A method for repairing large-area defects of rare earth magnesium alloy castings by argon arc welding

Abstract

The present application provides a rare earth magnesium alloy casting large area defect argon arc welding repair method, which comprises the following steps: (1) defect cleaning and welding preparation before repair; (2) repair implementation; (3) heat treatment after repair. The rare earth magnesium alloy casting large area defect argon arc welding repair method can obtain a magnesium alloy casting repair quality without pores, cracks and high strength, realize the repair of large area defect rare earth magnesium alloy casting products, greatly reduce the cost of magnesium alloy casting products, improve the economic benefit, and further promote the wider application of magnesium alloy lightweight structure, which has very important practical significance for promoting the development of green manufacturing.

Description

Technical Field

[0001] This invention relates to an argon arc welding repair method for casting defects in rare earth magnesium alloy castings, belonging to the field of magnesium alloy welding technology. Background Technology

[0002] Magnesium alloys are the lightest metallic structural materials used in engineering applications, possessing advantages such as low density, high specific strength, good electromagnetic shielding, ease of processing, and easy recycling. They are increasingly widely used in aerospace, military, and transportation industries. However, ordinary magnesium alloys have relatively low strength and poor heat and corrosion resistance, limiting their larger-scale application. Since most rare earth elements have high solid solubility with magnesium, adding a certain amount of rare earth elements to magnesium alloys can effectively improve their microstructure and microstructure through good solid solution strengthening and precipitation strengthening effects. This significantly improves the room temperature and high temperature mechanical properties of magnesium alloys, and enhances their corrosion and heat resistance. Therefore, in the field of magnesium alloys, various rare earth-containing magnesium alloys have been developed, such as Mg-Zn-RE-Zr magnesium alloys, Mg-RE-Ag-Zr magnesium alloys, and Mg-Y-RE-Zr magnesium alloys, which possess high strength, heat resistance, and corrosion resistance, greatly expanding the application areas of magnesium alloys. However, rare earth magnesium alloys have poor plasticity at room temperature, making them relatively difficult to process and form. Currently, they are mainly used in the form of castings. Casting defects are common in magnesium alloy castings. In addition to optimizing the casting process, welding repair of casting defects is an essential repair measure.

[0003] In the aerospace, military, and other fields, rare earth magnesium alloy castings are large in size and complex in structure to meet equipment requirements. Therefore, the casting process involves long pouring times, uneven temperatures, and high stress, making them highly susceptible to casting defects such as cracks, porosity, gas bubbles, and inclusions, resulting in large-area defects in the castings. Argon arc welding (argon arc welding) offers advantages such as good molten pool protection, good visibility of the arc and molten pool, and ease of operation, making it suitable for repairing large and complex castings. However, for repairing large-area defects in magnesium alloy castings, the repair process is time-consuming, involves high heat input, and generates significant welding stress, leading to severe oxidation and volatilization of magnesium. Therefore, a suitable argon arc welding repair method is needed to achieve the required repair quality. Developing a high-quality argon arc welding repair method for rare earth magnesium alloy castings can not only improve the mechanical properties and service life of magnesium alloy castings but also significantly reduce the cost of magnesium alloy casting products, further promoting the wider application of lightweight magnesium alloy structures, which is of great practical significance.

[0004] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions in this specification and facilitating understanding by those skilled in the art. The fact that these solutions have been described in the background section of this specification should not be construed as meaning that the aforementioned technical solutions are known to those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address large-area casting defects in large-sized, complex-structured rare-earth magnesium alloy castings. This invention provides an argon arc welding repair method for large-area defects in rare-earth magnesium alloy castings. The method includes techniques such as casting defect cleaning and beveling, selection of filler electrodes, preheating before welding, implementation of the repair, and post-weld heat treatment. This method can achieve a repair quality with no porosity, no cracks, and high strength, reducing the scrap rate of rare-earth magnesium alloy castings and improving economic efficiency.

[0006] The present invention is achieved through the following technical measures: a method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings, comprising the following steps:

[0007] (a) Defect cleaning and preparation for repair welding

[0008] S1: Use non-destructive testing methods to determine the location and distribution of casting defects in rare earth magnesium alloy castings;

[0009] S2: The depth of the bevel is determined based on the location of the deepest casting defect on the surface of the rare earth magnesium alloy casting. The bevel depth should be greater than or equal to 2 mm. An angle α is formed between the sidewall of the bevel and the surface of the rare earth magnesium alloy casting, and the angle α ≤ 45°.

[0010] S3: Use machining equipment to clean the defects, prepare the weld bevel, and trim the bevel to make the overall bevel a frustum shape;

[0011] S4: Use fine-diameter magnesium alloy welding rods as filler material. Before welding, clean the oxide film on the surface of the welding wire and then wipe it clean with ethanol.

[0012] S5: Place the rare earth magnesium alloy casting into a preheating furnace for preheating at a temperature of 200℃~300℃ for 1h~2h.

[0013] (II) Implementation of Welding Repair

[0014] S6: Remove the rare earth magnesium alloy casting that has been preheated in step S5 from the preheating furnace and immediately repair it by manual AC argon arc welding.

[0015] S7: After completing step S6, strike an arc at the bottom of the bevel on the rare earth magnesium alloy casting, heat for 5~10 seconds, and then melt the molten droplet at the tip of the welding rod into the molten pool.

[0016] S8: After completing step S7, move the argon arc welding torch and feed the welding rod, so that the welding torch moves along the circumferential direction of the bevel sidewall, from the bottom sidewall of the bevel to the middle of the bevel, and performs supplementary welding in a spiral upward path to fill the bevel.

[0017] S9: After the bevel is filled, when ending the arc, the welding current should be reduced slowly, and the welding rod should be fed in continuously so that the welding repair position is 2-3mm higher than the surface of the rare earth magnesium alloy casting, for post-weld grinding and correction.

[0018] (III) Insulation and heat treatment after welding repair

[0019] S10: After the welding is completed, the repaired rare earth magnesium alloy casting is transferred to a heat treatment furnace and kept at 200℃~300℃ for 1 hour, and then cooled to room temperature with the furnace; or the repaired rare earth magnesium alloy casting is covered and wrapped with ≥10mm thick thermal insulation asbestos, and the rare earth magnesium alloy casting is cooled to room temperature.

[0020] S11: After the rare earth magnesium alloy casting has been cooled to room temperature, it is subjected to T6 heat treatment, and the surface of the repaired area is ground smooth to complete the argon arc welding repair of large-area defects in the rare earth magnesium alloy casting.

[0021] Preferably, the thickness of the defective part of the rare earth magnesium alloy casting is ≥10mm, and the repair area is: the diameter φ of the bevel on the surface of the rare earth magnesium alloy casting after cleaning the casting defect is ≥30mm, and the distance H between the bottom of the bevel after cleaning the casting defect and the back of the rare earth magnesium alloy casting is ≥2mm.

[0022] Preferably, the diameter of the magnesium alloy welding rod is in the range of 2.0 mm to 3.0 mm, and the other alloying elements of the magnesium alloy welding rod are 92% to 95% of the mass fraction of the corresponding other alloying elements in the magnesium alloy casting being repaired.

[0023] Preferably, the welding current range of the argon arc welding is 150A~180A, and the arc length range is 2mm~3mm.

[0024] Preferably, the tungsten electrode of the argon arc welding torch is cerium tungsten, and the diameter of the tungsten electrode ranges from 2.4 mm to 3.0 mm. The diameter of the ceramic nozzle in the argon arc welding torch ranges from 9.5 mm to 16 mm, and the ceramic nozzle is equipped with a filter screen connector.

[0025] Preferably, dry, moisture-free argon gas with a purity of 99.99% or higher is used for protection during the repair welding process, and the argon gas flow rate is 10~15L / min.

[0026] Preferably, during the repair welding process, the angle between the magnesium alloy welding rod and the center line of the argon arc welding torch is in the range of 80°~100°, and the moving speed of the argon arc welding torch and the filling speed of the magnesium alloy welding rod are 0.2m / min~0.3m / min.

[0027] Preferably, during the repair welding process, the temperature of the rare earth magnesium alloy casting is monitored in real time. If the temperature of the rare earth magnesium alloy casting is lower than 150°C, the repair welding should be stopped, and the rare earth magnesium alloy casting should be placed in a preheating furnace for preheating. The preheating temperature range is 200°C to 300°C, and the preheating time range is 1 hour to 2 hours. Then, the rare earth magnesium alloy casting is removed, the magnesium oxide on the bevel surface is quickly cleaned, and the repair welding is immediately continued.

[0028] Preferably, during the repair welding process, when magnesium alloy oxide deposits are found around the molten pool, the repair welding should be stopped, the magnesium alloy oxide should be quickly cleaned off, and then the repair welding should be carried out.

[0029] Preferably, after the bevel is filled, the arc-closing current is 80A~110A and the descent time is 3~10s when the arc is closed.

[0030] The beneficial effects of this invention can be understood from the description of the above scheme. In this method for repairing large-area defects in rare earth magnesium alloy castings using argon arc welding, after completely and effectively removing the casting defects, the ceramic nozzle of the argon arc welding torch will not interfere with the bevel during the welding process, which facilitates the operation of the argon arc welding repair process. Since magnesium alloys are prone to evaporation and volatilization, especially during the repair of large-area defects, the amount of magnesium alloy evaporation is significant. By using magnesium alloy welding rods with high magnesium content, the elemental loss due to magnesium alloy evaporation can be compensated, making the composition of the repair weld area close to that of the base material. This can effectively control the microstructure and properties of the repair weld area and reduce the inhomogeneity between the repair weld area and the rare earth magnesium alloy casting base material area. Using fine-diameter magnesium alloy welding rods and matching welding current improves the controllability of the weld pool and eliminates the generation of porosity in the weld. Based on effective preheating before welding, the spiral-ascending welding repair path reduces the welding stress generated by long-term welding of large-area defects. Combined with post-weld heat preservation treatment, welding crack defects are completely eliminated. Finally, through appropriate heat treatment, a high-strength, porosity-free, crack-free argon arc welded repair of rare earth magnesium alloy castings can be obtained. Therefore, compared with existing technologies, this invention has outstanding substantive features and significant progress, and its beneficial effects are obvious. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the bevel shape of a rare earth magnesium alloy casting after cleaning defects, as shown in a specific embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the argon arc welding repair path that spirals upward from the bottom of the bevel in a specific embodiment of the present invention.

[0033] Figure 3 This is a diagram illustrating the implementation effect of argon arc welding repair of rare earth magnesium alloy castings according to a specific embodiment of the present invention.

[0034] In the figure: φ - diameter of the bevel on the surface of the rare earth magnesium alloy casting after cleaning casting defects; α - angle between the sidewall of the bevel and the surface of the rare earth magnesium alloy casting; H - distance between the bottom of the bevel after cleaning casting defects and the back of the rare earth magnesium alloy casting. Specific Implementation

[0035] To clearly illustrate the technical features of the present invention, the following detailed embodiments, in conjunction with the accompanying drawings, will be used to describe the present invention.

[0036] The following uses a ZM6 rare earth magnesium alloy casting based on the Mg-Nd-Zn-Zr system as an example to illustrate the argon arc welding repair method for large-area defects in rare earth magnesium alloy castings of the present invention.

[0037] A method for repairing large-area defects in rare earth magnesium alloy castings using argon arc welding, comprising the following steps:

[0038] (a) Defect cleaning and preparation for repair welding

[0039] S1: Use non-destructive testing methods (such as magnetic particle testing, X-ray testing, etc.) to accurately detect and determine the location and distribution of casting defects such as porosity, cracks, and inclusions in rare earth magnesium alloy castings;

[0040] S2: The bevel depth is determined based on the location of the deepest casting defect on the surface of the rare earth magnesium alloy casting, and the bevel depth is 15mm. To avoid interference between the ceramic nozzle of the argon arc welding torch and the bevel during the repair welding process, which would affect the repair welding operation, such as... Figure 1 As shown, an angle α is formed between the bevel sidewall and the surface of the rare earth magnesium alloy casting, wherein the angle α = 45°;

[0041] S3: Use machining equipment (such as pneumatic milling cutters, CNC machine tools, etc.) to clean the defects, removing the deepest casting defects from the surface of the rare earth magnesium alloy casting, preparing a weld bevel, and trimming the bevel after removing the casting defects to make the bevel a frustum shape; the thickness of the defective part of the rare earth magnesium alloy casting is 12mm, such as... Figure 1 As shown, the area to be repaired by welding is: the diameter of the bevel on the surface of the rare earth magnesium alloy casting after cleaning the casting defects is φ = 40 mm, and the distance H between the bottom of the bevel after cleaning the casting defects and the back of the rare earth magnesium alloy casting is 2.5 mm. A precision grinder was used to clean the surface oxide film, casting scale, and other contaminants within a 15 mm range of the bevel surface.

[0042] S4: Use a 3.0mm diameter magnesium alloy welding rod as filler material. The Nd, Zn and Zr elements in the magnesium alloy welding rod are 95% of the corresponding elements in the ZM6 rare earth magnesium alloy casting. Before welding, clean the oxide film on the surface of the welding wire and then wipe it clean with ethanol.

[0043] S5: Place the ZM6 rare earth magnesium alloy casting into a preheating furnace for preheating at a temperature of 200℃ for 1 hour.

[0044] (II) Implementation of Welding Repair

[0045] S6: Remove the ZM6 rare earth magnesium alloy casting that has been preheated in step S5 from the preheating furnace and immediately repair it by manual AC argon arc welding. The welding current of the argon arc welding is 160A and the arc length is 2mm.

[0046] S7: After completing step S6, strike an arc at the bottom of the bevel on the ZM6 rare earth magnesium alloy casting, heat for 8 seconds, melt out the molten pool, and melt the molten droplets at the tip of the welding rod into the molten pool.

[0047] S8: After completing step S7, move the TIG welding torch and feed the welding rod, so that the TIG welding torch moves along the circumferential direction of the bevel sidewall, from the bottom sidewall of the bevel to the middle of the bevel, in a spiral upward path to fill the bevel. The diameter of the ceramic nozzle in the TIG welding torch is 12mm, and the ceramic nozzle has a filter screen connector. The tungsten electrode of the TIG welding torch is cerium tungsten, and the diameter of the tungsten electrode is 2.5mm. During the repair welding process, the angle between the magnesium alloy welding rod and the center line of the TIG welding torch is 90°. The moving speed of the TIG welding torch and the filling speed of the magnesium alloy welding rod are 0.25m / min. During the repair welding process, when magnesium alloy oxide deposits around the molten pool, the repair welding should be stopped, the magnesium alloy oxide should be quickly cleaned off, and then the repair welding should be continued. During the repair welding process, dry, moisture-free argon gas with a purity of 99.99% or higher is used for protection, and the argon gas flow rate is 12L / min. During the repair welding process, the temperature of the ZM6 rare earth magnesium alloy casting should be monitored in real time. If the temperature of the ZM6 rare earth magnesium alloy casting is lower than 150℃, the repair welding should be stopped and the ZM6 rare earth magnesium alloy casting should be placed in a preheating furnace for preheating. The preheating temperature range is 250℃ and the preheating time range is 1 hour. Then, the ZM6 rare earth magnesium alloy casting should be taken out, the magnesium oxide on the bevel surface should be quickly cleaned, and the repair welding should be continued immediately.

[0048] S9: After the bevel is filled, when the arc is closed, the welding current should be reduced slowly. The arc closing current is 100A and the reduction time is 5s. At the same time, the welding rod should continue to be fed so that the repair welding position is 2mm higher than the surface of the rare earth magnesium alloy casting, so that the repair weld has a 2mm excess height for post-weld grinding and correction.

[0049] (III) Insulation and heat treatment after welding repair

[0050] S10: After the welding is completed, the ZM6 rare earth magnesium alloy casting that has been repaired is quickly transferred to a heat treatment furnace and kept at 200°C for 1 hour, and then cooled to room temperature with the furnace.

[0051] S11: After the ZM6 rare earth magnesium alloy casting has cooled to room temperature, it undergoes T6 heat treatment: holding at 530℃ for 16 hours and air cooling; then holding at 205℃ for 16 hours and air cooling. The surface of the repaired area of ​​the ZM6 rare earth magnesium alloy casting, after cooling to room temperature, is ground smooth and corrected, completing the argon arc welding repair of the large-area defect in the ZM6 rare earth magnesium alloy casting.

[0052] The beneficial effects of the present invention can be determined according to Figure 3 The implementation effect diagram of the argon arc welding repair of rare earth magnesium alloy castings shown can be seen from the observation of the upper surface of the repair area, X-ray non-destructive testing, and cross-section of the repair area. It can be shown that the argon arc welding repair method for large-area defects in rare earth magnesium alloy castings provided by this invention can obtain high-quality argon arc welding repair of rare earth magnesium alloy castings without porosity or cracks.

[0053] Technical features not described in this invention can be implemented using existing technologies and will not be elaborated upon here. This invention is not limited to the specific embodiments described above; any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of this invention should also fall within the protection scope of this invention.

Claims

1. A method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings, characterized by: It includes the following steps: (a) Defect cleaning and preparation for repair welding S1: Use non-destructive testing methods to determine the location and distribution of casting defects in rare earth magnesium alloy castings; S2: The depth of the bevel is determined based on the location of the deepest casting defect on the surface of the rare earth magnesium alloy casting. The bevel depth should be greater than or equal to 2 mm. An angle α is formed between the sidewall of the bevel and the surface of the rare earth magnesium alloy casting, and the angle α ≤ 45°. S3: Use machining equipment to clean the defects, prepare the weld bevel, and trim the bevel to make the overall bevel a frustum shape; S4: Use fine-diameter magnesium alloy welding rods as filler material. Before welding, clean the oxide film on the surface of the welding wire and then wipe it clean with ethanol. S5: Place the rare earth magnesium alloy casting into a preheating furnace for preheating at a temperature of 200℃~300℃ for 1h~2h. (II) Implementation of Welding Repair S6: Remove the rare earth magnesium alloy casting that has been preheated in step S5 from the preheating furnace and immediately repair it by manual AC argon arc welding. S7: After completing step S6, strike an arc at the bottom of the bevel on the rare earth magnesium alloy casting, heat for 5~10 seconds, and then melt the molten droplet at the tip of the welding rod into the molten pool. S8: After completing step S7, move the argon arc welding torch and feed the welding rod, so that the welding torch moves along the circumferential direction of the bevel sidewall, from the bottom sidewall of the bevel to the middle of the bevel, and performs supplementary welding in a spiral upward path to fill the bevel. During the repair welding process, if magnesium alloy oxide deposits are found around the molten pool, the repair welding should be stopped, the magnesium alloy oxide should be quickly cleaned off, and then the repair welding should be carried out again. During the repair welding process, the temperature of the rare earth magnesium alloy casting should be monitored in real time. If the temperature of the rare earth magnesium alloy casting is lower than 150℃, the repair welding should be stopped and the rare earth magnesium alloy casting should be placed in a preheating furnace for preheating. The preheating temperature range is 200℃~300℃ and the preheating time range is 1h~2h. Then, the rare earth magnesium alloy casting should be taken out, the magnesium oxide on the bevel surface should be quickly cleaned, and the repair welding should be continued immediately. S9: After the bevel is filled, when ending the arc, the welding current should be reduced slowly, and the welding rod should be fed in continuously so that the welding repair position is 2-3mm higher than the surface of the rare earth magnesium alloy casting, for post-weld grinding and correction. (III) Insulation and heat treatment after welding repair S10: After the welding is completed, the repaired rare earth magnesium alloy casting is transferred to a heat treatment furnace and kept at 200℃~300℃ for 1 hour, and then cooled to room temperature with the furnace; or the repaired rare earth magnesium alloy casting is covered and wrapped with ≥10mm thick thermal insulation asbestos, and the rare earth magnesium alloy casting is cooled to room temperature. S11: After the rare earth magnesium alloy casting has been cooled to room temperature, it is subjected to T6 heat treatment, and the surface of the repaired area is ground smooth to complete the argon arc welding repair of large-area defects in the rare earth magnesium alloy casting.

2. The method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings according to claim 1, characterized in that: The thickness of the defective part of the rare earth magnesium alloy casting is ≥10mm. The repair area is: the diameter φ of the bevel on the surface of the rare earth magnesium alloy casting after cleaning the casting defect is ≥30mm, and the distance H between the bottom of the bevel after cleaning the casting defect and the back of the rare earth magnesium alloy casting is ≥2mm.

3. The method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings according to claim 2, characterized in that: The diameter of the magnesium alloy welding rod is in the range of 2.0mm to 3.0mm, and the other alloying elements of the magnesium alloy welding rod are 92% to 95% of the mass fraction of the corresponding other alloying elements in the magnesium alloy casting being repaired.

4. The method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings according to claim 3, characterized in that: The welding current range of the argon arc welding is 150A~180A, and the arc length range is 2mm~3mm.

5. The method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings according to claim 4, characterized in that: The tungsten electrode of the argon arc welding torch is cerium tungsten, and the diameter of the tungsten electrode ranges from 2.4 mm to 3.0 mm. The diameter of the ceramic nozzle in the argon arc welding torch ranges from 9.5 mm to 16 mm, and the ceramic nozzle is equipped with a filter screen connector.

6. The method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings according to claim 5, characterized in that: During the repair welding process, dry, moisture-free argon gas with a purity of over 99.99% is used for protection, and the argon gas flow rate is 10~15L / min.

7. A method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings according to claim 6, characterized in that: [The method involves...] During the welding process, the angle between the magnesium alloy welding rod and the center line of the argon arc welding torch is between 80° and 100°, and the moving speed of the argon arc welding torch and the filling speed of the magnesium alloy welding rod are between 0.2 m / min and 0.3 m / min.

8. The method for argon arc welding repair of large-area defects in rare earth magnesium alloy castings according to claim 7, characterized in that: After the bevel is filled, the arc-closing current is 80A~110A and the descent time is 3~10s.

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