A reverse design method of rolling process parameters for controllable microstructure of magnesium alloy rolled plate

Abstract

This invention discloses a reverse design method for controllable microstructure of magnesium alloy rolled plates, belonging to the field of metal material plastic processing technology. It aims to solve the problem of directly converting the target microstructure into specific process parameter combinations before rolling magnesium alloy plates. The method establishes mathematical relationship models between microstructure characteristic parameters such as stress triaxiality and average grain size, and texture strength; rolling process parameters such as stress triaxiality and pass reduction rate, and fast / slow roll speed ratio; and yield strength, elongation after fracture, and average grain size and texture strength. Based on these models, the combination of rolling process parameters is derived in reverse according to the target thickness and target mechanical properties. Based on the matching principle of process parameters corresponding to different target microstructures, parameters are determined within the effective process window, and rolling is performed according to the optimized parameters to obtain the target microstructure. This invention can achieve directional control of the microstructure of magnesium alloy rolled plates, improving the scientific nature and efficiency of process parameter optimization design.

Description

Technical Field

[0001] This invention belongs to the field of metal material plastic processing technology, specifically relating to a reverse design method for rolling process parameters with controllable microstructure of magnesium alloy rolled plates. Background Technology

[0002] Magnesium alloys possess advantages such as low density and high specific strength, making them promising candidates for applications in aerospace, transportation, and other fields. However, during the rolling process of magnesium alloys, the final properties of the sheet metal primarily depend on the microstructure, including grain size and texture strength. These microstructures are influenced by process parameters such as roll temperature difference and rolling speed ratio. Due to the complex coupling relationship between the target sheet microstructure and rolling process parameters, it is difficult to directly convert the target microstructure into a specific combination of process parameters before rolling. This affects the stable preparation and engineering application of magnesium alloy sheets, becoming a significant factor limiting the stability of the magnesium alloy sheet rolling process and its engineering applications.

[0003] Currently, the design and microstructure control of magnesium alloy sheet rolling processes largely rely on trial and error, lacking a quantitative and reversible control model between process parameters and microstructure. This makes it difficult to accurately set rolling parameters based on the target microstructure, thus hindering the targeted design and stable preparation of sheet properties. Therefore, there is an urgent need for an optimization method that can scientifically and accurately correlate rolling process parameters with microstructure and enable reverse process design, thereby improving the scientific rigor, accuracy, and controllability of magnesium alloy sheet rolling process design. Summary of the Invention

[0004] To address the difficulty in directly converting the desired microstructure of magnesium alloy sheets into specific process parameter combinations before rolling, this invention provides a reverse design method for rolling process parameters that allows for controllable microstructure of magnesium alloy sheets.

[0005] This method provides a reverse design method for rolling process parameters with controllable microstructure of magnesium alloy rolled plates. The specific steps are as follows: Step 1: Establish a mathematical model between stress triaxiality and characteristic parameters characterizing microstructure, including average grain size and texture intensity as a crystal orientation quantification parameter; Step 2: Establish a mathematical model between stress triaxiality and rolling process parameters, including pass reduction rate, fast and slow roll speed ratio, fast and slow roll temperature difference, linear velocity of the sheet entering the roll deformation zone, and temperature of the low-temperature slow roll. Step 3: Establish a mathematical model between the mechanical properties of the sheet metal and the characteristic parameters characterizing the microstructure. The mechanical properties include yield strength and elongation after fracture, and the characteristic parameters include average grain size and texture strength. Step 4: Based on the target mechanical properties of the board, and using the mathematical model from Step 3, obtain the microstructure characteristics parameters that match the target mechanical properties of the board. Step 5: Determine the reduction rate based on the target plate thickness and the original plate thickness. Then, based on the target microstructure determined in Step 4 and the mathematical model established in Step 1 and Step 2, obtain the rolling process parameter range that matches the target microstructure. Step Six: Within the matching relationship range obtained in Step Five, and on the premise of satisfying the rollability of the sheet, determine the matching relationship between the fast and slow roll speed ratio, the fast and slow roll temperature difference, and the low-temperature slow roll temperature based on the grain size and texture intensity of the target microstructure. Step 7: Roll the sheet metal according to the obtained process parameters.

[0006] Compared with the prior art, the present invention has the following advantages: (1) This invention is the first to establish a dual quantitative correlation model of "process parameters → stress triaxiality → microstructure" to achieve a scientific description of the low-temperature (below recrystallization temperature) rolling process of magnesium alloys, overcoming the blindness of the traditional experience trial and error method; (2) This invention proposes a reverse design approach based on the reverse derivation of process parameters from the target microstructure, which can accurately and efficiently determine the rolling process window that meets specific performance requirements, and realize the directional and predictable control of the microstructure of magnesium alloy rolled plates. (3) The process parameter matching principle and effective process window given in this invention provide clear operation guidelines for the realization of different microstructure targets (such as fine grain weak texture, fine grain strong texture, etc.), which significantly improves the efficiency and success rate of process development. (4) This method has good process applicability. By adjusting the model parameters, it can be applied to the low-temperature (below recrystallization temperature) rolling process of magnesium alloy plates with different composition systems, providing a general process design tool for the customized preparation of high-performance magnesium alloy plates. (5) The present invention adopts low-temperature rolling conditions below recrystallization temperature, which is beneficial to suppress abnormal grain growth during rolling, retain and accumulate high deformation energy, and promote grain refinement and texture control. At the same time, low-temperature rolling can reduce energy consumption and oxidation risk caused by high-temperature heating, and help improve the uniformity of magnesium alloy sheet structure, dimensional stability and predictability of subsequent mechanical property control. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0008] Figure 1 This is a flowchart of the reverse design method for magnesium alloy rolling mill process parameters according to the present invention.

[0009] Figure 2 The image shows the metallographic structure of the sheet metal after rolling according to optimized process parameters.

[0010] Figure 3 The image shows a statistical chart of grain size of the sheet after rolling according to optimized process parameters. The average grain size is 8.1 μm.

[0011] Figure 4 The image shows the texture analysis of the sheet metal after rolling according to the optimized process parameters. The texture strength is 7.256.

[0012] Figure 5 The stress-strain curve of the plate after rolling according to the optimized process parameters is shown. The yield strength is 233.82 MPa and the elongation after fracture is 16.88%. Specific implementation methods

[0013] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are merely some embodiments of the invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the protection scope of this invention.

[0014] A reverse design method for rolling process parameters with controllable microstructure of magnesium alloy rolled plates, characterized by establishing the following steps sequentially: This embodiment uses commercially available hot-rolled AZ31 magnesium alloy slabs as the research object. The slab size is 100mm×50mm×3mm (RD×TD×ND), and the element content (wt.%) is shown in the table.

[0015] AZ31 Magnesium Alloy Element Content Table (wt.%) 2.85 0.88 0.36 0.01 0.005 0.1 0.003 Bal.

[0016] 1. Establish a quantitative relationship between stress triaxiality and the characterization of microstructure. ; Wherein, η is the stress triaxiality, and the value of η ranges from -0.58 to 0.58; d is the average grain size, characterized by the Feret diameter. The Feret diameter refers to the perpendicular distance between two parallel lines tangent to the outer contour of the grain in any direction in a metallographic or EBSD microscopic image. The average Feret diameter is obtained by measuring the Feret diameter of a single grain at multiple angles and taking the arithmetic mean, and then statistically averaging the average Feret diameters of no less than 50 effective grains in the detection area. The resulting value is the average grain size described in this invention, and the value of d ranges from 1 μm to 20 μm; T ex For texture strength, T ex The value range is 3 to 40.

[0017] 2. Establish the mathematical relationship between stress triaxiality and rolling process parameters. ; Where R is the reduction rate, ranging from 0 to 20%; A is the ratio of the fast and slow roller speeds, which is the ratio of the surface linear velocity of the fast roller to the surface linear velocity of the slow roller, ranging from 1 to 4; ΔT is the temperature difference between the fast and slow rollers, ranging from 50 to 150℃.

[0018] 3. Establish a mathematical model between the mechanical properties of the sheet metal and the characteristic parameters characterizing its microstructure. The mechanical properties include yield strength and elongation after fracture, and the characteristic parameters include average grain size and texture strength. ; Where is the yield strength, ranging from 100 to 300 MPa; d is the average grain size, ranging from 1 to 20 μm; T ex The texture strength ranges from 3 to 40. ; Where δ is the elongation after fracture, ranging from 10% to 30%; d is the average grain size, ranging from 1 to 20 μm; T ex The texture strength is 3 to 40.

[0019] 4. Based on the target mechanical properties of the sheet material, the target yield strength is 235 MPa and the target elongation after fracture is 16%. According to the mathematical model in step three, the microstructure characteristics matching the target mechanical properties of the sheet material are obtained, with an average grain size of 8 μm and a texture strength of 7.

[0020] 5. Determine the reduction rate based on the target thickness and the original thickness of the sheet. The original thickness of the sheet is 3.0 mm, and the target thickness is 2.4 mm, therefore the reduction rate is 20%. Based on the target microstructure determined in step four, and according to the mathematical model established in steps one and two, obtain the rolling process parameter range that matches the target microstructure.

[0021] 6. Within the matching range obtained in step five, and on the premise of satisfying the rollability of the sheet, determine the matching relationship between the fast and slow roll speed ratio, the fast and slow roll temperature difference, and the low-temperature slow roll temperature based on the grain size and texture strength of the target microstructure. The final process parameters are: reduction rate of 20%, fast and slow roll speed ratio of 1.5, fast and slow roll temperature difference of 145℃, linear velocity of the sheet entering the roll deformation zone of 10mm / s, and high-temperature fast roll temperature of 190℃.

[0022] 7. Rolling was performed according to the obtained process parameters. The final microscopic characteristics of the rolled plate were as follows: average grain size of 8.1 μm and texture strength of 7.256. The final mechanical properties of the rolled plate were: yield strength of 233.82 MPa and elongation after fracture of 16.88%, which were basically consistent with the target input.

[0023] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for reverse design of rolling process parameters for controllable microstructure of magnesium alloy rolled plates, characterized in that, For magnesium alloy sheets with a thickness ≤6mm, when rolled using a differential temperature shearing process at low temperatures (below the recrystallization temperature), a method is proposed to set process parameters based on the target microstructure, which addresses the difficulty in matching the target microstructure with the set process parameters. The method includes the following steps: Step 1: Establish a mathematical model between stress triaxiality and characteristic parameters characterizing microstructure, including average grain size and texture intensity as a crystal orientation quantification parameter; Step 2: Establish a mathematical model between stress triaxiality and rolling process parameters, including pass reduction rate, fast and slow roll speed ratio, fast and slow roll temperature difference, linear velocity of the sheet entering the roll deformation zone, and temperature of the low-temperature slow roll. Step 3: Establish a mathematical model between the mechanical properties of the sheet metal and the characteristic parameters characterizing the microstructure. The mechanical properties include yield strength and elongation after fracture, and the characteristic parameters include average grain size and texture strength. Step 4: Based on the target mechanical properties of the board, and using the mathematical model from Step 3, obtain the microstructure characteristic parameters that match the target mechanical properties of the board. Step 5: Determine the reduction rate based on the target thickness and the original thickness of the sheet. Then, based on the target microstructure determined in Step 4 and the mathematical model established in Step 1 and Step 2, obtain the rolling process parameter range that matches the target microstructure. Step Six: Within the range of rolling process parameters obtained in Step Five, and on the premise of satisfying the rollability of the sheet, determine the matching relationship between the fast and slow roll speed ratio, the fast and slow roll temperature difference, and the low-temperature slow roll temperature based on the grain size and texture strength of the target microstructure. Step 7: Roll the sheet metal according to the obtained process parameters.

2. The reverse design method for controllable rolling process parameters of magnesium alloy rolled plates as described in claim 1, characterized in that, During the rolling process, the upper work roll is a low-temperature slow roll, and the lower work roll is a high-temperature fast roll.

3. The reverse design method for controllable rolling process parameters of magnesium alloy rolled plates as described in claim 1, characterized in that, The mathematical model between the stress triaxiality η mentioned in step one and the characteristic parameters characterizing the microstructure is as follows: ； Wherein, η is the stress triaxiality, and the value of η ranges from -0.58 to 0.58; d is the average grain size, characterized by the Feret diameter. The Feret diameter refers to the perpendicular distance between two parallel lines tangent to the outer contour of the grain in any direction in a metallographic or EBSD microscopic image. The average Feret diameter is obtained by measuring the Feret diameter of a single grain at multiple angles and taking the arithmetic mean, and then statistically averaging the average Feret diameters of no less than 50 effective grains in the detection area. The resulting value is the average grain size described in this invention, and the value of d ranges from 1 μm to 20 μm; T ex For texture strength, T ex The value range of a is 3~40; a0, a1, a2, a3, a4, a5 are functions of plate temperature, the value range of plate temperature is 25℃~200℃, the value range of a0 is -25~7, the value range of a1 is -6~4, the value range of a2 is -2~5, the value range of a3 is -1~1, the value range of a4 is -1~1, and the value range of a5 is 0~1.

4. The reverse design method for controllable rolling process parameters of magnesium alloy rolled plates as described in claim 1, characterized in that, The mathematical model between the stress triaxiality η and the rolling process parameters mentioned in step two is as follows: ； Where R is the reduction rate, ranging from 0 to 20%; A is the speed ratio of the fast and slow rolls, which is the ratio of the surface linear velocity of the fast roll to the surface linear velocity of the slow roll, ranging from 1 to 4; ΔT is the temperature difference between the fast and slow rolls, ranging from 50 to 150℃; and k... R k A k RA The coupling coefficients have values ​​ranging from 0.3 to 0.8, 0.02 to 0.05, and 0.1 to 0.4, respectively.

5. The reverse design method for controllable rolling process parameters of magnesium alloy rolled plates as described in claim 1, characterized in that, The mathematical model between the yield strength and the characteristic parameters characterizing the microstructure in step three is as follows: ； in, For yield strength, The value ranges from 100 to 300 MPa; is the basic strength term, used to characterize the matrix strength contribution of the material without considering grain size strengthening and texture correction terms. It can include matrix lattice resistance, solid solution strengthening, precipitation or second-phase strengthening, dislocation strengthening, and other strength contributions caused by material composition and preparation process, with a value range of 0 to 250 MPa; d is the average grain size, with a value range of 1 to 20 μm; T ex The texture intensity, with a value ranging from 3 to 40; k d k is the grain size strengthening factor, with a value ranging from −200 to 200. I This is the texture intensity correction factor, with a value range of −50 to 50.

6. The reverse design method for controllable rolling process parameters of magnesium alloy rolled plates as described in claim 1, characterized in that, The mathematical model between the elongation after fracture and the characteristic parameters characterizing the microstructure state mentioned in step three is as follows: ； Wherein, δ is the elongation after fracture, ranging from 10% to 30%; δ0 is the basic plasticity term, used to characterize the matrix plasticity contribution of the material without considering the influence of grain size, texture strength, and their coupling effect. It can include the comprehensive influence of material composition, initial microstructure, second phase distribution, dislocation state, and preparation process on plasticity, ranging from 0% to 40%; d is the average grain size, ranging from 1 to 20 μm; T ex k1 is the texture intensity, with a value ranging from 3 to 40; k2 is the grain size influence coefficient, with a value ranging from -5% to 5%; k3 is the texture intensity influence coefficient, with a value ranging from -5% to 5%; k4 is the coupling coefficient, with a value ranging from -1% to 1%.

7. The reverse design method for controllable rolling process parameters of magnesium alloy rolled plates as described in claim 1, characterized in that, The effective process window for the rolling process parameters mentioned in step six is ​​as follows: the temperature difference between the fast and slow rolls is 50~150℃, the speed ratio between the fast and slow rolls is 1~4, the linear velocity of the sheet entering the deformation zone of the rolls is 10~50mm / s, and the temperature of the high-temperature fast roll is 150~200℃.

8. The reverse design method for controllable rolling process parameters of magnesium alloy rolled plates as described in claim 1, characterized in that, The matching relationship described in step six is ​​as follows: when the target microstructure has fine grains and low texture strength, a higher high-speed-slow-roller ratio, a higher high-speed-slow-roller temperature difference, and a lower low-temperature-slow-roller temperature are used; when the target microstructure has fine grains and high texture strength, a lower high-speed-slow-roller ratio, a lower high-speed-slow-roller temperature difference, and a lower low-temperature-slow-roller temperature are used; when the target microstructure has large grains and low texture strength, a higher high-speed-slow-roller ratio, a lower high-speed-slow-roller temperature difference, and a higher low-temperature-slow-roller temperature are used. Here, "higher" and "lower" refer to the effective process window for each process parameter.

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