JP7410542B2 - magnesium alloy plate - Google Patents

Description

The present invention relates to a magnesium alloy plate.

Magnesium alloy has the lowest specific gravity among all practical metals, and is therefore expected to be used as a lightweight material in the fields of aircraft, automobiles, and electronic devices.

On the other hand, the crystal structure of a magnesium alloy is a close-packed hexagonal lattice structure, which has a problem of having a small number of slip systems near room temperature and poor formability at room temperature (for example, 0° C. to 40° C.). This is because in the crystal texture of AZ31 alloy (containing 3% Al and 1% Zn), which is a general magnesium alloy plate, the (0001) plane of the close-packed hexagonal lattice structure is on the plate surface (rolled surface). This is because the (0001) planes are arranged parallel to each other and the degree of integration of the (0001) planes is high, so that sliding deformation can only occur on the (0001) planes at room temperature.

To solve this problem, a method has been proposed in which the orientation of the (0001) plane is randomized by applying shear deformation at room temperature using a roller leveler and then performing recrystallization heat treatment multiple times (Patent Document 1). . Furthermore, a method has been proposed in which the orientation of the (0001) plane is randomized by performing rolling near the solidus line and then performing recrystallization heat treatment (Patent Document 2). Furthermore, a method has been proposed in which the orientation of the (0001) plane is randomized by adding a trace amount of a specific element such as a rare earth element or calcium to an Mg--Zn alloy (Patent Document 3).

Japanese Patent Application Publication No. 2005-298885 Japanese Patent Application Publication No. 2010-133005 Japanese Patent Application Publication No. 2010-13725

However, according to the experiments conducted by the present inventors, the magnesium alloy plates manufactured by the methods of Patent Documents 1 to 3 have the disadvantage that their strength is lower than that of magnesium alloy plates that are not subjected to the same treatment. It was confirmed that In recent years, lightweight materials used in automobiles, mobile home appliances, etc. are required to have both moldability at room temperature and higher strength. It is difficult to obtain a magnesium alloy that satisfactorily meets the demand for higher strength.

On the other hand, as a way to simply increase the strength of a magnesium alloy plate, it is possible to use conventionally known methods such as precipitation strengthening or solid solution strengthening, but in the case of such methods, ductility (elongation) This results in a significant deterioration in workability. In particular, magnesium alloys have poor workability at room temperature, leading to further deterioration of workability. Generally, the relationship between strength and ductility (elongation) is referred to as "strength-ductility balance," and a material that is said to have a good strength-ductility balance refers to a material that has both high strength and ductility. It has not been easy to obtain a magnesium alloy plate that has high strength and high elongation, that is, an excellent strength-ductility balance, as a lightweight material.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnesium alloy plate that has excellent formability at room temperature and high strength.

In order to solve the above problems, the present invention provides a magnesium alloy plate containing Ag and Ca,
The content of Ag is 0.3 to 6.0% by mass,
The content of Ca is 0.05 to 1.0% by mass,
The remainder consists of magnesium and unavoidable impurities,
It is characterized in that the degree of integration of (0001) planes in the dense hexagonal lattice structure is less than 3.5.

The magnesium alloy member of the present invention is characterized in that the magnesium alloy plate is processed.

The method for producing a magnesium alloy plate of the present invention is a method for producing a magnesium alloy plate containing Ag and Ca, comprising:
The following steps:
A magnesium alloy billet having an Ag content of 0.3 to 6.0% by mass, a Ca content of 0.05 to 1.0% by mass, and the balance consisting of magnesium and inevitable impurities. Casting process to produce;
It is characterized by comprising a rolling step of rolling the magnesium alloy billet or its processed product at 200° C. to 500° C.; and an annealing step of slowly cooling it at 200° C. to 500° C. after the rolling step.

The magnesium alloy plate of the present invention has excellent formability at room temperature and high strength. The method for producing a magnesium alloy plate of the present invention can yield a magnesium alloy plate that has excellent formability at room temperature and high strength. Therefore, the magnesium alloy plate of the present invention can be applied to, for example, the outer panels of automobiles that require sufficient dent resistance, and can reduce the weight of automobiles.

(0001) plane texture of (1) Comparative Example 1, (2) Example 1, (3) Example 2, (4) Example 4, (5) Example 5, (6) Example 6 It is a figure showing the result of analysis by line diffraction. (1) The structures of Example 1, (2) Example 2, (3) Example 5, (4) Example 6, (5) Comparative Example 2, and (6) Comparative Example 4 were qualitatively analyzed by X-ray diffraction. It is a figure showing the result of analysis.

As mentioned above, conventional Mg-Zn-Ca based alloys have excellent room temperature formability, but their strength is low, making it difficult to use them as automotive parts that require a balance between high strength and ductility. . The present inventors targeted Mg-Ag-Ca alloys with excellent age hardenability, and by adjusting the alloy additive concentration and considering specific rolling conditions, we succeeded in reducing the aggregation during recrystallization. It has been found that the accumulation of (0001) planes in the dense hexagonal lattice structure of the tissue acts in a weakening direction. Furthermore, it has been found that high formability at room temperature can be maintained by adjusting the composition of the alloy. The present invention has been made based on such novel findings.

An embodiment of the present invention will be described below.

The magnesium alloy plate of the present invention is a Mg--Ag--Ca based alloy containing magnesium as a main component and containing Ag and Ca.

The content of Ag is 0.3 to 6.0% by mass. When the Ag content is 0.3% by mass or more, there will be a sufficient amount of Ag solid-solved inside the magnesium (matrix), and Ag will segregate at the grain boundaries, effectively forming the (0001) plane. The orientation of can be randomized. On the other hand, when the Ag content exceeds 6.0% by mass, crystallized substances such as AgMg ₄ and CaAg ₂ are generated, making it impossible to obtain high moldability at room temperature. The content of Ag is more preferably 1.0 to 6.0% by mass.

The content of Ca is 0.05 to 1.0% by mass. When the Ca content is 0.05% by mass or more, there will be a sufficient amount of Ca dissolved inside Mg (matrix), and Ca will segregate at grain boundaries, effectively forming the (0001) plane. The orientation of can be randomized. On the other hand, if the Ca content exceeds 1.0% by mass, crystallized phases such as Mg ₂ Ca will be generated, making it impossible to obtain high moldability at room temperature.

The remainder other than Ag and Ca consists of magnesium and inevitable impurities. Examples of unavoidable impurities include Fe, Ni, and C.

In the magnesium alloy plate of the present invention, the degree of integration of the (0001) planes of the close-packed hexagonal lattice structure on the plate surface (rolled surface) is less than 3.5. Since the orientation of the (0001) plane is suppressed, the magnesium alloy plate has excellent room temperature formability. Note that the degree of integration of the (0001) plane is a value measured by, for example, the XRD method (Schulz reflection method).

Currently, research is being conducted on the mechanism that randomizes the orientation of the (0001) plane texture after rolling and annealing, mainly in Mg-Zn-Ca alloys. For example, Griffiths reported that Zn and Ca dissolved in magnesium segregate in the grain boundaries, and as a result, dynamic recrystallization is suppressed due to the drag effect, and as a result, the orientation of the (0001) plane is suppressed. (D. Griffiths: Mater. Sci. Technol., Vol. 31 (2015), pp. 10-24.) Regarding Mg-Ag-Ca alloys, by the same mechanism, Ag and Ca dissolved in magnesium segregate in the grain boundaries, and as a result, dynamic recrystallization is suppressed by the drag effect, and as a result, (0001) It can be considered that the orientation of the plane is suppressed.

The magnesium alloy plate of the present invention has excellent formability at room temperature, and also has high strength and age hardenability. That is, the magnesium alloy plate of the present invention has an excellent strength-ductility balance and has high strength and ductility. Regarding formability, magnesium alloy sheets have formability comparable to that of aluminum alloys (Erichsen value of 6.5 or more) or comparable to aluminum alloys (Erichsen value of 8.0 or more) at room temperature (approximately 30°C). have.

Therefore, the magnesium alloy plate of the present invention can be processed into various magnesium alloy members such as aircraft parts, electronic equipment, automobile parts, outer panels, and the like.

Next, an embodiment of the method for manufacturing a magnesium alloy plate of the present invention will be described.

In the method for manufacturing a magnesium alloy plate of the present invention, the content of Ag is 0.3 to 6.0% by mass, the content of Ca is 0.05 to 1.0% by mass, and the balance is A magnesium alloy billet consisting of magnesium and inevitable impurities is produced (casting process).

Next, the magnesium alloy billet or its processed product is rolled at 200°C to 500°C (rolling step). Specifically, warm extrusion and/or rough rolling are performed to produce a rolling material having a plate thickness of approximately 4 mm to 10 mm, for example. Thereafter, warm rolling (approximately 200° C. to 350° C.) or hot rolling (350° C. to 500° C.) can be performed to a desired thickness. Normally, it can be rolled to a thickness of about 0.5 mm to 2.0 mm, which is the thickness applied to electronic devices, automobiles, etc.

After the rolling process, it is slowly cooled at 200°C to 500°C (annealing (recrystallization heat treatment) process). The time for the annealing step can be set as appropriate, and may be, for example, about 30 minutes to 6 hours.

In addition, in addition to the above-mentioned steps, the method for manufacturing a magnesium alloy plate of the present invention may include, for example, known plastic working such as extrusion, forging, and drawing.

The magnesium alloy plate and the manufacturing method thereof of the present invention are not limited to the above embodiments.

Hereinafter, the magnesium alloy plate of the present invention and the manufacturing method thereof will be explained along with Examples, but the magnesium alloy plate of the present invention and the manufacturing method thereof are not limited to the following Examples.

(1) Production of magnesium alloy plate Magnesium alloy billets having the chemical components shown in Table 1 were produced by melting and casting (casting process). Thereafter, extrusion processing was performed at 380°C or 400°C (extrusion temperatures are shown in Table 1) to obtain a plate with a thickness of 5 mm. The sample was then rolled at a temperature of 450°C or 350°C (rolling temperatures are shown in Table 1) to obtain a plate with a thickness of 1.0 mm (rolling process). After rolling, these plates were annealed (recrystallization heat treatment) for 1.5 hours at 350°C according to a conventional manufacturing process (annealing process).

(2) Room-temperature formability of magnesium alloy plate In order to evaluate the room-temperature formability of the produced magnesium alloy plate, an Erichsen test was conducted. The Erichsen test is based on JIS B7729 and JIS Z2247. Note that the blank shape was φ60 mm (thickness 1 mm) due to the shape of the plate material. The mold (sample) temperature was 30° C., the molding speed was 5 mm/min, and the wrinkle pressing force was 10 kN. Graphite grease was used as the lubricant.

The (0001) plane texture of the above magnesium alloy plate material was measured by the XRD method (Schulz reflection method). For the measurements, a sample of 20 mm x 20 mm x 1 mm was cut out from the rolled material, the RD-TD surface was milled to a thickness of 0.5 mm, and the surface was polished with #4000 SiC abrasive paper. . The tube voltage at the time of measurement was 40 kV, and the current value was 40 mA (the tube used was a Cu tube). The α angle measurement range was 15 to 90°, and the measurement step angle was 2.5°. The measurement range of the β angle was 0 to 360°, and the measurement step angle was 2.5°. Note that background measurements were not performed. After normalizing the measured data with random data (internal standard data), a pole figure was drawn with the vertical direction as the RD direction and the horizontal direction as the TD direction (FIG. 1).

The measurement results of the (0001) plane texture by X-ray diffraction and the results of the Erichsen test are shown in FIG. 1 and Table 2.

(1) to (6) in Figure 1 are samples obtained by rolling a Mg-0.1%Ca alloy with 0 to 12% Ag added to a thickness of 5 mm to 1 mm at a sample temperature of 350°C or 450°C. This is a (0001) plane texture of a plate material produced by annealing. The degree of integration indicates the maximum intensity of the pole figure. Note that the contour lines shown in the pole figure shown in FIG. 1 are relative intensities, and the contour lines are drawn with the degree of accumulation as the maximum value.

Figure 1 (1) is Comparative Example 1, Figure 1 (2) is Example 1, Figure 1 (3) is Example 2, Figure 1 (4) is Example 4, Figure 1 (5) is Example 5, FIG. 1(6) corresponds to Comparative Example 2.

Figure 1 (1) shows the (0001) plane texture of the Mg-0.1%Ca alloy, and a texture in which the (0001) planes are arranged parallel to the plate surface, which is unique to general-purpose magnesium alloy rolled materials, is observed. be done. That is, the peak of the (0001) plane appears at a position parallel to the ND direction (vertical direction). On the other hand, in the Mg-Ag-Ca alloy in which Ag is added to the Mg-0.1%Ca alloy, in Figs. A pole appears, and the degree of integration of the (0001) plane is less than 3.5, confirming that the orientation is randomized. It was confirmed that the Mg-Ag-Ca based alloy in which the orientation of the (0001) plane was suppressed exhibited excellent room temperature formability.

As shown in Table 2, Mg-Ag-Ca alloys containing 0.3% to 6% Ag and 0.1% to 1% Ca have room temperature Erichsen values exceeding 7.5. (Examples 1 to 8). On the other hand, alloys outside the above composition range showed room temperature Erichsen values below 6.5 (Comparative Examples 1 to 4).

In addition, the crystallized substances were identified by X-ray diffraction. The tube voltage at the time of measurement was 40 kV, and the current value was 40 mA (the tube used was a Cu tube). Measurements were performed every 0.01°, and the scan speed was 1°/min.

The results of identification of crystallized substances by X-ray diffraction are shown in FIG. Figure 2 (1) to (5) shows the reduction rate per pass of Mg-0.1%Ca alloy with 0.3% to 12% silver added at a sample temperature of 350°C or 450°C. These are the results of qualitative analysis of the composition by XRD of a plate material prepared by annealing a sample rolled from 5 mm to 1 mm in thickness at 20%/pass. Further, (6) in FIG. 2 shows the results of qualitative analysis of the composition by XRD of a plate material produced by rolling a Mg-1.5%Ag-2%Ca alloy under the same conditions as above.

Figure 2 (1) is Example 1, Figure 2 (2) is Example 2, Figure 2 (3) is Example 5, Figure 2 (4) is Example 6, Figure 2 (5) is Comparative Example 2, FIG. 2(6) corresponds to comparative example 4.

Paying attention to (1) to (5) in Figure 2, it shows a Mg single-phase structure up to an Ag concentration of 3%, but when the Ag concentration increases to 6%, crystallized AgMg ₄ and CaAg ₂ are formed. A peak appears. When the Ag concentration increases to 12%, the peak rises, indicating that a relatively large amount of the above-mentioned crystallized substances are crystallized. Moreover, when paying attention to FIG. 2(6), it can be seen that when the Ca concentration increases to 2%, the peak of Mg ₂ Ca increases, and a relatively large amount of the above-mentioned crystallized substances are crystallized. In this way, if Ag and Ca are added excessively, a relatively large amount of the above-mentioned crystallized substances will crystallize, and the crystallized substances will become the starting point of destruction. Even if the orientation of the (0001) plane is randomized, Also, high room temperature moldability cannot be obtained. For example, the Mg-12%Ag-0.1%Ca alloy has a (0001) plane texture with an integration degree of 3.6, as shown in Table 2 and (6) in Figure 1, but (5) in Figure 2 As shown in the figure, high room temperature moldability cannot be obtained due to the presence of crystallized substances such as AgMg ₄ and CaAg ₂ .

As mentioned above, from FIG. 1 and Table 2, in a magnesium alloy in which the Ag content is 0.3 to 6.0 mass% and the Ca content is 0.05 to 1.0 mass%, (0001 ) It can be seen that the degree of accumulation of surface texture is less than 3.5. In addition, from Figure 2, when Ag and/or Ca is added in excess of the predetermined amount, the amount of crystallized products such as AgMg ₄ , CaAg ₂ , Mg ₂ Ca, etc. that become the starting point of fracture during molding increases. I know that.

The degree of integration of the (0001) plane texture in Comparative Examples 1 and 2, in which a predetermined amount of Ag or Ca was not added, was higher than 3.5, and as a result, the room temperature Erichsen It was confirmed that the value was shown. In addition, in Comparative Example 4, although the degree of accumulation of the (0001) plane texture was less than 3.5, it was confirmed that the amount of crystallized products produced by Ca increased and the room temperature Erichsen value was less than 6.5. It was done.

On the other hand, the degree of accumulation of the (0001) plane texture of Examples 1 to 7 in which the Ag content is 0.3 to 6.0 mass % and the Ca content is 0.05 to 1.0 mass %. showed a value lower than 3.5, and as a result, it was confirmed that the room temperature Erichsen value was 6.5 or more. Furthermore, Examples 2 to 6 exhibited room temperature Erichsen values of 8 or more, and it was confirmed that they exhibited room temperature stretch formability comparable to that of aluminum alloys.

(3) Age Hardenability of Magnesium Alloy Sheet Among the Mg-Ag-Ca alloy sheets mentioned above, the age hardenability of Examples 3, 6, 7, and 8 and Comparative Example 2 was investigated. The results are shown in Table 3. In investigating age hardenability, the plate material was kept in an oil bath kept at a predetermined temperature (170° C.) for a predetermined period of time, and then its Vickers hardness was evaluated. The Vickers hardness test is based on JIS Z2244. The load during the test was 0.2 kgf, the holding time was 10 seconds, the maximum value and minimum value were removed from the obtained 10 test values, and the average value of 8 points was taken as Vickers hardness.

As shown in Table 3, it can be confirmed that significant age hardening occurs in all alloys when the Ca concentration is changed or when the Ag concentration is changed. In this way, the Mg-Ag-Ca based alloy can obtain both excellent room temperature formability and age hardenability by selecting predetermined Ca and Ag concentrations.

The magnesium alloy plate obtained by the present invention improves the workability or formability at room temperature of Mg-Ag-Ca alloys that have excellent age hardenability, and can be formed by conventional room temperature forming. This solves the problem that magnesium alloys had, namely their low strength. As a result, it is possible to perform more complex processing at room temperature, and it is possible to obtain parts with high strength, making it a material that can contribute to reducing the weight of electronic devices and automobile parts. In particular, for automobile exterior panels, moldability and dent resistance are required, and this material can meet these requirements.

Claims (3)

A magnesium alloy plate containing Ag and Ca,
The content of Ag is 0.3 to 6.0% by mass,
The content of Ca is 0.05 to 1.0% by mass,
The remainder consists of magnesium and unavoidable impurities,
A magnesium alloy plate characterized in that the degree of integration of (0001) planes in a dense hexagonal lattice structure is less than 3.5. A magnesium alloy member obtained by processing the magnesium alloy plate according to claim 1. A method for manufacturing a magnesium alloy plate containing Ag and Ca, the method comprising:
The following steps:
A magnesium alloy billet having an Ag content of 0.3 to 6.0% by mass, a Ca content of 0.05 to 1.0% by mass, and the balance consisting of magnesium and inevitable impurities. Casting process to produce;
a rolling step of rolling the magnesium alloy billet or its processed product at 200°C to 500°C; and an annealing step of holding the magnesium alloy billet or its processed product at a temperature of 200°C to 500°C below the temperature of the rolling step after the rolling step;
A method for producing a magnesium alloy plate , the method comprising: obtaining a magnesium alloy plate in which the degree of integration of (0001) planes in a dense hexagonal lattice structure is less than 3.5 .

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