A variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys

Abstract

This invention provides a variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys. The process involves determining the recrystallization temperature to lock in the preheating temperature; heating the difficult-to-deform aluminum or magnesium alloy billet to the preheating temperature; maintaining a die temperature 50-200°C higher than the billet temperature; implementing an initial temperature transfer deformation process on a forging press, with the die at a high temperature and the billet at a low temperature; ensuring the die temperature is 50-200°C higher than the billet temperature; performing plastic deformation at the same temperature for both the die and the billet when the forging deformation reaches 1 / 3-2 / 3 of the stage; maintaining pressure with the die temperature 50-100°C lower than the billet temperature; water quenching the formed forging, followed by aging heat treatment. This variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys reduces the tendency for deformation damage during deformation, ensures low-temperature deformation of the workpiece without damage or cracking, improves the deformation uniformity of the workpiece, and optimizes its microstructure and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of metal material plastic processing technology, specifically relating to a variable temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys. Background Technology

[0002] Aluminum and magnesium alloys possess advantages such as low density, high specific strength and stiffness, high thermal conductivity, and good damping, making them promising for applications in aerospace, defense, rail transportation, and electrical and electronic fields. Plastic deformation is a crucial method for improving the microstructure and mechanical properties of aluminum or magnesium alloys. In plastic processing, both the mold and the workpiece are typically heated, with the workpiece temperature often exceeding the mold temperature. However, when the hot workpiece comes into contact with the cold mold, the workpiece surface cools rapidly, with the external temperature dropping faster than the internal temperature. This increases the temperature difference between the surface and the core, easily causing surface damage and cracking, and resulting in severe inhomogeneity in the workpiece's microstructure and properties. This situation is particularly pronounced when dealing with highly alloyed, difficult-to-deform aluminum or magnesium alloys. To improve the forming quality of difficult-to-deform aluminum or magnesium alloys, previous processes mostly adopted a workpiece temperature compensation scheme by increasing the preheating temperature. However, three problems still exist: 1) The cooling problem of the workpiece surface has not been solved, and the temperature difference between the internal and external deformation still exists. The resulting uneven workpiece deformation can still cause workpiece damage and cracking; 2) The high preheating temperature, combined with the temperature rise of the core, results in near-high temperature deformation of the workpiece core. The improvement of the workpiece's microstructure and properties is limited, and even excessively high temperatures can lead to intergranular cracking and high-temperature brittleness; 3) Uneven workpiece deformation will also reduce the consistency of microstructure and properties, making it difficult to guarantee the overall high performance of the workpiece.

[0003] Therefore, isothermal forging is commonly used to solve the above problems. Isothermal forging refers to a process in which the workpiece is heated to a certain temperature while the die temperature is controlled within approximately the same range as the workpiece's heating temperature, allowing the workpiece to slowly undergo plastic deformation under conditions where its temperature remains essentially constant. During isothermal forging, the die heating temperature is generally 95-105% of the workpiece's heating temperature, and the pressure holding time is typically from a few minutes to tens of minutes, sometimes even up to 1 hour. However, the workpiece cannot be further heated during the forging process, and the surface temperature of the billet still decreases, inevitably leading to workpiece deformation and damage. This is particularly evident in difficult-to-deform aluminum or magnesium alloys with structural defects or poor plastic processing capabilities. Summary of the Invention

[0004] The purpose of this invention is to provide a variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys. This process solves the problem of how to reduce the tendency of deformation damage during the deformation of aluminum or magnesium alloys, ensuring that the workpiece can be deformed at low temperatures without damage or cracking. It can better utilize the microstructure evolution mechanism to improve the microstructure of the workpiece, enhance its mechanical properties, and improve the deformation uniformity of the workpiece, thereby optimizing the uniformity of microstructure and mechanical properties.

[0005] A variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys, specifically including the following steps: Step S1: Determine the recrystallization temperature based on the composition of the difficult-to-deform aluminum or magnesium alloy, and thus lock the preheating temperature of the difficult-to-deform aluminum or magnesium alloy. The recrystallization temperature is -50℃ ≤ preheating temperature ≤ recrystallization temperature +50℃. Step S2: Based on the preheating temperature obtained in step S1, heat the difficult-to-deform aluminum alloy or magnesium alloy billet to the preheating temperature and hold it at that temperature. At the same time, the forging die is also preheated so that the die temperature is 50-200℃ higher than the billet temperature; Step S3: Implement the initial temperature transfer deformation process of high temperature mold and low temperature billet on the forging press, and monitor the temperature of mold and billet in real time; When the mold temperature is less than or equal to the billet temperature, reheat both the mold and the billet, ensuring that the mold temperature is 50-200℃ higher than the billet temperature. Step S4: When the forging deformation reaches the 1 / 3-2 / 3 stage, plastic deformation of the mold and the billet at the same temperature begins, realizing isothermal forging on the forging press. The billet is deformed, and pressure is maintained when the forging press reaches full load. In the initial heat transfer deformation stage, the initial structural defects of the billet have been improved, and the plasticity of the billet has been enhanced. At this time, isothermal deformation can be used to optimize the structure of the billet and improve the overall structure and properties of the billet. Step S5: During the holding pressure, the final stage of temperature transfer deformation between the high temperature of the billet and the low temperature of the mold begins. The outside of the mold is cooled down (preferably by air cooling) so that the temperature of the mold is 50-100°C lower than the temperature of the billet. After the holding pressure is completed, the forging is removed from the furnace. Step S6: The obtained forging is quenched in water, followed by aging heat treatment. The aging temperature is 100-200℃ and the aging time is 3-48h.

[0006] In step S2, the heating rate of the die in the forging press is 40-50℃ / h, and the heating coefficient of the billet is 1.0-2.0mm / min. In steps S3 and S4, the deformation rate of the billet is no greater than 0.3mm / s. In step S5, the forging press holds pressure for 5-20 minutes when it reaches full load.

[0007] The aluminum alloy is Al-Cu based, wherein Cu ≥ 4.5%.

[0008] The aluminum alloy is an Al-Zn-Mg-Cu system, wherein Zn+Mg+Cu≥10% and Zn+Mg≥8%.

[0009] The magnesium alloy is a Mg-Al-Zn series magnesium alloy, wherein Al ≥ 9%.

[0010] The magnesium alloy is a Mg-Zn-Zr series magnesium alloy, wherein Zn≥5% and Zr≥0.4%.

[0011] The magnesium alloy is a Mg-RE magnesium alloy, wherein RE involves one or more combinations of rare earth elements such as Gd, Y, and Nd, and RE ≥ 10%.

[0012] The positive effects of this invention are as follows: (1) When the mold temperature is higher than the workpiece temperature, the chilling effect on the hot workpiece surface is significantly reduced, which improves the material fluidity and maintains the excellent thermoplasticity of the material. In addition, It also reduces deformation resistance. Since the workpiece as a whole is kept at the optimal plasticity temperature, the required forging pressure will be significantly reduced, which is very beneficial to equipment and molds. More complex parts can be forged and the mold life can be extended. (2) The initial billet has severe internal structural defects. In the initial stage of deformation, these structural defects are easily damaged and cracked when subjected to low-temperature large deformation. In particular, the edge of the billet cools down quickly and the stress state is not triaxial compressive stress, making it more prone to premature cracking during deformation. If a deformation method with high temperature of mold and low temperature of billet is adopted, the cooling of the edge of the billet can be delayed. Specifically, it has two aspects of value: On the one hand, after the edge of the billet comes into contact with the high-temperature mold, the surface and core of the billet undergo almost isothermal deformation. The temperature gradient from the surface to the core is very small, which can reduce the temperature difference between the internal and external deformation of the billet, achieve uniform deformation of the billet, and benefit the uniformity of the billet structure and mechanical properties. On the other hand, when preheating the billet, the preheating temperature does not need to be too high, which reduces energy consumption. At the same time, the surface and core of the billet undergo near-isothermal deformation, which reduces the concentration of internal shear stress and ensures that the billet does not crack during the forming process. This allows for the ultimate deformation of the billet at low temperatures, which is more conducive to improving the billet's structure and mechanical properties. (3) During the isothermal forging process, the workpiece and the mold reach a dynamic thermal equilibrium state; stable isothermal deformation keeps the material at a constant and optimal plastic temperature, which brings excellent metal fluidity and can prevent damage and cracking during complex processes, such as filling extremely complex cavities to produce thin-walled, high-ribbed, and clearly contoured precision forgings. It also has the following technical effects: Extremely low deformation resistance and flow stress, and the lowest yield strength of the material at constant high temperature, make it possible to forge large parts with relatively small tonnage presses. The uniformity of structure and properties, and the constant temperature avoid the differences in recrystallization degree and grain size caused by temperature unevenness, which helps to form a uniform and fine equiaxed grain structure throughout the forging. Eliminating the influence of shrinkage in hot forging dies: In traditional forging dies, the billet (workpiece) shrinks as it cools from a high temperature to the die temperature, and shrinkage needs to be reserved when designing the die. Under isothermal conditions, the workpiece and the die are at the same temperature, and the shrinkage of the forging after it is removed from the die and cooled to room temperature is the only factor that needs to be considered. This simplifies the die design and improves dimensional accuracy. (4) When the mold temperature is lower than the workpiece temperature, this stage usually occurs after the workpiece forming is completed. If the mold temperature drops rapidly and is significantly lower than the high-temperature workpiece temperature, it has the following technical effects: To achieve controllable cooling and grain refinement, when a high-temperature forging comes into contact with a low-temperature mold, a relatively controllable cooling process will begin. By designing the temperature difference between the mold and the workpiece, the material cooling process can be controlled, which can suppress the abnormal growth of workpiece grains and promote the formation of finer microstructures. To facilitate demolding, the surface of the workpiece, which is in contact with the cooler mold, will shrink slightly before the core. This helps to reduce the friction between the forging and the mold cavity, making the ejection process smoother and reducing ejection deformation and surface scratches. Fixing the workpiece shape and rapid surface cooling allows the workpiece surface to quickly gain strength, which helps maintain its precise shape after ejection and prevents deformation due to its own weight or residual stress. (5) Combining these three stages, this process route (initial temperature transfer, isothermal temperature transfer, and final temperature transfer) brings the following core advantages to the deformation of aluminum or magnesium alloys: significantly reducing the tendency for damage and cracking, achieving near-net-shape forming, and improving yield; obtaining uniform and fine grain structure, optimizing the mechanical properties and uniformity of the workpiece; complete filling, clear outline, smooth surface, and small deformation; enabling the manufacture of complex shapes and thin-walled structures that cannot be achieved by traditional forging; lower deformation resistance and avoidance of thermal shock, significantly reducing mold wear and fatigue; ultimately achieving the technical effects of crack prevention, low-temperature deformation, and reduced surface-to-core temperature difference. (6) It should be noted that, unlike the prior art, this solution does not consider lubricant. By controlling the temperature changes of the mold and the workpiece, the technical problems of poor workpiece formability and large deformation resistance can be solved. Finally, the coupling of variable temperature forging process and material composition was carried out to realize low temperature large plastic deformation of difficult-to-deform aluminum alloy or magnesium alloy, which greatly improves the mechanical properties of difficult-to-deform materials, greatly promotes the application of difficult-to-deform lightweight alloys in the load-bearing field, and thus achieves the feasibility analysis of maximizing technical effect, which has important guiding significance for production practice. Attached Figure Description

[0013] Figure 1 This is a microstructure and grain diagram of test group 1 in Example 1 of this scheme.

[0014] Figure 2 This is a microstructure and grain diagram of comparative group 2 in Example 1 of this scheme.

[0015] Figure 3 This is a microstructure and grain diagram of test group A in Example 2 of this scheme.

[0016] Figure 4 This is a microstructure and grain diagram of comparative group 1B in Example 2 of this scheme. Detailed Implementation

[0017] To more clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution. Example

[0018] A variable-temperature forging process for difficult-to-deform lightweight aluminum alloys specifically includes the following steps: Step S1: Determine the recrystallization temperature based on the composition of the difficult-to-deform aluminum or magnesium alloy, and thus lock the preheating temperature of the difficult-to-deform aluminum or magnesium alloy. The recrystallization temperature is -50℃ ≤ preheating temperature ≤ recrystallization temperature +50℃. Step S2: Based on the preheating temperature obtained in step S1, heat the difficult-to-deform aluminum alloy billet to the preheating temperature and hold it at that temperature; At the same time, the forging die is also preheated so that the die temperature is 50-200℃ higher than the billet temperature; Step S3: Implement the initial temperature transfer (reverse temperature transfer) deformation process on the forging press with high temperature of the die and low temperature of the billet, and monitor the temperature of the die and the billet in real time; When the mold temperature is less than or equal to the billet temperature, reheat both the mold and the billet, ensuring that the mold temperature is 50-200℃ higher than the billet temperature. Step S4: When the forging deformation reaches the 1 / 3-2 / 3 stage, plastic deformation of the mold and the billet at the same temperature begins, realizing isothermal forging on the forging press. The billet is deformed, and pressure is maintained when the forging press reaches full load. In the initial heat transfer (reverse heat transfer) deformation stage, the initial structural defects of the billet have been improved, and the plasticity of the billet has been enhanced. At this time, isothermal deformation can be used to optimize the structure of the billet and improve the overall structure and properties of the billet. Step S5: During the holding pressure, the final stage of heat transfer (forward heat transfer) deformation of the billet at high temperature and the die at low temperature begins. The outside of the die is cooled by air cooling so that the temperature of the die is 50-100℃ lower than the temperature of the billet. After the holding pressure is completed, the die is taken out of the furnace and cooled to obtain the formed forging. Step S6: The obtained forging is quenched in water, followed by aging heat treatment. The aging temperature is 100-200℃ and the aging time is 3-48h.

[0019] In step S2, the heating rate of the die in the forging press is 40-50℃ / h, and the heating coefficient of the billet is 1.0-2.0mm / min. In steps S3 and S4, the deformation rate of the billet is no greater than 0.3mm / s. In step S5, the forging press holds pressure for 5-20 minutes when it reaches full load.

[0020] The aluminum alloy is Al-Cu based, wherein Cu ≥ 4.5%.

[0021] The aluminum alloy is an Al-Zn-Mg-Cu system, wherein Zn+Mg+Cu≥10% and Zn+Mg≥8%.

[0022] The magnesium alloy is a Mg-Al-Zn series magnesium alloy, wherein Al ≥ 9%.

[0023] The magnesium alloy is a Mg-Zn-Zr series magnesium alloy, wherein Zn≥5% and Zr≥0.4%.

[0024] The magnesium alloy is a Mg-RE magnesium alloy, wherein RE involves one or more combinations of rare earth elements such as Gd, Y, and Nd, and RE ≥ 10%.

[0025] In Example 1, an Al-Cu aluminum alloy was used as an example for the following experimental analysis. The Cu content was 5.8%, which is close to the composition of Chinese alloy grade 2219 high-strength duralumin, and its dynamic recrystallization occurred at approximately 450℃. The study investigated the changes in the comprehensive mechanical properties of the mold and billet under different heating temperatures. Except for the temperatures of the mold and billet (workpiece) during the forming process, the values ​​of all other parameters were taken as minimum values, and the following multiple sets of experiments were designed: Test Group 1: The preheating temperature of the test sample (billet) was 350℃, and the preheating temperature of the forging die was 400℃; Test Group 2: The preheating temperature of the test sample (billet) was 400℃, and the preheating temperature of the forging die was 450℃; Test Group 3: The preheating temperature of the test sample (billet) was 450℃, and the preheating temperature of the forging die was 500℃; Comparison Group 1: The mold temperature is lower than the workpiece temperature. The preheating temperature of the test sample (blank) is 450℃, and the mold temperature is 250℃. Comparison Group 2: The mold temperature is lower than the workpiece temperature. The preheating temperature of the test sample (blank) is 450℃, and the mold temperature is 350℃. Comparison Group 3: The mold temperature is equal to the workpiece temperature. The preheating temperature of the test sample (blank) is 450℃, and the mold temperature is 450℃. Table 1 shows the performance test results of the workpiece samples obtained under each test group.

[0026] Table 1 shows the performance test results of the workpiece samples obtained under each test group.

[0027] As can be seen from Table 1, compared with control groups 1, 2, and 3, the tensile strength, yield strength, and average grain size parameters of test groups 1, 2, and 3 designed in this embodiment 1 are all superior to those of control groups 1-3. This indicates that the variable-temperature forging process in this embodiment 1 is effective in improving the comprehensive mechanical properties of forged products and is feasible in actual production. With the increase of the preheating temperature of the test sample (billet) and the preheating temperature of the forging die, the tensile strength and yield strength first increase and then decrease, while the average grain size first decreases and then increases (see Table 1). Figure 1 and Figure 2 , Figure 1 The fibrous structure shows that the dynamic recrystallization of the aluminum alloy is not obvious (this is due to the slightly lower heating temperature). Therefore, the preheating temperature of the test sample (billet) and the preheating temperature of the forging die need to be set to appropriate values ​​to achieve the best technical effect, which is also in line with reality. Finally, it can be seen from the comparison group 1 that in the prior art, when the die temperature is lower than the workpiece temperature and the temperature difference between the two is large, the workpiece is prone to cracking. However, no cracking problem exists in test groups 1-3 of this embodiment 1.

[0028] Example 2 Based on Example 1, Example 2 is presented here.

[0029] In Example 2, a Mg-RE magnesium alloy with Gd ≥ 9%, Y ≥ 4%, and a dynamic recrystallization temperature of approximately 440℃ was used. The study investigated the changes in the comprehensive mechanical properties of the mold and billet under different heating temperatures. Except for the temperatures of the mold and billet (workpiece) during the forming process, all other parameters were taken as minimum values, and the following multiple sets of experiments were designed: Test Group A: The preheating temperature of the test sample (billet) is 300℃, and the preheating temperature of the forging die is 400℃; Test Group B: The preheating temperature of the test sample (billet) is 350℃, and the preheating temperature of the forging die is 450℃; Test Group C: The preheating temperature of the test sample (billet) is 400℃, and the preheating temperature of the forging die is 500℃; Comparison Group 1A: The mold temperature is lower than the workpiece temperature. The preheating temperature of the test sample (blank) is 400℃, and the mold temperature is 200℃. Comparison Group 1B: The mold temperature is lower than the workpiece temperature. The preheating temperature of the test sample (blank) is 400℃, and the mold temperature is 300℃. Comparative Group 1C: The mold temperature is equal to the workpiece temperature. The preheating temperature of the test sample (blank) is 400℃, and the mold temperature is 400℃. Table 2 shows the performance test results of the workpiece samples obtained under each test group.

[0030] Table 2 Performance test results of workpiece samples obtained under each test group

[0031]

[0032] Table 2 shows the performance test results of the workpiece samples obtained under each test group. Combination Figures 3-4 As can be seen from Table 2, the variation patterns of test data in experimental group AC, control group 1A, control group 1B, and control group 1C in Example 2 are basically similar to the parameter test patterns in Table 1 of Example 1, indicating that the variable temperature forging process in Example 2 is effective. With the increase of the preheating temperature of the test sample (billet) and the forging die, the tensile strength and yield strength first increase and then decrease, while the average grain size first decreases and then increases. Therefore, the preheating temperatures of the test sample (billet) and the forging die need to be appropriately set to achieve the best technical effect. Finally, as can be seen from control group 1A, in the prior art, when the die temperature is lower than the workpiece temperature and the temperature difference between the two is large, workpiece cracking is likely to occur. However, no cracking problem exists in experimental group AC in Example 2.

[0033] Furthermore, Tables 1 and 2 show the increase rate of test data from the control group to the test group, indicating that the changes in tensile strength and yield strength of magnesium alloys in each test group are greater. For example, in Table 1, the increase rate of tensile strength in test group 1 compared to control group 2 is 1.30%, and the increase rate of yield strength is 3.13%; in Table 2, the increase rate of tensile strength in test group A compared to control group 1B is 3.97%, and the increase rate of yield strength is 10.5%. It can be seen that applying this variable temperature forging process to the forging of magnesium alloys has a more significant improvement effect on the overall mechanical properties compared to the aluminum alloy in Example 1. This indicates that the material composition of the workpiece affects the technical effect of variable temperature forging. Therefore, through a large number of experiments, the material composition most suitable for the variable temperature forging process in this scheme can be selected, and then the technical effectiveness can be maximized through the coupling of variable temperature forging process and material.

[0034] It should be noted that the other test parameters not detailed in Examples 1-2 can be implemented according to the conventional operation of those skilled in the art and are consistently applied in the test group and control group, and will not be detailed here.

[0035] The technical features of this invention not described can be implemented by or using existing technology, and will not be repeated here. Of course, the above description is not a limitation of this invention, and this invention is not limited to the examples above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention should also be within the protection scope of this invention.

Claims

1. A variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys, characterized in that, Specifically, the steps include the following: Step S1: Determine the recrystallization temperature based on the composition of the difficult-to-deform aluminum or magnesium alloy, and thus lock the preheating temperature of the difficult-to-deform aluminum or magnesium alloy. The recrystallization temperature is -50℃ ≤ preheating temperature ≤ recrystallization temperature +50℃. Step S2: Based on the preheating temperature obtained in step S1, heat the difficult-to-deform aluminum alloy or magnesium alloy billet to the preheating temperature and hold it at that temperature. At the same time, the forging die is also preheated so that the die temperature is 50-200℃ higher than the billet temperature; Step S3: Implement the initial temperature transfer deformation process of high temperature mold and low temperature billet on the forging press, and monitor the temperature of mold and billet in real time; When the mold temperature is less than or equal to the billet temperature, reheat both the mold and the billet, ensuring that the mold temperature is 50-200℃ higher than the billet temperature. Step S4: When the forging deformation reaches the 1 / 3-2 / 3 stage, plastic deformation of the mold and the billet at the same temperature begins, realizing isothermal forging on the forging press. The billet is deformed, and pressure is maintained when the forging press reaches full load. Step S5: During the holding pressure, the final stage of temperature transfer deformation between the high temperature of the billet and the low temperature of the mold begins. The outside of the mold is cooled down so that the temperature of the mold is 50-100℃ lower than the temperature of the billet. After the holding pressure is completed, the billet is removed from the furnace to obtain the formed forging. Step S6: The obtained forging is quenched in water, followed by aging heat treatment. The aging temperature is 100-200℃ and the aging time is 3-48h.

2. The variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys according to claim 1, characterized in that, In step S5, the forging press holds pressure for 5-20 minutes when it reaches full load.

3. The variable-temperature forging process for difficult-to-deform aluminum / magnesium alloys according to claim 1, characterized in that, The aluminum alloy is Al-Cu based, wherein Cu ≥ 4.5%.

4. The variable-temperature forging process for difficult-to-deform aluminum / magnesium alloys according to claim 1, characterized in that, The aluminum alloy is an Al-Zn-Mg-Cu system, wherein Zn+Mg+Cu≥10% and Zn+Mg≥8%.

5. The variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys according to claim 1, characterized in that, The magnesium alloy is a Mg-Al-Zn series magnesium alloy, wherein Al ≥ 9%.

6. The variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys according to claim 1, characterized in that, The magnesium alloy is a Mg-Zn-Zr series magnesium alloy, wherein Zn≥5% and Zr≥0.4%.

7. The variable-temperature forging process for difficult-to-deform lightweight aluminum / magnesium alloys according to claim 1, characterized in that, The magnesium alloy is a Mg-RE magnesium alloy, wherein RE involves one or more combinations of rare earth elements such as Gd, Y, and Nd, and RE ≥ 10%.

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