Pretreatment mode for improving forming performance of magnesium alloy

Abstract

The invention discloses a pretreatment mode for improving the forming performance of a magnesium alloy, the pretreatment mode comprises a solid solution treatment process, a pre-deformation process treatment and an aging treatment process, and a magnesium alloy microstructure subjected to the pretreatment process has a nanoscale spherical precipitated phase. By regulating and controlling the structure of the magnesium alloy, the morphology of the precipitated phase of the magnesium alloy is changed in the aging process, the activation energy of the material is reduced by the nanoscale spherical precipitated phase, the hot working temperature range of the material is expanded, the room-temperature and high-temperature toughness of the magnesium alloy and the thermal stability of the material are improved, and the processing range is expanded; the processing performance and the forming performance of the material are improved; the magnesium alloy is simple in processing technology, low in equipment requirement, simple and convenient to operate, relatively low in cost and high in production efficiency; application and popularization of the magnesium alloy have important significance.

Description

Technical Field

[0001] The invention relates to a pretreatment method for improving the forming performance of a magnesium alloy, belongs to the technical field of magnesium alloy processing, and particularly relates to improving the forming performance of a magnesium alloy. Background Art

[0002] Magnesium alloy is an alloy based on magnesium and formed by adding other elements. Its main characteristics include low density (about 1.8g / cm 3 ), high strength, large elastic modulus, good heat dissipation, excellent shock absorption performance, and high impact bearing capacity, and good corrosion resistance to organic matter and alkali. The types currently widely used include magnesium-aluminum alloys, magnesium-manganese alloys, and magnesium-zinc-zirconium alloys, which are mainly used in industrial sectors such as aviation, aerospace, transportation, chemical industry, and rockets. Magnesium-aluminum alloy is one of the most widely used magnesium alloys in commercial applications, and its main forms are cast and aged. The cast structure is mainly composed of α-Mg and Mg17Al12, most of which is distributed in the grain boundary in a coarse network (DPs), while a small amount of granular Mg17Al12 (CPs) is distributed in the grain. During the deformation process, the coarse Mg17Al12 at the grain boundary is easily broken and cracked, thereby hindering dynamic recrystallization, adversely affecting the forming properties of the alloy, and limiting the application range of the alloy. Therefore, how to improve its forming properties is a technical problem that needs to be solved urgently to meet the needs of expanding the application range of the alloy. Summary of the invention

[0003] In order to improve the forming performance of magnesium alloy, the present invention provides a pretreatment method of magnesium alloy, and the specific technical scheme is as follows.

[0004] 1. A pretreated magnesium alloy, characterized in that: the mass percentage composition of the magnesium alloy is Al: 8.5% to 9.5%, Ca: 0.6% to 1.2%, and the rest is magnesium and unremovable impurity elements. The magnesium alloy is obtained by sequentially undergoing a solution treatment process, a pre-deformation treatment process, and an aging treatment process. Nano-scale spherical precipitation phases exist in the microstructure of the magnesium alloy after the pretreatment process.

[0005] By adopting the above-mentioned technical scheme, the Mg17Al12 phase is dissolved into the matrix of the magnesium alloy as much as possible through a solid solution treatment process, and a large number of twins can be obtained in the magnesium alloy by subjecting the magnesium alloy to a twin pre-deformation process with a small deformation amount; the AZ series magnesium alloy with a large number of twins and no Mg17Al12 phase precipitated will undergo static precipitation during the aging process, and the precipitation is concentrated around the twins, and the precipitated phase is dispersed spherical, thereby significantly improving the forming performance of the magnesium alloy.

[0006] Furthermore, the temperature of the solution treatment process is 400-430°C, and the holding time is 10-18h.

[0007] Furthermore, the twin pre-deformation process adopts a compression process or a hammering process.

[0008] Furthermore, the compression process is as follows: the compression temperature is 20°C - 150°C, the compressive strain is 0.05 - 0.1 (the thickness is reduced by 5% - 10%), the strain rate is 1×10-4 - 2×10-4 s, and the compression deformation is maintained for more than 5 minutes.

[0009] Based on the same inventive concept, the present invention also relates to a processing method of the above magnesium alloy. The above magnesium alloy is prepared by a water-cooled semi-continuous casting method. Pure magnesium ingots with a mass fraction greater than 99.9%, pure aluminum ingots with a mass fraction greater than 99.9%, and Al-Ca master alloy are melted and cast to obtain the as-cast microstructure of the magnesium alloy.

[0010] The pre-deformed magnesium alloy obtained by the present invention has the following beneficial effects compared with the prior art.

[0011] 1. Through the solution treatment of the magnesium alloy, the Mg17Al12 phase is dissolved into the matrix of the magnesium alloy as much as possible. Reducing the existence of the lamellar Mg17Al12 phase is beneficial to improving the room temperature and high temperature toughness of the magnesium alloy. At the same time, it is ensured that there is enough Al element reserve in the matrix during the subsequent aging process treatment, so that precipitation occurs during aging. The precipitated phase around the twins is spherical, and the spherical precipitated phase can effectively inhibit the diffusion and migration of dislocation movement during the hot deformation process, improve the thermal stability of the material, expand the processing temperature range, and enhance the formability of the material.

[0012] 2. Only a small amount of pre-deformation is required to obtain a large number of twins. A small amount of deformation is not easy to generate cracks inside the magnesium alloy structure, and the pre-deformation with a small amount of deformation will not have an adverse impact on the formability.

[0013] 3. The addition of Ca element can improve the thermal stability of the magnesium-aluminum series magnesium alloy above 150°C. At the same time, the formed Al2Ca phase can promote dynamic recrystallization through the PSN mechanism and improve the formability.

[0014] 4. The magnesium alloy processing process of the present invention is simple, has low equipment requirements, is easy to operate, has low costs, and has high production efficiency.

[0015] 5. Through a simple pretreatment method, the present invention significantly improves the formability of the magnesium alloy, which has important significance for the application and popularization of this magnesium alloy. Description of the Drawings

[0016] Figure 1 It is a calculation curve graph and activation energy comparison graph of Comparative Example 1, Comparative Example 2, Example 1 and Example 2;

[0017] Figure 2 It is a schematic diagram of the scanning structure and microstructure evolution of Comparative Example 1;

[0018] Figure 3 It is a schematic diagram of the scanning structure and microstructure evolution of Comparative Example 2;

[0019] Figure 4 It is a schematic diagram of the scanning structure and microstructure evolution of Example 1;

[0020] Figure 5 It is a schematic diagram of the scanning structure and microstructure evolution of Example 2. Detailed implementation manners

[0021] The following examples are intended to further illustrate the present invention, rather than limiting the present invention.

[0022] Comparative Example 1

[0023] The magnesium alloy of this comparative example was prepared by water-cooled semi-continuous casting. Pure magnesium ingots with a mass fraction greater than 99.9%, pure aluminum ingots with a mass fraction greater than 99.9%, and Al-Ca master alloy were melted and cast to obtain the as-cast structure of the magnesium alloy. The mass percentage composition of the magnesium alloy was Al: 9.5%, Ca: 1.2%, and the rest were magnesium and non-removable impurity elements.

[0024] The as-cast structure was solution-treated at 420 °C for 12 h; then hot pressing experiments were carried out on the solution-treated structure. The experimental conditions were temperatures of 200 °C, 250 °C, and 300 °C; rates of 0.1 s-1, 0.01 s-1, and 0.001 s-1.

[0025] The specimens were observed by scanning electron microscopy. The schematic diagrams of their scanning structures and structure evolutions are as shown in Figure 1 Shown. Data analysis was carried out on the hot pressing experimental data, and the activation energy was obtained as 144.528 KJ / mol. The analysis curve diagram is as shown in Figure 5 Shown. From the Figure 1 scanning structure, large-sized non-recrystallized regions can be seen.

[0026] Comparative Example 2

[0027] The magnesium alloy of this comparative example was prepared by water-cooled semi-continuous casting. Pure magnesium ingots with a mass fraction greater than 99.9%, pure aluminum ingots with a mass fraction greater than 99.9%, and Al-Ca master alloy were melted and cast to obtain the as-cast structure of the magnesium alloy. The mass percentage composition of the magnesium alloy was Al: 9.0%, Ca: 1.2%, and the rest were magnesium and non-removable impurity elements.

[0028] The as-cast microstructure was solution-treated at 420 °C for 12 h; then the solution-treated microstructure was aged at 180 °C for 12 h; then a hot pressing experiment was carried out on the aged microstructure, and the experimental conditions were temperatures of 200 °C, 250 °C, and 300 °C; rates of 0.1 s-1, 0.01 s-1, and 0.001 s-1.

[0029] The specimens were observed by scanning electron microscopy, and the scanning microstructure and schematic diagram of microstructure evolution are as Figure 2 shown in. Data analysis was carried out on the hot pressing experimental data, and the activation energy was obtained as 151.962 KJ / mol, and its calculated curve is as Figure 5 shown in. By observing the Figure 2 scanning microstructure in, it can be seen that the lamellar Mg17Al12 phase is broken during the hot deformation process, thus hindering the occurrence of dynamic recrystallization. This results in the activation energy of this comparative example being greater than that of Comparative Example 1, and therefore the forming performance is reduced.

[0030] Example 1

[0031] A magnesium alloy was prepared by the water-cooled semi-continuous casting method. Pure magnesium ingots (Mg 99.9%) and pure aluminum ingots (Al 99.9%) and Al-Ca master alloy were melted and cast to obtain the as-cast microstructure of the magnesium alloy. The mass percentage composition of the magnesium alloy was Al: 9%, Ca: 0.9%, and the rest was magnesium and non-removable impurity elements.

[0032] The as-cast microstructure was solution-treated at 425 °C for 18 h; then the solution-treated microstructure was compressed with a small deformation amount (pre-deformation process), the compression temperature was 25 °C, the compressive strain was 0.08 (thickness reduction of 8%), the strain rate was 1x10-4 s-1, and the compression deformation was maintained for more than 5 min. The strain rate was calculated as the compression rate / specimen length. For example, if the compression speed was 6 mm / min and the specimen length was 24 mm, the strain rate calculation method was 0.1 mms-1 / 24 mm, and the strain rate was obtained as 0.00416 s-1; then the pre-deformed microstructure was aged at 180 °C for 12 h; then a hot pressing experiment was carried out on the aged microstructure, and the experimental conditions were temperatures of 200 °C, 250 °C, and 300 °C; rates of 0.1 s-1, 0.01 s-1, and 0.001 s-1.

[0033] The specimens were observed by scanning electron microscopy, and the scanning microstructure and schematic diagram of microstructure evolution are as Figure 3 shown in. Data analysis was carried out on the hot pressing experimental data, and the activation energy was obtained as 119.345 KJ / mol, and its analysis curve is as Figure 5 shown in. In Figure 3In the scanning microstructure diagram, a large number of twins introduced during the room-temperature pre-deformation process can be clearly observed. After aging treatment, a large number of fine spherical Mg17Al12 precipitates around the twins. This fine spherical phase helps to promote dynamic recrystallization during the hot deformation process. Therefore, the activation energy of this embodiment is lower than that of Comparative Example 2, indicating an improvement in its formability. However, although twins contribute to the precipitation of fine spherical Mg17Al12, they also make the recrystallization nucleation conditions more stringent, resulting in the presence of twin structures and a large number of unrecrystallized regions in the high-stress and low-strain regions.

[0034] Example 2

[0035] A magnesium alloy was prepared by the water-cooled semi-continuous casting method. Pure magnesium ingots (Mg 99.9%) and pure aluminum ingots (Al 99.9%) and Al-Ca master alloy were melted and cast to obtain the as-cast microstructure of the magnesium alloy. The mass percentage composition of the magnesium alloy was Al: 9%, Ca: 0.6%, and the rest was magnesium and non-removable impurity elements.

[0036] The as-cast microstructure was solution-treated at 425 °C for 18 h; then the solution-treated microstructure was compressed with a small deformation amount (pre-deformation process), the compression temperature was 150 °C, the compressive strain was 0.08 (thickness reduction of 8%), the strain rate was 1×10−4 s−1, and the compression deformation was maintained for more than 5 min; then the pre-deformed microstructure was aged at 180 °C for 12 h; then the aged microstructure was subjected to hot pressing experiments, and the experimental conditions were temperatures of 200 °C, 250 °C, and 300 °C; rates of 0.1 s−1, 0.01 s−1, and 0.001 s−1.

[0037] The specimens were observed by scanning electron microscopy, and the scanning microstructure and microstructure evolution schematic diagrams are as shown in Figure 4 In the scanning microstructure diagram, the phenomenon of grain boundary dislocation pile-up caused by high-temperature pre-deformation can be clearly observed, which helps to promote the precipitation of fine spherical Mg17Al12 phases during the aging process. The activation of non-basal plane dislocations is not only related to the texture of the material but also affected by the deformation temperature. As the deformation temperature increases, non-basal plane dislocations are activated, thereby suppressing the formation of twins. By adjusting the pre-deformation temperature, the volume fraction of twins can be controlled while fine spherical Mg17Al12 precipitates. Therefore, the suppression effect of twins is eliminated, and the fine spherical Mg17Al12 phases and the piled-up prismatic dislocations during high-temperature pre-deformation act together to further promote the occurrence of dynamic recrystallization. The activation energy of this embodiment is lower than that of Example 1, further improving the formability of the material. Figure 5 as shown in Figure 4 In the scanning microstructure diagram, the phenomenon of grain boundary dislocation pile-up caused by high-temperature pre-deformation can be clearly observed, which helps to promote the precipitation of fine spherical Mg17Al12 phases during the aging process. The activation of non-basal plane dislocations is not only related to the texture of the material but also affected by the deformation temperature. As the deformation temperature increases, non-basal plane dislocations are activated, thereby suppressing the formation of twins. By adjusting the pre-deformation temperature, the volume fraction of twins can be controlled while fine spherical Mg17Al12 precipitates. Therefore, the suppression effect of twins is eliminated, and the fine spherical Mg17Al12 phases and the piled-up prismatic dislocations during high-temperature pre-deformation act together to further promote the occurrence of dynamic recrystallization. The activation energy of this embodiment is lower than that of Example 1, further improving the formability of the material.

Claims

1. A pretreated magnesium alloy, characterized in that: The mass percentage composition of the magnesium alloy is: Al: 8.5% to 9.5%, Ca: 0.6% to 1.2%, and the rest is magnesium and irremovable impurity elements; the magnesium alloy is obtained by sequentially undergoing a solid solution treatment process, a pre-deformation treatment process, and an aging treatment process.

2. A pretreated magnesium alloy according to claim 1, characterized in that: The temperature of the solution treatment process is 400-430° C., and the holding time is 10-18 hours.

3. A pretreated magnesium alloy according to claim 1, characterized in that: The deformation process adopts a compression process, and the compression process is: the compression temperature is 20°C-150°C, the compressive strain is 0.05-0.1, the strain rate is 1×10-4-2×10-4s, and the compression deformation is maintained for more than 5 minutes.

4. A pretreated magnesium alloy according to claim 1, characterized in that: The temperature of the aging treatment process is 150-200° C., and the insulation time is 8-15 hours.

5. A processing method for a pretreated magnesium alloy as described in any one of claims 1 to 4, comprising preparing the above-mentioned magnesium alloy by a water-cooled semi-continuous casting method, melting pure magnesium ingots with a mass fraction greater than 99.9%, pure aluminum ingots with a mass fraction greater than 99.9% and Al-Ca intermediate alloys, and casting to obtain a cast structure of the magnesium alloy, then subjecting the cast structure to a solid solution treatment, then subjecting the solid solution structure to a pre-deformation process, then subjecting the structure obtained by the pre-deformation process to an aging treatment, and then subjecting the structure obtained after the aging treatment to a hot pressing test.

Images