High-bake-hardening magnesium alloy material and preparation method thereof

Abstract

The invention relates to the technical field of magnesium alloys, and discloses a high-bake-hardening magnesium alloy material and a preparation method thereof. The invention discloses a high bake hardening magnesium alloy material which comprises the following chemical components in percentage by weight: 0.3-6.0% of Zn, 0.1-1.0% of Ca and the balance of grain refinement elements, magnesium and inevitable impurities, wherein the grain refinement element comprises 0.1 to 3.0 wt.% of A < l >, 0.1 to 0.7 wt.% of Mn or 0.1 to 0.7 wt.% of Zr. According to the high-bake-hardening magnesium alloy material disclosed by the invention, a high-density nano GP region and nano clusters can be formed in a matrix after bake-hardening treatment, and the high-bake-hardening magnesium alloy material has rapid aging response capability, is low in cost, simple in process implementation and capable of realizing large-scale production, and has bake-hardening performance matched with bake-hardening steel.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and more particularly, to a high bake-hardening magnesium alloy material and a preparation method thereof. Background Art

[0002] As one of the green structural metal materials with the greatest development potential in the 21st century, magnesium alloys have the advantages of low density, large reserves, and environmental friendliness. Promoting the application of magnesium alloys in the field of automotive lightweighting, especially in components such as body sheets, can effectively reduce energy consumption. However, automotive body sheets need to have medium yield strength and high bake-hardening characteristics (Bake-hardening, BH). Typical representatives are 6xxx series aluminum alloys and BH steels. Bake-hardening in industry is a common treatment process for automotive sheets, which requires alloy sheets to have rapid aging kinetics, that is, the aging peak can be reached in a short time (170 °C, 20 min) after solution treatment and 2% prestrain. Unfortunately, the aging hardening ability of commercial magnesium alloys is poor, and the peak aging time is up to dozens of hours. Therefore, it is very difficult for commercial magnesium alloys to effectively improve their strength through aging treatment and they do not have bake-hardening ability, which greatly limits the application of magnesium alloys in fields such as automotive body sheets.

[0003] Studies have found that microalloying can enhance the aging hardening response of magnesium alloys. For example, adding Ag and Ca to Mg-Zn-based alloys, and adding alloy elements such as Zn, Al, and Na to Mg-Sn-based alloys. After analysis, the reason why microalloying can enhance the aging hardening response of magnesium alloys is attributed to the fact that in the early stage of aging, the high-density clusters induced by microalloying serve as new nucleation points, and the uniform and dispersed distribution of the dominant strengthening phase, etc. However, microalloyed magnesium alloys still require long-term aging treatment to reach the aging peak.

[0004] By jointly adding Zn and Ca elements, the magnesium alloy has rapid aging kinetics and can reach the aging peak within one hour. This unique rapid aging response is due to the formation of high-density nano Guinier Preston (GP) zones and nano clusters in the matrix. This rapid aging behavior different from commercial magnesium alloys has stimulated the development and attempt of the bake-hardening mechanism in magnesium alloys.

[0005] Based on this, providing a high bake-hardening magnesium alloy material and a preparation method thereof has become an urgent technical problem to be solved by those skilled in the art. Summary of the Invention

[0006] The object of the present invention is to provide a high bake-hardening magnesium alloy material and a preparation method thereof. The high bake-hardening magnesium alloy material has low cost, simple process implementation, can be mass-produced, and has bake-hardening performance matching that of BH steel.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention:

[0009] A high bake-hardenable magnesium alloy material, comprising the following chemical components: Zn 0.3 - 6.0 wt.%, Ca 0.1 - 1.0 wt.%, and the balance being grain refinement elements, magnesium, and inevitable impurities;

[0010] Among them, the grain refinement elements are Al 0.1 - 3.0 wt.% + Mn 0.1 - 0.7 wt.% or Zr 0.1 - 0.7 wt.%.

[0011] Another technical solution of the present invention:

[0012] The preparation method of the above high bake-hardenable magnesium alloy material comprises the following steps:

[0013] 1) Melting and ingot casting: Using an inert gas as a protective gas, according to the above chemical components, pure magnesium, pure zinc, pure aluminum, ZK60 alloy, Mg-30 wt.% Ca master alloy, and Mg-3 wt.% Mn master alloy are placed in a vacuum induction furnace for melting to obtain a liquid mixed metal, and then the liquid mixed metal is cast into a low-carbon steel mold and cooled to room temperature to obtain a magnesium alloy ingot;

[0014] 2) Homogenization: The magnesium alloy ingot prepared in step 1) is placed in a muffle furnace for primary heat preservation, then heated up, and secondary heat preservation is carried out to obtain a magnesium alloy ingot blank;

[0015] 3) Hot rolling: The magnesium alloy ingot blank prepared in step 2) is preheated, and then the magnesium alloy ingot blank is subjected to multi-pass rolling until the thickness is 1 mm to obtain a magnesium alloy rolled plate;

[0016] 4) Solution treatment: The magnesium alloy rolled plate prepared in step 3) is subjected to solution treatment to obtain the high bake-hardenable magnesium alloy material.

[0017] Further, in step 1), the melting temperature is 710 °C and the duration is 10 min.

[0018] Further, in step 1), the carbon steel mold needs to be preheated to 250 °C in advance.

[0019] Further, in step 2), the temperature of the primary heat preservation is 300 °C and the duration is 4 h.

[0020] Further, in step 2), the heating-up specifically is: controlling the heating-up rate to 7.5 °C / min and heating up to 400 °C.

[0021] Further, in step 2), the temperature of the secondary heat preservation is 400 °C and the duration is 6 h.

[0022] Further, in step 3), before preheating the magnesium alloy ingot blank, chamfers need to be prefabricated on the edge parts of the magnesium alloy ingot blank.

[0023] Further, in step 3), the temperature of the preheating is 300 °C and the duration is 0.5 h.

[0024] Further, in step 3), the multi-pass rolling is specifically as follows: multi-pass rolling is carried out with a reduction of 15% per pass.

[0025] Further, in step 3), after each pass of rolling, it is necessary to keep warm at 300 °C for 10 min.

[0026] Further, in step 4), the temperature of the solution treatment is 400 °C and the duration is 1 h.

[0027] The third technical solution of the present invention:

[0028] The application of the above-mentioned high bake-hardening magnesium alloy material in automobile body sheets.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] A high bake-hardening property magnesium alloy sheet provided by the present invention, based on the Mg-Zn series magnesium alloy, forms a supersaturated Mg-Zn-Ca based magnesium alloy solid solution by changing the contents of Zn and Ca elements, promotes rapid aging kinetics, presents high bake-hardening properties, and has bake-hardening performance matching that of BH steel, solving the problems that commercial magnesium alloys have slow aging response and do not have bake-hardening properties;

[0031] A high bake-hardening property magnesium alloy sheet provided by the present invention mainly uses cheap Zn and Ca elements and does not contain rare earth elements, so the preparation cost is relatively low;

[0032] A preparation method of a high bake-hardening property magnesium alloy sheet provided by the present invention can be obtained by unidirectional rolling and solution treatment, is similar to the conventional sheet processing process, is simple and easy to implement, and is suitable for industrial application. Description of the drawings

[0033] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0034] Figure 1Microstructure diagram of the high bake-hardening magnesium alloy material prepared in Example 1;

[0035] Figure 2 Test results of the bake-hardening ability of the high bake-hardening magnesium alloy material prepared in Example 1. Detailed implementation manners

[0036] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be regarded as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only used to describe specific implementation manners and are not used to limit the present invention.

[0037] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0038] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0039] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0040] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, that is, they are intended to include but not be limited to.

[0041] In the following examples, a preparation method of a high bake-hardening magnesium alloy material includes the following steps:

[0042] 1) Melting and ingot casting: Using inert gas as the protective gas, with Zn 0.3 - 6.0 wt.%, Ca 0.1 - 1.0 wt.%, and the balance being grain refinement elements, magnesium, and inevitable impurities; among them, the grain refinement elements are Al 0.1 - 3.0 wt.% + Mn 0.1 - 0.7 wt.% or Zr 0.1 - 0.7 wt.%. Put pure magnesium, pure zinc, pure aluminum, ZK60 alloy, Mg-30 wt.% Ca master alloy, and Mg-3 wt.% Mn master alloy into a vacuum induction furnace, melt at 710 °C for 10 min to obtain liquid mixed metal, and then pour the liquid mixed metal into a low-carbon steel mold preheated to 250 °C, and cool to room temperature to obtain a magnesium alloy ingot;

[0043] 2) Homogenization: Place the magnesium alloy ingot prepared in step 1) in a muffle furnace, hold at 300 °C for 4 h, then control the heating rate to 7.5 °C / min and heat up to 400 °C, hold for 6 h, and cool to room temperature to obtain a magnesium alloy ingot blank;

[0044] 3) Hot rolling: Chamfer the edges of the magnesium alloy ingot blank prepared in step 2), preheat at 300 °C for 0.5 h, and then perform multi-pass rolling with a reduction of 15% per pass until the thickness reaches 1 mm, and hold at 300 °C for 10 min after each pass of rolling to obtain a magnesium alloy rolled plate;

[0045] 4) Solution treatment: Solution-treat the magnesium alloy rolled plate prepared in step 3) at 400 °C for 1 h to obtain the high bake-hardening magnesium alloy material.

[0046] Example 1

[0047] A high bake-hardening magnesium alloy material

[0048] 1) Melting and ingot casting: Using inert gas as the protective gas, with the chemical composition being: Zn 0.8 wt.%, Ca 0.3 wt.%, Al 0.2 wt.%, Mn 0.2 wt.%, and the balance being magnesium and inevitable impurities. Put pure magnesium, pure zinc, pure aluminum, Mg-30 wt.% Ca master alloy, and Mg-3 wt.% Mn master alloy into a vacuum induction furnace, melt at 710 °C for 10 min to obtain liquid mixed metal, and then pour the liquid mixed metal into a low-carbon steel mold preheated to 250 °C, and cool to room temperature to obtain a magnesium alloy ingot;

[0049] 2) Homogenization: Place the magnesium alloy ingot prepared in step 1) in a muffle furnace, hold at 300 °C for 4 h, then control the heating rate to 7.5 °C / min and heat up to 400 °C, hold for 6 h, and cool to room temperature to obtain a magnesium alloy ingot blank;

[0050] 3) Hot rolling: Chamfers are prefabricated on the edge parts of the magnesium alloy ingot blank prepared in step 2), and it is preheated at 300 °C for 0.5 h, and then multi-pass rolling is carried out with a reduction of 15% per pass until the thickness reaches 1 mm, and after each pass of rolling, it needs to be kept at 300 °C for 10 min to obtain a magnesium alloy rolled plate;

[0051] 4) Solution treatment: The magnesium alloy rolled plate prepared in step 3) is solution-treated at 400 °C for 1 h to obtain the high bake-hardening magnesium alloy material.

[0052] The microstructure diagram of the high bake-hardening magnesium alloy material prepared in Example 1 is as Figure 1 shown;

[0053] As Figure 1 can be seen, the high bake-hardening magnesium alloy material prepared in Example 1 is composed of equiaxed recrystallized grains, which indicates that the sample is completely recrystallized after solution treatment, the tissue distribution is uniform, and it is a typical weak basal texture.

[0054] The bake-hardening ability of the high bake-hardening magnesium alloy material prepared in Example 1 is detected. Detection method: The solution-treated sample is subjected to short-term bake-hardening (170 °C, 20 min) treatment after 2% pre-strain, and the difference between the yield strength of the sample after bake-hardening and the stress of the 2% pre-strained sample is the bake-hardening value;

[0055] The test results of the bake-hardening ability of the high bake-hardening magnesium alloy material prepared in Example 1 are as Figure 2 shown;

[0056] As Figure 2 can be seen, the bake-hardening value of the high bake-hardening magnesium alloy material prepared in Example 1 is about 50 MPa, and the strength after bake-hardening > 200 MPa, having good bake-hardening ability.

[0057] Example 2

[0058] A high bake-hardening magnesium alloy material

[0059] Same as Example 1, the difference is only that in step 1), according to the chemical composition: Zn 1.6 wt.%, Ca 0.3 wt.%, Al 0.2 wt.%, Mn 0.2 wt.%, and the balance is magnesium and unavoidable impurities, pure magnesium, pure zinc, pure aluminum, Mg-30 wt.% Ca master alloy and Mg-3 wt.% Mn master alloy are placed in a vacuum induction furnace.

[0060] The baking hardening ability of the high baking hardening magnesium alloy material prepared in Example 2 was tested. After testing, the baking hardening value of the high baking hardening magnesium alloy material prepared in Example 2 was about 50 MPa, and the strength after baking hardening was > 200 MPa, indicating good baking hardening ability.

[0061] Example 3

[0062] A high baking hardening magnesium alloy material

[0063] Same as Example 1, except that in step 1), according to the chemical composition: Zn 2.4 wt.%, Ca 0.3 wt.%, Al 0.2 wt.%, Mn 0.2 wt.%, and the balance being magnesium and unavoidable impurities, pure magnesium, pure zinc, pure aluminum, Mg-30 wt.% Ca master alloy, and Mg-3 wt.% Mn master alloy were placed in a vacuum induction furnace.

[0064] The baking hardening ability of the high baking hardening magnesium alloy material prepared in Example 3 was tested. After testing, the baking hardening value of the high baking hardening magnesium alloy material prepared in Example 3 was about 50 MPa, and the strength after baking hardening was > 200 MPa, indicating good baking hardening ability.

[0065] Example 4

[0066] A high baking hardening magnesium alloy material

[0067] Same as Example 1, except that in step 1), according to the chemical composition: Zn 3.2 wt.%, Ca 0.3 wt.%, Al 0.2 wt.%, Mn 0.2 wt.%, and the balance being magnesium and unavoidable impurities, pure magnesium, pure zinc, pure aluminum, Mg-30 wt.% Ca master alloy, and Mg-3 wt.% Mn master alloy were placed in a vacuum induction furnace.

[0068] The baking hardening ability of the high baking hardening magnesium alloy material prepared in Example 4 was tested. After testing, the baking hardening value of the high baking hardening magnesium alloy material prepared in Example 4 was about 50 MPa, and the strength after baking hardening was > 200 MPa, indicating good baking hardening ability.

[0069] Example 5

[0070] A high baking hardening magnesium alloy material

[0071] Same as Example 1, with the only difference being that in step 1), according to the chemical composition: Zn 4.0wt.%, Ca 0.3wt.%, Al 0.2wt.%, Mn 0.2wt.%, and the balance being magnesium and unavoidable impurities, pure magnesium, pure zinc, pure aluminum, Mg-30wt.% Ca master alloy, and Mg-3wt.% Mn master alloy are placed in a vacuum induction furnace.

[0072] The baking hardening ability of the high bake hardening magnesium alloy material prepared in Example 5 was tested. After testing, the baking hardening value of the high bake hardening magnesium alloy material prepared in Example 5 was approximately 50 MPa, and the strength after baking hardening > 200 MPa, indicating good baking hardening ability.

[0073] Example 6

[0074] A high bake hardening magnesium alloy material

[0075] Same as Example 1, with the only difference being that in step 1), according to the chemical composition: Zn 4.8wt.%, Ca 0.3wt.%, Al 0.2wt.%, Mn 0.2wt.%, and the balance being magnesium and unavoidable impurities, pure magnesium, pure zinc, pure aluminum, ZK60 alloy, Mg-30wt.% Ca master alloy, and Mg-3wt.% Mn master alloy are placed in a vacuum induction furnace.

[0076] The baking hardening ability of the high bake hardening magnesium alloy material prepared in Example 6 was tested. After testing, the baking hardening value of the high bake hardening magnesium alloy material prepared in Example 6 was approximately 50 MPa, and the strength after baking hardening > 200 MPa, indicating good baking hardening ability.

[0077] Example 7

[0078] A high bake hardening magnesium alloy material

[0079] Same as Example 1, with the only difference being that in step 1), according to the chemical composition: Zn 5.6wt.%, Ca 0.3wt.%, Al 0.2wt.%, Mn 0.2wt.%, and the balance being magnesium and unavoidable impurities, pure magnesium, pure zinc, pure aluminum, ZK60 alloy, Mg-30wt.% Ca master alloy, and Mg-3wt.% Mn master alloy are placed in a vacuum induction furnace.

[0080] The baking hardening ability of the high bake hardening magnesium alloy material prepared in Example 7 was tested. After testing, the baking hardening value of the high bake hardening magnesium alloy material prepared in Example 7 was approximately 50 MPa, and the strength after baking hardening > 200 MPa, indicating good baking hardening ability.

[0081] Example 8

[0082] A high bake-hardenable magnesium alloy material

[0083] Same as Example 1, except that in step 1), according to the chemical composition: Zn 0.8 wt.%, Ca 0.3 wt.%, Zr 0.3 wt.%, and the balance is magnesium and unavoidable impurities, pure magnesium, pure zinc, ZK60 alloy, and Mg-30 wt.% Ca master alloy are placed in a vacuum induction furnace.

[0084] The bake-hardening ability of the high bake-hardenable magnesium alloy material prepared in Example 8 was tested. After testing, the bake-hardening value of the high bake-hardenable magnesium alloy material prepared in Example 8 was about 50 MPa, and the strength after bake-hardening > 200 MPa, having good bake-hardening ability.

[0085] Example 9

[0086] A high bake-hardenable magnesium alloy material

[0087] Same as Example 1, except that in step 1), according to the chemical composition: Zn 1.6 wt.%, Ca 0.3 wt.%, Zr 0.3 wt.%, and the balance is magnesium and unavoidable impurities, pure magnesium, pure zinc, ZK60 alloy, and Mg-30 wt.% Ca master alloy are placed in a vacuum induction furnace.

[0088] The bake-hardening ability of the high bake-hardenable magnesium alloy material prepared in Example 9 was tested. After testing, the bake-hardening value of the high bake-hardenable magnesium alloy material prepared in Example 9 was about 50 MPa, and the strength after bake-hardening > 200 MPa, having good bake-hardening ability.

[0089] Example 10

[0090] A high bake-hardenable magnesium alloy material

[0091] Same as Example 1, except that in step 1), according to the chemical composition: Zn 2.4 wt.%, Ca 0.3 wt.%, Zr 0.3 wt.%, and the balance is magnesium and unavoidable impurities, pure magnesium, pure zinc, ZK60 alloy, and Mg-30 wt.% Ca master alloy are placed in a vacuum induction furnace.

[0092] The bake-hardening ability of the high bake-hardenable magnesium alloy material prepared in Example 10 was tested. After testing, the bake-hardening value of the high bake-hardenable magnesium alloy material prepared in Example 10 was about 50 MPa, and the strength after bake-hardening > 200 MPa, having good bake-hardening ability.

[0093] Example 11

[0094] A high bake-hardening magnesium alloy material

[0095] Same as Example 1, except that in step 1), according to the chemical composition: Zn 3.2 wt.%, Ca 0.3 wt.%, Zr 0.3 wt.%, the balance being magnesium and inevitable impurities, pure magnesium, pure zinc, ZK60 alloy and Mg-30 wt.% Ca master alloy are placed in a vacuum induction furnace.

[0096] The bake-hardening ability of the high bake-hardening magnesium alloy material prepared in Example 11 was tested. After testing, the bake-hardening value of the high bake-hardening magnesium alloy material prepared in Example 11 was about 50 MPa, and the strength after bake-hardening > 200 MPa, having good bake-hardening ability.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced, and any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A high bake hardening magnesium alloy material, characterized in that: The high bake hardening magnesium alloy material comprises the following chemical components: Zn 0.3-6.0wt.%, Ca 0.1-1.0wt.%, and the balance is grain refining elements, magnesium and unavoidable impurities; Wherein, the grain refining element is Al 0.1-3.0wt.%+Mn 0.1-0.7wt.% or Zr 0.1-0.7wt.%.

2. A method for preparing a high bake hardening magnesium alloy material as claimed in claim 1, characterized in that: The following steps are involved: 1) Melting ingot: using inert gas as protective gas, pure magnesium, pure zinc, pure aluminum, ZK60 alloy, Mg-30wt.%Ca master alloy and Mg-3wt.%Mn master alloy are placed in a vacuum induction furnace according to the above chemical composition, melted to obtain a liquid mixed metal, and then the liquid mixed metal is cast into a low-carbon steel mold, cooled to room temperature, and a magnesium alloy ingot is obtained; 2) Homogenization: placing the magnesium alloy ingot prepared in step 1) in a muffle furnace, keeping the temperature once, then heating it, and keeping the temperature twice to obtain a magnesium alloy ingot; 3) Hot rolling: preheating the magnesium alloy ingot prepared in step 2), and then performing multiple passes of rolling on the magnesium alloy ingot until the thickness reaches 1 mm, thereby obtaining a magnesium alloy rolled plate; 4) Solution treatment: The magnesium alloy rolled plate prepared in step 3) is subjected to solution treatment to obtain the high bake hardening magnesium alloy material.

3. The preparation method according to claim 2, characterized in that: In step 1), the smelting temperature is 710°C and the smelting time is 10 minutes; the carbon steel mold needs to be preheated to 250°C.

4. The preparation method according to claim 2, characterized in that: In step 2), the temperature of the first insulation is 300°C and the duration is 4 hours; the heating is specifically: controlling the heating rate to 7.5°C / min to increase the temperature to 400°C; the temperature of the second insulation is 400°C and the duration is 6 hours.

5. The preparation method according to claim 2, characterized in that: In step 3), before preheating the magnesium alloy ingot, the edge portions of the magnesium alloy ingot need to be pre-chamfered.

6. The preparation method according to claim 2, characterized in that: In step 3), the preheating temperature is 300° C. and the duration is 0.5 h; the multiple-pass rolling is specifically: multiple-pass rolling is performed with a downward pressure of 15% in each pass.

7. The preparation method according to claim 2, characterized in that: In step 3), after each rolling pass, the temperature must be kept at 300°C for 10 minutes.

8. The preparation method according to claim 2, characterized in that: In step 4), the temperature of the solution treatment is 400° C. and the duration is 1 hour.

9. Use of the high bake hardening magnesium alloy material as claimed in claim 1 in automobile body panels.

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