High-strength high-plasticity cast magnesium alloy and preparation method thereof

Abstract

The application discloses a high-strength and high-plasticity cast magnesium alloy and a preparation method thereof. The magnesium alloy comprises the following components in percentage by weight: Zn 1.0-6.0%, Gd 1.0-5.0%, Er 1.5-3.0%, Eu 0.1-2.0%, Ba 0.1-0.4%, Zr 0.1-1.0%, and the balance of Mg and inevitable impurities. The application can form a large number of LPSO structures in the matrix by jointly adding gadolinium and zinc elements, thereby effectively hindering dislocation slip, strengthening the matrix and improving the strength of the magnesium alloy. The gadolinium element can form a dispersed precipitated phase growing in a prismatic surface in the magnesium alloy matrix, further improving the strength of the magnesium alloy. The addition of erbium and europium can form a dispersed precipitated phase in the matrix, and the addition of barium can effectively refine the precipitated phase and increase the density of the precipitated phase, thereby improving the strength of the alloy while increasing the plasticity. In addition, the addition of Zr as a grain refiner can significantly refine the grains, improve the yield strength of the alloy and improve the plasticity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a high-strength and high-plasticity cast magnesium alloy and a preparation method thereof. BACKGROUND

[0002] Rare earth (such as Gd, Y, Nd, Sm) containing cast magnesium alloys have a significant precipitation strengthening effect, and are important high-strength cast magnesium alloys, and have a broad application prospect in the fields of aerospace, military industry and automobiles. The addition of Gd and Zn in magnesium alloys can form a long-range ordered structure (Long period stacking ordered structure, LPSO structure), which can effectively hinder dislocation slip and improve the strength. In addition, rare earth elements can form a sheet-shaped precipitated phase parallel to the column surface with magnesium, thereby strengthening the matrix.

[0003] However, although the precipitated phase can greatly improve the strength, it can significantly reduce the plasticity, which leads to low plasticity of magnesium rare earth alloys with high rare earth content. For example, a study on the microstructure and mechanical properties of Mg-Y-Gd-Zn-Zr alloys (2013, doctoral dissertation of Shanghai Jiaotong University) found that the addition of Gd and Y can significantly improve the tensile properties of magnesium alloys. The tensile strength, yield strength and elongation of the Mg-11Y-5Gd-2Zn-0.5Zr alloy after peak aging treatment are 307 MPa, 243 MPa and 1.4%, respectively. Although the magnesium alloy has high strength, the plasticity is low, which limits the industrial application. SUMMARY

[0004] In view of the above problems in the prior art, the purpose of the present application is to provide a high-strength and high-plasticity cast magnesium alloy and a preparation method thereof, which solves the technical problem that the strength and plasticity of the existing magnesium alloy are difficult to improve simultaneously.

[0005] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0006] The application discloses a high-strength and high-plasticity cast magnesium alloy, which comprises the following components in percentage by weight: Zn 1.0-6.0%, Gd 1.0-5.0%, Er 1.5-3.0%, Eu 0.1-2.0%, Ba 0.1-0.4%, Zr 0.1-1.0%, and the balance of Mg and inevitable impurities. The application controls the adding amount of Gd, Er and Eu in the corresponding range, can form a large number of precipitated phases, avoids the emergence of a large number of metal-based compounds, improves the strength, and does not significantly reduce the plasticity; the adding amount of Zn is controlled in the range of 1.0-6.0%, so that the Zn can be combined with Gd, Er and Eu to form a large number of LPSO structures and improve the strength of the alloy; the adding amount of Ba is controlled in the range of 0.1-0.4%, so that the precipitated phases can be effectively refined, and the formation of blocky hard and brittle second phases is avoided. The adding amount of Zr is controlled in the range of 0.1-1.0%, so that the grains can be effectively refined.

[0007] Further, the application further comprises the following components in percentage by weight: Zn 2.3-5.6%, Gd 1.5-4.6%, Er 1.6-2.7%, Eu 0.2-0.7%, Ba 0.1-0.4%, Zr 0.37-0.5%, the total amount of impurities is less than or equal to 0.15%, and the balance is Mg.

[0008] Further, the impurities in the magnesium alloy are as follows in percentage by weight: Fe <0.005%, Cu <0.015% and Ni <0.002%. In this way, the corrosion resistance of the magnesium alloy can be ensured.

[0009] Further, the magnesium alloy contains LPSO phases, and the LPSO phases comprise Zn and Gd, Er and Eu; the LPSO phases in the magnesium alloy are 5%-20% in percentage by weight.

[0010] Further, the magnesium alloy further comprises RE-containing phases, and the RE-containing phases comprise second phases containing Gd, Eu and Er; the RE-containing phases in the magnesium alloy are 2%-10% in percentage by weight.

[0011] A preparation method of a high-strength and high-plasticity cast magnesium alloy, comprising the following steps:

[0012] After industrial pure Mg is heated to complete melting, industrial pure Zn is added at 700 DEG C, when the melt temperature reaches 720 DEG C, Mg-Gd, Mg-Er, Mg-Eu intermediate alloy is added, after the intermediate alloy is melted, Ba is added, after the melt temperature rises to 780 DEG C, Mg-Zr intermediate alloy is added, is stirred 2 min to make it melt completely, is heated to 780 DEG C again, is kept for 20 min, is cooled to 750 DEG C, is refined for 6 min, after refining, is placed for 20 min, is removed surface dross after the metal liquid temperature is cooled to 740 DEG C and is cast, the cast magnesium alloy containing LPSO phase and RE-containing phase is obtained. The melting point of Mg-Gd, Mg-Er, Mg-Eu intermediate alloy is relatively high, therefore when the melt temperature reaches 720 DEG C, Mg-Gd, Mg-Er, Mg-Eu intermediate alloy is added again, and the chemical property of Ba is relatively active, therefore after the magnesium rare earth intermediate alloy is melted, Ba is added to reduce the burning loss and ensure the effect of refining precipitated phase. The melting point of Mg-Zr intermediate alloy is high, and if the melt is placed for too long, Zr particles will sink, reducing the grain refinement effect, therefore after the melt temperature rises to 780 DEG C, Mg-Zr intermediate alloy is added.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] 1. By jointly adding Gd and Zn elements, the LPSO structure can be formed in the matrix, thereby effectively hindering dislocation slip, strengthening the matrix and improving the strength of the magnesium alloy; the Gd element can form a dispersed precipitated phase growing in a prismatic surface in the magnesium alloy matrix, the addition of Er and Eu can form a dispersed precipitated phase in the matrix, the addition of Ba can effectively refine the precipitated phase and increase the density of the precipitated phase, thereby improving the strength and plasticity of the alloy. In addition, the addition of Zr as a grain refiner can significantly refine the grains, improve the yield strength of the magnesium alloy and improve the plasticity.

[0015] 2. The magnesium alloy prepared by the present application has good castability, significantly improved strength and good plasticity, so that the alloy can be widely applied to high-grade automobile engine cylinder blocks, gearbox housings or key structural parts of aerospace instruments with high requirements for strength and plasticity. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The metallographic graph of the magnesium alloy described in Example 1;

[0017] Figure 2 The transmission electron microscope graph of the magnesium alloy described in Example 1;

[0018] Figure 3 The metallographic graph of the magnesium alloy described in Example 2;

[0019] Figure 4Metallographic picture of the magnesium alloy as described in Example 3;

[0020] Figure 5 Metallographic picture of the magnesium alloy as described in Example 4;

[0021] Figure 6 Morphology picture of precipitated phase in the magnesium alloy as described in Example 4. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described in conjunction with the specific embodiments.

[0023] The numerical ranges recited herein are inclusive of the recited endpoints and of every integer and fraction within the range. Every smaller range that falls within the recited ranges is also included. The upper and lower limits of these smaller ranges can independently be included or excluded in the ranges.

[0024] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in full the methods and / or materials which are described therein. In case of conflict, the content of the present specification will control. As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to denote the presence of stated features, items, components, elements, or the like, but do not exclude the presence of one or more other features, items, components, elements, or the like.

[0025] The experimental methods used in the present application are conventional methods unless otherwise specified.

[0026] The materials, reagents and the like used in the present application can be purchased or synthesized by known methods unless otherwise specified.

[0027] The quantitative tests in the present application are set up with three repeated experiments, and the results are averaged.

[0028] I. The present application provides a high-strength and high-plasticity cast magnesium alloy, and the component content of the magnesium alloy is shown in Table 1.

[0029] Table 1 Component table of magnesium alloy of Examples 1-4 and Comparative Examples (in terms of weight percentage)

[0030]

[0031]

[0032] Figures 1-5Metallographic images of the magnesium alloys described in Examples 1-4 are shown below. Figures 1-5 It is known that the alloy contains LPSO phase and rare earth phases (including Gd, Eu, and Er), which are beneficial to improving the alloy's strength. The presence of numerous fine precipitates in the alloy significantly enhances its strength while maintaining good plasticity.

[0033] The morphology of the precipitated phases in the magnesium alloy described in Example 4 is shown in the figure below. Figure 6 As shown, by Figure 6 It can be seen that the alloy of the present invention has finely dispersed precipitates, which can effectively improve the strength of the alloy.

[0034] At room temperature, the stretching rate is 10. -3 Tensile tests were performed on the magnesium alloy obtained in Example 1 under the condition of / s. The room temperature tensile strength of the magnesium alloy was 379 MPa, the yield strength was 257 MPa, and the elongation was 6.7%.

[0035] At room temperature, the stretching rate is 10. -3 Tensile tests were performed on the magnesium alloy obtained in Example 2 under the condition of / s. The room temperature tensile strength of the magnesium alloy was 354 MPa, the yield strength was 216 MPa, and the elongation was 10.2%.

[0036] At room temperature, the stretching rate is 10. -3 Tensile tests were performed on the magnesium alloy obtained in Example 3 under the condition of / s. The room temperature tensile strength of the magnesium alloy was 372 MPa, the yield strength was 243 MPa, and the elongation was 7.3%.

[0037] At room temperature, the stretching rate is 10. -3 Tensile tests were performed on the magnesium alloy obtained in Example 4 under the condition of / s. The room temperature tensile strength of the magnesium alloy was 363 MPa, the yield strength was 254 MPa, and the elongation was 6.8%.

[0038] At room temperature, the stretching rate is 10. -3 Tensile tests were performed on the magnesium alloy described in the comparative example (WGZK1152) under the condition of / s, and the tensile strength was 307MPa, the yield strength was 243MPa and the elongation was 1.4%.

[0039] The magnesium alloy of the present invention contains an LPSO phase and a RE phase; the LPSO phase includes Zn and Gd, Er and Eu; the RE phase includes a second phase containing Gd, Eu and Er. By weight percentage, the magnesium alloy contains the following components: LPSO phase of 5% to 20% and RE phase (rare earth phase) of 2% to 10%.

[0040] In some embodiments, the content of the LPSO phase can be 5.0%, 10.0%, 15%, 18%, 20%, etc., and all ranges and sub-ranges between the above-mentioned values in terms of weight percentage; a large number of LPSO structures are formed in the matrix, effectively hindering dislocation slip, strengthening the matrix, and improving the strength of the magnesium alloy; the content of the RE-containing phase can be 2%, 4%, 6%, 8%, 10%, etc., and all ranges and sub-ranges between the above-mentioned values. The RE-containing phase includes Gd, Eu, and Er, the Gd element can form a diffuse precipitated phase with a prismatic surface growth in the magnesium alloy matrix, the addition of Er and Eu can form a diffuse precipitated phase in the matrix; the addition of Ba can effectively refine the precipitated phase and increase the density of the precipitated phase, thereby improving the strength of the alloy while increasing the plasticity. In addition, the addition of Zr as a grain refiner can significantly refine the grains, improve the yield strength of the magnesium alloy, and improve the plasticity. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0041] In some embodiments, the magnesium alloy contains the following components in terms of weight percentage: Zn 1.0-6.0%, Gd 1.0-5.0%, Er 1.5-3.0%, Eu 0.1-2.0%, Ba 0.1-0.4%, Zr 0.1-1.0%, total impurities ≤0.15%, and the balance being Mg. The content of Zn element can be 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, etc., and all ranges and sub-ranges between the above-mentioned values; the content of Gd element can be 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc., and all ranges and sub-ranges between the above-mentioned values; the content of Er element can be 1.5%, 2.0%, 2.5%, 3.0%, etc., and all ranges and sub-ranges between the above-mentioned values; the content of Eu element can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, etc., and all ranges and sub-ranges between the above-mentioned values; the content of Ba element can be 0.1%, 0.2%, 0.3%, 0.4%, etc., and all ranges and sub-ranges between the above-mentioned values; the content of Zr element can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.0%, etc., and all ranges and sub-ranges between the above-mentioned values. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0042] Secondly, the application also provides a preparation method of the high-strength and high-plasticity cast magnesium alloy, and the components are added according to any of the magnesium alloy compositions in Embodiments 1-4, which comprises the following steps:

[0043] After the industrial pure magnesium is heated to complete melting, the industrial pure zinc is added at 700℃, when the melt temperature reaches 720℃, the Mg-Gd, Mg-Er, Mg-Eu intermediate alloy is added, after the intermediate alloy is melted, the Ba is added, after the melt temperature rises to 780℃, the Mg-Zr intermediate alloy is added, after stirring for 2min, it is fully melted, after the temperature is raised to 780℃, it is kept for 20min, then the temperature is lowered to 750℃, after refining for 6min, it is placed for 20min, after the temperature of the metal liquid is cooled to 740℃, the surface dross is skimmed off for casting, the casting magnesium alloy is obtained.

[0044] In some embodiments, due to the LPSO phase high-temperature stable phase consisting of Zn and Gd, Er and Eu, the melting temperature has little effect on it; the LPSO phase will appear remelting or precipitation according to different temperatures, so the melting temperature is optimally controlled between 720℃-800℃, and further preferably 720℃-780℃, for example, the melting temperature can be 720℃, 740℃, 760℃, 780℃, etc., and all ranges and subranges between the above-mentioned values. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0045] The magnesium alloy prepared in the application significantly improves the strength and plasticity compared with the WGZK1152 magnesium alloy. This is because the Gd element can form a dispersed precipitated phase of elongated prismatic growth in the magnesium alloy matrix, the addition of Er and Eu can form a dispersed precipitated phase containing Er and Eu, the addition of Ba can effectively refine the precipitated phase and increase the density of the precipitated phase, which improves the strength of the alloy while maintaining good plasticity. Zn and Gd together can form a large number of long-range ordered stacking structures, which can hinder the basal plane slip of dislocations, strengthen the matrix, and further improve the strength of the alloy. In addition, the addition of Zr as a grain refiner can significantly refine the grains, improve the yield strength of the magnesium alloy, and improve the plasticity.

[0046] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the technical solutions, and those of ordinary skill in the art should understand that those who modify or equivalently replace the technical solutions of the present application without departing from the purpose and scope of the technical solutions should be covered in the scope of the claims of the present application.

Claims

1. A high-strength, high-ductility cast magnesium alloy, characterized in that, The composition by weight percentage includes the following components: Zn 1.0~6.0%, Gd 1.0~5.0%, Er 1.5~3.0%, Eu 0.1~2.0%, Ba 0.1~0.4%, Zr 0.1~1.0%, with the balance being Mg and unavoidable impurities; The magnesium alloy contains an LPSO phase, which includes Zn and Gd, Er and Eu; the LPSO phase in the magnesium alloy is 5% to 20% by weight. The magnesium alloy also includes a RE phase, which includes a second phase containing Gd, Eu and Er. The amount of RE phase in the magnesium alloy is 2% to 10% by weight.

2. The high-strength, high-ductility cast magnesium alloy according to claim 1, characterized in that, The composition by weight percentage includes the following components: Zn 2.3~5.6%, Gd 1.5~4.6%, Er 1.6~2.7%, Eu 0.2~0.7%, Ba 0.1~0.4%, Zr 0.37~0.5%, total impurities ≤0.15%, and the balance is Mg.

3. The high-strength, high-ductility cast magnesium alloy according to claim 1, characterized in that, The impurities, by weight percentage, contain Fe < 0.005%, Cu < 0.015%, and Ni < 0.002%.

4. A method for preparing a high-strength, high-ductility cast magnesium alloy as described in claim 1, characterized in that, Includes the following steps: Industrial pure Mg is heated to complete melting, and then industrial pure Zn is added at 700℃. When the melt temperature reaches 720℃, Mg-Gd, Mg-Er, and Mg-Eu master alloys are added. After the master alloys melt, Ba is added. When the melt temperature rises back to 780℃, Mg-Zr master alloy is added. The mixture is stirred for 2 minutes to ensure complete melting, then heated to 780℃ and held for 20 minutes before cooling to 750℃. The mixture is then refined for 6 minutes and allowed to stand for 20 minutes. After the molten metal cools to 740℃, the surface slag is skimmed off before casting to obtain a cast magnesium alloy containing LPSO and RE phases.

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