A method for preparing a high-strength and high-toughness magnesium alloy wheel without heat treatment

Abstract

The present application relates to the technical field of magnesium alloy wheel preparation, and in particular to a method for preparing a high-strength and high-toughness magnesium alloy wheel that does not require heat treatment, which comprises the following steps: blanking, heating, multi-directional forging, primary forging, heating, rotary forging, and forming. A blank with a specific chemical composition ratio is used, and the anisotropy of the magnesium alloy blank is eliminated to the maximum extent by multi-directional forging. The magnesium alloy round cake-shaped blank that has undergone primary forging is subjected to rotary forging for near-net forming. The formed magnesium alloy wheel can be used without processing or with very little processing, and finally a magnesium alloy wheel with high strength and high toughness mechanical properties that does not require heat treatment is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of magnesium alloy wheel preparation, and in particular to a method for preparing a high-strength and high-toughness magnesium alloy wheel without heat treatment. Background Art

[0002] As the concept of green environmental protection has become more popular, people are paying more attention to energy conservation and emission reduction of automobiles, and vehicle lightweighting has become an inevitable trend in automobile development. Among automobile parts, wheels have a rotational inertia effect, and their rotational inertia will affect the dynamic performance and energy consumption of the vehicle. The larger the wheel mass, the greater the rotational inertia, so wheel lightweighting plays an important role in automobile energy conservation and emission reduction.

[0003] Due to its advantages of high specific strength, high specific stiffness, good shock resistance, and good impact resistance, magnesium alloys are widely used in lightweight industries. The conventional preparation method of magnesium alloy wheels is to first select a suitable magnesium alloy blank, melt the magnesium alloy material and pour it into a preheated mold. After the metal liquid cools and solidifies in the mold, it is demolded to obtain a preliminary wheel blank. Subsequently, the wheel blank is subjected to heat treatment such as solid solution treatment, and then machining steps such as turning, drilling, milling, and finishing are performed, and finally the entire surface is subjected to corrosion resistance treatment.

[0004] Although the casting process is simple and has low production costs, cast magnesium alloy wheels have problems such as casting defects and poor comprehensive mechanical properties. They need to undergo specific processing steps such as heat treatment before they can be used under high speed and heavy load conditions. However, magnesium alloys are sensitive to temperature changes and have a narrow range of suitable processing temperatures. If the temperature is not properly controlled, heat treatment will cause defects such as deformation or surface cracks in the castings, which cannot meet the use requirements of subsequent castings and affect the product qualification rate. At the same time, a large number of machining steps such as cutting, drilling, and milling also lead to waste of raw materials. The materials removed by cutting and other methods become waste, affecting production costs. Therefore, it is of great significance to develop a method for preparing magnesium alloy wheels that can be nearly net-shaped and does not require heat treatment. Summary of the invention

[0005] In order to solve the problem of subsequent heat treatment of magnesium alloy wheels while controlling production costs, the present application provides a method for preparing high-strength and high-toughness magnesium alloy wheels without heat treatment.

[0006] The present application provides a method for preparing a high-strength and high-toughness magnesium alloy wheel without heat treatment, which adopts the following technical solution:

[0007] A method for preparing a high-strength and high-toughness magnesium alloy wheel without heat treatment comprises the following steps:

[0008] 1) Obtaining a magnesium alloy billet, placing the magnesium alloy billet in an oven for heating and keeping the billet warm to obtain a billet to be forged, and at the same time, placing a multi-directional forging die and a rotary forging die in a die heating furnace for heating and keeping the billet warm, wherein the magnesium alloy billet comprises the following chemical components by weight percentage: aluminum: 5.5-6.3wt%; manganese: 0.2-0.5wt%; rare earth elements: 3.0-5.5wt%; calcium: 0.2-0.4wt%; the balance is magnesium and unavoidable impurities, and the impurity mass is ≤0.2wt%; the rare earth element is one or more of La, Ce, Sc, and Sm;

[0009] 2) After the forged blank is forged into a rectangular shape by a three-way forging press, the heat-insulated multi-directional forging die is installed on the three-way forging press, the working inner cavity of the die is sprayed with lubrication, and then the rectangular magnesium alloy blank is placed in the multi-directional forging die for multi-directional forging. After the multi-directional forging is completed, the magnesium alloy blank is forged into a bar by a three-way forging press;

[0010] 3) The magnesium alloy bar after multi-directional forging is further forged on the multi-directional forging die, and after being forged into a round cake shape, it is placed in an oven for heating and heat preservation;

[0011] 4) The heated rotary forging die is installed on a forging press, the working inner cavity of the die is sprayed with lubrication, and the heated round cake-shaped magnesium alloy billet is placed in the rotary forging die for rotary forging to obtain a magnesium alloy wheel.

[0012] Preferably, in step 1, the magnesium alloy billet is placed in an oven at a temperature of 350±5°C and heated to a specified temperature of the oven and then kept warm for 2h to 5h.

[0013] Preferably, in step 1, the multi-directional forging die and the rotary forging die are heated in a die heating furnace at a temperature of 300±5°C, and are kept warm for 2h to 3h after being heated to a specified temperature of the die heating furnace.

[0014] Preferably, in step 2, the rectangular magnesium alloy billet is forged three times in different directions.

[0015] Preferably, in step 3, the initially forged round cake-shaped magnesium alloy billet is heated in an oven at a temperature of 350±5° C., and then kept at a specified temperature of the oven for 2 h to 5 h.

[0016] Preferably, in step 4, the heated round cake-shaped magnesium alloy billet is placed in a rotary forging die for rotary forging, with a forging speed of 2 to 5 mm / s and a rotation speed of 4 to 6 r / min.

[0017] The beneficial effects of the present application are as follows: firstly, a blank with a specific chemical composition ratio is used for preparation, and the rare earth elements in the blank preferentially react with the Al element to form Al-RE compounds, while reducing the formation of low-melting-point β-Mg 17 Al 12 The number of strengthening phases, Al-RE compounds belong to high temperature resistant strengthening phases, and their number and distribution are less affected by temperature. Secondly, the multi-directional forging method inhibits the formation of base surface texture in the magnesium alloy billet during thermal deformation, which can eliminate the anisotropy of the magnesium alloy billet, maximize the uniformity of the billet's structure, and make the deformation of the material uniform during the subsequent rotary forging process, avoiding the anisotropy of the mechanical properties of the formed magnesium alloy wheel; the rotary forging method can well ensure the uniformity of the mold temperature and the applied force, and then ensure the uniform deformation of the billet, so that the mechanical properties of the formed magnesium alloy wheel have good isotropy. The combination of the above factors makes the strengthening mechanism of the magnesium alloy in this application have both deformation strengthening and second phase strengthening, and the magnesium alloy wheel with uniform mechanical properties that does not require heat treatment is prepared by multi-directional forging and rotary forging near-net forming.

[0018] In summary:

[0019] 1. In the present application, Al element and rare earth elements La and Ce exist in the alloy matrix in the form of rod-shaped Al4RE compounds. In addition, Al element also forms a granular heat-resistant strengthening phase Al with rare earth elements La, Ce, Sc or Sm. 11 RE3, the presence of a large number of dispersed second phases makes the matrix grains refined, transforming from coarse dendrites to equiaxed crystals; due to the formation of Al-RE compounds by rare earth elements and Al elements, the formation of low-melting-point β-Mg 17 Al 12 The number of strengthening phases, therefore, the shape, distribution and quantity of most second phases in the alloy will not change with temperature. Therefore, the alloy can obtain excellent comprehensive mechanical properties without heat treatment and provide a larger material plasticity space for subsequent multi-directional forging.

[0020] 2. In the present application, the microstructure of the magnesium alloy bar blank processed by a sawing machine is composed of a large number of large deformed grains and a small number of fine equiaxed grains, and the macroscopic properties show strong anisotropy. After the magnesium alloy bar blank is subjected to multiple multi-directional forging processes, the large deformed grains in the magnesium alloy bar blank are mechanically divided into uniformly distributed small-sized band grains, and each band grain is surrounded by fine equiaxed grains. The microstructure uniformity of the blank is significantly improved, and the anisotropy of the magnesium alloy bar blank is eliminated to the greatest extent.

[0021] 3. In the present application, the magnesium alloy wheel prepared by rotary forging near net forming can achieve the shape and size of the finished part after a small amount of processing or without subsequent processing, and can be directly used as a mechanical component, thereby saving steps, saving raw materials, shortening the manufacturing cycle, and reducing production costs. In addition, the magnesium alloy wheel prepared by rotary forging near net forming has metal streamlines reasonably distributed along the contour, which makes its structure and performance better, thereby improving the quality and service life of the magnesium alloy wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the structure of the forging machine used in the rotary forging test process of this application.

[0023] Figure 2 Schematic diagram of sample deformation during the multi-directional forging test process of Example 1.

[0024] Figure 3 Schematic diagram of sampling of high-strength and high-toughness magnesium alloy wheels without heat treatment in Example 1.

[0025] Figure 4 This is the metallographic image of the magnesium alloy wheel sample obtained in Example 1.

[0026] Figure 5 This is a graph showing the room temperature tensile mechanical properties of the magnesium alloy wheel samples obtained in Example 1.

[0027] Figure 6 This is the metallographic image of the magnesium alloy wheel sample obtained in Example 2.

[0028] Figure 7 This is a graph showing the room temperature tensile mechanical properties of the magnesium alloy wheel samples obtained in Example 2.

[0029] Figure 8 This is the metallographic image of the magnesium alloy wheel sample obtained in Example 3.

[0030] Fig. 9 This is a graph showing the room temperature tensile mechanical properties of the magnesium alloy wheel samples obtained in Example 3.

[0031] Fig.10 This is the metallographic image of the magnesium alloy wheel sample obtained in the comparative example.

[0032] Fig.11 This is a graph showing the room temperature tensile mechanical properties of the magnesium alloy wheel samples obtained in the comparative example.

[0033] Explanation of the accompanying drawings: 1. Forging press upper platen; 2. Die connecting shaft; 3. Rotary forging upper die; 4. Rotary forging lower die side wall; 5. Rotary forging lower die base; 6. Rotating shaft; 7. Rotating motor; 8. Forging press base; 9. Processing area; 10. Accommodating area. DETAILED DESCRIPTION

[0034] The present application is further described in detail below in conjunction with the accompanying drawings and examples, but the implementation of the present application is not limited to the scope of the examples. The examples are only used to illustrate the present application, not to limit the scope of the present application.

[0035] Reference Figure 1 The forging press used in the rotary forging test process is composed of a forging press upper platen 1, a die connecting shaft 2, a rotary forging upper die 3, a rotary forging lower die side wall 4, a rotary forging lower die base 5, a rotating shaft 6, a rotating motor 7 and a forging press base 8. The forging press upper platen 1 is arranged directly above the forging press base 8, the lower end of the forging press upper platen 1 is provided with a rotary forging upper die 3 through the die connecting shaft 2, the upper end of the forging press base 8 is fixedly provided with a rotary forging lower die side wall 4, and a rotary forging lower die base 5 is arranged in the middle of the rotary forging lower die side wall 4. A processing area 9 is left between the lower end surface of the rotary forging upper die 3 and the upper end surface of the rotary forging lower die base 5.

[0036] The middle part of the forging press base 8 is hollow to form a receiving area 10, and the receiving area 10 extends upward with an opening. A rotating motor 7 is installed at the lower end of the middle part of the rotary forging lower die base 5 through a rotating shaft 6. The rotating shaft 6 passes through the opening at the upper end of the middle part of the forging press base 8, and the rotating motor 7 is accommodated in the receiving area 10.

[0037] The main structure, installation and coordination method of the main structure and working principle of the forging machine used in the rotary forging test process of the present application are the same as those of the existing forging machine. The only difference is that the rotary forging upper die 3, the rotary forging lower die side wall 4 and the rotary forging lower die base 5 in the forging machine used in the present application have been adaptively changed in shape according to needs to produce magnesium alloy wheels.

[0038] The method of using the device is as follows: fix the preheated rotary forging upper die 3, the rotary forging lower die side wall 4 and the rotary forging lower die base 5 in their respective positions, then place the blank in the processing area 9 and start forging. When the bottom end of the blank is formed, start the rotary motor 7, which drives the blank to rotate. At the same time, the rotary forging upper die 3 continues to maintain pressure forging until the magnesium alloy wheel is completely formed and the rotary forging stops. Example 1

[0039] 1) Purchase customized magnesium alloy bars. The customized magnesium alloy billets include the following chemical compositions by mass percentage: aluminum: 6.0wt%; manganese: 0.4wt%; rare earth element Ce: 2.0wt%; rare earth element Sc: 1.7wt%; calcium: 0.3wt%; the remainder is magnesium and unavoidable impurities, and the impurity mass is ≤0.2wt%. The purchased magnesium alloy bars (specification: Φ200±5mm) are processed into magnesium alloy billets (Φ200±5mm, 110±10mm) by sawing machine, and the magnesium alloy billets are placed in an oven set at 350℃ for heating. After the billets are heated to the same temperature as the oven, they are kept warm for 3h to obtain the billets to be forged; at the same time, the multi-directional forging die and the rotary forging die are placed in a die heating furnace set at 300℃ for heating. After both dies are heated to the same temperature as the heating furnace, they are kept warm for 2.5h.

[0040] 2) After the forged blank is forged into a rectangular shape by a three-way forging press, the heat-insulated multi-directional forging die is installed on the three-way forging press, and the working inner cavity of the die is sprayed with oil-based graphite for lubrication. Then, the rectangular magnesium alloy billet is placed in the multi-directional forging die for three forgings in different directions. During the multi-directional forging, the pressing speed of the three-way forging press is set to 5m / s, and the pressing amount each time is based on the closing of the multi-directional forging die. The schematic diagram of the deformation of the sample during the multi-directional forging test process is shown in FIG. Figure 2 As shown, after the multi-directional forging is completed, the magnesium alloy billet is forged into a rod using a three-directional forging press. When the magnesium alloy billet is converted between a rod and a rectangular parallelepiped, the forging press speed is set to 5 m / s.

[0041] 3) After multi-directional forging, the magnesium alloy bar continues to be pre-forged on the multi-directional forging die. When it is pre-forged into a round cake shape, the pressing speed of the three-way forging press is set to 5m / s, and the height of the magnesium alloy bar is forged from 110±10mm to 30±10mm. After the pre-forging into a round cake shape, it is placed in an oven set at 350℃ for heating. When the round cake-shaped aluminum alloy billet is heated to the same temperature as the oven, it is kept warm for 3h.

[0042] 4) The heated rotary forging die is installed on the forging press, and the working inner cavity of the die is sprayed with oil-based graphite for lubrication. Then, the heated round cake-shaped magnesium alloy billet is placed in the rotary forging die for rotary forging. The forging speed is 3 mm / s and the rotation speed is 5 r / min. The forging press used in the rotary forging process and the method of using the forging press are as shown above, and finally a magnesium alloy wheel is obtained.

[0043] The magnesium alloy wheel obtained in Example 1 was sampled horizontally and vertically respectively. The sampling method is as follows: Figure 3The metallographic microstructure analysis of the sample was performed to obtain the metallographic microstructure analysis diagrams of the vertical and horizontal sampling of the magnesium alloy wheel in Example 1, as shown in FIG. Figure 4 As shown. Comparing (a) and (b), it is found that the microstructures of the vertical and horizontal samples are both composed of equiaxed grains, and the grains used have no obvious directionality; in addition, the heat-resistant strengthening phase containing rare earth elements is uniformly segregated at the grain boundaries. The uniformly distributed equiaxed grains and heat-resistant strengthening phases will simultaneously improve the strength and plasticity of the wheel.

[0044] The room temperature tensile mechanical properties of the samples were tested, and the room temperature tensile mechanical properties of the magnesium alloy wheels sampled in the vertical direction and the horizontal direction were obtained, as shown in the figure. Figure 5 As shown. Analysis shows that: Curve 1 is the tensile stress-strain curve of the magnesium alloy wheel sampled in the vertical direction, with a tensile strength of 294MPa, a yield strength of 193MPa, and an elongation after fracture of 5.0%; Curve 2 is the tensile stress-strain curve of the magnesium alloy wheel sampled in the horizontal direction, with a tensile strength of 304MPa, a yield strength of 209MPa, and an elongation after fracture of 4.5%. This shows that the mechanical properties of the magnesium alloy wheel prepared by this patent are equivalent in the vertical and horizontal directions, and multi-directional forging eliminates the anisotropy of the magnesium alloy bar blank, making the mechanical properties of various parts of the magnesium alloy wheel similar. Example 2

[0045] 1) Purchase customized magnesium alloy bars. The customized magnesium alloy billets include the following chemical compositions by mass percentage: aluminum: 5.8wt%; manganese: 0.4wt%; rare earth element Ce: 1.5wt%; rare earth element Sc: 2.0wt%; calcium: 0.3wt%; the remainder is magnesium and unavoidable impurities, and the impurity mass is ≤0.2wt%. The purchased magnesium alloy bars (specification: Φ200±5mm) are processed into magnesium alloy billets (Φ200±5mm, 110±10mm) by sawing machine, and the magnesium alloy billets are placed in an oven set at 350℃ for heating. After the billets are heated to the same temperature as the oven, they are kept warm for 3h to obtain the billets to be forged; at the same time, the multi-directional forging die and the rotary forging die are placed in a die heating furnace set at 300℃ for heating. After both dies are heated to the same temperature as the heating furnace, they are kept warm for 2.5h.

[0046] 2) After the forged blank is forged into a rectangular shape by a three-way forging press, the heat-insulated multi-directional forging die is installed on the three-way forging press, and the working inner cavity of the die is sprayed with oil-based graphite for lubrication. Then, the rectangular magnesium alloy billet is placed in the multi-directional forging die for three forgings in different directions. During the multi-directional forging, the pressing speed of the three-way forging press is set to 5m / s, and the pressing amount each time is based on the closing of the multi-directional forging die. The schematic diagram of the deformation of the sample during the multi-directional forging test process is shown in FIG. Figure 2As shown, after the multi-directional forging is completed, the magnesium alloy billet is forged into a rod using a three-directional forging press. When the magnesium alloy billet is converted between a rod and a rectangular parallelepiped, the forging press speed is set to 5 m / s.

[0047] 3) After multi-directional forging, the magnesium alloy bar continues to be pre-forged on the multi-directional forging die. When it is pre-forged into a round cake shape, the pressing speed of the three-way forging press is set to 5m / s, and the height of the magnesium alloy bar is forged from 110±10mm to 30±10mm. After the pre-forging into a round cake shape, it is placed in an oven set at 350℃ for heating. When the round cake-shaped aluminum alloy billet is heated to the same temperature as the oven, it is kept warm for 3h.

[0048] 4) The heated rotary forging die is installed on a forging press, and the working inner cavity of the die is sprayed with oil-based graphite for lubrication. Subsequently, the heated round cake-shaped magnesium alloy billet is placed in the rotary forging die for rotary forging. The forging speed is 3 mm / s and the rotation speed is 5 r / min. The rotary forging process is the same as in Example 1, and finally a magnesium alloy wheel is obtained.

[0049] In Example 2, horizontal sampling and vertical sampling were performed at the same position of the magnesium alloy wheel in the same manner as in Example 1, and the obtained samples were subjected to metallographic microstructure analysis to obtain metallographic microstructure analysis diagrams of the vertical sampling and horizontal sampling of the magnesium alloy wheel in Example 2, as shown in FIG. Figure 6 As shown. Comparing (a) and (b), it is found that the organization of the vertical sampling and the horizontal sampling is composed of equiaxed grains, and all the grains have no obvious directionality, and the average grain size in the two directions is close; in addition, the heat-resistant strengthening phase containing rare earth elements is uniformly segregated at the grain boundary, and the uniformly distributed equiaxed grains and heat-resistant strengthening phases will simultaneously improve the strength and plasticity of the wheel.

[0050] The room temperature tensile mechanical properties of the samples were tested, and the room temperature tensile mechanical properties of the vertical and horizontal samples of the magnesium alloy wheel in Example 2 were obtained. Figure 7 The analysis shows that: Curve 1 is the tensile stress-strain curve of the magnesium alloy wheel sampled in the vertical direction, with a tensile strength of 266MPa, a yield strength of 158MPa, and an elongation of 6.2%; Curve 2 is the tensile stress-strain curve of the magnesium alloy wheel sampled in the horizontal direction, with a tensile strength of 270MPa, a yield strength of 187MPa, and an elongation of 6.0%.

[0051] This indicates that the mechanical properties of the magnesium alloy wheel prepared by this patent are comparable in vertical and horizontal directions, and multi-directional forging eliminates the anisotropy of the magnesium alloy bar billet, making the mechanical properties of various parts of the magnesium alloy wheel similar. Example 3

[0052] 1) Purchase customized magnesium alloy bars. The customized magnesium alloy billets include the following chemical compositions by mass percentage: aluminum: 5.5wt%; manganese: 0.3wt%; rare earth element Ce: 1.5wt%; rare earth element Sc: 1.5wt%; calcium: 0.3wt%; the remainder is magnesium and unavoidable impurities, and the impurity mass is ≤0.2wt%. The purchased magnesium alloy bars (specification: Φ200±5mm) are processed into magnesium alloy billets (Φ200±5mm, 110±10mm) by sawing machine, and the magnesium alloy billets are placed in an oven set at 353℃ for heating. After the billets are heated to the same temperature as the oven, they are kept warm for 3h to obtain the billets to be forged; at the same time, the multi-directional forging die and the rotary forging die are placed in a die heating furnace set at 300℃ for heating. After both dies are heated to the same temperature as the heating furnace, they are kept warm for 2.5h.

[0053] 2) After the forged blank is forged into a rectangular shape by a three-way forging press, the heat-insulated multi-directional forging die is installed on the three-way forging press, and the working inner cavity of the die is sprayed with oil-based graphite for lubrication. Then, the rectangular magnesium alloy billet is placed in the multi-directional forging die for three forgings in different directions. During the multi-directional forging, the pressing speed of the three-way forging press is set to 5m / s, and the pressing amount each time is based on the closing of the multi-directional forging die. The schematic diagram of the deformation of the sample during the multi-directional forging test process is shown in FIG. Figure 2 As shown, after the multi-directional forging is completed, the magnesium alloy billet is forged into a rod using a three-directional forging press. When the magnesium alloy billet is converted between a rod and a rectangular parallelepiped, the forging press speed is set to 5 m / s.

[0054] 3) After multi-directional forging, the magnesium alloy bar continues to be pre-forged on the multi-directional forging die. When it is pre-forged into a round cake shape, the pressing speed of the three-way forging press is set to 5m / s, and the height of the magnesium alloy bar is forged from 110±10mm to 30±10mm. After the pre-forging into a round cake shape, it is placed in an oven set at 353℃ for heating. When the round cake-shaped aluminum alloy billet is heated to the same temperature as the oven, it is kept warm for 3h.

[0055] 4) The heated rotary forging die is installed on a forging press, and the working inner cavity of the die is sprayed with oil-based graphite for lubrication. Subsequently, the heated round cake-shaped magnesium alloy billet is placed in the rotary forging die for rotary forging. The forging speed is 3 mm / s and the rotation speed is 5 r / min. The rotary forging process is the same as in Example 1, and finally a magnesium alloy wheel is obtained.

[0056] In Example 3, horizontal sampling and vertical sampling were performed at the same position of the magnesium alloy wheel in the same manner as in Example 1, and metallographic microstructure analysis was performed on the obtained samples to obtain metallographic microstructure analysis diagrams of the vertical sampling and horizontal sampling of the magnesium alloy wheel in Example 3, as shown in FIG. Figure 8As shown. Comparing (a) and (b), it is found that the microstructures of the vertical and horizontal samples are both composed of equiaxed grains, and all grains have no obvious directionality, and the average grain sizes in the two directions are close; in addition, the heat-resistant strengthening phase containing rare earth elements is uniformly segregated at the grain boundaries, and the large size of the equiaxed grains leads to low strength and plasticity of the wheel.

[0057] The room temperature tensile mechanical properties of the samples were tested, and the room temperature tensile mechanical properties of the vertical and horizontal samples of the magnesium alloy wheel in Example 3 were obtained. Fig. 9 The analysis shows that: Curve 1 is the tensile stress-strain curve of the magnesium alloy wheel sampled in the vertical direction, with a tensile strength of 210MPa, a yield strength of 114MPa, and an elongation of 5.0%; Curve 2 is the tensile stress-strain curve of the magnesium alloy wheel sampled in the horizontal direction, with a tensile strength of 214MPa, a yield strength of 131MPa, and an elongation of 4.1%.

[0058] This indicates that the mechanical properties of the magnesium alloy wheel prepared by this patent are comparable in vertical and horizontal directions, and multi-directional forging eliminates the anisotropy of the magnesium alloy bar billet, making the mechanical properties of various parts of the magnesium alloy wheel similar. Comparative Example 1

[0059] 1) Purchase customized magnesium alloy bars. The customized magnesium alloy billets include the following chemical compositions by mass percentage: aluminum: 6.0wt%; manganese: 0.4wt%; rare earth element Ce: 2.7wt%; rare earth element Sc: 2.0wt%; calcium: 0.3wt%; the remainder is magnesium and unavoidable impurities, and the impurity mass is ≤0.2wt%. The purchased magnesium alloy bars (specification: Φ200±5mm) are processed into magnesium alloy billets (Φ200±5mm, 110±10mm) by sawing machine, and the magnesium alloy billets are placed in an oven set at 350℃ for heating. After the billets are heated to the same temperature as the oven, they are kept warm for 3h to obtain the billets to be forged; at the same time, the primary forging mold and the rotary forging mold are placed in a mold heating furnace set at 300℃ for heating. After both molds are heated to the same temperature as the heating furnace, they are kept warm for 2.5h.

[0060] 2) The heated magnesium alloy billet is pre-forged on the pre-forging die. When it is pre-forged into a round cake shape, the pressing speed of the three-way forging press is set to 5m / s, and the height of the magnesium alloy bar is pre-forged from 110±10mm to 30±10mm. After the pre-forged round cake shape, it is placed in an oven set at 350℃ for heating. When the round cake aluminum alloy billet is heated to the same temperature as the oven, it is kept warm for 3h.

[0061] 3) The heated rotary forging die is installed on a forging press, and the working inner cavity of the die is sprayed with oil-based graphite for lubrication. Subsequently, the heated round cake-shaped magnesium alloy billet is placed in the rotary forging die for rotary forging. The forging speed is 3 mm / s and the rotation speed is 5 r / min. The rotary forging process is the same as in Example 1, and finally a magnesium alloy wheel is obtained.

[0062] Comparative Example 1: Horizontal sampling and vertical sampling were performed at the same position of the magnesium alloy wheel in the same manner as in Example 1, and the obtained samples were subjected to metallographic microstructure analysis to obtain metallographic microstructure analysis diagrams of vertical sampling and horizontal sampling of the magnesium alloy wheel in the comparative example, as shown in FIG. Fig.10 As shown in the figure. The structure of the vertical sampling is distributed in a strip-like manner along the deformation direction, with large deformed grains distributed in the strip-like direction, and a large number of dynamically recrystallized grains distributed around the large deformed grains; the structure of the horizontal sampling is composed of equiaxed grains, and these equiaxed grains have no obvious directionality. In the structures of the vertical and horizontal sampling, heat-resistant strengthening phase particles containing rare earth elements are also distributed in some grains.

[0063] The room temperature tensile mechanical properties of the samples were tested, and the room temperature tensile mechanical properties of the vertical and horizontal samples of the magnesium alloy wheel in Comparative Example 1 were obtained. Fig.11 As shown. The analysis found that the large deformation grains and dynamically recrystallized grains in the vertical direction are distributed in a strip-like structure along the deformation direction, which leads to an increase in its yield strength and tensile strength, while the unevenly distributed strengthening phase causes the appearance of crack sources, which leads to a decrease in its elongation after fracture. Its tensile strength is 335MPa, its yield strength is 244MPa, and its elongation after fracture is 3.7%. In the horizontal direction, it is composed of uniformly distributed equiaxed grains, and the large grain size leads to a decrease in its yield strength and tensile strength. The strengthening phase distributed at the grain boundary causes the appearance of crack sources, which leads to a decrease in its elongation after fracture. Its tensile strength is 263MPa, its yield strength is 170MPa, and its elongation after fracture is 4.3%.

[0064] It shows that the mechanical properties of the magnesium alloy wheel without multi-directional forging are quite different in vertical and horizontal directions, the magnesium alloy bar billet is anisotropic, and the microstructure and mechanical properties of different parts of the magnesium alloy wheel are quite different, which proves the necessity of multi-directional forging.

[0065] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a high-strength and high-toughness magnesium alloy wheel without heat treatment, characterized in that: The following steps are involved: 1) Obtaining a magnesium alloy billet, placing the magnesium alloy billet in an oven at a temperature of 350±5°C for heating, heating to a specified temperature of the oven and then keeping the temperature for 2h to 5h to obtain a billet to be forged, and at the same time, placing a multi-directional forging die and a rotary forging die in a die heating furnace for heating and keeping the temperature, wherein the magnesium alloy billet includes the following chemical components by mass percentage: aluminum: 5.5-6.3wt%; Manganese: 0.2~0.5wt%; Rare earth elements: 3.0~5.5wt%; Calcium: 0.2-0.4wt%; the balance is magnesium and unavoidable impurities, and the impurity mass is ≤0.2wt%; rare earth elements are one or more of La, Ce, Sc, Sm; 2) After the forged blank is forged into a rectangular shape by a three-way forging press, the heat-insulated multi-directional forging die is installed on the three-way forging press, the working inner cavity of the die is sprayed with lubrication, and then the rectangular magnesium alloy blank is placed in the multi-directional forging die for multi-directional forging. After the multi-directional forging is completed, the magnesium alloy blank is forged into a bar by a three-way forging press; 3) The magnesium alloy bar after multi-directional forging is further forged on the multi-directional forging die, and after being forged into a round cake shape, it is placed in an oven for heating and heat preservation; 4) The heated rotary forging die is installed on a forging press, the working inner cavity of the die is sprayed with lubrication, and the heated round cake-shaped magnesium alloy billet is placed in the rotary forging die for rotary forging to obtain a magnesium alloy wheel.

2. The method for preparing a heat-treatment-free high-strength and high-toughness magnesium alloy wheel according to claim 1, characterized in that: In step 1, the multi-directional forging die and the rotary forging die are heated in a die heating furnace at a temperature of 300±5°C, and are kept warm for 2h to 3h after being heated to a specified temperature of the die heating furnace.

3. The method for preparing a heat-treatment-free high-strength and high-toughness magnesium alloy wheel according to claim 1, characterized in that: In step 2, the rectangular magnesium alloy billet is forged three times in different directions.

4. The method for preparing a heat-treatment-free high-strength and high-toughness magnesium alloy wheel according to claim 1, characterized in that: In step 3, the initially forged round cake-shaped magnesium alloy billet is heated in an oven at a temperature of 350±5° C., and then kept at the specified temperature of the oven for 2 h to 5 h.

5. The method for preparing a heat-treatment-free high-strength and high-toughness magnesium alloy wheel according to claim 1, characterized in that: In step 4, the heated round cake-shaped magnesium alloy billet is placed in a rotary forging die for rotary forging, with a forging speed of 2 to 5 mm / s and a rotation speed of 4 to 6 r / min.

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