High-temperature small-deformation rolling process for high-strength rare earth magnesium alloy thick plate

Abstract

The invention discloses a high-temperature small-deformation rolling process for a high-strength rare earth magnesium alloy thick plate, and relates to the technical field of nonferrous metal materials and machining thereof. The method comprises the following steps of homogenization treatment, high-temperature single-phase region multi-pass rolling and isothermal aging treatment. Wherein the high-temperature multi-pass rolling is carried out at the temperature of 450 DEG C, an initial sample is the Mg-14Gd-0.3 Zr alloy with the thickness of 100 mm, the pressing amount of the first-pass rolling is 3%, the pressing amount of each subsequent pass is 15%, tempering is carried out at the temperature of 450 DEG C for 15 min between the passes, and finally cold water quenching is carried out; a plate with the thickness being 40 mm is obtained through six passes of rolling; the excellent solution strengthening and precipitation strengthening effects of the Gd element in a magnesium matrix are fully utilized, through high-temperature single-phase region rolling, the processing formability is improved, grain refinement is accelerated, precipitation and coarsening of a second phase are inhibited, and subsequent isothermal aging treatment is combined; the large-size and high-strength magnesium alloy plate is successfully prepared, and the method has important significance in promoting industrial application of magnesium alloy in large parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of processing of non-ferrous metal structural materials, and particularly relates to a high-temperature small-deformation rolling process for high-strength rare-earth magnesium alloy thick plates. Background Art

[0002] As the lightest metal structural material, magnesium alloys are widely used in the fields of aerospace, automotive manufacturing, and electronic products due to their high specific strength and specific stiffness, excellent damping performance, good biocompatibility, strong hydrogen storage capacity, and high theoretical specific capacity of batteries. However, the relatively low strength and plasticity of magnesium alloys severely limit their wider application in industry.

[0003] Currently, the main methods for improving the strength and plasticity of magnesium alloys include alloying and plastic deformation. Research shows that rare-earth elements significantly improve the strength and plasticity of magnesium alloys through solid-solution strengthening and precipitation strengthening, and among them, the Gd element is particularly crucial. At the solidus temperature of 548 °C, the solid-solution limit of Gd in magnesium alloys can reach 23.5 wt.%, but it rapidly decreases to less than 3 wt.% at the aging temperature of 200 °C, resulting in a significant precipitation strengthening effect. Based on this, the Mg-14Gd-0.3Zr alloy has become a typical material for research and application.

[0004] In terms of plastic deformation, the existing technologies usually adopt methods such as extrusion, rolling, and forging. However, these methods have significant limitations: Although the extrusion process can produce high-performance bars, the product size is limited; when forging large-size samples, the mechanical property uniformity is poor, and at the same time, it is prone to cracking under the impact of instantaneous loads; in contrast, the rolling process has become an ideal technical means because it is suitable for the processing of large-size magnesium alloy plates. However, currently, for magnesium alloy plates with a strength higher than 400 MPa prepared by rolling, their thickness is usually less than 10 mm, mainly because the large plastic deformation required to increase the strength results in the plate thickness not meeting the requirements of larger sizes.

[0005] In view of the urgent need for high-strength and large-size magnesium alloy plates in the aerospace field of our country, a new method combining alloy element optimization and small-deformation rolling technology in the high-temperature single-phase region is proposed. By reducing the cracking tendency of samples during rolling, accelerating the dynamic recrystallization process, refining the grain structure, and enhancing the strengthening effect of aging nano-precipitates, large-size and high-strength magnesium alloy plates that meet the requirements of industrial applications can be prepared. Summary of the Invention

[0006] To address the deficiencies in the existing technology, the objective of the present invention is to provide a new method that combines alloy element optimization and hot rolling technology with small deformation in the single-phase region at high temperature. By reducing the cracking tendency of samples during rolling, accelerating the dynamic recrystallization process, refining the grain structure, and enhancing the strengthening effect of age-hardening nano-precipitates, it is possible to fabricate large-sized, high-strength magnesium alloy sheets that meet the requirements of industrial applications.

[0007] To address the deficiencies in the existing technology, the technical solution adopted in the present invention is as follows.

[0008] The present invention provides a hot rolling process with small deformation at high temperature for high-strength rare-earth magnesium alloy thick plates, which specifically includes the following steps:

[0009] (1) To eliminate the coarse eutectic phase formed during the casting process and the dendritic segregation formed during the non-equilibrium solidification process, first, homogenization treatment is carried out on the Mg-14Gd-0.3Zr magnesium alloy ingot. The ingot is taken for homogenization treatment at 510 °C for 15 h. After the solution treatment is completed, it is immediately quenched in warm water at 60 - 100 °C.

[0010] (2) After homogenization, the ingot blank is kept at 450 °C for 20 min and rolled at a rolling speed of 0.1 m / s. The reduction of the first pass is 3%, aiming to cause pre-deformation of the alloy and optimize the subsequent deformation processing ability; the reduction of each subsequent pass is ~15%. After each pass of rolling, tempering treatment is carried out by keeping it at 450 °C for 15 min, and then the next pass of rolling is carried out; after 6 passes of rolling, the total deformation is 60%, and the final sheet thickness is 40 mm. After rolling is completed, the sample is rapidly quenched in cold water to avoid abnormal grain growth and retain the high density of dislocations introduced by rolling.

[0011] (3) The rolled sample is subjected to isothermal aging treatment at 200 °C for 40 hours to further improve the material strength.

[0012] For the rolled samples prepared according to the process method provided by the present invention, the yield strength along the rolling direction is ≥395 MPa, the ultimate tensile strength is ≥454 MPa, and the elongation is ≥5%.

[0013] The beneficial effects obtained by the technical solution of the present invention are as follows:

[0014] In the present invention, by using heavy rare earth Gd with high solid solubility as the main alloying element, non-basal slip is promoted, the plasticity of the alloy is significantly improved, and the cracking risk during hot rolling is effectively reduced, thereby obtaining a magnesium alloy thick plate with both high strength and good plasticity; adopting a hot rolling process in the single-phase region at high temperature inhibits the dynamic precipitation of micron-sized Mg5Gd phase and reduces the adverse effects of coarse precipitates on mechanical properties; meanwhile, high temperature promotes the massive solid solution and uniform diffusion of Gd element in the matrix, creating conditions for the high-density precipitation of nano-sized Mg7Gd phase during subsequent isothermal aging; the precipitated phase is small in size, uniformly distributed, and located on the columnar plane of the magnesium unit cell, which can effectively hinder basal slip and produce a significant precipitation strengthening effect.

[0015] Through the design of a processing temperature of 450 °C and a total deformation of 60%, a heterogeneous microstructure is formed, achieving additional work hardening and heterogeneous strengthening effects, further improving the strength and plasticity of the material. By optimizing the processing temperature and deformation, the present invention avoids the problem of accelerated recrystallization and formation of a homogeneous fine-grained structure due to too high temperature (475 °C or 500 °C), resulting in reduced plasticity; as well as the problem of the inability to form a heterogeneous structure or a homogeneous fine-grained structure due to insufficient or excessive deformation, ensuring the stability and consistency of material properties.

[0016] Through the above process, the present invention can prepare a high-performance rare earth magnesium alloy thick plate with a thickness of up to 40 mm and a strength exceeding 400 MPa, meeting the requirements of aerospace and other fields for high-strength and large-size magnesium alloy plates, and having important industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the metallographic structure of the high-strength rare earth magnesium alloy thick plate prepared in Example 2 of the present invention.

[0018] Figure 2 It is the stress-strain curve of the high-strength rare earth magnesium alloy thick plate prepared in Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Example 1

[0020] Take a Mg-14Gd-0.3Zr (wt.%) ingot, perform homogenization treatment at 510 °C for 15 h, and immediately quench it in warm water at 60 - 100 °C after the solution treatment. The homogenized ingot blank is kept at 450 °C for 20 min and then rolled, with a rolling speed of 0.1 m / s. The reduction in the first pass is 3%, and the reduction in subsequent passes is ~15%. After each pass of rolling, a tempering treatment is carried out at 450 °C for 15 min, and then the next pass of rolling is carried out. After 6 passes of rolling, the total deformation is 60%, and the final plate thickness is 40 mm. Subsequently, isothermal aging is carried out at 200 °C for 40 h.

[0021] The room temperature mechanical properties of the alloy prepared in Example 1 of the present invention were tested according to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The tensile direction was parallel to the rolling direction, and the test results are listed in Table 1.

[0022] Example 2

[0023] Take a Mg-14Gd-0.3Zr (wt.%) ingot, perform homogenization treatment at 510 °C for 15 h, and immediately quench it in warm water at 60-100 °C after solution treatment. After homogenization, the ingot blank was rolled at 450 °C for 20 min, and the rolling speed was 0.3 m / s. The reduction of the first pass was 2%, and the reduction of each subsequent pass was 15%-20%. After each pass of rolling, tempering treatment was carried out at 450 °C for 15 min, and then the next pass of rolling was carried out. After 5 passes of rolling, the total deformation was 60%, and the final sheet thickness was 40 mm. Subsequently, isothermal aging was carried out at 200 °C for 40 h.

[0024] The room temperature mechanical properties of the alloy prepared in Example 2 of the present invention were tested according to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The tensile direction was parallel to the rolling direction, and the test results are listed in Table 1.

[0025] Example 3

[0026] Take a Mg-14Gd-0.3Zr (wt.%) ingot, perform homogenization treatment at 510 °C for 15 h, and immediately quench it in warm water at 60-100 °C after solution treatment. After homogenization, the ingot blank was rolled at 475 °C for 20 min, and the rolling speed was 0.1 m / s. The reduction of the first pass was 2%, and the reduction of each subsequent pass was ~15%. After each pass of rolling, tempering treatment was carried out at 475 °C for 12 min, and then the next pass of rolling was carried out. After 6 passes of rolling, the total deformation was 60%, and the final sheet thickness was 40 mm. Subsequently, isothermal aging was carried out at 200 °C for 40 h.

[0027] The room temperature mechanical properties of the alloy prepared in Example 3 of the present invention were tested according to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The tensile direction was parallel to the rolling direction, and the test results are listed in Table 1.

[0028] Example 4

[0029] Take an Mg-14Gd-0.3Zr (wt.%) ingot, perform homogenization treatment at 510 °C for 15 h, and immediately quench it in warm water at 60 - 100 °C after solution treatment. After homogenization, keep the ingot blank at 500 °C for 20 min and then roll it with a rolling speed of 0.1 m / s. The reduction of the first pass is 2%, and the reduction of each subsequent pass is ~15%. After each pass of rolling, perform tempering treatment at 500 °C for 12 min, and then carry out the next pass of rolling. After 6 passes of rolling, the total deformation is 60%, and the final sheet thickness is 40 mm. Subsequently, perform isothermal aging at 200 °C for 40 h.

[0030] According to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", the room temperature mechanical properties of the alloy prepared in Example 3 of the present invention were tested, and the tensile direction was parallel to the rolling direction. The test results are listed in Table 1.

[0031] Example 5

[0032] Take an Mg-14Gd-0.3Zr (wt.%) ingot, perform homogenization treatment at 510 °C for 15 h, and immediately quench it in warm water at 60 - 100 °C after solution treatment. After homogenization, keep the ingot blank at 450 °C for 20 min and then roll it with a rolling speed of 0.1 m / s. The reduction of the first pass is 3%, and the reduction of each subsequent pass is ~15%. After each pass of rolling, perform tempering treatment at 450 °C for 15 min, and then carry out the next pass of rolling. After 5 passes of rolling, the total deformation is 40%, and the final sheet thickness is 60 mm. Subsequently, perform isothermal aging at 200 °C for 40 h.

[0033] According to the standard of GBT-228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", the room temperature mechanical properties of the alloy prepared in Example 1 of the present invention were tested, and the tensile direction was parallel to the rolling direction. The test results are listed in Table 1.

[0034] Example 6

[0035] Take an Mg-14Gd-0.3Zr (wt.%) ingot and perform homogenization treatment at 510 °C for 15 h. Immediately after solution treatment, quench it in warm water at 60-100 °C. After homogenization, keep the ingot blank at 450 °C for 20 min and then roll it, with a rolling speed of 0.1 m / s. The reduction of the first pass is 3%, and the reduction of each subsequent pass is ~15%. After each pass of rolling, perform tempering treatment by keeping it at 450 °C for 12 min, and then carry out the next pass of rolling. After 8 passes of rolling, the total deformation is 80%, and the final sheet thickness is 20 mm. Subsequently, perform isothermal aging at 200 °C for 40 h.

[0036] According to the standard of GBT-228.1-2021 "Metallic materials-Tensile testing-Part 1: Method of test at room temperature", test the room temperature mechanical properties of the alloy prepared in Example 3 of the present invention. The tensile direction is parallel to the rolling direction, and the test results are listed in Table 1.

[0037] The above are the implementation schemes of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle and core idea of the present invention patent, several modifications and improvements can still be made, and these modifications and improvements are also regarded as within the protection scope of the present invention patent.

[0038] Table 1. Room temperature mechanical properties of the alloys prepared in Examples 1 to 6 in the rolling direction

[0039]

Claims

1. A high-temperature small deformation rolling process for high-strength rare earth magnesium alloy thick plates, the steps of which are: (1) Take the ingot and perform homogenization treatment; (2) The homogenized ingot is kept at 450°C for 20 minutes and then rolled at a rolling speed of 0.1-0.3 m / s; the first pass is pressed by 2-3%, and the subsequent passes are pressed by 15-20%; after each rolling pass, it is tempered at 450-500°C for 12-15 minutes, and then the next rolling is carried out; after 5-8 rolling passes, the total deformation is 40-80%, and the final plate thickness is 20-60 mm.

2. According to the high-temperature and small deformation rolling process of a high-strength rare earth magnesium alloy thick plate as described in claim 1, the ingot is Mg-14Gd-0.3Zr (wt.%).

3. According to the high-temperature and small deformation rolling process of a high-strength rare earth magnesium alloy thick plate described in claim 1, the rolling speed is 0.1m / s, the first pass pressing amount is 3%, and the subsequent pressing amount is 15% per pass; after each rolling pass is completed, a tempering treatment is performed at 450°C for 15 minutes, followed by the next rolling pass.

4. According to the high-temperature small deformation rolling process of a high-strength rare earth magnesium alloy thick plate as described in claim 3, after 6 rolling passes, the total deformation is 60%, and the final plate thickness is 40 mm.

5. According to the high-temperature and small deformation rolling process of a high-strength rare earth magnesium alloy thick plate as described in claim 1, the first pass pressing amount is 2%, and after each rolling pass is completed, a tempering treatment is performed at 450°C for 15 minutes, followed by the next rolling pass.

6. According to the high-temperature small deformation rolling process of a high-strength rare earth magnesium alloy thick plate as described in claim 5, after 5 rolling passes, the total deformation is 60%, and the final plate thickness is 40 mm.

7. According to the high-temperature small deformation rolling process of the high-strength rare earth magnesium alloy thick plate described in claim 1, the ingot is homogenized at 510°C for 15 hours, and immediately quenched in warm water at 60-100°C after the solution treatment.

8. A high temperature and small deformation rolling process for high strength rare earth magnesium alloy thick plates according to any one of claims 1 to 7, wherein the rolled alloy is finally subjected to isothermal aging treatment.

9. A high temperature and small deformation rolling process for a high strength rare earth magnesium alloy thick plate according to claim 8, followed by isothermal aging at 200°C for 40 hours.

10. A high-temperature small deformation rolling process for high-strength rare earth magnesium alloy thick plates according to claim 9, wherein the yield strength of the rolled sample along the rolling direction is ≥395MPa, the ultimate tensile strength is ≥454MPa, and the elongation is ≥5%.

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