A bimodal magnesium alloy with room temperature single-pass severe cold rolling treatment and a preparation method thereof

Abstract

The application discloses a kind of bimodal magnesium alloy with room temperature single pass severe cold rolling treatment, and the element composition of magnesium alloy is as follows in percentage by mass: Y 6.0-10.0%, Ag 0.5-4.0%, Zr 0.2-0.5%, and the balance is Mg;With annealing treatment to obtain the Mg-Y-Ag-Zr alloy bimodal structure of size grain composition;Under room temperature condition, the maximum down pressure of single pass severe cold rolling treatment reaches 43%;The aging hardness of magnesium alloy reaches 80-105HV, the yield strength is 206-279MPa, the tensile strength is 293-369MPa, and the uniform elongation is 10-18%.Its preparation method includes the following steps:1, the preparation of magnesium alloy ingot;2, Mg-Y-Ag-Zr alloy pretreatment;3, Mg-Y-Ag-Zr alloy single pass severe cold rolling treatment;4, Mg-Y-Ag-Zr alloy annealing and aging treatment.

Description

Technical Field

[0001] This invention belongs to the field of alloy processing, specifically relating to a bimodal magnesium alloy with room temperature single-pass intensive cold rolling treatment and its preparation method. Background Technology

[0002] Magnesium alloys, as lightweight structural metal materials, have the characteristics of low density, high specific strength, good electromagnetic shielding performance, and easy recycling. They are widely used in the automotive, aerospace, and electronic communication fields. However, in order to improve the strength of magnesium alloys, the plasticity is significantly reduced, which in turn increases the difficulty of deformation processing.

[0003] To simultaneously improve the strength and plasticity of magnesium alloys, a bimodal microstructure is constructed within them. For example, existing literature 1 (Li Yongkang. Microstructure Regulation and Strength / Plasticity Enhancement Mechanism of Mixed-Crystal Magnesium Alloys [D]. Jilin University, 2021.) describes the preparation of magnesium alloys with a bimodal structure, obtaining both micron / submicron scale fine grains and tens of micron scale coarse grains, thus achieving high strength while maintaining high plasticity. Rolling is currently the main method for sheet metal manufacturing. However, magnesium alloys have poor low-temperature plasticity, thus requiring high deformation temperatures and low plastic deformation amounts during plastic deformation. This necessitates the conventional high-temperature multi-pass rolling method with small reductions, referred to as the high-temperature multi-pass method. Obviously, the high-temperature multi-pass method requires multiple high-temperature heating and holding processes, resulting in extremely low production efficiency; this problem is referred to as the high-temperature multi-pass problem.

[0004] To address the issue of high-temperature multi-pass rolling, existing literature 2 (Wang Huiyuan. A method for rolling magnesium alloy with large reduction: 201410123706.7[P]. 2016-02-03.) proposes adding hardened liner plates to the upper and lower surfaces of the magnesium alloy, uniformly applying high-temperature lubricant to the surfaces of the hardened liner plates and the magnesium alloy, and simultaneously heating the magnesium alloy and the hardened liner plates to 300–400℃, followed by a static holding period of 20–60 minutes before rolling. This allows for a single-pass reduction of up to 90% during synchronous rolling. While this technical solution achieves a single-pass process, its liner can only be used once. After rolling, the liner deforms severely and cannot be reused efficiently, directly leading to a significant increase in production costs. Furthermore, this technical solution requires the use of a high-temperature lubricant as a necessary technical feature. This feature directly results in poor coating consistency of the high-temperature lubricant and uneven micro-damage to the alloy surface. Additionally, after rolling, the remaining high-temperature lubricant on the material surface needs to be cleaned, increasing the complexity of the process. Moreover, this technical solution still requires rolling under high-temperature conditions. This problem directly leads to grain and precipitate growth in the magnesium alloy during the heating-holding process, significantly reducing the strengthening effect.

[0005] To fundamentally solve the problems of high-temperature rolling, adding yttrium and rare earth elements to improve room-temperature ductility allows for cold rolling at room temperature, a method known as cold rolling. Cold rolling directly avoids the problems associated with high-temperature rolling. For example, existing literature 3 (Yang Y, Liu Y, Yan S, et al. On the micromechanism of superior strength and ductility synergy in a heterostructured Mg-2.77 Yalloy[J]. Journal of Magnesium and Alloys, 2024, 12(7): 2793-2811.) successfully prepared and retained a bimodal structure of magnesium alloy by extruding and annealing Mg-2.77Y (wt.%) alloy, followed by cold rolling and annealing. The total rolling reduction reached 42%. However, achieving the above technical effect requires multi-pass rolling, with a single pass reduction of no more than 2% and more than 26 rolling passes! Therefore, this technical solution suffers from a long preparation cycle and cannot solve the problem of high production costs.

[0006] The analysis of existing literature above reveals that the current problems in preparing bimodal microstructures in magnesium alloy rolling are as follows: 1. Single-pass hot rolling is required, with rolling temperatures reaching over 300°C. The liner cannot be reused efficiently, and there are issues with applying and cleaning high-temperature lubricant before and after rolling. 2. Room temperature cold rolling requires multiple passes, which results in a long production cycle and low production efficiency. Summary of the Invention

[0007] The purpose of this invention is to provide a bimodal magnesium alloy with room temperature single-pass intensive cold rolling and its preparation method, resulting in a bimodal microstructure with mixed large and small grains, while simultaneously improving strength and plasticity, and enhancing the performance of the rolled sheet. The basic principle is as follows:

[0008] 1. Through compositional design, the aging precipitates of the alloy are mainly basal plane precipitates, because they have little hindering effect on basal plane dislocations, which is beneficial for room temperature deformation;

[0009] 2. Improve the rolling process by using single-pass high-pressure room temperature cold rolling, rapid annealing, and low-temperature aging to efficiently prepare bimodal microstructure with controlled properties. The role of the liner is to add hard alloy liners to reduce the stress in the rolling direction and increase the stress in the normal direction. The use of the liner increases the room temperature deformation of the alloy. The purpose of rapid annealing is to use high temperature and short time to eliminate the formation of precipitates and allow partial recrystallization to produce a bimodal microstructure. The purpose of low-temperature aging is to generate precipitates at low temperature.

[0010] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0011] A bimodal magnesium alloy with room temperature single-pass intensive cold rolling, wherein the elemental composition of the magnesium alloy, by mass percentage, is Y 6.0-10.0%, Ag 0.5-4.0%, Zr 0.2-0.5%, with the balance being Mg; and possesses a bimodal microstructure of Mg-Y-Ag-Zr alloy with large and small grains obtained by annealing.

[0012] At room temperature, the maximum reduction in a single-pass intense cold rolling process reaches 43%;

[0013] Magnesium alloys have an aging hardness of 80-105 HV, a yield strength of 206-279 MPa, a tensile strength of 293-369 MPa, and a uniform elongation of 10-18%.

[0014] A method for preparing a bimodal magnesium alloy with room temperature single-pass intensive cold rolling treatment includes the following steps:

[0015] Step 1, Preparation of magnesium alloy ingots: First, all raw materials, molds and tools are dried. Then, pure magnesium is completely melted under mixed protective gas conditions. After that, Mg-30Y master alloy, Mg-30Zr master alloy and pure Ag are added in sequence and completely melted. Finally, after slag removal, stirring, settling and removing slag, the ingots are cast to obtain Mg-Y-Ag-Zr alloy ingots.

[0016] In step 1, the drying conditions are: drying temperature of 200℃ and drying time of 20 min; stirring time of 10 min and standing time of 20 min.

[0017] In step 1, the mass ratio of Mg-30Y master alloy, Mg-30Zr master alloy, pure Ag and pure Mg satisfies Y:Ag:Zr:Mg=20:5:1:224;

[0018] In step 1, the mixed protective gas is a mixture of CO2 and SF6; the conditions for melting pure magnesium are a melting temperature of 720℃ and a holding time of 20min; the conditions for melting Mg-30Y master alloy, Mg-30Zr master alloy and pure Ag are a melting temperature of 780℃.

[0019] Step 2, Pretreatment of Mg-Y-Ag-Zr alloy: The Mg-Y-Ag-Zr alloy ingot obtained in Step 1 is subjected to homogenization, extrusion and solution treatment in sequence to obtain a solution-treated Mg-Y-Ag-Zr alloy.

[0020] In step 2, the homogenization conditions are: homogenization temperature of 460-500℃ and homogenization time of 3-8h.

[0021] In step 2, the extrusion conditions are: extrusion temperature of 390-430℃ and extrusion ratio of (11-20):1.

[0022] In step 2, the conditions for solution treatment are: solution treatment temperature of 460-500℃ and solution treatment time of 5-20h.

[0023] Step 3, single-pass intense cold rolling treatment of Mg-Y-Ag-Zr alloy: under the condition of room temperature cold rolling, the solid solution Mg-Y-Ag-Zr obtained in step 2 is subjected to single-pass intense cold rolling treatment to obtain cold-rolled Mg-Y-Ag-Zr alloy.

[0024] In step 3, the conditions for single-pass severe cold rolling are that two cemented carbide liners are added simultaneously to the upper and lower surfaces of the alloy, and the surfaces of the cemented carbide liners in contact with the magnesium alloy are smooth, and the cemented carbide liners are rolled synchronously with the magnesium alloy.

[0025] The single-pass reduction of the cemented carbide liner during the synchronous rolling process with the magnesium alloy is 40-43%.

[0026] Step 4, Annealing and aging treatment of Mg-Y-Ag-Zr alloy: The cold-rolled sample obtained in step 3 is subjected to annealing and low-temperature aging treatment to obtain aged Mg-Y-Ag-Zr alloy.

[0027] In step 4, the annealing treatment adopts the high-temperature short-time rapid annealing method, with an annealing temperature of 350-500℃ and an annealing time of 0-1min; the low-temperature aging conditions are as follows: the low-temperature aging temperature is 200℃ and the low-temperature aging time is 8-1024h.

[0028] The technical effectiveness of this invention can be seen from the following tests:

[0029] Rolling tests show that the maximum reduction in a single pass of cold rolling for Mg-Y-Ag-Zr is 43%, and it has good rolling forming effect.

[0030] EBSD testing showed that MgYAgZr-C, after annealing, exhibited a bimodal structure composed of large and small grains.

[0031] Microhardness testing showed that the aged hardness reached 80-105 HV, representing a hardness increase of 31%.

[0032] The room temperature tensile test showed that the yield strength was 206-279 MPa, the tensile strength was 293-369 MPa, and the uniform elongation was 10-18%, indicating a good match between strength and plasticity.

[0033] Therefore, the present invention has the following advantages:

[0034] 1. This invention enables single-pass cold rolling of high rare earth content magnesium alloys with large reduction in pressure at room temperature. The maximum reduction in pressure per pass can reach 43%. The process does not use the long-term high-temperature heating treatment of high-temperature hot rolling, and also reduces the repeated deformation process required for multi-pass rolling. This not only improves processing efficiency, but also helps to shorten the preparation cycle, and also expands the process range of room temperature plastic processing of high rare earth content magnesium alloys.

[0035] 2. This invention eliminates the need for preheating of the sample before rolling, as well as the use of high-temperature lubricants. Furthermore, it eliminates the need to heat the rolls during the rolling process, allowing the rolling process to be completed at room temperature. This effectively simplifies the process, reduces equipment requirements, decreases energy consumption, and lowers production costs.

[0036] 3. This invention achieves a combination of single-pass large-volume cold rolling and subsequent rapid annealing, resulting in an alloy that maintains good plasticity while increasing strength after low-temperature aging treatment.

[0037] In summary, this invention achieves comprehensive optimization of the strength, plasticity, and work hardening capacity of high rare earth content magnesium alloys through a process route combining solution treatment, single-pass large-volume room temperature cold rolling, rapid annealing, and low-temperature aging, without the need for complex heating and rolling conditions. This improves the problem of difficulty in balancing strength and plasticity in existing magnesium alloys and has good prospects for industrial application. Attached Figure Description

[0038] Figure 1 The image shows the backscattered electron configuration of the solid solution Mg-Y-Ag-Zr alloy obtained in step 2 of Example 1. Figure 2 The image shows the surface morphology of the Mg-Y-Ag-Zr alloy sample obtained in step 3 of Example 1 after a single pass cold rolling process (43%). Figure 3 The image shows the surface morphology of the Mg-Y-Ag-Zr alloy sample obtained in step 3 of Example 1 after a single-pass cold rolling process (48%). Figure 4 This is a morphological diagram of the annealed grain structure of the Mg-Y-Ag-Zr alloy obtained in step 4 of Example 1. Figure 5 This is the aging curve of the cold-rolled Mg-Y-Ag-Zr alloy obtained in step 4 of Example 1; Figure 6 The tensile properties of the Mg-Y-Ag-Zr alloy obtained in step 4 of Comparative Example 1 are shown in the figure. Figure 7 The image shows the surface morphology of the Mg-9Al-1Zn alloy sample obtained in Comparative Example 1 after a single-pass cold rolling process (43%). Detailed Implementation

[0039] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0040] Example 1

[0041] A method for preparing a bimodal magnesium alloy with room temperature single-pass intensive cold rolling treatment includes the following steps:

[0042] Step 1, Preparation of magnesium alloy ingot: First, dry all raw materials, molds and tools at a drying temperature of 200℃ for 20 min. Then, under mixed protective gas conditions, melt pure magnesium completely at a melting temperature of 720℃ for 20 min. After that, raise the temperature to 780℃ and add Mg-30Y master alloy, Mg-30Zr master alloy and pure Ag in sequence until completely melted. Finally, after slag removal, stirring, settling and removing slag, cast to obtain Mg-Y-Ag-Zr alloy ingot, abbreviated as MgYAgZr-A.

[0043] The mass ratio of the Mg-30Y master alloy, the Mg-30Zr master alloy, pure Ag and pure Mg satisfies Y:Ag:Zr:Mg=20:5:1:224;

[0044] The mixed protective gas is a mixture of CO2 and SF6.

[0045] The stirring time is 10 minutes, and the settling time is 20 minutes.

[0046] Step 2, Pretreatment of Mg-Y-Ag-Zr alloy: The MgYAgZr-A ingot obtained in Step 1 is subjected to homogenization, extrusion and solution treatment in sequence to obtain a solution-treated Mg-Y-Ag-Zr alloy, abbreviated as MgYAgZr-B.

[0047] The homogenization conditions are: homogenization temperature of 500℃ and homogenization time of 3h.

[0048] The extrusion treatment conditions are: extrusion temperature of 410°C and extrusion ratio of 17:1.

[0049] The conditions for the solution treatment are: a solution treatment temperature of 500°C and a solution treatment time of 6 hours.

[0050] To verify the microstructure of the MgYAgZr-B obtained in step 2, i.e., the solid solution effect, SEM-BSE testing was performed. The test results are as follows: Figure 1 As shown, MgYAgZr-B is an equiaxed crystal, and only a small amount of insoluble second phase is present. Test results indicate that step 2 achieves solid solution treatment, and the effect is good.

[0051] Step 3, single-pass intense cold rolling treatment of Mg-Y-Ag-Zr alloy: Under the condition that the cold rolling temperature is room temperature, MgYAgZr-B obtained in step 2 is subjected to single-pass intense cold rolling treatment to obtain cold-rolled Mg-Y-Ag-Zr alloy, abbreviated as MgYAgZr-C;

[0052] The conditions for the single-pass severe cold rolling process are as follows: two cemented carbide liners are simultaneously added to the upper and lower surfaces of the MgYAgZr-B alloy, and the surfaces of the cemented carbide liners in contact with the magnesium alloy are smooth, and the cemented carbide liners are rolled synchronously together with the magnesium alloy.

[0053] To demonstrate the maximum reduction of MgYAgZr-C in a single-pass intensive cold rolling process, a single-pass intensive cold rolling process was performed under different reduction conditions, and the surface morphology was tested.

[0054] The test results with a downward pressure of 43% are as follows: Figure 2 As shown, after a single-pass intensive cold rolling process, the surface of MgYAgZr-C is free of cracks and edge cracks.

[0055] The test results with a downward pressure of 48% are as follows: Figure 3 As shown, after a single-pass drastic cold rolling process, MgYAgZr-C undergoes deformation, and large cracks extending inward from the edge appear on the surface, resulting in poor rollability.

[0056] Test results show that the maximum compression of MgYAgZr-C is 43%, and it has good rolling forming effect.

[0057] Step 4, Annealing and aging treatment of Mg-Y-Ag-Zr alloy: The MgYAgZr-C sample obtained in Step 3 is subjected to annealing and low-temperature aging treatment to obtain aged Mg-Y-Ag-Zr alloy, abbreviated as MgYAgZr-D;

[0058] The annealing process adopts a high-temperature short-time rapid annealing method, with an annealing temperature of 400℃ and an annealing time of 15s;

[0059] The conditions for low-temperature aging are: a low-temperature aging temperature of 200°C and a low-temperature aging time of 1024 hours.

[0060] To demonstrate the effectiveness of the annealing treatment in step 4, EBSD characterization was performed. The test results are as follows: Figure 4 As shown, the MgYAgZr-C sample exhibits a bimodal structure composed of large and small grains after annealing.

[0061] To demonstrate the effectiveness of the low-temperature aging treatment in step 4, microhardness and room temperature tensile tests were performed.

[0062] Microhardness test results are as follows Figure 5 As shown, the unaged hardness of MgYAgZr-E is 80 HV, and the peak aged hardness is 105 HV. The precipitation strengthening effect caused by aging is obvious, and the hardness is increased by 25 HV.

[0063] Room temperature tensile test results are as follows Figure 6 As shown, the peak aged tensile strength of MgYAgZr-E is 369 MPa, and the uniform elongation is 10%.

[0064] Test results show that the present invention can produce magnesium alloy sheets with good strength and plasticity matching.

[0065] To demonstrate the effect of the magnesium alloy of the present invention on the single-pass severe cold rolling deformation treatment, Comparative Example 1 is provided, in which a conventional commercial magnesium alloy AZ91 is subjected to a single-pass severe cold rolling deformation treatment.

[0066] Comparative Example 1

[0067] A single-pass drastic cold rolling deformation treatment was performed on conventional commercial magnesium alloy AZ91.

[0068] The mass ratio of the conventional commercial magnesium alloy AZ91 satisfies Al:Zn:Mg = 9: 1: 90;

[0069] To demonstrate the rolling performance of AZ91, surface morphology tests were conducted. The test results are as follows: Figure 7 As shown, after a single pass of intense cold rolling, AZ91 cracked, and obvious cracks appeared on the surface.

[0070] Compared with Example 1, it can be seen that AZ91 cannot achieve a single-pass severe cold rolling deformation process with a reduction of 43%.

Claims

1. A bimodal magnesium alloy with room temperature single-pass intensive cold rolling treatment, characterized in that: The elemental composition of the magnesium alloy, by mass percentage, is Y 6.0-10.0%, Ag 0.5-4.0%, Zr 0.2-0.5%, with the balance being Mg; it possesses a bimodal microstructure of Mg-Y-Ag-Zr alloy with large and small grains obtained after annealing. At room temperature, the maximum reduction in a single pass of intense cold rolling reaches 43%.

2. The magnesium alloy according to claim 1, characterized in that: Magnesium alloys have an aging hardness of 80-105 HV, a yield strength of 206-279 MPa, a tensile strength of 293-369 MPa, and a uniform elongation of 10-18%.

3. A method for preparing a bimodal magnesium alloy with room temperature single-pass intensive cold rolling treatment, characterized in that... Includes the following steps: Step 1, Preparation of magnesium alloy ingots: First, all raw materials, molds and tools are dried. Then, pure magnesium is completely melted under mixed protective gas conditions. After that, Mg-30Y master alloy, Mg-30Zr master alloy and pure Ag are added in sequence and completely melted. Finally, after slag removal, stirring, settling and removing slag, the ingots are cast to obtain Mg-Y-Ag-Zr alloy ingots. In step 1, the drying conditions are: drying temperature of 200℃ and drying time of 20 min; stirring time of 10 min and standing time of 20 min. Step 2, Pretreatment of Mg-Y-Ag-Zr alloy: The Mg-Y-Ag-Zr alloy ingot obtained in Step 1 is subjected to homogenization, extrusion and solution treatment in sequence to obtain a solution-treated Mg-Y-Ag-Zr alloy. Step 3, single-pass intense cold rolling treatment of Mg-Y-Ag-Zr alloy: under the condition of room temperature cold rolling, the solid solution Mg-Y-Ag-Zr obtained in step 2 is subjected to single-pass intense cold rolling treatment to obtain cold-rolled Mg-Y-Ag-Zr alloy. Step 4, Annealing and aging treatment of Mg-Y-Ag-Zr alloy: The cold-rolled sample obtained in step 3 is subjected to annealing and low-temperature aging treatment to obtain aged Mg-Y-Ag-Zr alloy.

4. The preparation method according to claim 3, characterized in that: In step 1, the mass ratio of Mg-30Y master alloy, Mg-30Zr master alloy, pure Ag and pure Mg satisfies Y:Ag:Zr:Mg=20:5:1:224; In step 1, the mixed protective gas is a mixture of CO2 and SF6; the conditions for melting pure magnesium are a melting temperature of 720℃ and a holding time of 20min; the conditions for melting Mg-30Y master alloy, Mg-30Zr master alloy and pure Ag are a melting temperature of 780℃.

5. The preparation method according to claim 3, characterized in that: In step 2, the homogenization conditions are: homogenization temperature of 460-500℃ and homogenization time of 3-8h. In step 2, the extrusion conditions are: extrusion temperature of 390-430℃ and extrusion ratio of (11-20):

1. In step 2, the conditions for solution treatment are: solution treatment temperature of 460-500℃ and solution treatment time of 5-20h.

6. The preparation method according to claim 3, characterized in that: In step 3, the conditions for single-pass severe cold rolling are that two cemented carbide liners are added simultaneously to the upper and lower surfaces of the alloy, and the surfaces of the cemented carbide liners in contact with the magnesium alloy are smooth, and the cemented carbide liners are rolled synchronously with the magnesium alloy. The single-pass reduction of the cemented carbide liner during the synchronous rolling process with the magnesium alloy is 40-43%.

7. The preparation method according to claim 3, characterized in that: In step 4, the annealing treatment adopts the high-temperature short-time rapid annealing method, with an annealing temperature of 350-500℃ and an annealing time of 0-1min; the low-temperature aging conditions are as follows: the low-temperature aging temperature is 200℃ and the low-temperature aging time is 8-1024h.

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