JP6422304B2 - Manufacturing method of magnesium alloy products - Google Patents

Description

The present invention also relates to the production how of magnesium alloy products.

  Since the magnesium alloy is lightweight, energy saving can be realized by using the magnesium alloy as a raw material for processing as compared with an iron-based material during processing. Magnesium is present in nature such as in seawater and has abundant resources. Furthermore, it is known that magnesium alloys are easier to recycle than plastics.

  Further, it is known that a magnesium alloy can improve mechanical properties and heat resistance by an additive element added to the magnesium alloy. For example, Patent Document 1 below discloses a heat-resistant magnesium alloy in which mechanical properties and heat resistance are improved by adding aluminum and manganese to the magnesium alloy.

JP 05-33096 A

  As in the invention described in Patent Document 1 listed above, for example, a magnesium alloy to which an alloy element such as aluminum is added is subjected to plastic working on the magnesium alloy by improving mechanical properties and heat resistance by the additive element. It is necessary to hot work. Due to the mechanical properties and heat resistance improved by the additive elements, the processing temperature for processing the magnesium alloy must be higher than the recrystallization temperature of the magnesium alloy and further increased to the solution temperature of the magnesium alloy. was there. In that case, the processing temperature of the magnesium alloy becomes very high, and even if a magnesium alloy with high strength is manufactured, recrystallization and grain growth occur due to the processing temperature being very high, and the mechanical properties are lowered. There was a problem that it would end up.

  In order to solve the above-described problems, review of additive elements and review of plastic working processes have been performed. However, it has been desired to realize a technique for solving the above-described problems without reducing the heat resistance and metallographic effects imparted to the magnesium alloy by the additive elements.

  Therefore, the present invention has been made in view of the above-described problems, and its purpose is to provide high strength even at a low number of times of processing and a low degree of processing, exhibit easy formability at the time of molding, and use it for plastic processing. Another object of the present invention is to provide a magnesium alloy sheet, a method for producing a magnesium alloy sheet, a magnesium alloy product, a method for producing a magnesium alloy product, and a magnesium alloy final product.

A method for producing a magnesium alloy product according to the present invention is a magnesium alloy obtained by casting a molten magnesium alloy melt by a twin roll casting method in which the molten alloy is cast by a pair or a plurality of pairs of rolls, and adding plastic working after the casting. A method for manufacturing a product, wherein a cast plate having irregularities on a surface is cast at a stage where casting is performed, and the irregularities of the cast plate are processed by plastic processing performed after the casting, thereby remaining in a surface layer portion. The magnesium alloy includes AZ31, AZ61, AZ91 in which aluminum and zinc are added to magnesium, AZX311, AZX611, AZX711, AZX811, in which aluminum, zinc, and calcium are added to magnesium. AZX911, AZX1001, Magnesi One of AMX301, AMX601, AMX701, AMX801, AMX901, and AMX1001 with aluminum, manganese and calcium added thereto is selected, and the unevenness of the cast plate having unevenness on the surface is selected. The height difference is 0.04 mm or more and 0.3 mm or less, and the temperature at which the casting of the magnesium alloy is supplied between one or more pairs of rolls and the casting is started is 635 ° C. or more and 730 ° C. or less. And the surface temperature of the cast plate made into a plate shape is cooled to a range of 380 ° C. to 450 ° C. at a point where the magnesium alloy moves 300 mm through a pair or a plurality of pairs of rolls, and At a point where the magnesium alloy has moved 1000 mm by passing between one or more pairs of rolls. When the surface temperature of the cast plate rises to about 500 ° C., the internal latent heat inside the magnesium alloy is released to the surface of the cast plate, so that the surface layer portion that is the surface of the cast plate and the internal The cooling rate of the cast plate is 1143 K / s at a point where the cast plate passes through one or more pairs of rolls and moves 50 mm, and the pair or pairs of rolls are moved. It is 132 K / s at a point that passes 300 mm after passing, and further 61 K / s at a point that moves 2000 mm after passing through one or more pairs of rolls, and at a point that moves 1000 mm from one or more pairs of rolls. The internal latent heat generated in the central portion that is the inside of the cast plate is released to the surface layer portion that is the surface of the cast plate, thereby The temperature of the surface layer portion that is the surface of the cast plate rises, so that the cooling rate of the cast plate is in the range of −100 K / s to −50 K / s during casting. is there.

Also, a manufacturing method of a magnesium alloy product according to the present invention, the plastic working, it is possible to be a press working.

In addition, a manufacturing method of a magnesium alloy product according to the present invention may be a performing press working by sandwiching below 300 seconds 10 seconds in a mold while heating the cast plate above 250 ° C..

Still further , in the method for producing a magnesium alloy product according to the present invention, after the cast plate is annealed, the plastic working can be performed.

Furthermore, the manufacturing method of the magnesium alloy product according to the present invention, the temperature of the annealing is able to be at 250 ° C. or higher 350 ° C. or less.

According to the present invention, the low processing times and low working ratio in conjunction with indicating the moldability during molding a high strength, used in plastic forming for example a mold or the like and the contact portion is microstructures with a luma magnesium alloy it is possible to provide a product of the manufacture how.

It is a figure which shows the structural example of the casting apparatus which casts the magnesium casting board | plate material which concerns on this embodiment. It is a figure which shows the cross-sectional observation photograph of the magnesium casting board | plate material which concerns on this embodiment, and the fraction (a) in FIG. 2 is a micro observation photograph of the magnesium casting board | plate material cast using AZX611, The fractional drawing (b) is a micro observation photograph of a magnesium cast plate material cast using AZ61. It is a figure which shows the SEM observation photograph of the magnesium casting board | plate material which concerns on this embodiment, and the fraction (a) and parting drawing (b) in FIG. 3 are SEM observation photographs of the magnesium casting board | plate material cast using AZ61. 3 (c) and (d) are SEM observation photographs of a magnesium cast plate cast using AZX612, and (e) and (f) in FIG. 3 are AZX6112. It is a SEM observation photograph of the magnesium casting board | plate material cast using this. It is a figure which shows the measurement result of the mechanical property for every calcium content rate of the magnesium cast board which concerns on this embodiment, and the fraction (a) in FIG. 4 is a figure which shows the measurement result of a maximum tensile strength (UTS). 4 is a diagram showing measurement results of yield strength (YS), and FIG. 4 (c) is a diagram showing measurement results of elongation at break (EL). 4 is a diagram showing the measurement results of Vickers hardness (HV), and the diagram (e) in FIG. 4 is a diagram showing the results of the average crystal grain size. It is a figure which shows the measurement result of the magnesium alloy board | plate material which gave the magnesium cast board | plate material which concerns on this embodiment to plastic processing, and has shown the state which performed the rolling process once. It is a figure which shows the measurement result of the magnesium alloy board | plate material which gave the magnesium cast board | plate material which concerns on this embodiment to plastic processing, and has shown the state which performed the rolling process in multiple times. It is a figure which shows the cross-sectional observation photograph of the magnesium alloy board | plate material which concerns on this embodiment by which rolling as a plastic working was performed in multiple times, and the division | segmentation figure (a) and division | segmentation figure (b) in FIG. FIG. 8 is a micro-observation photograph of the surface layer portion and the center portion of a magnesium alloy sheet material to which a rate of 10% is imparted, and the fractional view (c) and fractional diagram (d) in FIG. 8 is a micro-observation photograph of the surface layer portion and the central portion of the magnesium alloy plate material, and the fractional view (e) and partial view (f) in FIG. 7 are the surface layers of the magnesium alloy plate material to which a total rolling reduction ratio of 30% is applied, respectively. FIG. 7 is a micro-observation photograph of the surface layer portion and the center portion of the magnesium alloy sheet having a total rolling reduction of 40%. It is. It is a figure which shows the SEM-EBSD observation of the magnesium alloy board | plate material which concerns on this embodiment in which the rolling as plastic working was performed in multiple times, More specifically, the uneven | corrugated recessed part of the magnesium alloy board | plate material processed by rolling was processed. It is a figure which shows the IPF (Inverse Pole Figure) map of the part which existed. FIG. 8A is a diagram showing an IPF map of a magnesium alloy sheet having a total reduction ratio (Reduction) of 0% as a comparative example, and FIG. It is a figure which shows the IPF map of the magnesium alloy board | plate material to which 10% of reduction ratio (Reduction) was provided, Moreover, the fractional drawing (c) in FIG. 8 is a magnesium alloy to which 40% of total reduction ratio (Reduction) was provided. It is a figure which shows the IPF map of a board | plate material. It is a figure which shows the cross-sectional observation photograph of the magnesium alloy product which concerns on this embodiment, and is a micro observation photograph of the magnesium alloy product using AZX611. It is a figure which shows the cross-sectional observation photograph of the magnesium alloy product which concerns on this embodiment, and the fraction (a) in FIG. 10 and the fraction (b) in FIG. 10 are the SEM observation photographs of the magnesium alloy product using AZX611. It is. It is a figure which shows the measurement result of the mechanical property for every calcium content rate of the magnesium cast board which concerns on this embodiment, and the fraction (a) in FIG. 11 is a figure which shows the measurement result of a maximum tensile strength (UTS). 11 is a diagram showing measurement results of yield strength (YS), and FIG. 11 (c) is a diagram showing measurement results of elongation at break (EL). 11 is a diagram showing the measurement results of Vickers hardness (HV), and the diagram (e) in FIG. 11 is a diagram showing the results of the average crystal grain size. It is a figure which shows the measurement result of the mechanical property for every aluminum content rate of the magnesium casting plate cast using the AZX type alloy, and the fractional drawing (a) in FIG. 12 shows the measurement result of the maximum tensile strength (UTS). 12 is a diagram showing a measurement result of yield strength (YS), and FIG. 12 (c) is a diagram showing a measurement result of elongation at break (EL). 12 is a diagram showing a measurement result of Vickers hardness (HV), and a diagram (e) in FIG. 12 shows a result of an average crystal grain size. FIG. It is a figure which shows the measurement result of the mechanical property for every aluminum content rate of the cast plate cast using the AMX system alloy, and the fractional drawing (a) in FIG. 13 shows the measurement result of the maximum tensile strength (UTS). 13 is a diagram showing a measurement result of yield strength (YS), and FIG. 13 (c) shows a measurement result of elongation at break (EL). 13 is a diagram showing a measurement result of Vickers hardness (HV), and FIG. 13 (e) is a diagram showing a result of an average crystal grain size. It is.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments for carrying out the invention will be described with reference to the drawings. The following embodiments do not limit the invention according to each claim, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. .

  As a result of earnest research for solving the above-mentioned problems, the inventors have formed irregularities on the surface of the magnesium cast plate, and plastic processing is performed on the magnesium cast plate on which the irregularities are formed. Residual stress is applied to the surface layer part, and due to the action of the residual stress, it is easy to form at the time of molding with high strength even at a low number of times and a low degree of processing, and is in contact with, for example, a mold used for plastic working The knowledge that a part can be made into a fine structure was acquired. Therefore, in the embodiment described below, a manufacturing method of a magnesium alloy plate material found by the inventors and an analysis result and a test result showing characteristics of the magnesium alloy plate material manufactured by the manufacturing method will be described.

[Magnesium alloy sheet]
The magnesium alloy plate material according to the present embodiment is obtained by casting a molten magnesium alloy and applying plastic processing after the casting, and is configured as a cast plate having irregularities on the surface at the stage of casting. Then, the unevenness of the cast plate is processed by plastic processing after casting, so that residual stress is applied to the surface layer portion. The magnesium alloy plate material according to the present embodiment can be applied to a thin plate material and a thick plate material.

[Magnesium cast plate]
First, the manufacturing method of the magnesium cast board in which the unevenness | corrugation which concerns on this embodiment was formed is demonstrated.

The magnesium alloy contains magnesium as a main component, and includes aluminum, manganese, zinc, calcium and the like. Aluminum can be added, for example, from 0% to 11% with respect to magnesium. Manganese can be added, for example, from 0% to 0.5% with respect to magnesium, and zinc can be added, for example, from 0% to 2.5% with respect to magnesium. For example, calcium can be added in an amount of 0.5% to 12% with respect to magnesium.

Examples of magnesium alloys include AZ alloys in which aluminum and zinc are added to magnesium, AZX alloys in which aluminum, zinc and manganese are added to magnesium, and AMX in which aluminum, manganese and calcium are added to magnesium. Alloys can be used. More specifically, as a magnesium alloy , for example, AZ31, AZ61, AZ91 in which aluminum and zinc are added to magnesium, AZX311, AZX611, AZX612, AZX615, AZX6112, and AZX611, in which aluminum, zinc, and calcium are added to magnesium. AZX711, AZX811, AZX911, AZX1001, AMX301, AMX601, AMX701, AMX801, AMX901, AMX1001, etc. in which aluminum, manganese, and calcium are added to magnesium can be used.

The magnesium alloy is cast by, for example, a twin roll casting method. In the twin roll casting method, a molten metal, which is a molten metal material, is cast by a pair or a plurality of pairs of rolls. As shown in FIG. 1, the twin roll casting apparatus 1 includes a molten metal furnace 10 that holds a molten metal material and a pair of casting rolls 20 for casting the metal material.

  The molten metal furnace 10 is a crucible that holds a molten metal material as a molten metal. In the molten metal furnace 10, for example, an opening 11 is formed on one end side in a direction in which a pair of casting rolls 20 described later is disposed. The opening 11 serves as an outlet for taking out the molten metal between the pair of casting rolls 20.

  The pair of casting rolls 20 are for casting a metal material. The pair of casting rolls 20 includes a first casting roll 21 and a second casting roll 22 that are arranged in a rotatable state. In addition, the pair of casting rolls 20 (21, 22) according to the present embodiment uses a hole-type roll corresponding to an uneven shape in order to form unevenness on the surface of the magnesium cast plate to be cast. In addition, although the roll peripheral speed of a pair of casting roll 20 (21, 22) is not specifically limited, It can be 20 m / min or more and 30 m / min or less.

The magnesium alloy as the metal material is heated and melted, for example, in a molten metal furnace 10 that holds the melted magnesium alloy . The molten magnesium alloy as molten metal is discharged from an opening 11 provided on one end side of the molten metal furnace 10 and supplied between a pair of casting rolls 20 (21, 22) for casting the magnesium alloy. While being pressed by a pair of casting rolls 20 (21, 22) having a hole shape corresponding to the concavo-convex shape formed on the cast plate, it passes between the pair of casting rolls 20 (21, 22), is cooled, and is cast into magnesium. A magnesium cast plate having a concavo-convex shape on the surface of the plate is produced. Here, FIG. 2 is a view showing a cross-sectional observation photograph of the magnesium cast plate according to the present embodiment, and a partial view (a) in FIG. 2 is a micro observation photograph of the magnesium cast plate cast using AZX611. 2 is a micro-observation photograph of a magnesium cast plate cast using AZ61.

  As shown in FIG. 2, unevenness is formed on the surface of the magnesium cast plate, and the height difference of the unevenness can be 0.04 mm or more and 0.3 mm or less. In this way, by forming irregularities on the surface of the magnesium cast plate, when the irregularities are processed by plastic working to process the irregularities formed on the magnesium cast plate, the residual stress is in the thickness direction of the magnesium cast plate. More will be given to the surface layer part. When plastic working is performed on a flat cast plate, the residual stress is uniformly applied to the cast plate, but plastic processing is performed on the cast plate with irregularities formed like the magnesium cast plate according to this embodiment. When applied, more residual stress can be applied to the surface layer portion of the magnesium cast plate than to the central portion of the magnesium cast plate. When the magnesium alloy sheet according to the present embodiment is plastically processed by the residual stress applied more to the surface layer portion of the magnesium cast sheet, the formation of fine grains is promoted.

  In the above, the manufacturing method of the magnesium cast plate which has an unevenness | corrugation which concerns on this embodiment was demonstrated. Next, the casting conditions of the magnesium cast plate according to this embodiment will be described.

The magnesium alloy is heated to, for example, 635 ° C. or higher and 730 ° C. or lower according to the component composition of the magnesium alloy , and is supplied between the pair of casting rolls 20 (21, 22). The temperature of the magnesium alloy after passing between the pair of casting rolls 20 (21, 22) is deprived of heat by the pair of casting rolls 20 (21, 22), and the pair of casting rolls 20 (21, 22). The surface temperature of the plate-shaped magnesium cast plate is cooled to a range of 380 ° C. to 450 ° C. at a point where it has moved between and about 300 mm. Thereafter, at a point moved about 1000 mm from the pair of casting rolls 20 (21, 22), the surface temperature of the magnesium cast plate rises to about 500 ° C. This is because internal latent heat generated in the magnesium cast plate (central portion) is released to the surface (surface layer portion) of the magnesium cast plate. A coarse structure is formed on the surface (surface layer portion) of the magnesium cast plate due to the temperature rise of the surface (surface layer portion) of the magnesium cast plate due to internal latent heat, and the inside (center portion) of the magnesium cast plate has a fine structure. Will be maintained. That is, the cooling rate is different between the inside (center portion) of the magnesium cast plate and the surface (surface layer portion) of the magnesium cast plate in contact with the pair of cast rolls 20 (21, 22), and the solidification form is also different. It becomes. More specifically, the cooling rate of the magnesium cast plate is 1143 K / s at a point where it has moved about 50 mm through the pair of casting rolls 20 (21, 22), and passes through the pair of casting rolls 20 (21, 22). It is 132 K / s at a point moved about 300 mm, and further 61 K / s at a point moved about 2000 mm through a pair of casting rolls 20 (21, 22). As described above, at a point moved about 1000 mm from the pair of casting rolls 20 (21, 22), internal latent heat generated in the central portion of the magnesium casting plate is released to the surface (surface layer portion) of the magnesium casting plate. As a result, the temperature of the surface (surface layer portion) of the magnesium cast plate rises. Therefore, the cooling rate of the magnesium cast plate is in the range of −100 K / s to −50 K / s during casting. In addition, when a magnesium cast plate is manufactured by the single roll method, the magnesium cast plate is composed of one surface of the magnesium cast plate in contact with the cast roll, a surface opposite to the surface in contact with the cast roll, and magnesium casting. The cooling rate is different from the inside of the plate, and the solidification form is also different.

  The inventors used a scanning electron microscope (SEM) (manufactured by JEOL Ltd., JEOL JCM-6000 Neo Scope and EDS system) for the magnesium cast plate manufactured under the above-described conditions. The composition image was observed by observing backscattered electrons, and the area ratio of the intermetallic compound was measured by image analysis using analysis software (Hulinks Sigma Scan Pro, manufactured by Hulinks Co., Ltd.). . The results are shown below. Here, FIG. 2 is a view showing an SEM observation photograph of the magnesium cast plate according to the present embodiment. 2 (a) and 2 (b) are SEM observation photographs of a magnesium cast plate cast using AZ61. FIG. 2 (a) is an uneven view of the magnesium cast plate. FIG. 2B is a diagram showing a central portion that is the inside of the magnesium cast plate. 2 (c) and (d) are SEM observation photographs of a magnesium cast plate cast using AZX612, and FIG. 2 (c) shows the surface layer of the magnesium cast plate. FIG. 2D is a diagram showing a central portion of the magnesium cast plate. 2 (e) and (f) are SEM observation photographs of a magnesium cast plate cast using AZX6112, and FIG. 2 (e) shows the surface layer portion of the magnesium cast plate. FIG. 2 is a diagram showing a central portion of a magnesium cast material.

  As shown in FIG. 2, it can be seen that an intermetallic compound is formed on the magnesium cast plate according to the present embodiment. In addition, Table 1 shows the measurement results of the area ratio of the intermetallic compound that appeared at the time of casting in the magnesium cast plate according to the present embodiment. In addition, although the intermetallic compound formed in a magnesium alloy can become a factor which inhibits a deformation | transformation of a magnesium alloy, since a desired shape can be obtained by heating a magnesium alloy to about 300 degreeC, an intermetallic compound is obtained. May remain present.

  As shown in Table 1, AZ61 in which the ratio of calcium added to magnesium is about 0%, AZX611 in which the ratio of calcium added to magnesium is about 1%, added to magnesium In the case of using AZX612 in which the ratio of calcium is about 2% and AZX615 in which the ratio of calcium added to magnesium is about 5%, the area ratio of the intermetallic compound is larger than the area ratio in the central portion. It turns out that the area ratio in a part is larger. On the other hand, when using AZX6112 in which the ratio of calcium added to magnesium is about 12%, the area ratio of the intermetallic compound is smaller in the area ratio in the surface layer than in the center. In addition, it was found that the area ratio of the intermetallic compound in the central portion and the surface layer portion of the magnesium casting was reversed by increasing the proportion of calcium added to magnesium. In addition, the intermetallic compound has a tilted structure in which crystal grains are joined with a crystal orientation difference. By having such a crystal structure, the magnesium cast plate according to the present embodiment is improved by an additive element added to magnesium, for example, creep characteristics, annealing characteristics, heat resistance, combustion resistance, and corrosion resistance. The properties such as can be maintained. Note that a part of the residual stress applied as described above may be released, and the crystal structure of the surface layer portion may be a fine structure.

The inventors have also analyzed the influence of the ratio of calcium added to magnesium on the mechanical properties. Using a magnesium alloy obtained by adding 0 wt% to 12 wt% calcium to AZ61 alloy, the mechanical properties of a magnesium cast plate cast by the twin roll method under the above-described casting conditions were measured. The measurement methods of the maximum tensile strength (UTS), the yield strength (YS), and the elongation at break (EL) were performed based on JIS standards. In the tensile test, JIS standard 13B or a unique test piece shape was used as a test piece, and the tensile speed was 2 mm / min at the crosshead speed. Here, in the original test piece shape, the plate width was 3 mm and the distance between the gauge points was 30 mm in the standard dimensions. The Vickers hardness (HV) was measured by applying a 300 g weight for 30 seconds with a Vickers hardness tester. Further, the intercept method was used to measure the average crystal grain size. The result is shown in FIG. Here, FIG. 4 is a figure which shows the measurement result of the mechanical property for every calcium content rate of the magnesium casting plate which concerns on this embodiment, and the fraction (a) in FIG. 4 shows the maximum tensile strength (UTS). FIG. 4 is a diagram showing measurement results, and FIG. 4 is a diagram (b) showing the measurement results of yield strength (YS), and FIG. 4 is a diagram (c) showing the elongation at break (EL). FIG. 4 is a diagram showing measurement results, in which FIG. 4 is a diagram (d) showing measurement results of Vickers hardness (HV), and FIG. 4 is a diagram (e) showing the average crystal grain size. It is a figure which shows a result.

  As shown in FIG. 4, it was found that the maximum tensile strength (UTS), yield strength (YS), and Vickers hardness (HV) increase as the proportion of calcium added to magnesium increases. On the other hand, it was found that the elongation at break (EL) is lower than that of the AZ61 alloy to which calcium is not added by adding calcium. The average crystal grain size became smaller when 12 wt% calcium was added.

  In the above, the casting condition of the magnesium cast plate and the analysis result of the magnesium cast plate cast according to the casting condition have been described. Next, the plastic working which processes the unevenness | corrugation which a magnesium cast plate has is demonstrated.

[Plastic processing]
Here, the plastic working refers to processing the unevenness formed on the magnesium cast plate. Inventors examined the rolling conditions suitable in order to perform the rolling as a plastic working to the magnesium cast plate in which the unevenness | corrugation was formed as mentioned above using the general rolling mill. The rolling mill has a plurality of rolling rolls, and the magnesium casting sheet can be rolled by passing the magnesium casting sheet one or more times between the plurality of rolling rolls. The result of the examination of the rolling conditions of the magnesium cast sheet using AZ61 as the magnesium alloy is shown below. Here, FIG. 5 and FIG. 6 are diagrams showing measurement results of a magnesium alloy plate material obtained by rolling the magnesium cast plate according to the present embodiment as plastic working. The partial diagram (a) in FIG. 5 shows a cross-sectional observation photograph of a magnesium alloy sheet that has been subjected to a rolling process once with a total reduction ratio (Reduction) of 10%, 20%, 30%, and 40%, FIG. 5B is a diagram showing the measurement results of the mechanical properties of the magnesium alloy sheet subjected to the rolling process once. FIG. 6A is a sectional view showing a cross-sectional observation photograph of a magnesium alloy sheet that has been subjected to a rolling process several times with a total reduction ratio (Reduction) of 10%, 20%, 30%, and 40%, respectively. FIG. 6B shows a measurement result of the mechanical properties of the magnesium alloy sheet that has been subjected to the rolling process a plurality of times. The yield strength (Yield Strength: YS), the maximum tensile strength (UTS), and the elongation at break (Elongation: El) were measured based on international standards.

  First, when a rolling process is performed once on a magnesium cast plate with irregularities formed, the magnesium cast plate is heated to 300 ° C. and heated to 160 ° C. with a rolling reduction of 10%, 20%, 30% and 40%, respectively. The rolling rolls were rolled by being passed once at a rolling peripheral speed of 15 m / min (single pass). As a result, as shown in the partial diagram (a) of FIG. 5, when the total rolling reduction is increased, the unevenness is naturally reduced. Regarding the mechanical properties, when the total reduction ratio (Reduction) is increased, the yield strength (YS) and the maximum tensile strength (UTS) are increased while the elongation at break (El) is decreased. And when the large rolling reduction of 1 time total rolling reduction of about 40% was given with respect to the magnesium cast plate, the surface layer part which has a residual stress will lose | disappear. This is considered to be due to heat generation by rolling. In addition, although the rolling conditions of the magnesium cast plate which concern on this embodiment are not specifically limited, While a magnesium cast plate shall be 200 degreeC or more and 450 degrees C or less, a rolling roll is heated to 160 degreeC or more and 300 degrees C or less, and the roll of a rolling roll It is preferable to roll the magnesium cast plate at a peripheral speed of 5 m / min to 15 m / min.

  Next, when the magnesium cast plate is rolled a plurality of times, the same temperature condition and the peripheral speed of the rolling roll as described above, with a reduction rate of 5% to 10% per pass, and a total reduction rate of 10%, The rolling was performed by passing between the rolling rolls a plurality of times (Multi pass) so as to be 20%, 30% and 40%. As a result, as shown in the partial diagram (a) of FIG. 6, as the total rolling reduction is increased, the unevenness is naturally reduced. At this time, residual stress could be effectively generated in the surface layer portion at the total rolling reductions of 30% and 40%. As for the mechanical properties, as shown in the partial diagram (b) of FIG. 6, the yield strength (YS) and the maximum tensile strength (UTS) increase as the total reduction ratio (Reduction) increases. However, the elongation at break (El) decreases as the total reduction ratio (Reduction) increases from 10% to 30%, whereas when the total reduction ratio is 40%, The reduction ratio was larger than when 30% was applied. That is, the elongation at break (El) was improved when the total rolling reduction to the cast magnesium plate was 40%. In addition, the measurement results of the mechanical properties of the magnesium cast plate according to the present embodiment show that the yield strength (YS) is 50 MPa or more and 350 MPa or less, the maximum tensile strength (UTS) is 160 MPa or more and 370 MPa or less, and the elongation at break ( El) was 1% or more and 37% or less.

  From the above, the inventors pass between the rolling rolls a plurality of times so that the total reduction rate is 10%, 20%, 30%, and 40%, respectively, at a reduction rate of 5% to 10% per pass. The method (Multi Pass) is considered to give a better magnesium alloy sheet, and moreover, regarding the magnesium alloy sheet subjected to Multi Pass rolling, FE-SEM (manufactured by JEOL Ltd., JSM) A back electron scattering diffraction (Electron Backscatter Diffraction: EBSD) measuring device (manufactured by TSL Solutions, Inc.) was attached to -7100F), and the microstructure was observed and measured by SEM-EBSD. The data collection and analysis software used was OIM 7.0 (manufactured by TSL Solutions Inc.). The results are shown in FIG. 6 and Tables 2 to 4. Here, FIG. 7 is a figure which shows the cross-sectional observation photograph of the magnesium alloy board | plate material which concerns on this embodiment by which rolling as a plastic working was performed in multiple times, and is the fractional view (a) in FIG. ) Are micro-observation photographs of the surface layer portion and the central portion of the magnesium alloy sheet to which a total rolling reduction of 10% is applied, respectively, and the fractional view (c) and the fractional view (d) in FIG. FIG. 8 is a micro observation photograph of a surface layer portion and a center portion of a magnesium alloy sheet material with a rolling reduction ratio of 20%, and a partial drawing (e) and a partial drawing (f) in FIG. 7 respectively give a total rolling reduction ratio of 30%. FIG. 8 is a micro-observation photograph of the surface layer portion and the center portion of the magnesium alloy sheet material obtained, and the fractional view (g) and partial diagram (h) in FIG. 7 show the surface layer portion of the magnesium alloy sheet material to which the total rolling reduction ratio is 40%. It is the micro observation photograph of the center part. Moreover, FIG. 8 is a figure which shows the SEM-EBSD observation of the magnesium alloy board | plate material which concerns on this embodiment in which the rolling as plastic working was performed in multiple times, More specifically, the magnesium alloy processed by rolling It is a figure which shows the IPF (Inverse Pole Figure) map of the part in which the uneven | corrugated recessed part of the board | plate material existed. FIG. 8A is a diagram showing an IPF map of a magnesium alloy sheet having a total reduction ratio (Reduction) of 0% as a comparative example, and FIG. FIG. 9 is a diagram showing an IPF map of a magnesium alloy sheet material with a reduction ratio (Reduction) of 10%. FIG. 8 (c) is a partial diagram (c) of the magnesium alloy sheet material with a total reduction ratio (Reduction) of 40%. It is a figure which shows an IPF map.

  As shown in the partial diagram (b) in FIG. 7, the magnesium alloy sheet material with a total reduction ratio (Reduction) of 10% is directly below the concave portion as compared with the partial diagram (a) in FIG. 8 as a comparative example. It can be seen that twins are formed. And by repeating rolling at a reduction rate of 5% to 10% per pass, the thickness of the surface layer portion having a residual stress increases in the magnesium alloy sheet material to which a total reduction rate (Reduction) of 40% is given. However, even if a recrystallized structure is formed, it is possible to have a shear band in which shearing occurs inside the magnesium alloy sheet. Here, with respect to the thickness of the surface layer portion having residual stress, the measurement results for each total rolling reduction are shown in Table 2.

  When the total rolling reduction is increased, the thickness of the surface layer portion having residual stress increases, and it can be seen that the results in Table 2 are consistent with the observation results in FIG. And the thickness of the surface layer part which has a residual stress is 9 micrometers or more and 361 micrometers or less. Therefore, the magnesium alloy sheet according to the present embodiment may have an inclined structure in which crystal grains are joined with a crystal orientation difference. Next, with respect to the crystal grain size of the magnesium phase, Table 3 and Table 4 show the measurement results for each total rolling reduction.

  The crystal grain size of the magnesium phase is 2 μm or more and 32 μm or less in the center portion and 1 μm or more and 75 μm or less in the surface layer portion when the total rolling reduction is 10%. When the total rolling reduction is 20%, the crystal grain size of the magnesium phase is 4 μm or more and 36 μm or less in the central part, and 1 μm or more and 63 μm or less in the surface layer part. When the total rolling reduction is 30%, the crystal grain size of the magnesium phase is 2 μm or more and 28 μm or less in the central part, and 1 μm or more and 42 μm or less in the surface layer part. When the total rolling reduction is 40%, the crystal grain size of the magnesium phase is 1 μm or more and 32 μm or less in the central part, and 1 μm or more and 62 μm or less in the surface layer part. That is, the crystal grain size of the magnesium phase is 1 μm or more and 75 μm or less in the surface layer portion, and 1 μm or more and 36 μm or less in the intermediate portion.

  As shown in Table 4, in the magnesium cast plate according to the present embodiment, the average crystal grain size is 9.0 μm at the central portion and 33.8 μm at the surface portion when the total rolling reduction is 10%. At a total rolling reduction of 20%, the average crystal grain size is 7.8 μm at the center and 31.9 μm at the surface layer. At a total rolling reduction of 30%, the average crystal grain size is 7.6 μm at the center and 22.7 μm at the surface layer. At a total rolling reduction of 40%, the average crystal grain size is 7.1 μm at the center and 16.7 μm at the surface layer.

  When rolling as a plastic working to a magnesium cast plate with irregularities, it is possible to make a large reduction that gives a reduction ratio of 40% or more in one rolling process, or to reduce the number of rolling processes to, for example, several tens of passes or more. When the amount is increased, it has been found that it is difficult to satisfactorily process the irregularities, leading to the formation of ear cracks and coarse structures. It was also found that the elongation at break (El) was improved by repeating the rolling at a reduction rate of 5% to 10% per pass. Therefore, although not particularly limited, the rolling as plastic working is 5% to 10% reduction per pass, and is a multi pass for rolling a magnesium cast plate a plurality of times, so that the total reduction rate is about 40%. It has been found that this is preferable. That is, according to the method for manufacturing a magnesium alloy sheet according to the present embodiment, due to the action of residual stress generated in the surface layer portion of the magnesium cast plate, the crystal of the surface layer portion accompanying the increase in the number of rolling processes as in the conventional technique. Since no grain refinement occurs, magnesium has high strength even at a low number of times and a low degree of processing and exhibits easy formability at the time of molding, and the part that comes into contact with, for example, a rolling roll used for plastic processing has a fine structure An alloy sheet can be obtained.

As described above, in the method for producing a magnesium alloy sheet according to the present embodiment, the magnesium cast sheet cast with irregularities formed therein has a crystal grain size that is coarse or equivalent to the crystal grains in the surface layer portion compared to the crystal grains in the central portion. When the magnesium cast plate is rolled under the above-described conditions as plastic working, the residual stress generated in the surface layer part acts, and the formation of fine grains is promoted. The grains have a grain size equivalent to that of the central portion, and a magnesium alloy plate material having a uniform structure can be obtained. Further, as described above, according to the method for manufacturing a magnesium alloy sheet according to the present embodiment, the strength is high even at a low number of times of processing and a low degree of processing, and easy formability is exhibited at the time of molding, and used for plastic processing, for example. It becomes possible to obtain a magnesium alloy sheet having a fine structure in contact with a rolling roll or the like. In the present embodiment, the case where AZ61 is used as the magnesium alloy has been described. However, for example, similar results were obtained when AMX601 or AZX612 was used as the magnesium alloy . In addition, as described above, the manufacturing method of the magnesium alloy plate material according to the present embodiment includes AZ31, AZ61, AZ91 in which aluminum and zinc are added to magnesium as a magnesium alloy , and aluminum, zinc, and calcium relative to magnesium. AZX311, AZX611, AZX615, AZX6112, AZX711, AZX811, AZX911, AZX1001, and AMX301, AMX701, AMX801, AMX901, AMX1001, etc. to which aluminum, manganese and calcium are added to magnesium can be applied. .

  In the above, the manufacturing method of the magnesium alloy plate material which concerns on this embodiment, and the analysis result and test result which show the characteristic of the magnesium alloy plate material manufactured by this manufacturing method were demonstrated. Next, a manufacturing method of a magnesium alloy product according to the present embodiment and an analysis result and a test result showing characteristics of the magnesium alloy product manufactured by the manufacturing method will be described. In addition, about the structure same or similar to embodiment mentioned above, the same code | symbol may be attached | subjected and description may be abbreviate | omitted.

[Magnesium alloy products]
The magnesium alloy product according to the present embodiment is obtained by casting a melted magnesium alloy and applying plastic working after the casting, and is configured as a cast plate having irregularities on the surface at the stage of casting. Then, the unevenness of the cast plate is processed by plastic processing after casting, so that residual stress is applied to the surface layer portion. The magnesium alloy product according to this embodiment can be formed into a desired shape by plastic working.

[Magnesium cast plate]
The magnesium alloy product according to this embodiment is obtained by applying plastic working to a magnesium cast plate cast under the above-described conditions.

The magnesium alloy contains magnesium as a main component, and includes aluminum, manganese, zinc, calcium and the like. Aluminum can be added, for example, from 0% to 11% with respect to magnesium. Manganese can be added, for example, from 0% to 0.5% with respect to magnesium, and zinc can be added, for example, from 0% to 2.5% with respect to magnesium. Calcium can be added, for example, 0.5% or more and 12% or less with respect to magnesium.

Examples of magnesium alloys include AZ alloys in which aluminum and zinc are added to magnesium, AZX alloys in which aluminum, zinc and manganese are added to magnesium, and AMX in which aluminum, manganese and calcium are added to magnesium. Alloys can be used. More specifically, as a magnesium alloy , for example, AZ31, AZ61, AZ91 in which aluminum and zinc are added to magnesium, AZX311, AZX611, AZX711, AZX811, AZX911, in which aluminum, zinc, and calcium are added to magnesium, AZX1001, AMX301, AMX601, AMX701, AMX801, AMX901, AMX1001, or the like in which aluminum, manganese, and calcium are added to magnesium can be used.

The magnesium alloy is heated and melted, for example, in a molten metal furnace 10 that holds the melted magnesium alloy . The molten magnesium alloy as molten metal is discharged from an opening 11 provided on one end side of the molten metal furnace 10 and supplied between a pair of casting rolls 20 (21, 22) for casting the magnesium alloy. While being pressed by a pair of casting rolls 20 (21, 22) having a hole shape corresponding to the concavo-convex shape formed on the cast plate, it passes between the pair of casting rolls 20 (21, 22), is cooled, and is cast into magnesium. A magnesium cast plate having a concavo-convex shape on the surface of the plate is produced. At this time, the roll peripheral speed of the pair of casting rolls 20 (21, 22) is not particularly limited, but can be 20 m / min or more and 30 m / min or less.

The magnesium alloy is heated to, for example, 635 ° C. or higher and 730 ° C. or lower according to the component composition of the magnesium alloy , and is supplied between the pair of casting rolls 20 (21, 22). The temperature of the magnesium alloy after passing between the pair of casting rolls 20 (21, 22) is deprived of heat by the pair of casting rolls 20 (21, 22), and the pair of casting rolls 20 (21, 22). The surface temperature of the plate-shaped magnesium cast plate is cooled to a range of 380 ° C. to 450 ° C. at a point where it has moved between and about 300 mm. Thereafter, at a point moved about 1000 mm from the pair of casting rolls 20 (21, 22), the surface temperature of the magnesium cast plate rises to about 500 ° C. As described above, due to the temperature rise of the surface of the magnesium casting plate due to internal latent heat, a coarse structure is formed on the surface (surface layer portion) of the magnesium casting plate, and the inside (center portion) of the magnesium casting plate is fine. The organization will be maintained. That is, the cooling rate is different between the inside (center portion) of the magnesium cast plate and the surface (surface layer portion) of the magnesium cast plate in contact with the pair of cast rolls 20 (21, 22), and the solidification form is also different. It becomes. More specifically, the cooling rate of the magnesium cast plate is 1143 K / s at a point where it has moved about 50 mm through the pair of casting rolls 20 (21, 22), and passes through the pair of casting rolls 20 (21, 22). It is 132 K / s at a point moved about 300 mm, and further 61 K / s at a point moved about 2000 mm through a pair of casting rolls 20 (21, 22). As described above, at a point moved about 1000 mm from the pair of casting rolls 20 (21, 22), internal latent heat generated in the central portion of the magnesium casting plate is released to the surface (surface layer portion) of the magnesium casting plate. As a result, the temperature of the surface (surface layer portion) of the magnesium cast plate rises. Therefore, the cooling rate of the magnesium cast plate is in the range of −100 K / s to −50 K / s during casting.

  Heretofore, an example of a method for producing a magnesium cast plate has been described. As described above, a magnesium alloy product can be obtained by subjecting a magnesium cast plate having irregularities to plastic working. Next, plastic working performed on the magnesium cast plate will be described.

[Plastic processing]
As described above, plastic working refers to processing the unevenness formed on the magnesium cast plate. In the present embodiment, in order to obtain a magnesium alloy product having a desired shape, the inventors performed press working on the above-described magnesium cast plate, although not particularly limited as plastic working. Press work refers to a process in which a workpiece is placed between dies and subjected to high pressure molding using a lever, a screw, water pressure, or the like. In the present embodiment, although not particularly limited, the magnesium cast plate described above is heated to 250 ° C. or higher, and sandwiched by a mold for about 10 seconds, thereby pressing the magnesium cast plate to obtain a magnesium alloy having a desired shape. Got the product. At this time, the thickness of the α-magnesium layer in the thickness direction showed growth from 8.1 μm to 8.5 μm, for example. The time for sandwiching the magnesium cast plate with the mold is not particularly limited, but is preferably 10 seconds or more and 300 seconds or less.

  The analysis results and test results showing the characteristics of the magnesium alloy product obtained by performing press working as plastic working will be described. Here, FIG. 9 is a view showing a cross-sectional observation photograph of the magnesium alloy product according to the present embodiment, and is a micro observation photograph of the magnesium alloy product using AZX611. FIG. 10 is a view showing a cross-sectional observation photograph of the magnesium alloy product according to the present embodiment. The partial diagram (a) in FIG. 10 and the partial diagram (b) in FIG. 10 are magnesium using AZX611. It is a SEM observation photograph of an alloy product. In addition, the measuring apparatus etc. used the same thing as the apparatus mentioned above.

  As shown in FIG. 9, in the magnesium alloy product according to the present embodiment, it can be seen that the crystal grains in the contact portion with the mold are finer than the crystal grains in the central portion. The crystal grain size of the α-magnesium phase is, for example, 13 μm in the surface layer portion and 21 μm in the central portion. Here, although not particularly limited, the thickness of the surface layer portion having a fine structure is about 40 μm from the surface of the magnesium alloy product which is a contact portion with the mold, and the thickness of the central portion having the α-magnesium phase is 15 μm or more. It is preferable that The surface layer portion having a fine structure includes a magnesium phase, an intermetallic compound phase, and a single phase such as calcium, aluminum, and zinc, or a mixed phase of two or more of these additive elements. In the surface layer portion, the α-magnesium phase and the intermetallic compound phase are laminated. At this time, the direction in which the α-magnesium phase and the intermetallic compound phase are laminated may not be one direction. This is because compressive stress and tensile stress act on the magnesium cast plate when the magnesium cast plate is pressed.

  As shown in FIG. 10, in the magnesium alloy product according to the present embodiment, the intermetallic compound is finely dispersed in the surface layer portion, but is scattered in the central portion, and the crystal grains are different in crystal orientation. It becomes the inclination structure | tissue which has and joins. At this time, in the cross section of the magnesium alloy product, the ratio of the surface layer portion where the intermetallic compound is finely dispersed and the central portion where the intermetallic compound is scattered is about 60% and about 40%, respectively. Yes. The intermetallic compound is present in the surface layer part at an area ratio of 2% or more and 3% or less, and is present in the center part at an area ratio of 1.5%.

  In the magnesium alloy product manufacturing method according to the present embodiment, as in the magnesium alloy sheet manufacturing method described above, the magnesium cast plate cast with irregularities formed therein has crystal grains in the surface layer portion and crystal grains in the central portion. Compared with this, the structure has coarse or equivalent crystal grains. However, the magnesium alloy product obtained by performing press working as a plastic working on a magnesium cast plate with irregularities has crystal grains that are finer or equivalent in crystal grains in the surface layer part than the crystal grains in the central part of the magnesium alloy product. It is a particle size and exhibits a uniform structure. Therefore, according to the method for manufacturing a magnesium alloy product according to the present embodiment, it has high strength even at a low number of times of processing and a low degree of processing, exhibits easy formability at the time of molding, and is in contact with, for example, a mold used for plastic processing. A magnesium alloy product in which the part to be formed has a fine structure can be obtained.

  In the above, the analysis result and test result which show the characteristic of the magnesium alloy product which concerns on this embodiment were demonstrated. In addition, the magnesium alloy product according to the present embodiment can be subjected to plastic working after annealing the magnesium cast plate on which the unevenness is formed. Below, in order to obtain the magnesium alloy product which concerns on this embodiment, the conditions suitable when performing annealing are demonstrated.

It is possible to increase the ductility of the magnesium cast plate by placing a weight on the magnesium cast plate having irregularities formed on the surface, applying a load to the magnesium cast plate, and performing annealing for about 2 hours. At this time, the annealing temperature is not particularly limited, but is preferably 250 ° C. or more and 350 or less. Annealing can be, for example, laminated annealing in which a magnesium cast plate is sandwiched between plates having a large specific gravity, such as an iron plate, and annealing is performed. When annealing is performed by such lamination annealing, the crystal grain size of the α-magnesium phase is 3 μm even if the magnesium cast plate is subjected to heat treatment at a temperature higher than the recrystallization temperature or the crystal grain growth temperature of the magnesium alloy. To 8.1 μm, and excessive crystal grain growth can be prevented. In some cases, the crystal grain size of the α-magnesium phase can be refined from about 25 μm to about 24 μm even when a load is applied to the magnesium cast plate and the temperature is further increased.

  And the press work as a plastic working will be given to the magnesium cast plate which annealed as mentioned above. At this time, for example, when the temperature of the magnesium cast plate is set to 350 ° C., the processing speed of the press working can be set to 2.7 mm / s.

  In the above, the manufacturing method of the magnesium alloy product which concerns on this embodiment, and the analysis result and test result which show the characteristic of the magnesium alloy product manufactured by this manufacturing method were demonstrated.

[Magnesium alloy final product]
By applying a forming process to obtain the desired shape on the magnesium alloy plate material and the magnesium alloy product described above, the residual stress generated in the surface layer portion of the magnesium alloy plate material and the magnesium alloy product acts, resulting in fine grains. It is possible to obtain magnesium alloy final products of various shapes having a structure in which the formation of is promoted.

  As mentioned above, although preferred embodiment of this invention was described, the technical scope of this invention is not limited to the range as described in the said embodiment. Various modifications or improvements can be added to the embodiment.

  For example, in the above-described embodiment, the magnesium cast plate with the irregularities formed on the surface is manufactured by a twin roll casting method, but for example, manufactured by an antigravity casting method such as semi-floating melting or vacuum suction casting. Can do.

The magnesium alloy is heated to, for example, 630 ° C. or higher and 750 ° C. or lower in accordance with the component composition of the magnesium alloy , and cast into a mold having an uneven shape by, for example, vacuum suction. The magnesium alloy is cooled and cast to a range of 440 ° C. to 550 ° C. by contacting with the mold, and then the internal latent heat generated in the central portion of the magnesium cast plate is applied to the surface (surface layer portion) of the magnesium cast plate. By releasing, a temperature rise of the surface (surface layer portion) of the magnesium cast plate occurs. Accordingly, a coarse structure is formed on the surface (surface layer portion) of the magnesium cast plate, and a cast plate having irregularities maintaining the fine structure is cast inside the magnesium cast plate (center portion). .

  When cooling was not performed when casting the magnesium cast plate, the cooling rate at the center was 2.8 K / s, and the cooling rate at the surface layer was 3.4 K / s. On the other hand, when the magnesium cast plate is cast with water at 30 ° C. or 90 ° C., the cooling rate at the center is 12 K / s, and the cooling rate at the surface layer is cooled with 30 ° C. water. In this case, it was 29.4 K / s, and when it was cooled with water at 90 ° C., it was 21.2 K / s.

Inventors analyzed the influence which the ratio of the calcium added with respect to magnesium has on the mechanical property about the magnesium cast plate obtained on the casting condition mentioned above. Using a magnesium alloy in which 0 wt% to 12 wt% calcium was added to AZ61 alloy, the mechanical properties of a magnesium cast plate cast by the antigravity casting method under the above-described casting conditions were measured. The measurement methods of the maximum tensile strength (UTS), the yield strength (YS), and the elongation at break (EL) were performed based on JIS standards. In the tensile test, JIS standard 13B or a unique test piece shape was used as a test piece, and the tensile speed was 2 mm / min at the crosshead speed. Here, in the original test piece shape, the plate width was 3 mm and the distance between the gauge points was 30 mm in the standard dimensions. The Vickers hardness (HV) was measured by applying a 300 g weight for 30 seconds with a Vickers hardness tester. Further, the intercept method was used to measure the average crystal grain size. The result is shown in FIG. Here, FIG. 11 is a figure which shows the measurement result of the mechanical property for every calcium content rate of the magnesium casting plate which concerns on this embodiment, and the fractional diagram (a) in FIG. 11 shows the maximum tensile strength (UTS). It is a figure which shows a measurement result, The fraction figure (b) in FIG. 11 is a figure which shows the measurement result of yield strength (YS), and the fraction figure (c) in FIG. 10 is a fracture elongation (EL). It is a figure which shows a measurement result, the fraction (d) in FIG. 11 is a figure which shows the measurement result of Vickers hardness (HV), and the fraction (e) in FIG. It is a figure which shows a result.

  As shown in FIG. 11, it was found that the maximum tensile strength (UTS), yield strength (YS), and Vickers hardness (HV) increase as the proportion of calcium added to magnesium increases. On the other hand, the elongation at break (EL) was found to decrease as the proportion of calcium added to magnesium increased.

In addition, the inventors analyzed the influence of the proportion of aluminum added to the magnesium alloy on the mechanical properties. Using a magnesium alloy obtained by adding 0 wt% to 10 wt% calcium to an AZX alloy or AMX alloy, the mechanical properties of a magnesium cast plate cast by the antigravity casting method under the above-described casting conditions were measured. The measurement methods of the maximum tensile strength (UTS), the yield strength (YS), and the elongation at break (EL) were performed based on JIS standards. In the tensile test, JIS standard 13B or a unique test piece shape was used as a test piece, and the tensile speed was 2 mm / min at the crosshead speed. Here, in the original test piece shape, the plate width was 3 mm and the distance between the gauge points was 30 mm in the standard dimensions. The Vickers hardness (HV) was measured by applying a 300 g weight for 30 seconds with a Vickers hardness tester. Further, the intercept method was used to measure the average crystal grain size. The results are shown in FIG. 12 and FIG. Here, it is a figure which shows the measurement result of the mechanical property for every aluminum content rate of the magnesium cast plate cast using the AZX type alloy, and the fraction (a) in FIG. 12 shows the maximum tensile strength (UTS). It is a figure which shows a measurement result, and the fraction (b) in FIG. 12 is a figure which shows the measurement result of yield strength (YS), and the fraction (c) in FIG. It is a figure which shows a measurement result, the fraction (d) in FIG. 12 is a figure which shows the measurement result of Vickers hardness (HV), and the fraction (e) in FIG. It is a figure which shows a result. FIG. 13 is a diagram showing measurement results of mechanical properties for each aluminum content of a cast plate cast using an AMX alloy, and a partial diagram (a) in FIG. 13 shows the maximum tensile strength (UTS). ) Is a diagram showing a measurement result, FIG. 13 is a partial diagram (b) is a diagram showing a measurement result of yield strength (YS), and FIG. 13 is a partial diagram (c) is an elongation at break (EL). ) Is a diagram showing a measurement result of FIG. 13, a fractional diagram (d) in FIG. 13 is a diagram showing a measurement result of Vickers hardness (HV), and a fractional diagram (e) in FIG. It is a figure which shows the result of a diameter.

As shown in FIG. 12, it can be seen that the Vickers hardness (HV) increases as the content of aluminum added to the magnesium alloy increases in the AZX alloy to which 1% zinc and 1% calcium are added. It was. In addition, the maximum tensile strength (UTS) and the yield strength (YS) show maximum values when the aluminum content added to the magnesium alloy is about 7 wt% to 9 wt%, and the aluminum content added is further increased. However, it was found to show a decrease or a constant value. On the other hand, it has been found that the elongation at break (EL) and the average crystal grain size tend to decrease as the content of aluminum added to the magnesium alloy increases.

As shown in FIG. 13, regarding the AMX-based alloy to which 0.1% manganese and 1% calcium are added, when the aluminum content added to the magnesium alloy increases, the yield strength (YS) and the Vickers hardness ( HV) was found to increase.

From the above examination, it was found that the ratio of aluminum added to the magnesium alloy according to the present embodiment is not particularly limited, but is preferably 6% or more and 10% or less.

  As described above, the mechanical properties of the magnesium cast plate cast by the antigravity casting method have been described. However, the magnesium cast plate cast by the antigravity casting method may be subjected to plastic working as in the above-described embodiment. it can. By applying plastic working to the magnesium cast plate with irregularities formed at the casting stage, the residual stress generated in the surface layer part acts as in the above-described embodiment, and the formation of fine grains is promoted. The crystal grain has a grain size equivalent to that of the central portion, and a magnesium alloy plate material having a uniform structure can be obtained.

  Further, for example, in the above-described embodiment, irregularities are formed on the surface of the magnesium casting plate at the stage where the magnesium casting plate is cast. After the magnesium casting plate is cast, The removal process which forms an unevenness | corrugation in the surface of a cast plate can be given, and an unevenness | corrugation can be formed in the surface of the said magnesium cast plate. Here, the removal process is a process for forming irregularities on the surface of the magnesium cast plate. As the removal process, for example, a cutting process, a polishing process, a rolling process, or the like can be used. And the magnesium cast board in which the unevenness | corrugation was formed in the surface by the removal process will be plastically processed similarly to the case where it mentioned above. As described above, by processing the irregularities formed on the surface of the magnesium cast plate, it is possible to obtain a magnesium alloy plate material or a magnesium alloy product in which residual stress is applied to the surface layer portion.

  It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 Twin roll casting apparatus, 10 molten metal furnace, 11 opening part, 20 casting roll, 21 1st casting roll, 22 2nd casting roll

Claims (5)

It is a method for producing a magnesium alloy product obtained by casting a molten magnesium alloy melt by a twin roll casting method in which it is cast by a pair or a plurality of pairs of rolls, and adding plastic working after the casting,
At the stage where casting is performed, cast a cast plate having irregularities on the surface,
By processing the unevenness of the cast plate by plastic processing performed after the casting , including a step of applying a residual stress to the surface layer portion ,
The magnesium alloy includes AZ31, AZ61, and AZ91 in which aluminum and zinc are added to magnesium, AZX311, AZX611, AZX711, AZX811, AZX911, AZX1001, and magnesium in which aluminum, zinc, and calcium are added to magnesium. One selected from AMX301, AMX601, AMX701, AMX801, AMX901, and AMX1001 to which aluminum, manganese and calcium are added,
The height difference of the unevenness of the cast plate having unevenness on the surface is 0.04 mm or more and 0.3 mm or less,
The temperature at which the molten magnesium alloy is supplied between a pair or a plurality of pairs and the casting is started is 635 ° C. or higher and 730 ° C. or lower,
At the point where the magnesium alloy has moved 300 mm by passing between one or more pairs of rolls, the surface temperature of the cast plate made into a plate is cooled to a range of 380 ° C. to 450 ° C.,
The surface temperature of the cast plate rises to approximately 500 ° C. at a point where the magnesium alloy has moved between a pair or a plurality of pairs and moved 1000 mm, so that the internal latent heat inside the magnesium alloy is increased to the cast plate. By being discharged to the surface of the casting plate, it is executed so that the cooling rate is different between the surface layer portion which is the surface of the cast plate and the central portion which is the inside,
The cooling rate of the cast plate is 1143 K / s at a point moved 50 mm through one or more pairs of rolls, 132 K / s at a point moved 300 mm through a pair or pairs of rolls, and It is 61 K / s at a point moved 2000 mm through a pair or a plurality of pairs of rolls, and further, an internal latent heat generated in the central portion inside the cast plate at a point moved 1000 mm from the pair or a plurality of pairs of rolls. However, when the temperature of the surface layer portion that is the surface of the cast plate is increased by being discharged to the surface layer portion that is the surface of the cast plate, the cooling rate of the cast plate is -100K in the middle of casting. / S to −50 K / s . In the manufacturing method of the magnesium alloy product of Claim 1 ,
The method for producing a magnesium alloy product, wherein the plastic working is press working. In the manufacturing method of the magnesium alloy product of Claim 2 ,
A method for producing a magnesium alloy product, characterized in that the cast plate is heated to 250 ° C. or higher and is pressed by a mold for 10 seconds to 300 seconds. In the manufacturing method of the magnesium alloy product according to claim 2 or 3 ,
A method for producing a magnesium alloy product, comprising subjecting the cast plate to annealing and then performing the plastic working. In the manufacturing method of the magnesium alloy product according to claim 4 ,
The method for producing a magnesium alloy product, wherein the annealing temperature is 250 ° C. or higher and 350 ° C. or lower.