High-performance magnesium / aluminum laminated composite plate and preparation method thereof

Abstract

The present application belongs to the technical field of aluminum alloy and heterogeneous material preparation, and relates to a high-performance magnesium / aluminum laminated composite plate and a preparation method thereof, and aims to provide a new idea for the preparation of magnesium / aluminum heterogeneous structure material, realizes the effective combination of magnesium / aluminum dissimilar metals while strengthening the matrix performance through the ingenious design of hot rolling and heat treatment process, which helps to expand the application scope of magnesium / aluminum heterogeneous structure material and has remarkable benefits. The magnesium / aluminum laminated composite plate structure composed of magnesium alloy plates and aluminum alloy plates alternately distributed has a total thickness of less than or equal to 6mm. Through low-temperature pre-solutionizing + high-temperature short-time solution treatment, combined with low internal stress quenching and double-stage aging, the heat treatment strengthening of the magnesium / aluminum laminated plate after hot rolling is realized. The design idea of the present application is ingenious and easy to operate, and can be extended to the preparation of similar layered heterogeneous structure materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of aluminum alloy and heterogeneous material preparation, and relates to a magnesium / aluminum heterogeneous structure material and a high-performance magnesium / aluminum laminated composite plate and a preparation method thereof. BACKGROUND

[0002] Magnesium and aluminum are classic light metals, which have the advantages of low density, high specific strength, easy processing and good economy. If aluminum and magnesium are combined to obtain a magnesium / aluminum heterogeneous structure material, the advantages of the two metals can be complementary, which is helpful for the weight reduction and cost control of aircraft and automobiles, which cannot be achieved by a single metal.

[0003] However, the promotion of aluminum / magnesium heterogeneous structure materials is limited by the characteristics of aluminum and magnesium metals. Domestic and foreign scholars usually use connection technologies such as fusion welding, diffusion welding, friction stir welding, explosive welding and rolling to combine the two metals into one. Although the above methods can obtain a magnesium / aluminum interface structure without obvious defects, the hard and brittle intermetallic compounds formed at the joint are the main reason for the low strength of the magnesium / aluminum interface, which seriously restricts its application range. Another application problem to be solved is the design of the heat treatment process of the magnesium / aluminum heterogeneous structure material. Generally, the heat treatment process of a metal can be summarized as solid solution-quenching-aging. Among them, solid solution is to uniformly dissolve alloying elements such as Cu, Mg, Zn, Si and Mn into the matrix to obtain a high-density supersaturated solid solution, which depends on the increase of temperature to improve the solid solubility of the matrix. For 2024 aluminum alloy, the conventional solid solution is at 493℃ for 2h, and for 7050 aluminum alloy, the conventional solid solution is at 466℃ for 2h. The above solid solution temperatures are higher than the eutectic reaction temperature of aluminum-magnesium (450℃). For the magnesium / aluminum heterogeneous structure material, if the conventional heat treatment system is directly used, it will inevitably lead to a violent interface reaction, generating a large amount of eutectic liquid phase at the magnesium / aluminum interface and seriously weakening the connection quality of the interface. The subsequent quenching is usually to rapidly cool the solid-solved metal to room temperature, which uses high cooling rate to maintain the supersaturation state of the aluminum alloy and lays a foundation for subsequent aging precipitation. However, due to the fact that the linear expansion coefficient of aluminum and magnesium matrix is significantly higher than that of the intermetallic compound at the magnesium / aluminum interface, the rapid cooling caused by water quenching will inevitably cause high thermal stress at the interface and cause magnesium / aluminum interface failure. Directly using the aluminum and magnesium matrix after heat treatment strengthening is also not feasible, because the aluminum / magnesium metal composite needs to be connected by heat connection technology, which will change the strengthening of the organization during the heating and cooling process and cause performance loss.

[0004] Obviously, the existing conventional aluminum alloy heat treatment system cannot be directly applied due to magnesium / aluminum interface phase transition, internal stress concentration and other factors. It is necessary to select a targeted composite process and design a new heat treatment system to improve the mechanical properties of the matrix while ensuring the integrity of the magnesium / aluminum interface, which has important practical significance for the application and promotion of aluminum / magnesium heterogeneous structure materials. Since the solid solution temperature of aluminum alloy is higher than the eutectic liquid phase reaction point of magnesium / aluminum interface, the conventional aluminum alloy heat treatment process is not suitable for magnesium / aluminum heterogeneous structure materials, which leads to the problem of low matrix strength of existing magnesium / aluminum heterogeneous structure materials, limiting its application and promotion. However, there is no public report on the heat treatment research specially for magnesium / aluminum heterogeneous structure materials. SUMMARY

[0005] The purpose of the present application is to provide a high-performance magnesium / aluminum laminated composite plate and a preparation method thereof, which realizes the connection of magnesium / aluminum dissimilar metals and strengthens the performance of the aluminum matrix through a heat treatment system. The performance indicators of the obtained composite material are as follows: interface shear strength 42-47 MPa, aluminum matrix tensile strength ≥485 MPa, and yield strength ≥410 MPa.

[0006] To solve this technical problem, the technical solution of the present application is:

[0007] On the one hand, a high-performance magnesium / aluminum laminated composite plate is provided, which is composed of magnesium plates and aluminum plates in direct contact and alternating distribution, and the number of layers of aluminum plates plus magnesium plates is ≥2, and the total thickness of the composite plate is ≤6 mm.

[0008] The aluminum plate is a 7050 aluminum alloy that can be heat treated for strengthening, and the magnesium plate is any one of Mg-Al-Zn, Mg-Al-Mn, and Mg-Al-Si alloys.

[0009] On the other hand, a preparation method of a high-performance magnesium / aluminum laminated composite plate is provided, which comprises the following steps:

[0010] Step one

[0011] Select aluminum plates and magnesium plates with a thickness of 2-5 mm for standby, polish the surface to be combined to remove the surface oxide layer and impurities;

[0012] Step two

[0013] Stack the aluminum plates and magnesium plates pretreated in step one in turn, put them into a package, and seal the package after pumping the inside to a low vacuum state of 100 Pa;

[0014] Step three

[0015] Heat the magnesium / aluminum laminated plate in the package in step two to 400-420℃, and then keep the temperature for 2-3 hours after reaching the temperature to complete the pre-solid solution treatment.

[0016] Step four

[0017] The magnesium / aluminum laminated plate pre-solid-soluted at low temperature is immediately taken out from the furnace for hot rolling and compounding, wherein the roller temperature is greater than or equal to 300 DEG C, the roller speed is set to 10-20 rpm, the reduction is 20%-30%, and the laminated plate is rolled for 2-3 passes;

[0018] Step five

[0019] The magnesium / aluminum laminated plate rolled in step four is placed in a large-size preheating pressing plate heated to 470-490 DEG C, and is kept for 90-150 s to complete high-temperature short-time solid solution treatment;

[0020] Step six

[0021] The magnesium / aluminum laminated plate pre-solid-soluted at high temperature in step five is immediately subjected to high-speed water mist cooling to complete low internal stress quenching;

[0022] Step seven

[0023] The quenched magnesium / aluminum laminated plate is subjected to double-pole aging treatment, i.e., kept at 116-126 DEG C for 7-9 hours and then kept at 173-179 DEG C for 8-10 hours to realize heat treatment strengthening of the aluminum matrix and ensure the integrity of the magnesium / aluminum interface structure.

[0024] The ladle material in step two can be 6063 aluminum alloy or pure aluminum.

[0025] The parameters of the high-speed water mist quenching in step six can be set as follows: gas-water ratio 4-6, and pressure 5-8 MPa. The purpose is to reduce the internal stress in the quenching process and avoid cracking of the magnesium / aluminum interface.

[0026] The transfer time in step six is within 10 s. For the thinner laminated plate in the present application, in order to have better quenching effect, the transfer time is set to be within 5 s in the preferred mode.

[0027] Preferably, the mechanical polishing is adopted in step one.

[0028] Preferably, the heating is carried out in a muffle furnace in step three.

[0029] The present application has the following beneficial effects:

[0030] The application adopts the idea of "low-temperature pre-solid solution + high-temperature short-time solid solution" to relieve the magnesium / aluminum interface liquefaction caused by too high solid solution temperature, ensure the integrity of the magnesium / aluminum interface structure and achieve the purpose of aluminum alloy solid solution, and the temperature of low-temperature pre-solid solution is set to the hot rolling temperature, so that the process flow is simplified. The process design fully considers the characteristics of aluminum alloy materials and the structure characteristics of the magnesium / aluminum interface. Combined with subsequent low internal stress quenching and double-stage aging treatment, the feasibility is provided for preparing a high-performance magnesium / aluminum laminated composite plate. Specifically,

[0031] Vacuum packaging is adopted before hot rolling to avoid high-temperature oxidation of magnesium and aluminum plates and thus affect the effect of rolling compounding. The low-temperature pre-solid solution of 400-420 DEG C is set, which is to promote the alloying elements to dissolve into the aluminum matrix as much as possible below the magnesium-aluminum eutectic reaction temperature, and to meet the hot rolling temperature of aluminum / magnesium laminates. The large-size preheating pressing plate of 470-490 DEG C is used for high-temperature solid solution, which utilizes the high-speed heat transfer effect of the pressing plate to make the aluminum plate complete solid solution in a short time of 90-150 seconds. At the same time, because the process is short, the eutectic liquid phase reaction of the magnesium / aluminum interface is significantly inhibited. After the solid solution, high-speed water mist quenching is adopted, which can reduce the cooling rate and relieve the internal stress of the magnesium / aluminum interface, and avoid cracking of the magnesium / aluminum interface due to too fast cooling speed.

[0032] The preparation method provided by the application not only can effectively realize the connection of magnesium / aluminum dissimilar metals, but also can significantly improve the performance of the aluminum matrix, which will help to expand the application scope of magnesium / aluminum dissimilar structure materials in the fields of aerospace, aviation, transportation and the like, and has great potential. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions implemented by the application, the drawings used in the examples of the application will be simply explained below. Obviously, the drawings described below are only some embodiments of the application, and other drawings can be obtained from these drawings without creative labor for those skilled in the art.

[0034] Figure 1 is the magnesium / aluminum interface microstructure scanning photograph of the magnesium / aluminum laminated composite plate prepared in Example 1

[0035] Figure 2 is the magnesium / aluminum interface microstructure scanning photograph of Comparative Example 2.

[0036] It can be seen from Figure 1 that the magnesium / aluminum interface of the obtained finished product is well combined without defects such as cracking and micropore; the magnesium / aluminum interface of Comparative Example 2 has eutectic liquid phase solidification structure due to too high temperature, and through-type cracks appear. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the drawings of the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0038] The features of various aspects of the embodiments of the present application will be described in detail below. In the following detailed description, many specific details are proposed in order to make a comprehensive understanding of the present application. However, it is obvious for those of ordinary skill in the art that the present application can also be implemented without these specific details. The following description of the embodiments is only for a better understanding of the present application by showing examples of the present application. The present application is not limited to any specific settings and methods provided below, but covers all product structures, any improvements, replacements and the like of the methods without departing from the spirit of the present application.

[0039] In various drawings and the following description, the well-known structures and technologies are not shown in order to avoid unnecessary obscuring of the present application.

[0040] Embodiment 1

[0041] The surfaces to be compounded of 2mm-thick 7050 aluminum alloy sheets and 2mm-thick AZ31 magnesium alloy sheets were polished bright with sandpaper, stacked according to the structural features of aluminum / magnesium / aluminum / magnesium, and loaded into an aluminum alloy package. The package was vacuumed to 100 Pa, and after sealing, was placed into a muffle furnace to heat to 400℃, and kept for 3 hours. After the end of the heat preservation, it was immediately taken out from the furnace and sent into a rolling mill for hot rolling compounding. Among them, the roller temperature was 300℃, the roller speed was 20 rpm, and the reduction was 20%. After 3 passes of rolling, the stacked composite plate was placed in a steel pressing plate at 470℃, kept for 150 S, and then air quenched within 5 s. After cooling to room temperature, two-stage aging was carried out: first at 120℃ for 8h, and then at 175℃ for 9h.

[0042] A magnesium / aluminum stacked composite plate was obtained, with an interface shear strength of 44 MPa, a 7050 aluminum alloy matrix fracture strength of 487 MPa, and a yield strength of 413 MPa.

[0043] Embodiment 2

[0044] A 5mm thick 7050 aluminum alloy sheet and a 5mm thick AZ31 magnesium alloy sheet were polished with sandpaper on the surfaces to be bonded, stacked in a magnesium / aluminum double layer structure, and placed in an aluminum alloy package. The package was evacuated to 100 Pa, sealed, and placed in a muffle furnace and heated to 420°C for 2 hours. After the heat preservation was completed, the stack was immediately removed from the furnace and fed into a rolling mill for hot rolling. The roll temperature was 300°C, the roll speed was 10 rpm, and the reduction was 30%. After 2 passes, the stack was placed in a steel press plate at 490°C for 90 seconds, and then cooled by high-speed water mist within 10 seconds. After cooling to room temperature, the stack was subjected to two-stage aging: 120°C for 8 hours, and then 175°C for 9 hours.

[0045] A magnesium / aluminum stack was obtained, with an interfacial shear strength of 42 MPa, a 7050 aluminum alloy matrix fracture strength of 496 MPa, and a yield strength of 421 MPa.

[0046] Example 3

[0047] A 3mm thick 7050 aluminum alloy sheet and a 3mm thick AZ31 magnesium alloy sheet were polished with sandpaper on the surfaces to be bonded, stacked in an aluminum / magnesium / aluminum double layer structure, and placed in an aluminum alloy package. The package was evacuated to 100 Pa, sealed, and placed in a muffle furnace and heated to 410°C for 2 hours. After the heat preservation was completed, the stack was immediately removed from the furnace and fed into a rolling mill for hot rolling. The roll temperature was 300°C, the roll speed was 20 rpm, and the reduction was 20%. After 3 passes, the stack was placed in a steel press plate at 480°C for 120 seconds, and then cooled by high-speed water mist within 5 seconds. After cooling to room temperature, the stack was subjected to two-stage aging: 120°C for 8 hours, and then 175°C for 9 hours.

[0048] A magnesium / aluminum stack was obtained, with an interfacial shear strength of 47 MPa, a 7050 aluminum alloy matrix fracture strength of 493 MPa, and a yield strength of 418 MPa.

[0049] Comparative Example 1

[0050] The 3mm thick 7050 aluminum alloy sheet and the 3mm thick AZ31 magnesium alloy sheet to be compounded were polished with sandpaper to a bright surface, stacked according to the structure of aluminum / magnesium / aluminum, and loaded into an aluminum alloy package. The package was vacuumed to 100 Pa, sealed, and then placed in a muffle furnace and heated to 430°C for 2 hours. After the end of the heat preservation, it was immediately taken out of the furnace and sent to the rolling mill for hot rolling. The roller temperature was 300°C, the roller speed was 10 rpm, and the reduction was 20%. After 3 passes of rolling, the stacked composite plate was placed in a steel press plate at 470°C for 150s, and then air quenched within 5s. After cooling to room temperature, two-stage aging was carried out: first at 120°C for 8h, then at 175°C for 9h.

[0051] Due to the high temperature of low-temperature pre-solution (more than 420°C), diffusion reaction occurs at the magnesium / aluminum interface, forming a brittle intermetallic compound layer, resulting in a magnesium / aluminum stacked composite plate with poor interfacial bonding performance and a shear strength of only 13MPa.

[0052] Comparative Example 2

[0053] The 3mm thick 7050 aluminum alloy sheet and the 3mm thick AZ31 magnesium alloy sheet to be compounded were polished with sandpaper to a bright surface, stacked according to the structure of aluminum / magnesium / aluminum, and loaded into an aluminum alloy package. The package was vacuumed to 100 Pa, sealed, and then placed in a muffle furnace and heated to 400°C for 3 hours. After the end of the heat preservation, it was immediately taken out of the furnace and sent to the rolling mill for hot rolling. The roller temperature was 300°C, the roller speed was 20 rpm, and the reduction was 20%. After 3 passes of rolling, the stacked composite plate was placed in a steel press plate at 500°C for 180s, and then air quenched within 5s. After cooling to room temperature, two-stage aging was carried out: first at 120°C for 8h, then at 175°C for 9h.

[0054] Due to the high temperature of high-temperature short-time solution (more than 490°C), eutectic liquid phase reaction is caused at the magnesium / aluminum interface. A magnesium / aluminum stacked composite plate is obtained, with a large number of eutectic liquid phase solidification structures appearing at the interface, accompanied by through cracks parallel to the interface.

[0055] Comparative Example 3

[0056] The surfaces of 3mm thick 7050 aluminum alloy sheet and 3mm thick AZ31 magnesium alloy sheet to be compounded are polished bright with sandpaper, stacked according to the structure characteristics of aluminum / magnesium / aluminum, and loaded into an aluminum alloy package. The package is vacuumized to 100 Pa, sealed, and then placed into a muffle furnace to be heated to 400℃, and kept for 3 hours. After the keeping, the stack is immediately taken out of the furnace and sent to a rolling mill for hot rolling. The roller temperature is 300℃, the roller speed is 20 rpm, and the reduction is 20%. After 3 passes of rolling, the stack is placed in a steel pressing plate at 470℃ for 90s, and then water quenched within 10s. Because of the too fast cooling speed, the magnesium / aluminum stack is delaminated and cracked.

[0057] Comparative Example 4

[0058] The surfaces of 3mm thick 7050 aluminum alloy sheet and 3mm thick AZ31 magnesium alloy sheet to be compounded are polished bright with sandpaper, stacked according to the structure characteristics of aluminum / magnesium / aluminum, and loaded into an aluminum alloy package. The package is vacuumized to 100 Pa, sealed, and then placed into a muffle furnace to be heated to 400℃, and kept for 3 hours. After the keeping, the stack is immediately taken out of the furnace and sent to a rolling mill for hot rolling. The roller temperature is 300℃, the roller speed is 20 rpm, and the reduction is 20%. After 3 passes of rolling, the stack is placed in a steel pressing plate at 470℃ for 90s, and then water quenched within 10s. Because of the too fast cooling speed, the magnesium / aluminum stack is delaminated and cracked.

[0059] Because only low-temperature pre-solutionizing is performed without high-temperature short-time solutionizing treatment, the magnesium / aluminum stack obtained has a 7050 aluminum alloy substrate with a fracture strength of only 422 MPa and a yield strength of 348 MPa.

[0060] It can be seen from the comparison of the examples that the magnesium / aluminum stack obtained by the preparation method of the application has not only good interface bonding strength (interface shear strength ≥ 42 MPa), but also significantly improved material strength of the aluminum substrate (fracture strength ≥ 487 MPa), and such high-performance magnesium / aluminum stack can meet more material application requirements.

[0061] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the application, but the protection scope of the application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the application, and these modifications or replacements should be covered within the protection scope of the application.

Claims

1. A method for preparing high-performance magnesium / aluminum laminated composite board, characterized by: The preparation method comprises the following steps: Step one, Select aluminum plate and magnesium plate for standby, the thickness is 2-5 mm, polish the surface to be compounded, remove the surface oxide layer and impurities; Step two, Stack the aluminum plate and magnesium plate pretreated in step one in turn, put them into an aluminum alloy package, and seal the package after pumping the inside to a low vacuum state of 100 Pa; Step three, Heat the magnesium / aluminum laminated plate in the package to 400-420℃, and keep the temperature for 2-3 hours after reaching the temperature, to complete the pre-solid solution treatment; Step four, Immediately perform hot rolling after taking the magnesium / aluminum laminated plate out of the furnace after the low-temperature pre-solid solution in step three; the roller temperature is greater than or equal to 300℃, the roller speed is set to 10-20 rpm, the reduction is 20%-30%, and the laminated plate is rolled for 2-3 passes; Step five, Put the magnesium / aluminum laminated plate after hot rolling in step four into a large-size preheating pressing plate heated to 470-490℃, and keep the temperature for 90-150 S to complete high-temperature short-time solid solution treatment; Step six, Immediately transfer the magnesium / aluminum laminated plate after high-temperature short-time solid solution in step five to perform high-speed water mist cooling to complete low internal stress quenching; Step seven, According to the double-stage aging treatment, the quenched magnesium / aluminum laminated plate is kept at 116-126℃ for 7-9 hours, and then kept at 173-179℃ for 8-10 hours to realize the heat treatment strengthening of the aluminum matrix and ensure the integrity of the magnesium / aluminum interface structure.

2. The method of claim 1, wherein: The magnesium / aluminum laminated plate is composed of magnesium plates and aluminum plates in direct contact and alternating distribution, the number of layers of aluminum plates plus magnesium plates is greater than or equal to 2, and the total thickness of the laminated plate is less than or equal to 6 mm.

3. The method of claim 1, wherein: The aluminum plate is a 7050 series alloy.

4. The method of claim 1, wherein: The magnesium plate is any one of Mg-Al-Zn series, Mg-Al-Mn series, and Mg-Al-Si series alloys.

5. The method of claim 1, wherein: The parameters of high-speed water mist quenching in step six are as follows: gas-water ratio 4-6, pressure 5-8 MPa.

6. The method of claim 1, wherein: The transfer time in step six is less than or equal to 10 seconds.

7. The method of claim 6, wherein: The transfer time in step six is less than or equal to 5 seconds.

8. The method of claim 1, wherein: Mechanical polishing is adopted in step one.

9. The method of claim 1, wherein: The package material in step two is 6063 aluminum alloy or pure aluminum.

10. The method of claim 1, wherein: The heating in step three is performed in a muffle furnace.

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