A weldable Mg-Zn series alloy seamless pipe and a preparation method thereof

Abstract

The present application relates to the technical field of alloy material, in particular to a kind of weldable Mg-Zn series alloy seamless pipe and preparation method thereof.The alloy composition of the weldable Mg-Zn series alloy seamless pipe is as follows: zinc 4.5-7.5%, zirconium 0.4-0.9%, rare earth element 1-3%, and the balance is magnesium, in percentage by weight.The specific method comprises the following steps: melting raw materials to obtain alloy solution;mixing the alloy solution with refining agent for refining, and then casting to form Mg-Zn series alloy cast bar;carrying out twice solid solution heat treatment, extrusion forming, to obtain Mg-Zn series alloy pipe;welding the Mg-Zn series alloy pipe under protective gas to obtain the weldable Mg-Zn series alloy seamless pipe.The present application solves the problem that the mechanical properties of existing magnesium alloy pipe after welding are significantly reduced compared with before welding.

Description

Technical Field

[0001] This invention relates to the field of alloy materials technology, specifically to a weldable Mg-Zn alloy seamless pipe and its preparation method. Background Technology

[0002] With the continuous deepening of materials research, the rapid development of basic metallic materials has brought about tremendous changes to the societies, economies, and cultures of countries around the world. Magnesium alloys are the third fastest-growing metallic material after aluminum alloys and steel. Magnesium alloys have advantages such as low density, high thermal conductivity, easy recycling, energy absorption and vibration damping, electromagnetic shielding, easy machining, and high specific strength and specific stiffness, and are used in aerospace, rail transportation, and electronic 3C products. Given the global shortage of non-renewable energy sources such as oil and natural gas and the severe environmental pollution, lightweight, high-performance magnesium alloy materials have attracted widespread market attention.

[0003] However, traditional magnesium alloy pipes suffer from poor plasticity, making it difficult to meet the requirements of subsequent forming processes. This is especially true for welded pipes, whose mechanical properties fail to meet usage requirements after welding. In high and low temperature service environments, the requirements for their mechanical properties are even more stringent. Therefore, the development of a weldable, seamless magnesium alloy pipe resistant to high and low temperatures is crucial for its widespread application.

[0004] To address these challenges, it is necessary to improve the post-weld mechanical properties of magnesium alloys, as well as their mechanical properties under high and low temperature environments, to meet the service requirements of magnesium alloys in complex environments. Currently, the main approach is to improve the mechanical properties of magnesium alloys by adding a certain proportion of rare earth elements. However, magnesium alloy pipes manufactured using existing processes exhibit significantly reduced mechanical properties after welding, failing to meet the strength requirements of magnesium alloys. This is especially true in extreme temperature environments, where the mechanical properties deteriorate significantly after welding, making it impossible to meet the service requirements in complex environments. Summary of the Invention

[0005] To address the problem that the mechanical properties of existing magnesium alloy pipes are significantly reduced after welding compared to before welding, especially the inability of their mechanical properties to meet service requirements in complex environments under extreme temperature conditions, the present invention aims to provide a weldable Mg-Zn alloy seamless pipe and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] The first aspect of the present invention provides a method for preparing a weldable Mg-Zn alloy seamless pipe, wherein the alloy composition of the weldable Mg-Zn alloy seamless pipe is, by weight percentage: 4.5-7.5% zinc, 0.4-0.9% zirconium, 1-3% rare earth elements, and the balance being magnesium.

[0008] The method for preparing the weldable Mg-Zn alloy seamless tube includes the following steps:

[0009] The raw materials containing the alloy components are melted to obtain an alloy solution;

[0010] The alloy solution is mixed with a refining agent for refining, and then cast to form Mg-Zn alloy rods;

[0011] The Mg-Zn alloy casting rod was subjected to two solution heat treatments to obtain a supersaturated solid solution;

[0012] The supersaturated solid solution is extruded to obtain seamless Mg-Zn alloy tubes;

[0013] Welding of Mg-Zn alloy pipes under a protective gas yields weldable seamless Mg-Zn alloy pipes.

[0014] In a preferred embodiment, the rare earth element is at least one selected from La, Ce, Nd, Y, Gd, Ho, Dy, and Er.

[0015] In a preferred embodiment, the raw materials containing the alloy composition include pure zinc, magnesium rare earth master alloy, magnesium zirconium master alloy, and pure magnesium.

[0016] In a preferred embodiment, the melting temperature is 730–760°C.

[0017] In a preferred embodiment, the refining agent is a mixture of potassium chloride, calcium chloride, sodium chloride, barium chloride, calcium fluoride, sodium hexafluoroaluminate, and gadolinium chloride;

[0018] The refining agent contains potassium chloride, calcium chloride, sodium chloride, barium chloride, calcium fluoride, sodium hexafluoroaluminate, and gadolinium chloride in a mass ratio of 49:18:3:16:5:3:6.

[0019] The mass ratio of molten alloy to refining agent is 49:1.

[0020] In a preferred embodiment, the two solution heat treatments are referred to as the first solution heat treatment and the second solution heat treatment, respectively.

[0021] The temperature for the first solution heat treatment is 330–340℃; the temperature for the second solution heat treatment is 380–400℃.

[0022] In a preferred embodiment, the holding time for the first solution heat treatment is 600–660 min; the holding time for the second solution heat treatment is 420–480 min.

[0023] In a preferred embodiment, the specific operation of the two solution heat treatments is as follows:

[0024] After removing the surface oxide scale from the Mg-Zn alloy cast rod, the cast rod is placed in a heat treatment furnace at a temperature of 330–340°C for 600–660 min. Then, the furnace temperature is increased to 380–400°C at a rate of 1–3°C / min and held for 420–480 min. Finally, it is air-cooled.

[0025] In a preferred embodiment, the extrusion speed is 0.5–0.8 m / min, the temperature of the cast rod is 380–400°C, the temperature of the extrusion cylinder is 380–400°C, and the extrusion ratio is 180–200:1.

[0026] In a preferred embodiment, the protective gas is argon, and the flow rate of the protective gas is 7–10 L / min; the welding speed is 80–100 mm / min; the welding method is AC TIG welding; and the diameter of the welding wire is 2–2.6 mm. The composition of the welding wire is the same as that of the profile.

[0027] A second aspect of the present invention provides a weldable Mg-Zn alloy seamless pipe, which is prepared by the preparation method described in the first aspect.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention primarily utilizes the addition of Zn element to achieve dual strengthening effects on magnesium alloys through solid solution strengthening and age-hardening. After aging, nanoscale rod-shaped precipitates and a small amount of basal plate-shaped precipitates are formed in the magnesium alloy matrix, both of which contribute to improving the strength of the pipe. The addition of Zr element not only significantly refines the grains and optimizes the microstructure, but also forms stable compounds with elements such as Fe, Si, and Mn, purifying the melt. Therefore, it solves the problem that the mechanical properties of traditional magnesium alloys after welding cannot meet practical applications. The addition of rare earth elements not only prevents further grain growth during casting but also reduces solid solubility during solidification, further refining the grains; moreover, it gives this Mg-Zn weldable magnesium alloy excellent high and low temperature resistance.

[0030] 2. The weldable Mg-Zn alloy seamless pipe prepared by this invention exhibits the following tensile strengths: at room temperature, the tensile strength before welding reaches ~347 MPa, and the tensile strength after welding reaches ~317 MPa; at 150°C, the tensile strength before welding reaches ~202 MPa, and the tensile strength after welding reaches ~161 MPa; at -196°C, the tensile strength before welding reaches ~474 MPa, and the tensile strength after welding reaches ~400 MPa. This weldable Mg-Zn alloy seamless pipe can be applied in aerospace, rail transportation, and electronic 3C products fields at both room temperature and extreme temperatures. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The first aspect of the present invention provides a method for preparing a weldable Mg-Zn alloy seamless pipe, wherein the alloy composition of the weldable Mg-Zn alloy seamless pipe is, by weight percentage: 4.5-7.5% zinc, 0.4-0.9% zirconium, 1-3% rare earth elements, and the balance being magnesium.

[0034] The method for preparing the weldable Mg-Zn alloy seamless tube includes the following steps:

[0035] The raw materials containing the alloy components are melted to obtain an alloy solution;

[0036] The alloy solution is mixed with a refining agent for refining, and then cast to form Mg-Zn alloy rods;

[0037] The Mg-Zn alloy casting rod was subjected to two solution heat treatments to obtain a supersaturated solid solution;

[0038] The supersaturated solid solution is extruded to obtain Mg-Zn alloy pipes;

[0039] Welding of Mg-Zn alloy pipes under a protective gas yields weldable seamless Mg-Zn alloy pipes.

[0040] In a preferred embodiment, the rare earth element is at least one selected from La, Ce, Nd, Y, Gd, Ho, Dy, and Er.

[0041] In a preferred embodiment, the raw materials containing the alloy composition include pure zinc, magnesium rare earth master alloy, magnesium zirconium master alloy, and pure magnesium.

[0042] In this embodiment of the invention, the addition of Zn element enables the magnesium alloy to have a dual strengthening effect of solid solution strengthening and age strengthening. After aging, nanoscale rod-shaped precipitates and a small amount of basal plate-shaped precipitates are formed in the magnesium alloy matrix. These two types of precipitates play a crucial role in improving the strength of the pipe.

[0043] The addition of Zr significantly refines the grain size and optimizes the microstructure. Furthermore, as a refractory metal, Zr has a strong affinity for gases. Zr not only reduces the solid solubility of Fe in magnesium but also forms the intermetallic compound Fe₂Zr with Fe. It can also form stable compounds with Fe, Si, Mn, and other elements, thus purifying the melt. Therefore, it solves the problem that the mechanical properties of traditional magnesium alloys after welding cannot meet the requirements for practical applications. Specifically, the tensile strength of Mg-Zn magnesium alloy pipes before welding can reach ~347 MPa, and the tensile strength after welding can reach ~317 MPa.

[0044] Adding one or more of the rare earth elements La, Ce, Nd, Y, Gd, Ho, Dy, and Er to Mg-Zn alloys can inhibit further grain growth during casting. Furthermore, their low solid solubility during solidification may lead to compositional supercooling at the solid-liquid interface, increasing the nucleation rate and refining the grains. The addition of rare earth elements improves the alloy's corrosion resistance and also forms high-temperature phase particles, giving this Mg-Zn weldable magnesium alloy excellent high-temperature performance. Specifically, at 150℃, the tensile strength of the magnesium alloy pipe before welding reaches ~202 MPa, and the tensile strength after welding reaches ~161 MPa; at 250℃, the tensile strength of the magnesium alloy pipe before welding reaches ~31 MPa, and the tensile strength after welding reaches ~65 MPa; at -196℃, the tensile strength of the magnesium alloy pipe before welding reaches ~474 MPa, and the tensile strength after welding reaches ~400 MPa.

[0045] In a preferred embodiment, the melting temperature is 730–760°C. Examples include 730°C, 740°C, 750°C, and 760°C.

[0046] In a preferred embodiment, the refining agent is a mixture of potassium chloride, calcium chloride, sodium chloride, barium chloride, calcium fluoride, sodium hexafluoroaluminate, and gadolinium chloride; wherein the mass ratio of potassium chloride, calcium chloride, sodium chloride, barium chloride, calcium fluoride, sodium hexafluoroaluminate, and gadolinium chloride in the refining agent is 49:18:

[0047] The mass ratio of molten alloy to refining agent is 49:1.

[0048] This invention primarily refines the alloy liquid by adding a refining agent. The refining agent removes hydrogen and floating oxide inclusions from the alloy liquid, making it purer. Furthermore, some components of the refining agent decompose at high temperatures, generating gases that readily react with hydrogen to remove it from the alloy liquid. The gas also has a strong adsorption capacity for oxide inclusions, allowing them to escape rapidly from the alloy liquid.

[0049] In a preferred embodiment, the two solution heat treatments are referred to as the first solution heat treatment and the second solution heat treatment, respectively.

[0050] The temperature of the first solution heat treatment is 330–340°C; for example, 330°C, 335°C, 340°C, etc.

[0051] The temperature for the second solution heat treatment is 380–400℃. For example, 380℃, 385℃, 390℃, 395℃, 400℃, etc.

[0052] In a preferred embodiment, the holding time for the first solution heat treatment is 600–660 min; for example, 600 min, 610 min, 620 min, 630 min, 640 min, 650 min, 660 min, etc. The holding time for the second solution heat treatment is 420–480 min; for example, 420 min, 430 min, 440 min, 450 min, 460 min, 470 min, 480 min, etc.

[0053] In a preferred embodiment, the specific operation of the two solution heat treatments is as follows:

[0054] After removing the surface oxide scale from the Mg-Zn alloy cast rod, the cast rod is placed in a heat treatment furnace at a temperature of 330–340°C for 600–660 min. Then, the furnace temperature is increased to 380–400°C at a rate of 1–3°C / min and held for 420–480 min. Finally, it is air-cooled.

[0055] In a preferred embodiment, the extrusion speed is 0.5–0.8 m / min, the temperature of the cast rod is 380–400°C, the temperature of the extrusion cylinder is 380–400°C, and the extrusion ratio is 180–200:1.

[0056] In a preferred embodiment, the protective gas is argon, and the flow rate of the protective gas is 7–10 L / min; the welding speed is 80–100 mm / min; the welding method is AC TIG welding; and the diameter of the welding wire is 2–2.6 mm. The composition of the welding wire is the same as that of the profile.

[0057] A second aspect of the present invention provides a weldable Mg-Zn alloy seamless pipe, which is prepared by the preparation method described in the first aspect.

[0058] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0059] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0060] Unless otherwise specified, the methods described in the following embodiments are conventional methods; the reagents and materials mentioned are commercially available unless otherwise specified.

[0061] The refining agent is a mixture of potassium chloride, calcium chloride, sodium chloride, barium chloride, calcium fluoride, sodium hexafluoroaluminate and gadolinium chloride in a mass ratio of 49:18:3:16:5:3:6.

[0062] Example 1

[0063] A method for preparing weldable Mg-Zn alloy seamless tubing includes the following steps:

[0064] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 6.5%, Zr 0.6%, Y 0.6%, Nd 0.7%, Gd 0.8%, and Mg 90.8%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0065] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0066] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 340℃ for 600 min for the first solution heat treatment. Then, the furnace temperature is heated to 400℃ at a rate of 1℃ / min and held for 480 min for the second solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0067] 4) Welding: The Mg-Zn alloy pipe is subjected to AC TIG welding at a welding speed of 90 mm / min under argon protection. The diameter of the welding wire is 2.4 mm and the alloy composition of the welding wire is the same as that of the base material. The argon flow rate is 10 L / min, and weldable Mg-Zn alloy seamless pipe is obtained.

[0068] Example 2

[0069] A method for preparing weldable Mg-Zn alloy seamless tubing differs from Example 1 in that the solution heat treatment conditions are different. The specific method includes the following steps:

[0070] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 6.5%, Zr 0.6%, Y 0.6%, Nd 0.7%, Gd 0.8%, and Mg 90.8%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0071] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0072] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 360℃ for 720 min for solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0073] 4) Welding: The Mg-Zn alloy pipe is subjected to AC TIG welding at a welding speed of 90 mm / min under argon protection. The diameter of the welding wire is 2.4 mm and the alloy composition of the welding wire is the same as that of the base material. The argon flow rate is 10 L / min, and weldable Mg-Zn alloy seamless pipe is obtained.

[0074] Example 3

[0075] A method for preparing weldable Mg-Zn alloy seamless tubing differs from Example 1 in that the alloy composition is different. The specific method includes the following steps:

[0076] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 6.0%, Zr 0.8%, Y 1.0%, Nd 0.4%, Ce 0.8%, Gd 0.2%, and Mg 90.8%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0077] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0078] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 340℃ for 600 min for the first solution heat treatment. Then, the furnace temperature is heated to 400℃ at a rate of 1℃ / min and held for 480 min for the second solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0079] 4) Welding: The Mg-Zn alloy pipe is subjected to AC TIG welding at a welding speed of 90 mm / min under argon protection. The diameter of the welding wire is 2.4 mm and the alloy composition of the welding wire is the same as that of the base material. The argon flow rate is 10 L / min, and weldable Mg-Zn alloy seamless pipe is obtained.

[0080] Example 4

[0081] A method for preparing weldable Mg-Zn alloy seamless tubing differs from Example 1 in that the alloy composition is different. The specific method includes the following steps:

[0082] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 7.5%, Zr 0.4%, Y 0.6%, Nd 0.2%, Gd 0.2%, and Mg 91.1%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0083] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0084] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 340℃ for 600 min for the first solution heat treatment. Then, the furnace temperature is heated to 400℃ at a rate of 1℃ / min and held for 480 min for the second solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0085] 4) Welding: The Mg-Zn alloy pipe is subjected to AC TIG welding at a welding speed of 90 mm / min under argon protection. The diameter of the welding wire is 2.4 mm and the alloy composition of the welding wire is the same as that of the base material. The argon flow rate is 10 L / min, and weldable Mg-Zn alloy seamless pipe is obtained.

[0086] Example 5

[0087] A method for preparing weldable Mg-Zn alloy seamless tubing differs from Example 1 in that the alloy composition is different. The specific method includes the following steps:

[0088] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 4.5%, Zr 0.9%, Y 1%, Nd 0.4%, Gd 0.8%, La 0.8%, and Mg 91.6%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0089] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0090] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 340℃ for 600 min for the first solution heat treatment. Then, the furnace temperature is heated to 400℃ at a rate of 1℃ / min and held for 480 min for the second solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0091] 4) Welding: The Mg-Zn alloy pipe is subjected to AC TIG welding at a welding speed of 90 mm / min under argon protection. The diameter of the welding wire is 2.4 mm and the alloy composition of the welding wire is the same as that of the base material. The argon flow rate is 10 L / min, and weldable Mg-Zn alloy seamless pipe is obtained.

[0092] Example 6

[0093] A method for preparing weldable Mg-Zn alloy seamless tubing differs from Example 1 in that the alloy composition is different. The specific method includes the following steps:

[0094] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 5.8%, Zr 0.9%, Y 1%, Nd 0.4%, Ce 0.8%, Gd 0.2%, Dy 0.1%, and Mg 90.8%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0095] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0096] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 340℃ for 600 min for the first solution heat treatment. Then, the furnace temperature is heated to 400℃ at a rate of 1℃ / min and held for 480 min for the second solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0097] 4) Welding: The Mg-Zn alloy pipe is subjected to AC TIG welding at a welding speed of 90 mm / min under argon protection. The diameter of the welding wire is 2.4 mm and the alloy composition of the welding wire is the same as that of the base material. The argon flow rate is 10 L / min, and weldable Mg-Zn alloy seamless pipe is obtained.

[0098] Comparative Example 1

[0099] A method for preparing Mg-Zn alloy tubing differs from Example 1 in that welding is not performed. The specific method includes the following steps:

[0100] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 6.5%, Zr 0.6%, Y 0.6%, Nd 0.7%, Gd 0.8%, and Mg 90.8%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0101] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0102] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 340℃ for 600 min for the first solution heat treatment. Then, the furnace temperature is heated to 400℃ at a rate of 1℃ / min and held for 480 min for the second solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0103] Comparative Example 2

[0104] A method for preparing Mg-Zn alloy pipes, differing from Example 2 in that welding is not performed, includes the following steps:

[0105] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 6.5%, Zr 0.6%, Y 0.6%, Nd 0.7%, Gd 0.8%, and Mg 90.8%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0106] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0107] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 360℃ for 720 min for solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0108] Comparative Example 3

[0109] A method for preparing weldable Mg-Zn alloy seamless tubing includes the following steps:

[0110] 1) Weigh the alloy components: By weight percentage, the alloy composition of the Mg-Zn alloy seamless pipe is Zn 6.5%, Y 0.6%, Nd 0.7%, Gd 0.8%, and Mg 91.4%. Place the above alloy components in a crucible, heat to 730-760℃, melt the above alloy components into a liquid state, stir to mix them evenly, and obtain an alloy solution.

[0111] 2) Semi-continuous melting and casting: A refining agent is added to the alloy solution to refine it. After refining, the solution is allowed to stand for 20 minutes. Then, the refined alloy solution is cast into a pure copper crystallizer through a semi-continuous casting process to prepare Mg-Zn alloy rods.

[0112] 3) Heating and extrusion: After removing the surface oxide scale from the cast Mg-Zn alloy rod, it is transferred to a heat treatment furnace and heated to 340℃ for 600 min for the first solution heat treatment. Then, the furnace temperature is heated to 400℃ at a rate of 1℃ / min and held for 480 min for the second solution heat treatment, so that the micron-scale crystalline phase can be dissolved as much as possible. Finally, it is air-cooled to obtain a supersaturated solid solution. Then, the heat-treated and homogenized supersaturated solid solution rod is extruded at a speed of 0.5 m / min, the extrusion barrel temperature is 400℃, and the extrusion ratio is 180:1 to obtain Mg-Zn alloy tubing.

[0113] 4) Welding: The Mg-Zn alloy pipe is subjected to AC TIG welding at a welding speed of 90 mm / min under argon protection. The diameter of the welding wire is 2.4 mm and the alloy composition of the welding wire is the same as that of the base material. The argon flow rate is 10 L / min, and weldable Mg-Zn alloy seamless pipe is obtained.

[0114] The performance of the pipes prepared in the above embodiments was tested.

[0115] Test 1: Effect of different solution heat treatment conditions on the mechanical properties of pipes before and after welding. The mechanical properties of the alloy pipes after welding in Examples 1-2 and the alloy pipes before welding in Comparative Examples 1-2 were tested. The results are shown in Table 1.

[0116] Table 1. Effects of different solution heat treatment conditions on the mechanical properties of pipes before and after welding.

[0117]

[0118]

[0119] As shown in Table 1, under the same alloy composition, the solution heat treatment conditions in Example 2 differ from those in Example 1. Example 2 employs a traditional single heat treatment method, while Example 1 uses an improved stepped heating heat treatment method. Example 1 of this invention improves the solution heat treatment method by using a stepped heating heat treatment method to enhance the uniformity of the microstructure, thereby improving the mechanical properties before and after welding to a certain extent. In particular, the room temperature and high / low temperature mechanical properties are improved before and after welding, and the yield is significantly increased.

[0120] Test 2: The effect of different alloy compositions on the mechanical properties of pipes after welding, see Table 2.

[0121] Table 2 Different Alloy Compositions

[0122] Example 1 6.5％ 0.6％ Y 0.6%, Nd 0.7%, Gd 0.8% 90.8％ Example 3 6.0％ 0.8％ Y1.0%, Nd0.4%, Ce0.8%, Gd0.2% 90.8％ Example 4 7.5％ 0.4％ Y 0.6%, Nd 0.2%, Gd 0.2% 91.1％ Example 5 4.5％ 0.9％ Y1%, Nd0.4%, Gd0.8%, La0.8% 91.6％ Example 6 5.8％ 0.9％ Y1%, Nd0.4%, Ce0.8%, Gd0.2%, Dy0.1% 90.8％ Comparative Example 3 6.5％ - Y 0.6%, Nd 0.7%, Gd 0.8% 91.4％

[0123] Table 3. Effects of different alloy compositions on the mechanical properties of pipes before and after welding.

[0124]

[0125] As can be seen from the results in Table 2-3, by adding appropriate amounts of Zr and rare earth elements to Mg-Zn alloys, seamless Mg-Zn alloy tubes can have good high and low temperature resistance.

[0126] This is mainly because the addition of Zn provides a dual strengthening effect on magnesium alloys through both solid solution strengthening and age-hardening. After aging, nanoscale rod-shaped precipitates and a small amount of basal plate-shaped precipitates are formed in the magnesium alloy matrix, both of which contribute to improving the strength of the pipe. The addition of Zr not only significantly refines the grains and optimizes the microstructure, but also forms stable compounds with elements such as Fe, Si, and Mn, purifying the melt. Therefore, it solves the problem that the mechanical properties of traditional magnesium alloys after welding cannot meet the requirements of practical applications. The addition of rare earth elements not only prevents further grain growth during casting but also reduces solid solubility during solidification, further refining the grains; moreover, it gives this Mg-Zn weldable magnesium alloy excellent high and low temperature resistance.

[0127] Therefore, the weldable Mg-Zn alloy seamless tubing prepared according to the embodiments of the present invention can be applied to aerospace, rail transportation, electronic 3C products and other fields at room temperature and extreme temperatures.

[0128] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing weldable Mg-Zn alloy seamless tubing, characterized in that, The alloy composition of the weldable Mg-Zn alloy seamless pipe, by weight percentage, is: zinc 4.5%~7.5%, zirconium 0.4%~0.9%, rare earth elements 1%~3%, and the balance being magnesium; the rare earth elements are at least one selected from La, Ce, Nd, Y, Gd, Ho, Dy, and Er. The method for preparing the weldable Mg-Zn alloy seamless tube includes the following steps: The raw materials containing the alloy components are melted to obtain an alloy solution; The alloy solution is mixed with a refining agent for refining, and then cast to form Mg-Zn alloy rods; The Mg-Zn alloy casting rods were subjected to two solution heat treatments to obtain a supersaturated solid solution. The specific operation of the two solution heat treatments is as follows: After the oxide scale on the surface of the Mg-Zn alloy casting rods was removed by machining, the cast rods were placed in a heat treatment furnace at a furnace temperature of 330~340℃ and a holding time of 600~660min. Then, the furnace temperature was heated to 380~400℃ at a heating rate of 1~3℃ / min and held for 420~480min. Finally, the rods were air-cooled. The supersaturated solid solution is extruded to obtain seamless Mg-Zn alloy tubes; Mg-Zn alloy pipes are welded under a protective gas to obtain weldable seamless Mg-Zn alloy pipes; the protective gas is argon, and the flow rate of the protective gas is 7~10L / min; the welding speed is 80~100mm / min; the welding method is AC TIG welding; the diameter of the welding wire is 2~2.6mm; the composition of the welding wire is the same as that of the profile.

2. The method for preparing weldable Mg-Zn alloy seamless tubing according to claim 1, characterized in that, The raw materials containing the alloy composition include pure zinc, magnesium rare earth master alloy, magnesium zirconium master alloy, and pure magnesium.

3. The method for preparing weldable Mg-Zn alloy seamless tubing according to claim 1, characterized in that, The smelting temperature is 730~760℃.

4. The method for preparing weldable Mg-Zn alloy seamless tubing according to claim 1, characterized in that, The refining agent is a mixture of potassium chloride, calcium chloride, sodium chloride, barium chloride, calcium fluoride, sodium hexafluoroaluminate, and gadolinium chloride; The refining agent contains potassium chloride, calcium chloride, sodium chloride, barium chloride, calcium fluoride, sodium hexafluoroaluminate, and gadolinium chloride in a mass ratio of 49:18:3:16:5:3:

6. The mass ratio of molten alloy to refining agent is 49:

1.

5. The method for preparing weldable Mg-Zn alloy seamless tubing according to claim 1, characterized in that, The extrusion speed of the extrusion molding is 0.5~0.8 m / min, the temperature of the cast rod is 380~400℃, the temperature of the extrusion cylinder is 380~400℃, and the extrusion ratio is 180~200:

1.

6. A weldable Mg-Zn alloy seamless pipe, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

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