MAGNESIUM ALLOY AND METHOD FOR MAKING THE SAME

Abstract

A magnesium alloy includes about 7.0 to about 8.0 wt % aluminum, about 0.45 wt % to about 0.90 wt % zinc, about 0.17 wt % to about 0.40 wt % manganese, about 0.50 wt % to about 1.5 wt % rare earth elements, about 0.00050 wt % to about 0.0015 wt % beryllium, and the rest being magnesium and unavoidable impurities. A method for making the magnesium alloy is also provided.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to a co-pending U.S. patent application, Ser. No. 13/279,282, filed on Oct. 23, 2011, and entitled "MAGNESIUM ALLOY AND METHOD OF MAKING THE SAME" In the aforementioned co-pending application, the inventors are Li et al. The co-pending application has the same assignee as the present application. The disclosure of the above identified application is incorporated herein by reference.

BACKGROUND

[0002] 1. Technical Field

[0003] The present disclosure relates to magnesium alloys, particularly to a magnesium alloy having good processing property and high corrosion resistance, and a method for making the same.

[0004] 2. Description of the Related Art

[0005] Magnesium alloys have low density, high mechanical strength, high thermal conductivity, high electrical conductivity, good electromagnetic interference shielding property, and good machining property, and have been widely used in the aerospace, automotive industries and consumer electronic devices. However, during processing, for example, extruding of magnesium alloy sheets, general-grade magnesium alloys have an unfavorable processing property due to the insufficient ductibility and toughness thereof, and products made from material thereof have a bad corrosion resistance.

[0006] Therefore, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Many aspects of the embodiments can be better understood with reference to the following drawings.

[0008] FIG. 1 shows a flowchart of a method for making a magnesium alloy of an illustrated embodiment.

[0009] FIG. 2 shows a table presenting the results of the mechanical properties of the magnesium alloy from an example 1 at room temperature.

[0010] FIG. 3 shows a table presenting the results of the mechanical properties of the magnesium alloy from an example 2 at room temperature.

[0011] FIG. 4 shows a table presenting the results of the mechanical properties of the magnesium alloy from an example 3 at room temperature.

[0012] FIG. 5 shows a table presenting the results of the mechanical properties of the magnesium alloy from the example 1 at 170° C.

[0013] FIG. 6 shows a table presenting the results of the mechanical properties of the magnesium alloy from the example 2 at 170° C.

[0014] FIG. 7 shows a table presenting the results of the mechanical properties of the magnesium alloy from the example 3 at 170° C.

[0015] FIG. 8 shows a table presenting the results of the mechanical properties of the AZ91D magnesium alloy at room temperature.

[0016] FIG. 9 shows a table presenting the results of the mechanical properties of the AZ91D magnesium alloy at 170° C.

[0017] FIG. 10 shows a table presenting the results of the mechanical properties of the magnesium alloy from an example 4 at room temperature.

[0018] FIG. 11 shows a table presenting the results of the mechanical properties of the magnesium alloy from the example 4 at 170° C. .

[0019] FIGS. 12(a)-(d) shows a plurality of microstructure images of the magnesium alloy obtained from the example 1 and the example 4.

[0020] FIG. 13 shows a table presenting the results of etching weight per square centimeter when dipping the magnesium alloy from the example 1 and the AZ91D magnesium alloy in salt water.

DETAILED DESCRIPTION

[0021] An embodiment of a magnesium alloy contains the following: about 7.0 weight (wt) % to about 8.0 wt % aluminum (Al), about 0.45 wt % to about 0.90 wt % zinc (Zn), about 0.17 wt % to about 0.40 wt % manganese (Mn), about 0.50 wt % to about 1.5 wt % rare earth elements (RE), about 0.0005 wt % to about 0.0015 wt % beryllium (Be), and the rest being magnesium (Mg) and unavoidable impurities. The preferred range of Al is about 7.2 wt % to about 7.8 wt %. RE is preferably made of one or more material selected from the group consisting of cerium (Ce), lanthanum (La), praseodymium (Pr), neodymium (Nd), yttrium (Y) and any suitable combination thereof. The preferred range of RE is about 0.50 wt % to about 0.8 wt %. In the illustrated embodiment, the RE is Nd.

[0022] Referring to FIG. 1, a method for making the above-described magnesium alloy of the illustrated embodiment includes the following steps.

[0023] In a first step S101, raw materials are provided. The raw materials contains: about 7.0 wt % to about 8.0 wt % Al, about 0.45 wt % to about 0.90 wt % Zn, about 0.17 wt % to about 0.40 wt % Mn, about 0.50 wt % to about 1.5 wt % RE, about 0.0005 wt % to about 0.0015 wt % Be, and the rest being Mg and impurities. Preferably, in the illustrated embodiment, the Al (composition) includes pure Al and an Al--Be inter-alloy, the Zn includes pure Zn, the Mn includes anhydrous manganese dichloride (MnCl₂), the RE includes a Mg--RE inter-alloy, the Be includes an Al--Be inter-alloy, and the Mg includes pure Mg and a Mg--RE inter-alloy. The RE (composition) can be one or more materials selected from the group consisting of Ce, La, Pr, Nd, Y, and any suitable combination thereof.

[0024] In a second step S102, a raw Mg--Al--Zn solution is formed. The pure Mg is melted, and the pure Al, the pure Zn, and the anhydrous MnCl₂ are added into the melted Mg at a temperature of about 700 degrees Celsius, such that the raw Mg--Al--Zn solution is obtained.

[0025] In a third step S103, a refined Mg--Al--Zn solution is formed. A refining flux is added into the above-mentioned raw Mg--Al--Zn solution to remove impurities at a temperature of about 720 degrees Celsius, and the temperature is maintained for 0.5 hours to obtain the refined Mg--Al--Zn solution. In the illustrated embodiment, the refining flux is a combination of chlorides and fluorides, such as magnesium dichloride (MgCl₂), potassium chloride (KCl), calcium fluoride (CaCl₂) and so on.

[0026] In a fourth step S104, a Mg--Al--Zn-RE solution is formed. The Mg--RE inter-alloy and the Al--Be inter-alloy are added into the refined Mg--Al--Zn solution at a temperature of about 730 degrees Celsius, and a mixture of the above-mentioned solution and alloys is stirred for about 0.5 hours to obtain the Mg--Al--Zn-RE solution. It is understood that the pure RE and the pure Be may be added instead of the Mg--RE inter-alloy and the Al--Be inter-alloy.

[0027] In a fifth step S105, a Mg--Al--Zn--RE alloy is formed. The above-mentioned Mg--Al--Zn--RE solution is cooled to a temperature of about 670 degrees Celsius, and then casted to obtain the Mg--Al--Zn--RE alloy.

[0028] In the illustrated embodiment, the preferred RE is Nd. It is understood that the RE can be one or more materials selected from the group consisting of Ce, La, Pr, Nd, Y, and any suitable combination thereof.

[0029] An example 1 of the method for making the magnesium alloy of the embodiment is as follows.

[0030] In a first step, a plurality of raw materials are provided. The raw materials contain about 7.5 wt % Al, about 0.68 wt % Zn, about 0.28 wt % Mn, about 0.50 wt % RE, about 0.0010 wt % Be, and the rest being Mg and unavoidable impurities. The Al (composition) includes pure Al and Al--Be inter-alloy, the Zn includes pure Zn, the Mn includes anhydrous manganese dichloride (MnCl₂), the RE includes a Mg--Nd inter-alloy, the Be includes an Al--Be inter-alloy, and the Mg includes pure Mg and a Mg--Nd inter-alloy. The weight ratio (in percent) of Nd in the Mg--Nd inter-alloy is about 20%.

[0031] In a second step, a raw Mg--Al--Zn solution is formed. The pure Mg is melted, and the pure Al, the pure Zn, and the anhydrous MnCl₂ are added into the melted Mg at a temperature of about 700 degrees Celsius, such that the raw Mg--Al--Zn solution is obtained.

[0032] In a third step, a refined Mg--Al--Zn solution is formed. A refining flux is added into the above-mentioned raw Mg--Al--Zn solution to remove impurities at a temperature of about 720 degrees Celsius, and the temperature is maintained for about 0.5 hours to obtain the refined Mg--Al--Zn solution.

[0033] In a fourth step, a Mg--Al--Zn--Nd solution is formed. The Mg--Nd inter-alloy and the Al--Be inter-alloy are added into the refined Mg--Al--Zn solution at a temperature of about 730 degrees Celsius, and a mixture of the above-mentioned solution and alloys is stirred for about 0.5 hours to obtain the Mg--Al--Zn--Nd solution.

[0034] In a fifth step, a Mg--Al--Zn--Nd alloy is formed. The above-mentioned Mg--Al--Zn--Nd solution is cooled to a temperature of about 670 degrees Celsius, and then casted to obtain the Mg--Al--Zn--Nd alloy.

[0035] An example 2 of the method for making the magnesium alloy of the embodiment is similar to the example 1 of the method for making the magnesium alloy of the embodiment. However, for the example 2, in the first step, the raw materials contain about 1.0 wt % RE. Meanwhile, the Al, Zn, Mn, and Be have the same respective wt % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

[0036] An example 3 of the method for making the magnesium alloy of the embodiment is similar to the example 1 of the method for making the magnesium alloy of the embodiment. However, for the example 3, in the first step, the raw materials contain about 1.5 wt % RE. Meanwhile, the Al, Zn, Mn, and Be have the same respective wt % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

[0037] An example 4 of the method for making the magnesium alloy of the embodiment is similar to the example 1 of the method for making the magnesium alloy of the embodiment. However, for the example 4, in the first step, the RE includes a Mg--RE inter-alloy, and the Mg includes pure Mg and a Mg--Ce--La inter-alloy. The RE contains the combination of Ce and La. The weight ratio (in percent) of Ce to RE is about 65%, and the weight ratio (in percent) of La to RE is about 35%. The total weight ratio (in percent) of Ce and La in the Mg--RE inter-alloy is about 20%.

[0038] The tensile strength, the percentage of elongation, and the yield strength of the magnesium alloy samples of the above examples 1, 2, and 3 and those of the AZ91D magnesium alloy sample were tested according to ASTM E8M-04 Standard Test Methods for Tension Testing of Metallic Materials at room temperature and at a temperature of about 170 degrees Celsius, respectively. The impact toughness of the magnesium alloy samples of the above examples 1, 2, and 3 and those of the AZ91D magnesium alloy sample were tested according to ASTM E3-04 Standard Test Methods for Notched Bar Impact Testing of Metallic Materials. The results are shown in FIGS. 2 through 9. The average values of the mechanical parameters of 30 samples obtained at room temperature and that of 10 samples obtained at a temperature 170 degrees Celsius are shown in Table 1.

TABLE-US-00001 TABLE 1 yield tensile percentage impact strength strength of elongation toughness sample (MPa) (MPa) (%) (J/cm²) room example 1 144 252 9.3 10.5 temperature example 2 142 246 7.8 8.8 example 3 142 248 8.2 10.7 AZ91D 149 224 4.6 4.1 170 degrees example 1 -- 139 29.6 -- Celsius example 2 -- 138 27.5 -- example 3 -- 139 29.1 -- AZ91D -- 147 14.5 --

[0039] Compared to the AZ91D magnesium alloy, the magnesium alloys of the embodiment of the instant disclosure have a relatively low Al content, and contains RE. As shown in FIGS. 2 through 9, and Table 1, the magnesium alloys of the respective examples 1, 2, and 3 have relatively excellent mechanical properties at room temperature, especially the percentage of elongation and the impact toughness. The magnesium alloys of the respective examples 1, 2, and 3 have relatively excellent percentage of elongation at a temperature of 170 degrees Celsius. When RE is added into the magnesium alloy, the RE element is concentrated along a solid-liquid interface, thereby resulting in constitutional supercooling and forming a supercooling region. A nucleating region is formed in the supercooling region, and a plurality of fine equiaxed grains are generated in the nucleating region. Additionally, the concentrated RE hinders the growth of the magnesium alloy grains, which refines the grains of the magnesium alloy, thereby enhanced the mechanical properties of the magnesium alloy. If the RE content is high, the percentage of elongation and the impact toughness will first be reduced and then increased afterwards; in addition, the higher the cost of the magnesium alloy becomes. Therefore, the RE content is preferably about 0.5 wt %.

[0040] To further test the mechanical property of the magnesium alloys containing different RE compositions, the tensile strength, the percentage of elongation, and the yield strength of the magnesium alloy from the above example 1 and 4 for the embodiment were tested according to ASTM E8M-04 Standard Test Methods for Tension Testing of Metallic Materials at room temperature and at a temperature of about 170 degrees Celsius, respectively.

[0041] The impact toughness of the magnesium alloy samples of the above examples 1 and 4 were tested according to ASTM E3-04 Standard Test Methods for Notched Bar Impact Testing of Metallic Materials. The test results are shown in FIGS. 10 and 11. The average values of the mechanical parameters of the examples 1 and 4 are shown in Table 2.

TABLE-US-00002 TABLE 2 yield tensile percentage impact strength strength of elongation toughness sample (MPa) (MPa) (%) (J/cm²) room example 1 144 252 9.3 10.5 temperature example 4 139 239 7.2 6.8 170 degrees example 1 -- 139 29.6 -- Celsius example 4 -- 138 21.7 --

[0042] As shown in FIGS. 10 and 11, and Table 2, compared to the magnesium alloy from the example 4, the magnesium alloy from the example 1 has relatively excellent mechanism properties at room temperature, especially the percentage of elongation and the impact toughness, and the magnesium alloy of the example 1 has relatively excellent percentage of elongation at a temperature of 170 degrees Celsius. Referring to FIGS. 12(a)-(d), the scale of grains of the magnesium alloy form the example 1 is smaller than that of grains of the magnesium alloy from the example 4, that is to say, in the illustrated embodiment, Nd has a better refining effect or capability for the magnesium alloy grains than that of the Ce--La combination. Thereby, the magnesium alloy added with Nd has an excellent set of material or mechanical properties.

[0043] The corrosion resistance of the magnesium alloy from the example 1 of the embodiment and the AZ91D magnesium alloy were tested by a salt water dipping method. The salt water dipping method includes the following steps: a magnesium alloy sample having a length of about 20 mm, a width of about 20 mm, and a thickness of about 5 mm is dipped into about 5 wt % sodium chloride solution for about 96 hours; the volume of hydrogen released during the time period is tested; and the corrosion weight per square centimeters of the sample is calculated according to the hydrogen volume. The test results are shown in FIG. 13. The average values of the corrosion weight of the example 1 and AZ91D are shown in Table 3.

TABLE-US-00003 TABLE 3 Corrosion weight per square sample centimeter (mg/cm²) sample number example 1 9.9 3 AZ91D 0.64 3

[0044] As shown in Table 3 and FIG. 13, the corrosion resistance of the magnesium alloy of the example 1 of the embodiment of instant disclosure is greater than that of the AZ91D magnesium alloy. Because the combining force between RE and oxygen is greater than that between magnesium and oxygen, during the melting process, RE can combine with oxygen to form RE oxide, such that the oxygen impurities can be removed. In addition, during the melting process, magnesium is easily reacted with water vapor to release hydrogen gas, such that gas hole can be caused in magnesium alloy casting, which negatively affects the corrosion resistance of the magnesium alloy. RE can react with hydrogen, thereby preventing the gas hole from forming, and thus the corrosion resistance can be improved.

[0045] Because of good mechanical properties and corrosion resistance, the magnesium alloys of the examples of the embodiment of instant disclosure have a good processing property, and products made from thereof have a good corrosion resistance.

[0046] It is to be understood, however, that even through numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. A magnesium alloy containing: about 7.0 wt % to about 8.0 wt % aluminum, about 0.45 wt % to about 0.90 wt % zinc, about 0.17 wt % to about 0.40 wt % manganese, over 1.0 wt % to about 1.5 wt % rare earth elements, about 0.00050 wt % to about 0.0015 wt % beryllium, and the rest being magnesium and unavoidable impurities.

2. The magnesium alloy of claim 1, wherein the rare earth element is selected from the group consisting of cerium, lanthanum, praseodymium, neodymium, yttrium, and combinations thereof.

3. The magnesium alloy of claim 2, wherein the rare earth element is neodymium.

4-17. (canceled)

18. A magnesium alloy containing: about 7.0 wt % to about 8.0 wt % aluminum, about 0.45 wt % to about 0.90 wt % zinc, about 0.17 wt % to about 0.40 wt % manganese, about 0.5 wt % rare earth elements, about 0.00050 wt % to about 0.0015 wt % beryllium, and the rest being magnesium and unavoidable impurities.

19. A magnesium alloy containing: about 7.0 wt % to about 8.0 wt % aluminum, about 0.45 wt % to about 0.90 wt % zinc, about 0.17 wt % to about 0.40 wt % manganese, about 0.8 wt % rare earth elements, about 0.00050 wt % to about 0.0015 wt % beryllium, and the rest being magnesium and unavoidable impurities.

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