that is, a fine crystal structure, in which a relatively small amount of a relatively small Al—Mn crystallized substance exists and is uniformly dispersed.

Sample No. The rolled sheet of 1-101 has very little compound containing Al and Mn (Al-Mn crystallized product). Sample No. The rolled plate of 1-201 has very few compounds containing Al and Mn, but has coarse particles.

The average crystal grain size was measured using the observation image of an optical microscope with respect to the rolling plate of each obtained sample. The results are shown in Table 1. The measurement of the average crystal grain size was performed based on “steel—microscopic test method of crystal grain size JIS G 0551 (2005), cutting method using linear test line”. When a straight line was drawn in the observed image in parallel with the thickness direction of the rolled plate and the line segment that cuts the straight line in the crystal grain was examined as the grain size, Sample No. 1-1-No. The average crystal grain size of the 1-5 rolled sheet is 10 μm or less. From this, sample no. 1-1-No. It can be seen that all the 1-5 rolled sheets have fine crystal grains.

About the obtained rolled plate of each sample, the above white grains were extracted as a compound containing Al and Mn (Al-Mn crystallized product) from the SEM image (binarized image obtained by converting the secondary electron image), The average particle diameter (μm) and maximum diameter (μm) of the extracted Al—Mn crystallized particles were examined. The results are shown in Table 1. The particle diameter of the Al—Mn crystallized product is the diameter of all particles present in the observation field (here, a 195 μm × 195 μm square region selected from the above-mentioned surface layer region), where the equivalent circle of the extracted particles is the diameter. Is the average particle size of the Al—Mn crystallized product. Further, among all the above-mentioned particle diameters, the largest value is the maximum diameter of the Al—Mn crystallized product.

About the obtained rolled plate of each sample, composition mapping by FE-EPMA was created for the observation visual field selected from the CP cross section described above, and the Mn concentration distribution was examined. Here, the concentration of Mn was analyzed under two conditions with different acceleration voltages of the electron gun. The conditions are shown below.
(1) Acceleration voltage of electron gun: 15 kV, irradiation current: 100 nA, measurement time: 50 ms, measurement element: Mn (LiFH), measurement area: square area of 195 μm × 195 μm (2) acceleration voltage of electron gun: 5 kV, Irradiation current: 100 nA, measurement time: 500 ms, measurement element: Mn (TAPH), measurement area: square area of 24 μm × 24 μm Condition (2) where the acceleration voltage is small is smaller than condition (1). However, even when the measurement area of the condition (2) is the same size as that of the condition (1), it has been confirmed that there is no significant difference in the measurement result (Mn concentration distribution).

FIG. FIG. 5 is a composition mapping of Mn by FE-EPMA when the condition (1) with an acceleration voltage of 15 kV is used for the rolled sheet of 1-1. The color scale is shown on the right side of FIG. This composition mapping expresses the density of Mn by white, pink, red, orange, yellow, green, light blue, blue, black, and the closer the color is to white, the higher the Mn concentration. The closer the color is to black, the lower the Mn concentration. In FIG. 3, the Mn level at the point showing the highest concentration of Mn is set to 135, the Mn level at the point not containing Mn is set to 0, and the Mn concentration at each point is expressed as a relative value with respect to the highest concentration, that is, Level: 135. . Then, the ratio of each Level is shown as an area ratio (AreaＡ%). As shown in the composition mapping of FIG. 3, it can be seen that there are many regions in which a red to blue color is solidified in a black background. Then, by comparing and referring to the existence position of the red to blue granular region shown in the composition mapping of FIG. 3 and the existence position of the white particle (see FIG. 2) shown in the SEM image (reflected electron image) in the same observation visual field. It can be said that the red to blue granular regions shown in the composition mapping are included in the compound containing Al and Mn (Al—Mn crystallized product). From this, sample no. It is considered that Mn in the 1-1 rolled sheet exists as an Al-Mn crystallized product. Therefore, here, all Mn is treated as existing as a compound with Al.

FIG. 4 is a graph showing the frequency and cumulative frequency of each level (Mn count number) of Mn created using the Mn composition mapping (15 kV) shown in FIG. In the graph of FIG. 4, the horizontal axis indicates the level of Mn (0 to 135; up to 110 is displayed in FIG. 4), the left vertical axis indicates the frequency of each level of Mn, and the right vertical axis indicates the accumulation of each level of Mn. Indicates the frequency (%).
The cumulative frequency can be said to be equivalent to the area ratio (Area%) of each level of Mn. Here, when the average S _Level of Mn _Level is taken, S _Level ≈10, and it can be seen that the Mn concentration is very low as a whole. Therefore, it is considered that Mn can be extracted more appropriately by treating it as a noise in a region where the level of Mn is about the average S _Level . As a result, it can be said that a compound containing Al and Mn (Al-Mn crystallized product) can be extracted more appropriately. Therefore, here, the standard deviation σ _Level of Mn _Level is obtained, the average S _Level + 3σ _Level is set as a threshold value, and the region where the Level of Mn is equal to or higher than the average S _Level + 3σ _Level is treated as an Al-Mn crystallized product. Then, the cumulative frequency (%) of average S _Level + 3σ _Level (here 11.3) or more is treated as the area ratio (%, 15 kV) of the Al—Mn crystallized product. The results are shown in Table 1.

左 The left figure in FIG. 1-1 is Mn composition mapping by FE-EPMA when the condition (2) with an acceleration voltage of 5 kV is used for the rolled plate 1-1, and the right figure shows an SEM image (reflection electron image) in the same observation field. Show. The composition mapping of FIG. 5 also shows the Mn concentration by color as in FIG. In the composition mapping of FIG. 5, the Mn Level at the point showing the highest concentration of Mn is 55, the Mn Level at the point not containing Mn is 0, and the presence ratio of each Level is shown as an area ratio (Area%). In the composition mapping shown in the left diagram of FIG. 5, since the irradiation energy of the electron gun is smaller than that in the condition (1), the information amount of Mn collected is smaller than that in the condition (1). As shown in the left figure of FIG. 5, it can be seen that the density of Mn can be grasped, and that red to blue are solidified in the same manner as the composition mapping of FIG. In addition, if the existence position of the red to blue granular region shown in the composition mapping in the left diagram of FIG. 5 is compared with the existence position of the white particle shown in the SEM image (reflection electron image) in the right diagram of FIG. It can be said that the red to blue granular region shown in the composition mapping is a compound containing Al and Mn (Al-Mn crystallized product).

FIG. 6 is a graph showing the frequency and cumulative frequency of each level of Mn (Mn count number) created using the Mn composition mapping (5 kV) shown in the left diagram of FIG. In the graph of FIG. 6, the horizontal axis indicates the level of Mn (0 to 55, displayed up to 50 in FIG. 6) as in the graph of FIG. 4, the left vertical axis indicates the frequency of each level of Mn, and the right vertical axis indicates The cumulative frequency (%) of each level of Mn is shown. Again, the average S Level of Mn _Level and the standard deviation σ _Level are obtained, the average S _Level + 3σ _Level is set as a threshold, and the cumulative frequency (%) of average S _Level + 3σ _Level (here 12) or more is expressed as Al and Mn. The area ratio (%, 5 kV) of the contained compound (Al—Mn crystallized product) was obtained. The results are shown in Table 1.

Sample No. 1-1-No. In the press-worked material of 1-5, the top plate portion to which bending or the like is not substantially given is observed in the same manner as the rolled plate. As a result, the crystal structure is as fine as the rolled plate. It had a structure in which a compound containing Al and Mn (Al-Mn crystallized product) was dispersed. In addition, the average crystal grain size of the top plate part, the average grain size, the maximum diameter, and the area ratio of the above compound are the same values as those of the rolled plate, and can be said to substantially have a rolled plate structure. .

Sample No. 1-1-No. As for the cast plate of 1-5, the metal structure was observed in the same manner as the rolled plate, and it had a fine crystal structure although the crystal grains were larger than the rolled plate. Sample No. 1-1-No. The cast plate of 1-5 also had a structure in which a compound containing Al and Mn was uniformly dispersed in at least the surface layer region. When the average particle diameter, maximum diameter, and area ratio (15 kV, 5 kV) of the above compound were examined, the values were similar to those of the rolled sheet. From this, sample no. 1-1-No. It can be said that the compound present in the 1-5 rolled sheet substantially maintains the compound in the cast sheet.

・ Tensile test (normal temperature, about 20 ℃)
A plate-like test piece (JIS Z 2201 (1998)) of JIS 13B was prepared from the obtained rolled plate (thickness: 0.7 mm) of each sample, and a metal material tensile test method of JIS Z 2241 (1998). Based on the above, a tensile test (mark distance GL = 50 mm) was performed. Here, tensile strength (MPa), 0.2% proof stress (MPa), and elongation at break (%) were measured (evaluation number: all n = 1). The results are shown in Table 2.

・ Impact resistance test (room temperature, about 20 ℃)
A 30 mm × 30 mm plate piece is cut out from the obtained rolled plate (thickness: 0.7 mm) of each sample, and this cut plate piece is used as a test piece. In this test, as shown in FIG. 7, a support base 20 having a circular hole 21 having a diameter d = 20 mm on a horizontal surface was prepared. The depth of the circular hole 21 was set to a size that allows a cylindrical rod 10 described later to be sufficiently inserted. The test piece 1 is arranged so as to close the circular hole 21. In this state, a cylindrical rod 10 made of ceramic having a weight of 100 g, a tip r = 5 mm, and a ceramic is placed at a point 200 mm in height from the test piece 1. The central axis of the circular hole 21 is coaxial. Then, the cylindrical bar 10 is freely dropped from the 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. The results are shown in Table 2.

-Workability The presence or absence of cracks in the corner R portion was visually confirmed in the press-processed material (corner drawing material) of each sample obtained, and the case where there was no crack was evaluated as Good, and the case where there was a crack was evaluated as Bad. The results are shown in Table 2.

-Productivity In a casting process, when the molten metal temperature is 690 degrees C or less, it determines with productivity being good.

As shown in Table 1, the average particle diameter of the particles of the compound containing Al and Mn is 0.3 μm or more and 1 μm or less, and the area ratio of the particles of the compound is 3.5% or more and 25 or more in the FE-EPMA analysis. % Of sample No. 1-1-No. In each of samples 1-5, sample Nos. It has the same strength, proof stress, elongation, and plastic workability as 1-101, and it has high strength, high toughness and excellent plastic workability regardless of the composition. In this test, sample no. 1-1-No. 1-5 has a tensile strength of 300 MPa or more, a 0.2% proof stress of 230 MPa or more, and a breaking elongation of more than 6%. Such sample No. 1-1-No. It can be seen that 1-5 does not easily cause cracks or cracks when press working such as corner drawing is performed. Furthermore, sample no. Sample No. 1 has a larger area ratio of particles of the above compound than that of 1-101. 1-1-No. In all of Nos. 1-5, the dent amount is 0.5 mm or less. Excellent impact resistance than 1-101. Sample No. 1-1-No. As one of the reasons why 1-5 is excellent in impact resistance, mechanical properties, and plastic workability, it is relatively fine even if the compound is present to some extent. 1. A good dispersion strengthening effect was obtained. This is thought to be because the above compound was less likely to be a starting point for cracking or the like.

Furthermore, sample no. 1-1-No. The following can be seen for 1-5.
The maximum diameter of the compound is 1.2 μm or less. From this, it is thought that the crack etc. which originated from the said compound were able to be suppressed more effectively.
The crystal is also fine, and the average crystal grain size is 10 μm or less. From this fact, it is considered that the impact resistance, mechanical properties, and plastic workability are excellent because cracks and the like starting from coarse crystal grains can be effectively suppressed.
In continuous casting, the temperature of the molten metal is low, so that thermal deterioration of the equipment can be suppressed. From this, it can be said that productivity is also excellent.

Furthermore, from this test, in the analysis of FE-EPMA, when the acceleration voltage of the electron gun was 5 kV or 15 kV, the sample No. 1-1-No. Sample No. 1-5 It can be seen that the area ratio is higher than those of 1-101 and 1-201, and a compound containing Al and Mn is sufficiently present.
In this test, the sample No. 1-1-No. Sample No. 1-5 having an area ratio of 5% or more and less than 3.5%. It is higher than 1-101, 1-201.
In this test, the sample No. 1-1-No. Sample No. 1-5 having an area ratio of 10% or more and 9.4% or less. It is higher than 1-101, 1-201.

And, such a magnesium alloy excellent in impact resistance, mechanical properties, plastic workability, and productivity is compared with the temperature of the molten metal immediately before contacting the mold as described above between 630 ° C. and 690 ° C. It can be seen that it can be produced by lowering the cooling rate of the molten metal and quenching the molten metal at 560 ° C./second or more. Also, from this test, by adjusting the temperature and cooling rate of the molten metal within the above range, even if the composition is changed, the compound containing Al and Mn satisfies the above specific amount and the specific average particle size. It can be seen that a magnesium alloy having impact resistance, mechanical properties, and plastic workability can be produced with high productivity.

On the other hand, even though the temperature of the molten metal is very high, the sample No. 1-201 is Sample No. It can be seen that although there are few compounds containing Al and Mn compared to 1-1, there are coarse particles (2.5 μm or more in this case). In addition, this sample No. 1-201 is a sample No. 1 having the same composition. It can be seen that the impact resistance, mechanical properties, and plastic workability are inferior to those of 1-1. The reason for this result is considered to be that the time during which the above compound is maintained at around 630 ° C., which is a temperature range in which the compound is easily generated and grown, is increased. In addition, the coarse particles of the above-mentioned grown compounds may become the starting point of cracking, and the dispersion strengthening effect due to fine compounds may be insufficient, resulting in impact resistance, mechanical properties, plastic workability. Is thought to have decreased.

On the other hand, sample no. In 1-101, it can be seen that the compound containing Al and Mn is extremely reduced by increasing the temperature of the molten metal and increasing the cooling rate. Sample No. 1-101 is a sample No. 1 having the same composition. Compared with 1-1, it is particularly inferior in impact resistance. The reason for this is considered that the dispersion strengthening by the fine compound was insufficient.

Sample No. 1-1-No. For the press-formed material of 1-5, a test piece similar to the above-mentioned rolled plate was produced from the top plate portion and subjected to a tensile test (room temperature) and an impact resistance test (room temperature) in the same manner as the rolled plate. The result was almost the same as the board. That is, the press-processed material was also excellent in impact resistance and mechanical properties. One of the reasons is that at least a part of the pressed material substantially maintains the structure of the rolled sheet, that is, has a fine crystal structure and a specific size of Al and Mn. This is presumably because the compound containing a has a uniformly dispersed structure.

It should be noted that the present invention is not limited to the above-described examples, but is defined by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims. For example, in the above test example, the composition (type of additive element, content), the shape, size (thickness, length, width, etc.) of the magnesium alloy plate, manufacturing conditions (in the casting conditions, the specifications of the mold, the mold The temperature, the hot water temperature, the cooling rate, the thickness of the cast plate, etc.) can be appropriately changed.

マ グ ネ シ ウ ム The magnesium alloy and magnesium alloy plate of the present invention can be suitably used as a material for plastic working members (magnesium alloy members) subjected to various plastic workings such as press working, bending and forging. In particular, this magnesium alloy plate is a member that is desired to have characteristics such as light weight, thinness, high strength, vibration damping, such as various electronic / electrical devices (personal computer (PC), tablet PC, smartphone, folding type). It can be suitably used for materials such as casings of mobile phones such as mobile phones, digital cameras, etc., exterior members such as covers, components of transportation equipment such as automobiles and aircraft, skeleton members, bags, and various protective cases. The magnesium alloy and magnesium alloy member of the present invention can be suitably used for, for example, exterior members such as the above-described casing, constituent members of the above transportation equipment, skeleton members, bags, protective cases, and the like. The manufacturing method of the magnesium alloy of this invention can be utilized suitably for manufacture of magnesium alloys, such as the said magnesium alloy plate and the said magnesium alloy member.

1 Test piece 10 Cylindrical rod 20 Support stand 21 Circular hole

Claims (6)

1. In mass%, Al is contained 1% or more and 12% or less, Mn is contained 0.1% or more and 5% or less,
   Comprising a structure in which particles of a compound containing Al and Mn are dispersed;
   The average particle size of the particles of the compound is 0.3 μm or more and 1 μm or less,
   A magnesium alloy having an area ratio of particles of the compound of 3.5% or more and 25% or less.
2. The magnesium alloy according to claim 1, wherein the maximum particle diameter of the compound is less than 2.5 μm.
3. The magnesium alloy according to claim 1 or 2, wherein the magnesium alloy has an average crystal grain size of 10 µm or less.
4. A magnesium alloy plate comprising the magnesium alloy according to any one of claims 1 to 3.
5. A magnesium alloy member comprising the magnesium alloy according to any one of claims 1 to 3 and having a plastic working portion at least partially subjected to plastic working.
6. A step of continuously casting a molten magnesium alloy containing 1% to 12% Al and 0.1% to 5% Mn in mass%,
   The temperature of the molten metal immediately before contacting the mold is set to 630 ° C. or more and 690 ° C. or less,
   A method for producing a magnesium alloy, wherein the molten metal is cooled at a rate of 560 ° C./second or more.

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