Dual-mode structure ZK60 magnesium alloy plate and rolling process thereof

Abstract

The invention relates to the technical field of metal materials, in particular to a ZK60 magnesium alloy plate with a dual-mode tissue structure and a rolling process thereof, and the rolling process comprises the following steps: carrying out multi-pass hot rolling on a ZK60 magnesium alloy ingot, and preparing the ZK60 magnesium alloy plate with the dual-mode tissue structure by accurately regulating and controlling the rolling process and an intermediate annealing process; wherein the fine grain structure accounts for 40-80%, and the average grain size is smaller than 10 microns; texture strengthening and dislocation strengthening of coarse deformed grains and fine grain strengthening and toughening of fine recrystallized structures are comprehensively utilized, so that the tensile strength of the plate at the room temperature is not lower than 280 MPa, and the elongation is not lower than 20%; the process is simple, large-breadth and high-performance ZK60 magnesium alloy plates can be prepared in batches, and the urgent weight reduction requirements in the fields of aerospace, traffic transportation and the like are met.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a ZK60 high-performance magnesium alloy plate with a dual-mode structure and a rolling process thereof. Background Art

[0002] Magnesium alloy is the lightest metal structural material, boasting a density only one-quarter that of steel and two-thirds that of aluminum alloy. It offers a range of advantages, including damping and vibration reduction, electromagnetic shielding, rapid thermal conductivity and heat dissipation, excellent biocompatibility, easy machinability, and recyclability. It is widely used in the automotive, electronics and home appliances, household goods, leisure and fitness equipment, bicycles, aerospace, aviation, and defense industries. Furthermore, my country is a major magnesium resource country, with approximately 70% of global magnesium ore resources and salt lake resources, resulting in the world's largest magnesium reserves. Therefore, fully leveraging this resource advantage and vigorously promoting the application of magnesium alloys in my country is of great significance to the lightweighting development of various industries and the achievement of my country's "dual carbon" goals.

[0003] The transportation sector is a major carbon emission disaster area, and there is an urgent need for lightweighting. Wide-width plates with excellent performance that can be mass-produced are important raw materials for the production of parts for transportation vehicles such as automobiles, subways, and high-speed railways, and are used in extremely large quantities. If magnesium alloy materials can be replaced, it will make a huge contribution to energy conservation and emission reduction in my country. However, since magnesium and most magnesium alloys have a close-packed hexagonal crystal structure and poor deformation capacity, the production of rolled plates is difficult. Usually, they need to be opened through early extrusion or forging, which makes it impossible to prepare wide-width plates and continuous mass production, resulting in high plate costs. Moreover, some magnesium alloy plates have low strength and poor plasticity, making it difficult to meet application requirements.

[0004] Bimodal structure, also known as mixed crystal structure or heterogeneous structure, is a microstructure composed of two types of grains with significant size differences. Generally speaking, the coarse grains are the soft phase and the fine grains are the hard phase. During the deformation process, the two coordinate with each other, and the geometric dislocations must accumulate at the interface, resulting in back stress strengthening, and a higher work hardening ability can be obtained, so that the material has excellent room temperature mechanical properties. The patent with application number CN202010205821.4 successfully prepared a pure copper sample with a mixed crystal structure by cam rolling, achieving a synergistic improvement in strength and plasticity. The patent with application number 201910822560.8 achieved the preparation of a magnesium alloy material with a mixed crystal structure by introducing a stir friction processing process with controlled cooling, the addition of second phase particles and a subsequent heat treatment process. Its strength-plasticity product can reach 4446.75~4764.42MPa%. Patent CN202010696498.5 also discloses a method for preparing a high-strength and plastic mixed crystal structure magnesium alloy. By combining a variety of processes including conventional extrusion + equal channel extrusion + cold rolling, a magnesium alloy deformed material with a mixed crystal structure was successfully prepared, with a room temperature tensile strength exceeding 400 MPa. Obviously, mixed crystal structure can significantly improve the mechanical properties of metal materials. However, none of the above preparation processes can achieve continuous batch production of large coil weight and wide width magnesium alloy sheets. Summary of the Invention

[0005] To address the poor performance of existing magnesium alloy rolled sheets and the difficulty in producing high-performance, wide-width magnesium alloy sheets with large coil weights, the present invention provides a ZK60 high-performance magnesium alloy sheet with a dual-mode microstructure and a rolling process thereof. Using conventional commercial ZK60 magnesium alloy ingots as raw material and utilizing conventional rolling equipment, the ZK60 magnesium alloy sheet with a dual-mode microstructure is produced through precise control of the rolling process and intermediate annealing. By comprehensively utilizing the texture strengthening and dislocation strengthening of coarse deformed grains, as well as the grain refinement and toughening of fine recrystallized structures, the sheet achieves a room-temperature tensile strength of no less than 280 MPa and an elongation of no less than 20%. This simple process enables the mass production of wide-width, high-performance ZK60 magnesium alloy sheet, meeting the urgent weight reduction needs of industries such as aerospace and transportation.

[0006] The technical solution of the present invention is:

[0007] A ZK60 high-performance magnesium alloy sheet with a dual-mode microstructure, with the following specific features:

[0008] The chemical composition of the ZK60 magnesium alloy sheet meets the requirements of the national standard (GB / T 5153-2016) for ZK60 / ZK61 alloys, and rare earth elements of no more than 1 wt.% may be added;

[0009] The microstructure of the ZK60 magnesium alloy plate is composed of fine recrystallized grains and coarse deformed grains.

[0010] In the microstructure, the proportion of recrystallized grains is 40-80%, the average grain size is less than 10 microns, the weak texture has a RD-TD reference surface (0002) pole figure texture intensity lower than 8 m.r.d.

[0011] In the microstructure, the long axis size of the deformed grains is greater than 30 microns, the strong texture has a RD-TD reference surface (0002) pole figure texture intensity higher than 10 m.r.d.

[0012] The plate has a tensile strength higher than 280 MPa and an elongation higher than 20% in the RD direction at room temperature.

[0013] The rolling process of the ZK60 high-performance magnesium alloy plate with a bimodal microstructure structure comprises the following steps and processes:

[0014] The ZK60 magnesium alloy ingot is used as the initial blank for rolling the plate, and the blank thickness is 10-500 mm; the blank needs to be subjected to solid solution treatment before rolling;

[0015] The rolling process is divided into two parts, i.e., breakdown rolling and microstructure control rolling.

[0016] The rolling temperature of the breakdown rolling is 350-400 DEG C, the pass reduction is 2-10%, the total reduction is 10-30%, the rolling speed is 1-50 m / min, and the roller temperature is 50-300 DEG C.

[0017] The rolling temperature of the microstructure control rolling is 300-400 DEG C, the pass reduction is 10-50%, the total reduction is 30-70%, the rolling speed is 1-50 m / min, and the roller temperature is 50-300 DEG C.

[0018] During the multi-pass rolling process, annealing is performed once in each / two passes, the annealing temperature is the same as the rolling temperature of the next pass, and the annealing time is 10-30 min.

[0019] The present application has the following advantages and technical effects:

[0020] Although the rolling process is a conventional preparation process for metal plates, magnesium alloys are generally of a close-packed hexagonal crystal structure and have poor plastic deformation capacity, and ZK60 magnesium alloy is a high-strength magnesium alloy with high Zn content, which is more likely to cause deformation cracking. Therefore, it is often difficult to form a plate directly by rolling the cast blank. Even if it is forced to form, the obtained structure is usually a single deformed structure with strong texture or a single fully recrystallized structure with weak texture, the former has high strength but poor plasticity, and the latter has good plasticity but low strength, so it is difficult to achieve a good match of strength and plasticity. Although the use of extrusion or forging processes before rolling can indeed improve the subsequent rolling performance of ZK60 alloy magnesium alloy and the mechanical properties of the plate, it severely limits the width of the plate that can be prepared, and it also disrupts the continuity of the process, resulting in low production efficiency, small plate specifications, high cost, and inability to meet application requirements.

[0021] To solve the above problems, through a large number of experimental studies, the evolution law of the microstructure, texture and related mechanical properties of ZK60 magnesium alloy during rolling is mastered, and a plate can be directly rolled and formed from a ZK60 ingot. Through the good cooperation and precise control of the rolling and annealing processes, a ZK60 magnesium alloy plate with a bimodal microstructure is obtained, which has high strength and good plasticity, and the mechanical properties are much better than those of ZK61 magnesium alloy plate in the national standard (GB / T 5154-2022 Magnesium and Magnesium Alloy Plates and Strips).

[0022] The main advantages of the present application are as follows:

[0023] 1. The present application uses a bimodal microstructure to prepare a high-strength and high-plasticity magnesium alloy plate, but it is different from the heterogeneous microstructure of traditional metal materials. The coarse deformed grains have strong basal texture and are hard in the direction of plate stretching, while the fine recrystallized grains have weak texture and good plastic deformation capacity, which are soft and can coordinate deformation. The combination of the two makes the plate have excellent room temperature mechanical properties.

[0024] 2. The present application uses traditional rolling equipment and processes, and based on a deep understanding and good research of the plastic deformation mechanism of ZK60 magnesium alloy, the preparation of a ZK60 magnesium alloy plate with a bimodal microstructure can be realized only by precise control of the rolling process and intermediate annealing process. The process is simple, the processing cost is low, and batch continuous production can be realized.

[0025] 3. The present application uses cast ZK60 magnesium alloy as the initial blank, without the need for extrusion and forging. It can be well connected with continuous casting or semi-continuous casting process to realize continuous batch production of large coil weight, wide width and high performance magnesium alloy plates, and meet the urgent weight reduction needs in various fields, especially in the transportation field. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1The metallographic structure of ZK60 magnesium alloy rolled plate with dual-mode structure.

[0027] Figure 2 It is the RD-TD reference plane (0002) pole figure of coarse deformed grains in ZK60 magnesium alloy rolled plate with bimodal structure.

[0028] Figure 3 It is the pole figure of the RD-TD reference plane (0002) of fine recrystallized grains in the rolled ZK60 magnesium alloy plate with dual-mode structure.

[0029] Figure 4 Room temperature tensile curve of ZK60 magnesium alloy rolled plate with dual-mode structure.

[0030] Table 1 is the chemical composition (wt.%) of ZK60 alloy ingot

[0031] DETAILED DESCRIPTION

[0032] Example 1

[0033] 1) Semi-continuously cast ZK60 alloy ingots were used as the initial billet. The chemical composition of the alloy is shown in Table 1. The ingots were solution treated at 320°C for 4 h, 380°C for 2 h, and 420°C for 6 h. After solution treatment, they were air-cooled and samples measuring 70 mm × 30 mm × 10 mm (length × width × thickness, the same below) were cut from the ingots. The surfaces were sanded and chamfered in preparation for rolling, with the 70 mm length oriented in the rolling direction.

[0034] 2) Heat the rolls to 200°C, raise the furnace temperature to 400°C, place the sample in the roll, hold for 30 minutes, and then begin rolling. Bloom rolling: Rolling temperature: 400°C, 10% reduction per pass, 10% total reduction, rolling speed: 8 m / min. Return the rolled sample to the furnace for annealing at 400°C for 20 minutes.

[0035] 3) Microstructure Control Rolling: After slab rolling and furnace annealing, the sample was removed and subjected to microstructure control rolling. The rolling temperature was 400°C, the pass reduction was 20%, and the rolled sample was furnace annealed at 400°C for 20 minutes. The annealed sample was removed and continued with the next pass rolling at 400°C, the pass reduction was 30%, and the rolled sample was furnace annealed at 350°C for 20 minutes. The annealed sample was removed and continued with the next pass rolling at 350°C, the pass reduction was 30%, and air cooling was performed after rolling. The total reduction for the three passes was 61%, and the rolling speed was 8 m / min.

[0036] 4) Conduct microstructure characterization and mechanical property testing on rolled plates.

[0037] Its metallographic structure is as follows Figure 1 As shown in the figure, its microstructure consists of coarse deformed grains and fine recrystallized grains; among them, the coarse deformed grains are elongated along the rolling direction, with the length direction as their grain size, the particle size distribution range is 23 to 141 μm, and the average grain size is 43 μm; the fine recrystallized grains are equiaxed grains, with the particle size distribution range of 2 to 19 μm, the average grain size is 6 μm, and the area occupied by recrystallized grains is 79%.

[0038] Figure 2 and Figure 3 They are the (0002) pole figures of coarse deformed grains and fine recrystallized grains, respectively. Among them, the coarse deformed grains have a strong texture, and the maximum intensity of the (0002) pole figure is 13.78 mrd; the fine recrystallized grains have a weak texture, and the maximum intensity of the (0002) pole figure is only 6.25 mrd.

[0039] Figure 4 This is a room temperature tensile curve. The tensile direction is parallel to the rolling direction (RD). The room temperature tensile strength of the plate is 292 MPa, the yield strength is 202 MPa, and the elongation is 24%.

[0040] Example 2

[0041] 1) Semi-continuously cast ZK60 alloy ingots were used as the initial billet. The chemical composition of the alloy is shown in Table 1. The ingots were solution treated at 320°C for 4 h, 380°C for 2 h, and 420°C for 6 h. After solution treatment, they were air-cooled. Samples measuring 100 mm × 50 mm × 20 mm were cut from the ingots, their surfaces polished and chamfered with sandpaper, and prepared for rolling. The 100 mm length was in the rolling direction.

[0042] 2) Heat the rolls to 200°C, raise the furnace temperature to 400°C, place the sample, hold for 30 minutes, and then begin rolling. Bloom rolling: Rolling temperature 400°C, 5% reduction per pass, return the rolled sample to the furnace for annealing at 400°C for 20 minutes. Remove the annealed sample and continue rolling in the next pass at 400°C, 10% reduction per pass, return the rolled sample to the furnace for annealing at 400°C for 20 minutes. The total reduction for both passes is 14.5%, and the rolling speed is 8 m / min.

[0043] 3) Microstructure control rolling: the sample after finish rolling and reheat annealing was taken out, and microstructure control rolling was carried out. The rolling temperature was 400°C, the pass reduction was 20%, the rolled sample was reheat annealed, the annealing temperature was 400°C, and the annealing time was 20 min; the annealed sample was taken out, and the next pass rolling was continued, the rolling temperature was 400°C, the pass reduction was 30%, the rolled sample was reheat annealed, the annealing temperature was 350°C, and the annealing time was 20 min; the annealed sample was taken out, and the next pass rolling was continued, the rolling temperature was 350°C, the pass reduction was 30%, and the sample was air cooled after rolling; the total reduction was 61%, and the rolling speed was 8 m / min.

[0044] 4) Microstructure characterization and mechanical property test were carried out on the rolled plate. The microstructure was composed of coarse deformed grains and fine recrystallized grains; the coarse deformed grains were elongated along the rolling direction, and the length direction was taken as the grain size, the grain size distribution range was 26-151 μm, and the average grain size was 55 μm; the fine recrystallized grains were equiaxed grains, the grain size distribution range was 3-19 μm, and the average grain size was 8 μm; the area fraction of the recrystallized grains was 65%. The coarse deformed grains were strong texture, and the maximum intensity of (0002) pole figure was 15.22 m.r.d.; the fine recrystallized grains were weak texture, and the maximum intensity of (0002) pole figure was only 7.33 m.r.d. The tensile strength at room temperature of the plate in RD direction was 281 MPa, the yield strength was 190 MPa, and the elongation was 20%.

[0045] Comparative Example 1

[0046] 1) A semi-continuous cast ZK60 alloy ingot was taken as the initial billet, and the chemical composition of the alloy was shown in Table 1. The ingot was subjected to solid solution treatment, and the solid solution treatment process was: 320°C for 4 h-380°C for 2 h-420°C for 6 h. After solid solution, a 70 mm x 30 mm x 10 mm sample was cut from the ingot, the surface was polished and chamfered with water sandpaper, and the sample was prepared for rolling, wherein the 70 mm length direction was the rolling direction.

[0047] 2) The roller temperature was heated to 50°C, the furnace temperature was raised to 350°C, the sample was put in, and after 30 min of heat preservation, rolling was started. The rough rolling was carried out at a rolling temperature of 350°C, a pass reduction of 30%, a total reduction of 30%, and a rolling speed of 8 m / min. The rolled sample cracked.

[0048] Analysis and summary: ZK60 magnesium alloy has poor plasticity processing capability, the casting microstructure has coarse grains, and there are casting defects such as porosity. If the rolling is directly started from the ingot, and the process is not properly controlled, it is very easy to crack.

[0049] Comparative Example 2

[0050] 1) The semi-continuous casting ZK60 alloy ingot is used as the initial blank, and the chemical composition of the alloy is shown in Table 1. The ingot is subjected to solid solution treatment, and the solid solution treatment process is: 320℃ for 4h-380℃ for 2h-420℃ for 6h. After solid solution, the sample of 100mm×50mm×20mm is taken out, the surface is polished and chamfered with water sandpaper, and is prepared for rolling, wherein the 100mm length direction is the rolling direction.

[0051] 2) The roller temperature is heated to 200℃, the furnace temperature is raised to 400℃, the sample is put in, and after 30min of heat preservation, rolling is started. The breakdown rolling is: the rolling temperature is 400℃, the pass reduction is 5%, the rolled sample is annealed in a furnace, the annealing temperature is 400℃, and the annealing time is 20min; the annealed sample is taken out, and the next pass rolling is continued, the rolling temperature is 400℃, the pass reduction is 10%, the rolled sample is annealed in a furnace, the annealing temperature is 400℃, and the annealing time is 20min. The total reduction of the two passes is 14.5%, and the rolling speed is 8m / min.

[0052] 3) The sample after the breakdown rolling and annealing in a furnace is taken out, and is subjected to structure regulation rolling. The rolling temperature is 400℃, the pass reduction is 30%, the rolled sample is annealed in a furnace, the annealing temperature is 400℃, and the annealing time is 20min; the annealed sample is taken out, and the next pass rolling is continued, the rolling temperature is 400℃, the pass reduction is 50%, the rolled sample is annealed in a furnace, the annealing temperature is 350℃, and the annealing time is 20min; the annealed sample is taken out, and the next pass rolling is continued, the rolling temperature is 350℃, the pass reduction is 60%, and the sample is air-cooled after rolling. The total reduction is 86%, and the rolling speed is 8m / min.

[0053] 4) The rolled plate is subjected to structure characterization and mechanical property testing. The microstructure is a complete recrystallized structure, and all is fine recrystallized equiaxed grains, the proportion of the recrystallized grains is 100%, and the average grain size is 15μm. The maximum intensity of the pole figure is 6.13m.r.d., and is a weak texture. The room temperature tensile strength of the plate in the RD direction is 265MPa, the yield strength is 160MPa, and the elongation is 25%. Analysis and summary: the process in the breakdown rolling stage is in the process range of the present application, the plate is not cracked and can be formed. In the subsequent structure regulation rolling stage, the process is not properly controlled, the complete recrystallized structure is formed, and the texture is weak. Therefore, the plate has good plasticity, but the strength is lower than that of the bimodal structure ZK60 magnesium alloy plate prepared by the process of the present application, and high strength and high plasticity cannot be realized at the same time.

Claims

1. Dual-mode ZK60 magnesium alloy sheet, characterized by: The microstructure includes or consists of fine recrystallized grains and coarse deformed grains.

2. The ZK60 magnesium alloy sheet according to claim 1, characterized in that: In the microstructure, the proportion of recrystallized grains is 40-80% (preferably 60-80%), the average grain size is less than or equal to 10 μm, it has a weak texture, and the RD-TD reference plane (0002) pole figure texture strength is less than or equal to 8 m.rd.

3. The ZK60 magnesium alloy sheet according to claim 1, characterized in that: In the microstructure, the major axis size of the deformed grains is greater than or equal to 30 μm, the microstructure has a strong texture, and the RD-TD reference plane (0002) pole figure texture intensity is greater than or equal to 10 m.rd.

4. The ZK60 magnesium alloy sheet according to claim 1, characterized in that: The chemical composition of the ZK60 magnesium alloy sheet meets the requirements of the national standard (GB / T 5153-2016) for ZK60 / ZK61 alloys, and rare earth elements less than or equal to 1 wt.% may be added; the plate has a room temperature tensile strength in the RD direction greater than or equal to 280 MPa, and an elongation greater than or equal to 20%.

5. The rolling process for ZK60 magnesium alloy sheet according to claim 1, 2, 3 or 4, characterized in that: The initial billet used in the rolling is a ZK60 magnesium alloy ingot, which is subjected to multiple hot rolling processes. The rolling process is divided into billet rolling and microstructure control rolling, and annealing is required between rolling passes.

6. The rolling process according to claim 5, characterized in that: The ZK60 magnesium alloy ingot used for rolling has a billet thickness of 10 to 500 mm (preferably 10 to 200 mm); the billet needs to be solution treated before rolling.

7. The rolling process according to claim 5, characterized in that: For bloom rolling, the rolling temperature is 350-400°C (preferably 380-400°C), the pass reduction is 2-10% (preferably 5-10%), the total reduction is 10-30% (preferably 10-20%), and the rolling speed is 1-50m / min (preferably 5-30m / min).

8. The rolling process according to claim 5, characterized in that: The rolling is carried out under structural control, with a rolling temperature of 300-400°C (preferably 350-400°C), a pass reduction of 10-50% (preferably 20-40%), a total reduction of 30-70% (preferably 50-70%), and a rolling speed of 1-50 m / min (preferably 5-30 m / min).

9. The rolling process according to claim 5, characterized in that: During the multi-pass rolling process, annealing treatment is performed every one or two passes. The annealing temperature is the same as the next rolling temperature, and the annealing time is 10 to 30 minutes (preferably 20 to 30 minutes).

10. The rolling process according to claim 5, characterized in that: The roller temperature is 50 to 300°C (preferably 150 to 300°C).

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