A method for preparing magnesium alloy by low temperature rotary forging

Abstract

The application relates to the technical field of magnesium alloy, in particular to a method for preparing magnesium alloy by low-temperature rotary swaging. The method for preparing magnesium alloy by low-temperature rotary swaging comprises the following steps: performing low-temperature multi-pass rotary swaging on a magnesium alloy rod after hot extrusion to obtain the magnesium alloy; the deformation temperature of the low-temperature multi-pass rotary swaging is-30 DEG C to-10 DEG C; the pass deformation amount is 2 to 6%; the deformation pass is 7 to 18 passes, and the total deformation amount is 30 to 80%; the temperature of the hot extrusion is 300 to 480 DEG C, and the extrusion ratio is 18 to 22; and the material of the magnesium alloy is VW93M magnesium alloy. The prepared magnesium alloy has more uniform impurity element distribution, and the strength and corrosion resistance of the magnesium alloy are synergistically improved. The yield strength of the prepared magnesium alloy can be up to 657 MPa at most, the tensile strength can be up to 719 MPa at most, and the self-corrosion current density can be up to 1.94*10 ‑5 A / cm 2 at most.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of magnesium alloys, and in particular to a method for preparing a magnesium alloy by low-temperature rotary swaging. BACKGROUND

[0002] The magnesium alloy has excellent damping performance, shock absorption and noise reduction, and electromagnetic interference resistance, and has great application prospects in the fields of automobile industry, communication and electronics industry, and aerospace, but the strength of the magnesium alloy is relatively low, which greatly limits the application of the magnesium alloy in the industry.

[0003] In the prior art, the strength of the magnesium alloy is often improved by changing alloy components or preparation processes, for example, the application No. 202410054888.0 discloses a room-temperature super-high-plasticity high-strength high-damping high-thermal-conductivity corrosion-resistant magnesium alloy and a preparation method thereof, the prepared magnesium alloy has a yield strength of 200-250 MPa, a tensile strength of 220-260 MPa, a room-temperature elongation of 50-60%, and a corrosion rate of 0.3-0.5 mm / y at room temperature; the application No. 202210099151.1 discloses a high-strength corrosion-resistant magnesium alloy based on coherent precipitate phase regulation and a preparation method thereof, the prepared magnesium alloy has a tensile strength of 280-330 MPa and a corrosion rate of 1-6 mm / year; and the application No. 202210185992.4 discloses a Mg-Zn-Zr-Gd alloy super-high-pressure heat treatment method, the prepared magnesium alloy has a corrosion current density of 7.6x10-6-6.7x10-5 A / cm 2 However, the yield strength is relatively low, only 220-240 MPa, and the elongation is 12-16%. However, the strength and corrosion resistance of the alloys in the prior art are not high. SUMMARY

[0004] The application aims to provide a method for preparing a magnesium alloy by low-temperature rotary swaging.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0006] A method for preparing a magnesium alloy by low-temperature rotary swaging, comprising the following steps: low-temperature multi-pass rotary swaging a magnesium alloy rod after hot extrusion to obtain the magnesium alloy; the deformation temperature of the low-temperature multi-pass rotary swaging is-30 DEG C to-10 DEG C; the pass deformation amount is 2-6%; the deformation pass is 7-18 passes, and the total deformation amount is 30-80%; the temperature of the hot extrusion is 300-480 DEG C, and the extrusion ratio is 18-22.

[0007] The material of the magnesium alloy is VW93M magnesium alloy.

[0008] In the rotary swaging process of the present application, the deformation temperature is strictly controlled in the low temperature range of-30~-5℃. This key low temperature deformation condition aims to take full advantage of the regulation of low temperature on the plastic deformation mechanism of VW93M magnesium alloy: at low temperature, the activation of slip systems in magnesium alloy is inhibited, thus facilitating the excitation and promotion of twinning deformation as the dominant deformation mechanism. As a result, a high density of twin boundaries is formed inside the material. Twin boundaries can relieve the internal stress between the corrosion product layer and the metal matrix due to the difference in properties, thereby significantly reducing the cracking tendency of the protective layer. In this way, the penetration channel of the corrosion medium into the material is effectively blocked, and the entire corrosion process is thus slowed down. The present application optimizes the microstructure of the material through the low-temperature rotary swaging process with precise temperature control, and finally realizes the significant improvement of the corrosion resistance of magnesium alloy.

[0009] The present application limits the temperature of multi-pass rotary swaging in the above range. Too low rotary swaging temperature will increase deformation resistance, and too high rotary swaging temperature will result in coarse grains, reduced strength, impurity element segregation at grain boundaries, increased potential difference between matrix and phase, and decreased corrosion resistance of the alloy.

[0010] Therefore, the present application cooperatively improves the strength and corrosion resistance of magnesium alloy through a specific multi-pass rotary swaging process.

[0011] According to the embodiments of the present application, the present application can be further optimized, and the following is the technical scheme formed after optimization:

[0012] In one preferred embodiment, the temperature of low-temperature multi-pass rotary swaging is-20℃~-10℃.

[0013] In one preferred embodiment, the deformation pass of low-temperature multi-pass rotary swaging is 7~15 passes, preferably 9~13 passes.

[0014] The present application limits the deformation pass of multi-pass rotary swaging in the above range, so that the dislocation accumulation in the magnesium alloy bar, the core structure is deformed sufficiently, the grains are refined, and the impurity elements are uniformly distributed.

[0015] In one preferred embodiment, the pass deformation of low-temperature multi-pass rotary swaging is 3~6%, preferably 3~5%, and most preferably 4~5%.

[0016] The present application limits the pass deformation of multi-pass rotary swaging in the above range. Too small pass deformation will not deform the core structure of the magnesium alloy bar sufficiently, too large pass deformation will cause the bar to break easily, and impurity elements will segregate.

[0017] In one preferred embodiment, the total deformation of low-temperature multi-pass rotary swaging is 30~70%, preferably 40~60%.

[0018] The total deformation amount of the multi-pass rotary swaging is limited in the above range in the present application, the grain cannot be refined sufficiently if the total deformation amount is too small, the structure is not uniform, the alloy strength and corrosion resistance are poor, the work hardening is caused if the total deformation amount is too large, cracks are easily produced, even the sample is broken, and the impurity elements are segregated.

[0019] In one preferred embodiment, the feeding direction is changed after every 2 passes in the low-temperature multi-pass rotary swaging process.

[0020] The feeding direction is changed after every 2 passes to ensure the straightness of the rod.

[0021] In one preferred embodiment, the temperature of the hot extrusion is 360-420℃, and the extrusion ratio is 19-20.

[0022] In the present application, the internal structure of the sample is recrystallized during the hot extrusion, forming a fully recrystallized structure, reducing the grain size, and improving the strength of the magnesium alloy. In the present application, the temperature and the extrusion ratio of the hot extrusion are limited in the above range, if the extrusion temperature is too low and the extrusion ratio is too high, the deformation resistance is too large, the performance requirement of the die is high, the cost is increased, and the grain size is large, cracks are easily produced, and other defects are caused, if the extrusion temperature is too high and the extrusion ratio is too low, the grain size is large, the impurity elements are segregated at the grain boundaries, and the structure composition is not uniform.

[0023] In one preferred embodiment, the method for preparing a magnesium alloy by low-temperature rotary swaging further comprises a homogenization treatment step of the magnesium alloy ingot before the hot extrusion.

[0024] In one preferred embodiment, after the hot extrusion is completed, the hot extruded magnesium alloy rod is cooled.

[0025] The operation of the cooling is not specially limited in the present application, and the operation cooling to room temperature known to those skilled in the art can be used.

[0026] In one preferred embodiment, the temperature of the homogenization treatment is 400-520℃, further preferably 420-500℃, and more preferably 440-480℃.

[0027] In one preferred embodiment, the time of the homogenization treatment is 16-24h, preferably 18-22h, and more preferably 19-20h.

[0028] In one preferred embodiment, the homogenization treatment is preferably carried out under argon protection.

[0029] The magnesium alloy ingot is subjected to homogenization treatment to obtain a homogenized magnesium alloy.

[0030] The homogenization treatment parameters are limited in the above range, which can make the magnesium alloy composition more uniform, inhibit the segregation of impurity elements at the grain boundaries, and improve the corrosion resistance of the magnesium alloy.

[0031] In one preferred embodiment, after the homogenization treatment is completed, the homogenized magnesium alloy is subjected to air cooling and face milling in sequence to obtain a homogenized alloy.

[0032] The operation of the air cooling is not particularly limited, and the operation cooling to room temperature known to those skilled in the art can be used.

[0033] The operation of the face milling is not particularly limited, and the face milling operation known to those skilled in the art can be used. In the present application, the face milling is used to remove surface defects of the ingot.

[0034] In one preferred embodiment, the homogenized alloy needs to be preheated before hot extrusion.

[0035] In one preferred embodiment, the preheating temperature is 300-480℃, preferably 360-420℃.

[0036] The preheating temperature is consistent with the hot extrusion temperature.

[0037] In one preferred embodiment, the preheating time is 30-40min, further preferably 34-37min.

[0038] In the present application, the preheating is to prevent cracks on the surface of the alloy after extrusion and reduce die wear.

[0039] Based on the same inventive concept, the present application also claims the magnesium alloy prepared by the above preparation method.

[0040] Based on the same inventive concept, the present application also claims the application of the above magnesium alloy in the fields of automobiles, communication electronics and aerospace.

[0041] Compared with the prior art, the present application has the following advantages:

[0042] The magnesium alloy provided by this invention, with appropriate amounts of Gd and Y, can significantly accelerate grain refinement and enhance the grain refinement effect, resulting in a substantial increase in the strength of the magnesium alloy. After hot extrusion, the average grain size of the magnesium alloy is reduced to 10-30 μm. Subsequent low-temperature rotary forging, by controlling the forging temperature, number of deformation passes, deformation amount per pass, and total deformation, further refines the grains, reducing the grain size from 10-30 μm to 55-70 nm. Furthermore, the low temperature inhibits the segregation of impurity elements at grain boundaries, reducing the potential difference between the matrix and the phase, and improving the corrosion resistance of the magnesium alloy. This is because grain boundaries affect the concentration of Cl in NaCl solution. - The movement of the material is hindered, and the magnesium alloy grains are significantly refined after multi-pass rotary forging, with increased grain boundary density. This hindering effect becomes more pronounced, slowing down the corrosion process and thus improving the corrosion resistance of the magnesium alloy. The ultra-fine-grained magnesium alloy prepared by this invention has a finer grain size and a more uniform distribution of impurity elements, which synergistically improves the strength and corrosion resistance of the magnesium alloy. Extensive experimental data demonstrate that the magnesium alloy prepared by this invention has a grain size below 100 nm, a yield strength up to 657 MPa, a tensile strength up to 719 MPa, and a self-corrosion current density as low as 1.94 × 10⁻⁶. -5 A / cm 2 . Detailed Implementation

[0043] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or alterations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0044] In this invention, the magnesium alloy ingot is made of VW93M magnesium alloy. This invention does not have special requirements regarding the source of the aforementioned magnesium alloy grades; magnesium alloy ingots of the corresponding grades prepared using commercially available materials or conventional casting methods are acceptable.

[0045] In VW93M magnesium alloy, Gd induces the formation of fine twin lamellae after rotary forging, increasing the activity of non-basal plane dislocations and gradually increasing the number of basal plane stacking faults. This promotes the formation of dislocation arrays, and the numerous dislocations cut the grains, resulting in a significant refinement of the grain size. The addition of Gd in this invention improves the internal microstructure of the alloy, significantly refining the grain size, increasing grain boundary density, and improving the strength of the magnesium alloy. Because grain boundaries affect the concentration of Cl in NaCl solution... -Gd hinders the movement of magnesium alloy grains, significantly refining the grain size and increasing grain boundary density. This hindering effect becomes even more pronounced, leading to a substantial reduction in corrosion products. The erosion of the MgO protective film on the Mg matrix surface slows down, and the small amount of corrosion products generated covers areas without MgO protective film, forming a complete surface film that further hinders the movement of Mg. 2+ The diffusion of the material slows down the corrosion process, thereby improving the corrosion resistance of magnesium alloys.

[0046] The mechanism by which Y (yet) refines the grain size of VW93M magnesium alloy is similar to that of Gd (gd). In the VW93M magnesium alloy, Y causes the formation of numerous fine twin lamellae layers within the forged magnesium alloy, and the formation of numerous dislocation arrays further refines these twin lamellae layers. Both the addition of Gd and Y can refine the grain size and improve the strength of the magnesium alloy. Because grain boundaries affect the Cl- content in NaCl solution... - The movement of γ-rays (γ) is hindered, while Y promotes significant grain refinement in magnesium alloys, increasing grain boundary density and making the hindering effect even more pronounced. Corrosion products are also greatly reduced, slowing down the wear of the MgO protective film on the Mg matrix surface. The small amount of corrosion products generated covers areas without MgO protective film, forming a complete surface film that further hinders the movement of Mg. 2+ The diffusion of the material slows down the corrosion process, thereby improving the corrosion resistance of magnesium alloys.

[0047] Example 1

[0048] A method for synergistically improving the strength and corrosion resistance of magnesium alloys using cold deformation includes the following steps:

[0049] (1) The magnesium alloy ingot is homogenized under the protection of argon atmosphere; wherein the material of the magnesium alloy ingot is VW93M magnesium alloy prepared by conventional melting and casting method; the homogenization temperature is 440℃, the homogenization time is 20h, after the homogenization is completed, it is air-cooled to room temperature, and then the surface defects of the ingot are removed by milling to obtain a homogeneous alloy.

[0050] (2) The homogeneous alloy was preheated at 380°C for 33 min and then hot extruded at 380°C with an extrusion ratio of 20. After cooling to room temperature, magnesium alloy rods were obtained.

[0051] (3) The magnesium alloy bar was subjected to multi-pass rotary forging at a temperature of -5℃. The deformation amounts per pass were 3.8%, 3.5%, 4.1%, 4.3%, 4.4%, 4.5%, 4.6%, 4.9%, 5.4%, 5.2%, 5.1%, 4.8%, and 5.3%, respectively. The number of deformation passes was 13. The feeding direction was changed after every 2 passes. The total deformation amount was 42.8%, resulting in an ultra-fine-grained magnesium alloy with an average grain size of 70nm.

[0052] The magnesium alloy prepared in Example 1 was subjected to tensile property testing according to GB / T16865-2013. The yield strength was 640 MPa, the tensile strength was 710 MPa, and the elongation was 5%.

[0053] Electrochemical experiments were conducted on the magnesium alloy prepared in Example 1, and the self-corrosion current density was 2.11 × 10⁻⁶. -5 A / cm 2 .

[0054] Example 2

[0055] A method for synergistically improving the strength and corrosion resistance of magnesium alloys using cold deformation includes the following steps:

[0056] (1) The magnesium alloy ingot is homogenized under the protection of argon atmosphere; wherein the material of the magnesium alloy ingot is VW93M magnesium alloy prepared by conventional melting and casting method; the homogenization temperature is 480℃, the homogenization time is 18h, after the homogenization is completed, it is air-cooled to room temperature, and then the surface defects of the ingot are removed by milling to obtain a homogeneous alloy.

[0057] (2) The homogeneous alloy was preheated at 390°C for 38 minutes and then hot extruded at 390°C with an extrusion ratio of 22. After cooling to room temperature, magnesium alloy rods were obtained.

[0058] (3) The magnesium alloy bar was subjected to multi-pass rotary forging at a temperature of -30℃. The deformation amounts per pass were 4.3%, 4.4%, 3.7%, 3.9%, 4.9%, 4.7%, 5.2%, 5.4%, 5.5%, 4.7%, 4.5%, 5.1%, and 5.3%, respectively. The number of deformation passes was 13. The feeding direction was changed after every 2 passes. The total deformation amount was 46.8%, resulting in an ultra-fine-grained magnesium alloy with an average grain size of 55nm.

[0059] The magnesium alloy prepared in Example 2 was subjected to tensile property testing according to GB / T16865-2013. The yield strength was 657 MPa, the tensile strength was 719 MPa, and the elongation was 4%.

[0060] Electrochemical experiments were conducted on the magnesium alloy prepared in Example 2, and the self-corrosion current density was 1.94 × 10⁻⁶. -5 A / cm 2 .

[0061] Comparative Example 1

[0062] A method for synergistically improving the strength and corrosion resistance of magnesium alloys using cold deformation is based on Example 1, but omitting step (3) of multi-pass rotary forging, while the rest is the same as in Example 1. The average grain size of the obtained magnesium alloy rod is 15 μm.

[0063] The magnesium alloy prepared according to GB / T16865-2013 was subjected to tensile property testing. The yield strength was 205 MPa, the tensile strength was 318 MPa, and the elongation was 13%.

[0064] Electrochemical experiments were conducted on the magnesium alloy prepared in Comparative Example 1, and the self-corrosion current density was 2.59 × 10⁻⁶. -5 A / cm 2 .

[0065] Comparative Example 2

[0066] A method for synergistically improving the strength and corrosion resistance of magnesium alloys using cold deformation is based on Example 1, wherein the temperature of the multi-pass rotary forging in step (3) is adjusted to 200°C, and the rest is the same as in Example 1. The average grain size of the obtained magnesium alloy rod is 305 nm.

[0067] The magnesium alloy prepared according to GB / T16865-2013 was subjected to tensile property testing. The yield strength was 577 MPa, the tensile strength was 625 MPa, and the elongation was 3%.

[0068] Electrochemical experiments were conducted on the magnesium alloy prepared in Comparative Example 2, and the self-corrosion current density was 2.32 × 10⁻⁶. -5 A / cm 2 .

[0069] Comparative Example 3

[0070] A method for synergistically improving the strength and corrosion resistance of magnesium alloys using cold deformation is based on Example 1, wherein the temperature of the multi-pass rotary forging in step (3) is adjusted to 0°C, and the rest is the same as in Example 1. The resulting magnesium alloy rod has an average grain size of 80 nm.

[0071] The magnesium alloy prepared according to GB / T16865-2013 was subjected to tensile property testing. The yield strength was 621 MPa, the tensile strength was 695 MPa, and the elongation was 5%.

[0072] Electrochemical experiments were conducted on the magnesium alloy prepared in Comparative Example 3, and the self-corrosion current density was 2.26 × 10⁻⁶. -5 A / cm 2 .

[0073] The magnesium alloy provided by this invention utilizes appropriate amounts of Gd and Y to promote the formation of twin lamellae, refine grains, improve alloy strength, increase grain boundary density, hinder corrosion propagation, slow down the corrosion process, and enhance the alloy's corrosion resistance. The magnesium alloy ingot undergoes homogenization treatment, with controlled homogenization time and temperature to ensure uniform alloy composition distribution. After preheating, hot extrusion is performed, with controlled hot extrusion temperature and extrusion ratio to refine grains. Then, low-temperature rotary forging is performed, with controlled rotary forging temperature, number of deformation passes, deformation per pass, and total deformation to further reduce grain size. The grain refinement effect is significant, improving the strength of the magnesium alloy. Furthermore, the low temperature inhibits the segregation of impurity elements at grain boundaries, reducing the potential difference between the matrix and the phase, and enhancing the corrosion resistance of the magnesium alloy.

[0074] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing magnesium alloys using low-temperature rotary forging, characterized in that, Includes the following steps: Magnesium alloy bars that have been hot-extruded are subjected to low-temperature multi-pass rotary forging to obtain magnesium alloys; the deformation temperature of the low-temperature multi-pass rotary forging is -30℃ to -10℃; the deformation per pass is 2 to 6%; the number of deformation passes is 7 to 18, and the total deformation is 30 to 80%; the hot extrusion temperature is 300 to 480℃, and the extrusion ratio is 18 to 22. The magnesium alloy is made of VW93M magnesium alloy.

2. The method according to claim 1, characterized in that, The temperature of the low-temperature multi-pass rotary forging is -20℃ to -10℃; the number of deformation passes in the low-temperature multi-pass rotary forging is 7 to 15; and the deformation amount per pass in the low-temperature multi-pass rotary forging is 3 to 6%.

3. The method according to claim 1, characterized in that, The total deformation of the low-temperature multi-pass rotary forging is 30-70%.

4. The method according to claim 1, characterized in that, The hot extrusion temperature is 360~420℃, and the extrusion ratio is 19~20.

5. The method according to claim 1, characterized in that, The method for preparing magnesium alloys using low-temperature rotary forging also includes a homogenization treatment step for the magnesium alloy ingot before hot extrusion.

6. The method according to claim 5, characterized in that, The homogenization treatment temperature is 400~520℃, and the homogenization treatment time is 16~24h; the homogenization treatment is carried out under argon protection.

7. The method according to claim 1, characterized in that, The homogenized alloy needs to be preheated before hot extrusion.

8. The method according to claim 7, characterized in that, The preheating temperature is 300~480℃, and the preheating time is 30~40 minutes.

9. A magnesium alloy prepared by the method according to any one of claims 1-8.

10. The application of the magnesium alloy according to claim 9 in the fields of automobiles, communications electronics and aerospace.