Forming process of a Mg-Y-Zn magnesium alloy bar

Abstract

The present invention discloses a forming process for Mg-Y-Zn magnesium alloy bars, comprising the following steps: A. Melting and semi-continuously casting Mg-Y-Zn alloy bars; B. Performing homogenization annealing treatment on the ingots; C. After the homogenization annealing treatment, taking out the ingot blank and air-cooling it to room temperature, turning the skin, and using a hydraulic press to perform upsetting deformation with a reduction speed of 10-50 mm / s by 30-40% to obtain Mg-Y-Zn alloy bars, and machining them to a diameter of Φ125-135 mm; D. Before extrusion, keeping the blank and the die at 380-460 °C for 1-3 h; after the heat preservation is completed, performing horizontal forward extrusion with an eccentric hole die, the distance between the hole center and the center of the die is 20-35 mm, extruding a bar with a diameter of Φ20 mm from the die hole; the advancing speed of the hydraulic rod is 0.5-3.5 mm / s; the bar is air-cooled after extrusion; E. Performing aging treatment on the extruded bar. The magnesium alloy bars prepared by using this process exhibit high strength and high elongation at low temperature, broadening the application scenarios of magnesium alloy components.

Description

Technical Field

[0001] The present invention relates to the field of magnesium alloy deformation processing, and particularly relates to a plastic forming process for Mg-Y-Zn magnesium alloy bars. Background Art

[0002] Magnesium alloys have the advantages of low density, high specific strength, good damping and shock absorption properties, and easy recyclability, showing broad development prospects in fields such as aerospace and the automotive industry. However, the basal plane slip mechanism that dominates at room temperature in magnesium alloys can only provide 2 independent slip systems, which is less than the 5 required for uniform plastic deformation, resulting in a low room temperature elongation rate. When the temperature is further reduced below zero, the gap between the critical shear stress of non-basal plane slip and basal plane slip in magnesium alloys is even greater. When loaded, it is more difficult to initiate non-basal plane slip, and the dislocation multiplication rate and pile-up degree are higher, leading to a sharp drop in the elongation rate of magnesium alloy components under low temperature conditions and prone to brittle fracture accidents.

[0003] With the continuous improvement of requirements for energy conservation, emission reduction, and environmental protection in the engineering field, the application potential of lightweight magnesium alloy materials is constantly increasing. Especially under low temperature conditions in fields such as aerospace, deep sea exploration, cryogenic separation of petroleum and gas, and storage and transportation of high-pressure fluids, to give full play to the lightweight advantages of magnesium alloys, it is necessary to overcome their low temperature brittleness to prevent brittle fracture of equipment parts without any signs during use, causing personal injury or economic losses. In order to give full play to China's magnesium resource advantages, expand the application scope and added value of magnesium products, it is necessary to develop a series of high-strength, high-toughness and low-temperature-resistant magnesium alloys. Summary of the Invention

[0004] In order to obtain high-strength, tough and low-temperature-resistant magnesium alloy bars, the present invention provides a forming process for Mg-Y-Zn magnesium alloy bars. The specific technical solutions are as follows.

[0005] A forming process for Mg-Y-Zn magnesium alloy bars, characterized in that: the mass percentage composition of Mg-Y-Zn magnesium alloy is Y: 6.0 - 10.0%, Zn: 0.5 - 2.5%, and the rest is Mg and non-removable impurities. The forming process includes the following steps:

[0006] A. Melting and semi-continuously casting Mg-Y-Zn alloy bars;

[0007] B. Performing homogenization annealing treatment on the ingot;

[0008] C. After the homogenization annealing treatment, taking out the ingot blank and air-cooling it to room temperature, turning the skin, and using a hydraulic press to perform upsetting deformation with a reduction rate of 10 - 50 mm / s and a deformation amount of 30 - 40% to obtain Mg-Y-Zn alloy bars, and machining to a diameter of Φ125 - 135 mm;

[0009] D. Before extrusion, heat the blank and the die at 380 - 460 °C for 1 - 3 h; after the heat preservation is completed, take out the ingot blank and load it into the extrusion cylinder, and perform horizontal forward extrusion using an eccentric hole die. The distance between the hole center and the center of the die is 20 - 35 mm, and extrude a rod with a diameter of Φ20 mm from the die hole; during horizontal forward extrusion, the advancing speed of the hydraulic rod is 0.5 - 3.5 mm / s; after the rod is extruded, it is air-cooled;

[0010] E. Perform aging treatment on the extruded rod.

[0011] Preferably, the diameter of the Mg - Y - Zn alloy rod in step A is Φ105 - 120 mm and the length is 140 - 180 mm.

[0012] Preferably, in step B, the annealing process is: heat at 420 - 460 °C for 4 - 6 h, then raise the temperature to 500 - 520 °C and heat for 20 - 30 h.

[0013] Preferably, in step D, the diameter of the extrusion hole is Φ20 mm.

[0014] Preferably, in step E, the aging process is: heat at 180 - 220 °C for 30 - 80 h, and then air-cool.

[0015] Among them, after the aging treatment in step E, the yield strength of the rod at a low temperature of - 100 °C is ≥300 MPa, the tensile strength is ≥380 MPa, and the elongation after fracture is ≥10%.

[0016] In the above solution, the purpose of homogenizing the ingot is to eliminate dendritic segregation, promote compositional uniformity, remove residual stress, etc., so as to improve the plastic forming ability of the ingot blank. The morphology of the LPSO phase in the ingot will change during homogenization annealing. Scientifically selecting the homogenization annealing temperature and holding time can provide the best initial morphology of the LPSO phase for subsequent extrusion and aging. Through a large number of experimental verifications, it is found in this patent application that the two-stage homogenization annealing process of holding at 420 - 460 °C for 4 - 6 h, then heating to 500 - 520 °C and holding for 20 - 30 h followed by air cooling can make the LPSO phase between grains in the alloy regular and the number of LPSO phases in grains scarce. This not only prevents the dynamic recrystallization during extrusion from being inhibited by the LPSO phase in grains, but also promotes the dynamic precipitation of an appropriate amount of LPSO phase inside the recrystallized grains during extrusion; performing 20 - 50% upsetting deformation to avoid cracking of the ingot blank, and at the same time forming a compression basal texture, making the c-axis of some grains in the ingot blank parallel to the upsetting direction, and it is difficult for lattice rotation to occur during the subsequent extrusion deformation process, ultimately resulting in the retention of this crystal orientation. Adopting an extrusion process at 380 - 460 °C with a hydraulic rod propulsion speed of 0.5 - 3.5 mm / s can ensure sufficient recrystallization and grain refinement of the homogenized alloy. The key is to dynamically precipitate needle-shaped LPSO phases with appropriate size and density inside the recrystallized grains. These LPSO phases have an obvious effect of promoting non-basal slip of the magnesium matrix in a low-temperature environment and do not hinder twinning deformation. Using an eccentric hole die makes the metal far from the die hole flow to a certain extent perpendicular to the extrusion direction at the front of the extruded die, thereby making the c-axis of these grains parallel to the extrusion direction, further strengthening this type of texture component, and promoting the generation of tensile twins at low temperature to coordinate strain and make up for the deficiency of slip systems, thus improving the plasticity of the alloy. At low temperature, non-basal slip and twinning simultaneously participate in coordinating deformation, which is crucial for improving the low-temperature toughness of magnesium alloys. The aging system (holding at 180 - 220 °C for 30 - 80 h and air cooling) set based on the material composition, homogenization annealing, and extrusion process can promote the precipitation of an appropriate amount of nano-sized precipitate phases, and improve the strength of the alloy without significantly reducing the elongation. Finally, a high-strength, high-toughness, low-temperature-resistant magnesium alloy rod with a yield strength ≥ 300 MPa, tensile strength ≥ 380 MPa, and elongation after fracture ≥ 10% at -100 °C is obtained.

[0017] The main advantages of the present invention are as follows: Traditional forging and extrusion plastic forming equipment can meet the production of the rod. Through scientific process design and integration, a high-strength, high-toughness, low-temperature-resistant magnesium alloy rod is prepared to meet the urgent needs of aerospace and other fields for magnesium alloys with a wide temperature range, especially low-temperature resistance. Brief Description of the Drawings

[0018] Figure 1 is a macroscopic photograph of the Mg - Y - Zn alloy rod in Example 1;

[0019] Figure 2 It is the pole figure and grain orientation schematic diagram of the Mg-Y-Zn alloy bar of Example 1;

[0020] Figure 3 It is the scanning electron micrograph of the Mg-Y-Zn alloy bar of Example 1;

[0021] Figure 4 It is the pole figure and grain orientation schematic diagram of the Mg-Y-Zn alloy bar of Example 2;

[0022] Figure 5 It is the scanning electron micrograph of the Mg-Y-Zn alloy bar of Example 2;

[0023] Figure 6 It is the pole figure and grain orientation schematic diagram of the Mg-Y-Zn alloy bar of Comparative Example 1;

[0024] Figure 7 It is the scanning electron micrograph of the Mg-Y-Zn alloy bar of Comparative Example 1;

[0025] Figure 8 It is the pole figure and grain orientation schematic diagram of the Mg-Y-Zn alloy bar of Comparative Example 2;

[0026] Figure 9 It is the pole figure and grain orientation schematic diagram of the Mg-Y-Zn alloy bar of Comparative Example 3. Detailed implementation manners

[0027] The present invention has conducted a large number of comparative experiments by adjusting the composition and processing parameters. Some examples are given below to further illustrate the present invention. These examples are used to illustrate the present invention, rather than limiting the present invention. Any improvement of the process of the present invention under the premise of the inventive concept belongs to the scope of protection of the present invention.

[0028] Example 1:

[0029] The Mg-Y-Zn alloy bars with a diameter of Φ105mm and a length of 145mm are melted and semi-continuously cast; the mass percentage content of the alloy is Mg-6.0Y-1.3Zn. The ingot is subjected to homogenization annealing treatment, and the annealing process is: holding at 460°C for 4h and then heating to 520°C for 20h; after the homogenization annealing treatment, the ingot blank is taken out and air-cooled to room temperature, skinned, and subjected to 40% upsetting deformation at a pressing speed of 35mm / s by a hydraulic press to obtain Mg-Y-Zn alloy bars with a diameter of about Φ135mm and a length of 87mm, and machined to a diameter of Φ125mm; before extrusion, the blank and the die are held at 460°C for 1h; after the holding is completed, the ingot blank is taken out and loaded into an extrusion cylinder with a diameter of Φ150mm, and horizontal forward extrusion is carried out using an eccentric hole die. The distance between the hole center and the center of the die is 35mm, and a bar with a diameter of Φ20mm is extruded from the die hole; during horizontal forward extrusion, the advancing speed of the hydraulic rod is 2mm / s; the extruded bar is air-cooled. The extruded bar is subjected to aging treatment, and the process is: holding at 220°C for 30h and air-cooling. The macroscopic photograph of the obtained bar is shown in the appendix Figure 1 , the pole figure and the schematic diagram of the grain orientation are shown in the appendix Figure 2 , the scanning electron micrograph is shown in the appendix Figure 3 , the mechanical property test results at -100°C are shown in Table 1.

[0030] Example 2:

[0031] The Mg-Y-Zn alloy bars with a diameter of Φ120mm and a length of 140mm are melted and semi-continuously cast; the mass percentage content of the alloy is Mg-10.0Y-2.5Zn. The ingot is subjected to homogenization annealing treatment, and the annealing process is: holding at 430°C for 4h and then heating to 505°C for 25h; after the homogenization annealing treatment, the ingot blank is taken out and air-cooled to room temperature, skinned, and subjected to 30% upsetting deformation at a pressing speed of 50mm / s by a hydraulic press to obtain Mg-Y-Zn alloy bars with a diameter of about Φ143mm and a length of 98mm, and machined to a diameter of Φ135mm; before extrusion, the blank and the die are held at 400°C for 2h; after the holding is completed, the ingot blank is taken out and loaded into an extrusion cylinder with a diameter of Φ150mm, and horizontal forward extrusion is carried out using an eccentric hole die. The distance between the hole center and the center of the die is 25mm, and a bar with a diameter of Φ20mm is extruded from the die hole; during horizontal forward extrusion, the advancing speed of the hydraulic rod is 3.5mm / s; the extruded bar is air-cooled. The extruded bar is subjected to aging treatment, and the process is: holding at 180°C for 80h and air-cooling. The pole figure and the schematic diagram of the grain orientation of the obtained bar are shown in the appendix Figure 4 , the scanning electron micrograph is shown in the appendix Figure 5 , the mechanical property test results at -100°C are shown in Table 1.

[0032] Example 3:

[0033] The Mg-Y-Zn alloy bars with a diameter of Φ110 mm and a length of 180 mm were melted and semi-continuously cast; the mass percentage content of the alloy was Mg-7.5Y-0.5Zn. The ingots were subjected to homogenization annealing treatment, and the annealing process was as follows: holding at 420 °C for 4.5 h and then heating to 505 °C and holding for 28 h; after the homogenization annealing treatment, the ingot blanks were taken out and air-cooled to room temperature, skinned, and subjected to 40% upsetting deformation at a pressing speed of 10 mm / s by a hydraulic press to obtain Mg-Y-Zn alloy bars with a diameter of about Φ142 mm and a length of 108 mm, and then machined to a diameter of Φ130 mm; before extrusion, the billet and the die were held at 380 °C for 3 h; after the holding was completed, the ingot blanks were taken out and loaded into an extrusion cylinder with a diameter of Φ150 mm, and horizontal forward extrusion was carried out using an eccentric hole die, the distance between the hole center and the center of the die was 20 mm, and bars with a diameter of Φ20 mm were extruded from the die hole; during horizontal forward extrusion, the advancing speed of the hydraulic rod was 0.5 mm / s; the extruded bars were air-cooled. The extruded bars were subjected to aging treatment, and the process was: holding at 215 °C for 40 h and air-cooling. The mechanical property test results of the obtained bars at -100 °C are shown in Table 1.

[0034] Comparative Example 1:

[0035] The Mg-Y-Zn alloy bars with a diameter of Φ105 mm and a length of 145 mm were melted and semi-continuously cast; the mass percentage content of the alloy was Mg-6.0Y-2.7Zn. The ingots were subjected to homogenization annealing treatment, and the annealing process was as follows: holding at 460 °C for 4 h and then heating to 520 °C and holding for 20 h; after the homogenization annealing treatment, the ingot blanks were taken out and air-cooled to room temperature, skinned, and subjected to 40% upsetting deformation at a pressing speed of 35 mm / s by a hydraulic press to obtain Mg-Y-Zn alloy bars with a diameter of about Φ135 mm and a length of 87 mm, and then machined to a diameter of Φ125 mm; before extrusion, the billet and the die were held at 460 °C for 1 h; after the holding was completed, the ingot blanks were taken out and loaded into an extrusion cylinder with a diameter of Φ150 mm, and horizontal forward extrusion was carried out using an eccentric hole die, the distance between the hole center and the center of the die was 35 mm, and bars with a diameter of Φ20 mm were extruded from the die hole; during horizontal forward extrusion, the advancing speed of the hydraulic rod was 2 mm / s; the extruded bars were air-cooled. The pole figure and grain orientation schematic diagram of the obtained bars are shown in the appendix Figure 6 and the scanning electron micrographs are shown in the appendix Figure 7 and the mechanical property test results at -100 °C are shown in Table 1.

[0036] Comparative Example 2:

[0037] The Mg-Y-Zn alloy bars with a diameter of Φ120 mm and a length of 140 mm are melted and semi-continuously cast; the mass percentage content of the alloy is Mg-10.0Y-2.5Zn. The ingot is subjected to homogenization annealing treatment, and the annealing process is as follows: After holding at 430 °C for 4 h, it is heated to 505 °C and held for 25 h; after the homogenization annealing treatment, the ingot blank is taken out and air-cooled to room temperature, skinned, and subjected to 18% upsetting deformation with a pressing speed of 50 mm / s by a hydraulic press to obtain Mg-Y-Zn alloy bars with a diameter of about Φ132 mm and a length of 115 mm, and then machined to a diameter of Φ125 mm; before extrusion, the blank and the die are held at 400 °C for 2 h; after the holding is completed, the ingot blank is taken out and loaded into an extrusion cylinder with a diameter of Φ150 mm, and horizontal forward extrusion is carried out using an eccentric hole die. The distance between the hole center and the center of the die is 25 mm, and a bar with a diameter of Φ20 mm is extruded from the die hole; during horizontal forward extrusion, the advancing speed of the hydraulic rod is 3.5 mm / s; the extruded bar is air-cooled. The extruded bar is subjected to aging treatment, and the process is as follows: Hold at 180 °C for 80 h and air-cool. The pole figure and grain orientation schematic diagram of the obtained bar are shown in the appendix Figure 8 , and the mechanical property test results at -100 °C are shown in Table 1.

[0038] Comparative Example 3:

[0039] The Mg-Y-Zn alloy bars with a diameter of Φ110 mm and a length of 180 mm are melted and semi-continuously cast; the mass percentage content of the alloy is Mg-7.5Y-0.5Zn. The ingot is subjected to homogenization annealing treatment, and the annealing process is as follows: After holding at 420 °C for 4.5 h, it is heated to 505 °C and held for 28 h; after the homogenization annealing treatment, the ingot blank is taken out and air-cooled to room temperature, skinned, and subjected to 40% upsetting deformation with a pressing speed of 10 mm / s by a hydraulic press to obtain Mg-Y-Zn alloy bars with a diameter of about Φ142 mm and a length of 108 mm, and then machined to a diameter of Φ130 mm; before extrusion, the blank and the die are held at 380 °C for 3 h; after the holding is completed, the ingot blank is taken out and loaded into an extrusion cylinder with a diameter of Φ150 mm, and horizontal forward extrusion is carried out using an eccentric hole die. The distance between the hole center and the center of the die is 15 mm, and a bar with a diameter of Φ20 mm is extruded from the die hole; during horizontal forward extrusion, the advancing speed of the hydraulic rod is 0.5 mm / s; the extruded bar is air-cooled. The extruded bar is subjected to aging treatment, and the process is as follows: Hold at 215 °C for 40 h and air-cool. The pole figure and grain orientation schematic diagram of the obtained bar are shown in the appendix Figure 9 , and the mechanical property test results at -100 °C are shown in Table 1.

[0040] Table 1 Mechanical properties of magnesium alloy components in Examples and Comparative Examples at -100 °C

[0041]

[0042]

[0043] As can be seen from Table 1, the comprehensive mechanical properties of the magnesium alloy bars in Examples 1-3 are significantly better than those in Comparative Examples 1-3 at a low temperature of -100 °C, and they have both high strength and toughness and low-temperature resistance characteristics.

[0044] From Figure 1 it can be seen that the surface of the Mg-Y-Zn magnesium alloy bar prepared in Example 1 is regular, smooth and crack-free. From Figure 2 and 4 it is known that abnormal textures appear in Examples 1 and 2, that is, the basal plane tends to be perpendicular to the extrusion direction. This texture component causes twinning deformation to easily occur when stretching along the extrusion direction, and coordinates plastic strain to generate a high elongation rate when the low-temperature slip system is blocked. From Figure 3 and 5 it can be seen that the magnesium matrix of the extruded bars in Examples 1 and 2 recrystallizes sufficiently and the grain size is significantly refined. The LPSO phase is oriented along the extrusion direction and the volume fraction is moderate, which promotes the improvement of the strength of the bars in the examples.

[0045] Combined with Figure 2 and Figure 6 and Figure 3 and Figure 7 , by comparing Example 1 and Comparative Example 1, when the Zn content exceeds 2.5%, excessive and coarse LPSO phases are formed, which are prone to stress concentration and strain incoordination under loading, thereby reducing both the strength and plasticity of the alloy; in addition, the excessive LPSO phases cause the bars in Comparative Example 1 to fail to form abnormal textures. Combined with Figure 4 and Figure 8 , by comparing Example 2 and Comparative Example 2, it can be seen that too small upsetting deformation is difficult to form abnormal textures, resulting in a significant reduction in both the strength and plasticity of the bars. At the same time, by comparing Example 3 and Comparative Example 3, the distance between the hole center and the center of the die being too close also causes the extruded bars in Comparative Example 3 to be difficult to form abnormal textures (as shown in Figure 9 ), resulting in insufficient low-temperature comprehensive mechanical properties.

[0046] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. Without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims. These all fall within the protection scope of the present invention.

Claims

1. A forming process for Mg-Y-Zn magnesium alloy bars, characterized in that: The mass percentages of the Mg-Y-Zn magnesium alloy components are Y: 6.0 - 10.0%, Zn: 0.5 - 2.5%, and the rest are Mg and non-removable impurities. The preparation process includes the following steps: A. Melting and semi-continuously casting an Mg-Y-Zn alloy ingot; B. Performing homogenization annealing treatment on the ingot; C. After the homogenization annealing treatment, taking out the ingot blank and air-cooling it to room temperature, turning the skin, and using a hydraulic press to perform upsetting deformation of 30 - 40% at a pressing speed of 10 - 50 mm / s to obtain an Mg-Y-Zn alloy ingot blank, and machining it to a diameter of Φ125 - 135 mm; D. Before extrusion, keeping the blank and the die at 380 - 460 °C for 1 - 3 h; after the heat preservation is completed, taking out the ingot blank and loading it into the extrusion cylinder, and performing horizontal forward extrusion using an eccentric hole die. The distance between the hole center and the center of the die is 20 - 35 mm, and extruding a bar with a diameter of Φ20 mm from the die hole; when performing horizontal forward extrusion, the advancing speed of the hydraulic rod is 0.5 - 3.5 mm / s; after the bar is extruded, air-cool it; E. Performing aging treatment on the extruded bar.

2. A forming process for Mg-Y-Zn magnesium alloy bars according to claim 1, characterized in that, The diameter of the Mg-Y-Zn alloy ingot in step A is Φ105 - 120 mm and the length is 140 - 180 mm.

3. A forming process for Mg-Y-Zn magnesium alloy bars according to claim 1, characterized in that, In step B, the annealing process is: keeping at 420 - 460 °C for 4 - 6 h and then heating to 500 - 520 °C and keeping for 20 - 30 h.

4. A forming process for Mg-Y-Zn magnesium alloy bars according to claim 1, characterized in that, In step D, the aperture of the die hole is Φ20 mm.

5. A forming process for Mg-Y-Zn magnesium alloy bars according to claim 1, characterized in that, In step E, the aging process is: keeping at 180 - 220 °C for 30 - 80 h and air-cooling.

6. A forming process for Mg-Y-Zn magnesium alloy bars according to claim 1, characterized in that, After the aging treatment in step E, the yield strength of the bar is ≥300 MPa, the tensile strength is ≥380 MPa, and the elongation after fracture is ≥10% under the low temperature condition of -100 °C.

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