A method for preparing high-strength, high-elongation seamless magnesium alloy tubes and their applications

Abstract

A method for preparing high-strength, high-elongation seamless magnesium alloy tubes and its application are disclosed, belonging to the field of magnesium alloy technology. The preparation method includes the following steps: material preparation—melting—preparation of alloy billet—pre-extrusion—piercing needle extrusion—double-stage aging heat treatment—annealing heat treatment, to obtain high-strength, high-elongation Mg-Zn-Nd-Y-Zr seamless magnesium alloy tubes; and the application of high-strength, high-elongation Mg-Zn-Nd-Y-Zr seamless magnesium alloy tubes prepared by the above method in the preparation of oxygen storage cylinders is also disclosed. This invention adopts a micro-alloying design, introducing trace amounts of rare earth elements Y and Nd into ordinary Mg-Zn-Zr alloys. Through the melt purification of rare earth elements Y and Nd, the synergistic strengthening and refining effect of forming dispersed LPSO with Zn elements, high-quality ingots are prepared, thereby realizing the forming of seamless magnesium alloy tubes. This solves the problem of extrusion bar head bending during traditional extrusion and improves material utilization.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy technology, specifically relating to a method for preparing high-strength, high-elongation seamless magnesium alloy tubes and their applications. Background Technology

[0002] Oxygen cylinders are small, portable pressure vessels widely used in various sectors of the national economy and in people's daily lives. Because oxygen cylinders are used in specific environments, our efforts in finding new materials and improving manufacturing processes focus on lighter weight and more reliable mechanical properties. Early oxygen cylinders were primarily made of metal steel, but due to their weight, aluminum alloy was used as an alternative. In the early 1920s, fiberglass was wrapped around steel or aluminum liners to further reduce weight, but this still wasn't lightweight enough. For firefighters, in addition to carrying oxygen cylinders, they also need to carry other firefighting equipment and instruments, highlighting the crucial importance of reducing cylinder weight. Magnesium alloy, being the lightest structural material, would be of great significance if used in oxygen cylinder construction. Summary of the Invention

[0003] To address the shortcomings of the existing technology, the present invention aims to provide a method for preparing high-strength, high-elongation seamless magnesium alloy tubes and their applications.

[0004] This invention is achieved through the following technical solution: a method for preparing a high-strength, high-elongation seamless magnesium alloy tube, comprising the following steps:

[0005] S1. Raw material preparation: Weigh out pure zinc ingots, Mg-25%Zr master alloy, Mg-20%Nd master alloy, Mg-20%Y master alloy and magnesium ingot as raw materials, and the chemical element composition and mass percentage of the raw materials are as follows: Zn: 4.5%~6.5%, Zr: 0.15%~0.45%, Nd: 0.05%~0.4%, Y: 0.01%~0.1%, with the remainder being Mg;

[0006] S2, Smelting:

[0007] First, preheat the crucible to 450°C and add Mg ingots, then continue heating until the Mg ingots in the crucible melt.

[0008] Secondly, when the magnesium liquid temperature reaches 740℃, Zn ingots are added and manually stirred; when the melt temperature reaches 750℃, preheated Mg-20Nd, Mg-20Y, and Mg-25Zr are added in sequence.

[0009] Next, after all the raw materials have melted, add the refining agent and perform gas stirring refining for 25 minutes;

[0010] Finally, the melt was allowed to stand at 760°C for 30 minutes, and then the melt was electromagnetically stirred and semi-continuously cast at a casting temperature of 735°C, an electromagnetic frequency of 15 Hz, and a casting speed of 80 mm / min to obtain an alloy ingot.

[0011] S3. The alloy ingot prepared in step S2 is successively sawed, homogenized, and peeled off with a lathe tool to obtain an alloy billet; the homogenization process is as follows: the alloy ingot is heated to 380°C in a heat treatment furnace and held at that temperature for 6 to 24 hours, and then air-cooled to room temperature.

[0012] S4. Pre-extrusion: The alloy billet prepared in step S3 is placed in an induction furnace and heated to 350°C. After holding at the temperature for half an hour, the alloy billet is hot-extruded on a press with an extrusion ratio of 2 to 5 to obtain a pre-extruded billet.

[0013] S5. Piercing needle extrusion: After reheating the pre-extruded billet from step S4 to 350°C, it is fed into the extrusion cylinder. The pre-extruded billet is then piled up to fill the extrusion cylinder. Then, the piercing needle is moved to pierce the billet. Finally, the movement of the extrusion rod and the piercing needle are controlled simultaneously to extrude the billet and obtain a seamless tube blank.

[0014] S6. Two-stage aging heat treatment: The seamless tube blank prepared in step S5 is first heated to 90°C and held for 4 to 8 hours, then heated to 180°C and held for 8 to 16 hours, and then air-cooled to room temperature.

[0015] S7. Annealing heat treatment: Heat the age-treated seamless tube blank to 360℃ and hold for 2~10 hours, then air cool to room temperature to obtain a high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tube.

[0016] Application of a high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tube prepared by the above method in the manufacture of oxygen storage cylinders.

[0017] Furthermore, the method for fabricating oxygen storage cylinders using high-strength, high-elongation Mg-Zn-Nd-Y-Zr seamless magnesium alloy tubes includes the following steps:

[0018] First, high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tubes are used as the raw material. The diameter of the raw material is 330mm~505mm. The tube blanks are extruded and deformed by a 7500-ton extrusion press to obtain tube blanks with a diameter of 180mm~330mm.

[0019] Secondly, the tube blank is extruded by a double-acting 3600T extruder into seamless tubes with an outer diameter of 160mm~220mm and an inner diameter of 80mm~140mm;

[0020] Next, the seamless tube is heated to 150°C and spun thinned, drawn and spun at both ends using a spinning machine. The final thinning rate is 60%~80%, and oxygen storage cylinder blank is obtained.

[0021] Finally, the oxygen storage cylinder blank is aged at 150℃~300℃ for 8 hours to obtain a magnesium alloy oxygen storage cylinder.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. By adopting microalloying design, trace amounts of rare earth elements Y and Nd are introduced into ordinary Mg-Zn-Zr alloys. Through the melt purification of rare earth elements Y and Nd, the synergistic strengthening and refining effect of forming dispersed LPSO with Zn elements, high-quality ingots are prepared.

[0024] 2. Pre-deformation extrusion and piercing needle extrusion are used to form recrystallized grains with relatively random orientation. High-density precipitates are formed through two-stage aging. Then, annealing is used to dissolve the precipitates and promote the segregation of solute elements (Nd, Y and Zn) at the grain boundaries. This effectively reduces the driving force for recrystallized grain growth, thereby further strengthening the matrix and obtaining a high-strength and high-ductility magnesium alloy seamless tube.

[0025] 3. The use of perforated needle extrusion has enabled the forming of seamless magnesium alloy tubes, solving the problem of bending of the extrusion bar head during traditional extrusion and improving material utilization. Attached Figure Description

[0026] Figure 1 Tensile curves and tensile fracture morphology diagrams of high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tubes.

[0027] Figure 2 This is a SEM image of the seamless tube after heat treatment. Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the following description.

[0029] A method for preparing a high-strength, high-elongation seamless magnesium alloy tube includes the following steps:

[0030] S1. Material preparation: Weigh out pure zinc ingots, Mg-25%Zr master alloy, Mg-20%Nd master alloy, Mg-20%Y master alloy and magnesium ingot as raw materials, and the chemical element composition and mass percentage of the raw materials are: Zn: 5.5%, Zr: 0.45%, Nd: 0.1%, Y: 0.1%, and the remainder is Mg;

[0031] S2, Smelting:

[0032] First, preheat the crucible to 450°C and add Mg ingots, then continue heating until the Mg ingots in the crucible melt.

[0033] Secondly, when the magnesium liquid temperature reaches 740℃, Zn ingots are added and manually stirred; when the melt temperature reaches 750℃, preheated Mg-20Nd, Mg-20Y, and Mg-25Zr are added in sequence.

[0034] Next, after all the raw materials have melted, add the refining agent and perform gas stirring refining for 25 minutes;

[0035] Finally, the melt was allowed to stand at 760°C for 30 minutes, and then the melt was electromagnetically stirred and semi-continuously cast at a casting temperature of 735°C, an electromagnetic frequency of 15 Hz, and a casting speed of 80 mm / min to obtain an alloy ingot with a length of 530 mm.

[0036] S3. The alloy ingot prepared in step S2 is successively sawed, homogenized, and peeled off with a lathe tool to obtain an alloy billet; the homogenization process is as follows: the alloy ingot is heated to 380°C in a heat treatment furnace and held at that temperature for 18 hours, and then air-cooled to room temperature.

[0037] S4. Pre-extrusion: The alloy billet prepared in step S3 is placed in an induction furnace and heated to 350°C. After holding at the temperature for half an hour, the alloy billet is hot-extruded on a 7500-ton press with an extrusion ratio of 2.3 to obtain a pre-extruded billet with a length of 330 mm.

[0038] S5. Piercing needle extrusion: After reheating the pre-extruded billet from step S4 to 360°C, it is fed into the extrusion cylinder. The pre-extruded billet is thickened to fill the extrusion cylinder. Then, the piercing needle is moved to pierce the billet. Finally, the movement of the extrusion rod and the piercing needle are controlled simultaneously to extrude the billet and obtain a seamless tube blank.

[0039] S6. Two-stage aging heat treatment: The seamless tube blank prepared in step S5 is first heated to 90°C and held for 6 hours, then heated to 180°C and held for 12 hours, and then air-cooled to room temperature.

[0040] S7. Annealing heat treatment: The age-treated seamless tube blank is heated to 350℃ and held for 8 hours, then air-cooled to room temperature to obtain a high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tube. Its mechanical properties are shown in Table 1. The tensile strength is 358 MPa, the yield strength is 318 MPa, and the elongation is 18.5%.

[0041] Table 1

[0042] from Figure 1The tensile curves show that the seamless tube has a high yield strength ratio and high plasticity. The fracture morphology shows that it has a large number of dimples, which is a typical ductile fracture, proving that it has good plastic deformation capacity.

[0043] Figure 2 The SEM microstructure of the seamless tube after heat treatment is shown in the figure. Figure 2 As can be seen from the two-stage aging and annealing treatment, it has a small grain size (4.26 μm), and the surface scan microstructure shows a large number of dispersed precipitates, which promote non-basal plane slip and hinder dislocation movement, thus resulting in high strength and elongation.

[0044] Application of a high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tube prepared by the above method in the manufacture of oxygen storage cylinders.

[0045] Furthermore, the method for fabricating oxygen storage cylinders using high-strength, high-elongation Mg-Zn-Nd-Y-Zr seamless magnesium alloy tubes includes the following steps:

[0046] First, high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tubes are used as the raw material. The diameter of the raw material is 505 mm. It is extruded and deformed by a 7500-ton extrusion press to obtain a tube blank with a diameter of 330 mm.

[0047] Secondly, the tube blank is extruded into seamless tubes with an outer diameter of 220 mm and an inner diameter of 140 mm by a double-acting 3600T extrusion press;

[0048] Next, the seamless tube is heated to 150°C and spun thinned, drawn and spun at both ends using a spinning machine. After spinning, the outer diameter is 159 mm, the inner diameter is 142 mm, and the wall thickness is about 8.5 mm, thus obtaining the oxygen storage cylinder blank.

[0049] Finally, the oxygen storage cylinder blank was heated to 180°C and aged for 8 hours to obtain a magnesium alloy oxygen storage cylinder.

[0050] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a high-strength, high-elongation seamless magnesium alloy tube, characterized in that, Includes the following steps: S1. Raw material preparation: Weigh out pure zinc ingots, Mg-25%Zr master alloy, Mg-20%Nd master alloy, Mg-20%Y master alloy and magnesium ingot as raw materials, and the chemical element composition and mass percentage of the raw materials are as follows: Zn: 4.5%~6.5%, Zr: 0.15%~0.45%, Nd: 0.05%~0.4%, Y: 0.01%~0.1%, with the remainder being Mg; S2, Smelting: First, preheat the crucible to 450°C and add Mg ingots, then continue heating until the Mg ingots in the crucible melt. Secondly, when the magnesium liquid temperature reaches 740℃, Zn ingots are added and manually stirred; when the melt temperature reaches 750℃, preheated Mg-20Nd, Mg-20Y, and Mg-25Zr are added in sequence. Next, after all the raw materials have melted, add the refining agent and perform gas stirring refining for 25 minutes; Finally, the melt was allowed to stand at 760°C for 30 minutes, and then the melt was electromagnetically stirred and semi-continuously cast at a casting temperature of 735°C, an electromagnetic frequency of 15 Hz, and a casting speed of 80 mm / min to obtain an alloy ingot. S3. The alloy ingot prepared in step S2 is successively sawed, homogenized, and peeled off with a lathe tool to obtain an alloy billet; the homogenization process is as follows: the alloy ingot is heated to 380°C in a heat treatment furnace and held at that temperature for 6 to 24 hours, and then air-cooled to room temperature. S4. Pre-extrusion: The alloy billet prepared in step S3 is placed in an induction furnace and heated to 350°C. After holding at the temperature for half an hour, the alloy billet is hot-extruded on a press with an extrusion ratio of 2 to 5 to obtain a pre-extruded billet. S5. Piercing needle extrusion: After reheating the pre-extruded billet from step S4 to 360°C, it is fed into the extrusion cylinder. The pre-extruded billet is thickened to fill the extrusion cylinder. Then, the piercing needle is moved to pierce the billet. Finally, the movement of the extrusion rod and the piercing needle are controlled simultaneously to extrude the billet and obtain a seamless tube blank. S6. Two-stage aging heat treatment: The seamless tube blank prepared in step S5 is first heated to 90°C and held for 4 to 8 hours, then heated to 180°C and held for 8 to 16 hours, and then air-cooled to room temperature. S7. Annealing heat treatment: Heat the age-treated seamless tube blank to 350℃ and hold for 2~10 hours, then air cool to room temperature to obtain a high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tube.

2. The application of a high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tube prepared by the method described in claim 1 in the manufacture of oxygen storage cylinders.

3. The application according to claim 2, characterized in that: The method for manufacturing oxygen storage cylinders using high-strength, high-elongation Mg-Zn-Nd-Y-Zr seamless magnesium alloy tubes includes the following steps: First, high-strength, high-elongation Mg-Zn-Nd-Y-Zr magnesium alloy seamless tubes are used as the raw material. The diameter of the raw material is 330mm~505mm. The tube blanks are extruded and deformed by a 7500-ton extrusion press to obtain tube blanks with a diameter of 180mm~330mm. Secondly, the tube blank is extruded by a double-acting 3600T extruder into seamless tubes with an outer diameter of 160mm~220mm and an inner diameter of 80mm~140mm; Next, the seamless tube is heated to 150°C and spun thinned, drawn and spun at both ends using a spinning machine. The final thinning rate is 60%~80%, and oxygen storage cylinder blank is obtained. Finally, the oxygen storage cylinder blank is aged at 150℃~300℃ for 8 hours to obtain a magnesium alloy oxygen storage cylinder.

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