A method for repairing defects of a large ZM6 casting

Abstract

The present application belongs to the technical field of magnesium alloy repair welding, and particularly relates to a method for repairing defects of large ZM6 castings; the method comprises the steps of preparing welding wire, cleaning, preheating, repair welding, cleaning, heat treatment, X-ray inspection and the like. The present application increases the penetration of the repair welding weld, refines the weld grain, and reduces the porosity defects by preparing the active agent powder with a proper proportion, so that the weld is well formed. The process method ensures that the repair welding part will not produce defects such as cracks, incomplete penetration or incomplete fusion, meets the repair welding technical requirements, and improves the production qualification rate of the castings.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnesium alloy repair welding, and particularly relates to a method for repairing defects of large ZM6 castings. BACKGROUND

[0002] With the continuous development of the fields of aerospace and automobiles, the application of magnesium alloys is mainly in the form of castings. Various casting defects are easily generated in the magnesium alloy casting process, and defects are also formed in the machining and transportation processes of the castings, so that the castings become unqualified products, causing material waste and affecting product delivery and use. In view of this problem, in addition to taking corresponding process measures and process control in the magnesium alloy casting process, repair welding of the casting defects has become an essential repair measure. Therefore, the quality requirements for the repair welding of magnesium alloy castings are becoming higher and higher.

[0003] ZM6 is a typical grade of cast magnesium alloy, and is increasingly widely used in the field of aerospace. The addition of the rare earth element Nd to the magnesium alloy makes it have the advantages of high strength, excellent creep resistance and excellent corrosion resistance. In the casting process of large ZM6, the thermal conductivity of the magnesium alloy is large, and the heat dissipation is fast, so some local defects such as cracks, slag inclusions and porosity are inevitably generated, and the repair welding process needs to be performed to repair them. However, in actual production, due to unreasonable pre-welding cleaning, unsuitable repair welding process parameters or large skill gaps of welders, defects such as pores, cracks or incomplete penetration may still be generated in the weld after repair welding, which greatly limits the application range of the magnesium alloy.

[0004] At present, some related patent technologies are studied. A patent document with the application number CN201210543774.X discloses a repair process for surface defects of a magnesium alloy casting, which includes the steps of cleaning and processing defects, cleaning welding wires, preheating, repair welding and heat preservation. The repair process is used to repair large ZM6 castings, but the pore or porosity defects are still not effectively solved. A patent document with the application number CN201110245767.7 discloses a repair welding method for high-strength heat-resistant magnesium alloy. The repair welding method is not easy to generate repair welding cracks, and improves the mechanical properties, but still does not improve the defects such as pores and slag inclusions. Therefore, a repair welding process method suitable for defects of large ZM6 castings needs to be provided to improve the product qualification rate. SUMMARY

[0005] In order to solve the above technical problems, the application provides a method for repairing defects of large ZM6 castings.

[0006] Specifically, the method is implemented by the following technical scheme:

[0007] 1. A method for repairing defects of large ZM6 castings, comprising the following steps:

[0008] (1)Preparation of welding wire: the magnesium alloy rod extruded from cast ZM6 is used as the welding wire, the active agent powder is fully ground and mixed to a particle size of 5-35 μm, then according to the mass percentage, anhydrous ethanol and the active agent powder are mixed in a ratio of 95-99%:1-5% to form a suspension, and the suspension is uniformly coated on the surface of the welding wire, and the suspension is heated in a drying oven at a temperature of 35-50℃ until the ethanol is completely volatilized;

[0009] Further, the diameter of the welding wire is 4-6 mm, and the surface roughness is 6.3 μm or 12.5 μm;

[0010] Further, the active agent powder is composed of the following substances according to the mass percentage: 20-50% ZnCl2, 0-30% CdCl2, 20-50% TiO2, and 0-30% CaO;

[0011] The chemical composition of the magnesium alloy welding wire is consistent with that of the cast base material ZM6. Coating the active agent powder on the surface of the welding wire can increase the penetration of the repair welding seam, ensure that no incomplete penetration or incomplete fusion defects are generated after repair welding, and avoid the multi-layer and multi-pass repair welding process, thereby simplifying the repair welding process and improving the repair welding efficiency. In addition, the interaction between the active agent elements and the molten pool metal changes the metal flow pattern, which is beneficial to the floating and discharge of the gas hole defects in the molten pool, and reduces the material porosity of the magnesium alloy castings.

[0012] (2) Cleaning: an angular grinding machine is used to make a groove with a diameter of 10-30 mm, a groove angle of 45° or 60°, and a depth of 3 mm-10 mm at the defect position of the casting, and the surface is polished with sandpaper and a steel wire brush until the metal luster is exposed, and the oil stains are removed with acetone;

[0013] By pre-preparing the cleaning groove, the actual defect position of the casting is removed. By polishing the surface to luster with sandpaper and a steel wire brush and removing the oil stains with acetone, the surface oxide film, oil stains and other impurities can be effectively removed, and the oxidation and inclusion defects in the magnesium alloy welding process are prevented.

[0014] (3) Preheating: the casting is covered with asbestos board, aluminum silicate cotton or ceramic fiber cloth, and is placed in an oven, and is heated to 150℃-250℃, and is kept at the temperature for 1.5 h-3 h; after preheating, stainless steel, graphite or copper plate is used as the backing plate for the repair welding of the back surface of the casting defect.

[0015] In the application, the casting is covered with asbestos board, aluminum silicate cotton or ceramic fiber cloth to improve the preheating effect and reduce the crack defects after repair welding. The use of stainless steel, graphite or copper plate as the backing plate for repair welding can reduce the heat loss of the casting during welding, and can greatly reduce the generation of magnesium alloy welding cracks. Combined with heating and keeping in the oven, the crack resistance of the large casting base can be improved.

[0016] (4) Repair welding: repair welding is performed by using manual AC tungsten argon arc welding, welding parameters: current 120A-250A, tungsten diameter 4mm-6mm, argon purity 99.99%, argon flow rate 8L / min-15L / min, arc striking and staying time 2s-5s. Welding 1-3 layers, removing slag after upper layer repair welding and then welding next layer;

[0017] (5) Cleaning: cleaning the oxide, slag and other excess substances around the weld, polishing the repair welding part and the cast base material to smooth transition;

[0018] (6) Heat treatment: placing the cast after repair welding in a heat treatment furnace for aging treatment, temperature 200℃-300℃, holding for 1h-6h;

[0019] (7) Inspection: using X-ray to detect the weld fusion zone of the cast to observe the internal quality.

[0020] Under the holding condition, the welding parameters of the present application can effectively reduce the generation of weld defects. The heat treatment can effectively prevent cracks after repair welding. The X-ray inspection can observe the internal quality of the repair welding part.

[0021] In summary, the present application has the following advantages: the welding wire prepared by the present application uses active agent powder with appropriate mixing ratio, which increases the penetration of repair welding seam, refines the weld grain, reduces the porosity defects, and the weld forms well. Through cleaning, preheating, repair welding, cleaning, heat treatment and X-ray inspection, the generation of porosity, slag inclusion and cracks is reduced, and more refined grains can be obtained. The repair welding part does not have defects such as cracks, incomplete penetration, incomplete fusion, undercut, etc., the internal quality of the cast is improved, the repair welding of large ZM6 cast defects is realized, and the qualified rate of cast production is improved. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described in detail, but the present application is not limited to these embodiments, any improvement or replacement within the basic spirit of the present embodiments still belongs to the scope of protection claimed by the present application.

[0023] Example 1

[0024] 1. A method for repairing defects of large ZM6 cast, comprising the following steps:

[0025] (1) Preparing welding wire: using a magnesium alloy rod of ZM6 cast by extrusion forming as welding wire, the diameter is 4mm, and the surface roughness is 12.5μm. Grinding the active agent powder particles of 50% ZnCl2 and 50% TiO2 to 15μm. Mixing 97% anhydrous ethanol and 3% active agent powder to form a mixed solution, uniformly coating the mixed suspension liquid on the surface of the welding wire, and placing it in a drying box to heat at 35℃ until the alcohol is completely volatilized.

[0026] (2) Cleaning: Use an angular grinder to make a groove with a diameter of 20 mm, a cutting angle of 45°, and a depth of 8 mm at the casting defect. Polish the surface with sandpaper and a steel wire brush until the metal luster is exposed. Remove oil stains with acetone.

[0027] (3) Preheating: Cover the casting with ceramic fiber cloth and place it in an oven. Heat to 200°C and maintain for 1.5 h. After preheating, use a stainless steel plate as a backing plate for the back of the casting defect repair welding.

[0028] (4) Repair welding: Use manual AC tungsten argon arc welding. Welding parameters: current 200 A, tungsten electrode diameter 5 mm, argon purity 99.99%, argon flow rate 15 L / min, arc starting and staying time 5 s. Weld 2 layers, remove the slag after the upper layer of repair welding and then weld the next layer.

[0029] (5) Cleaning: Clean the oxides, slag, and other excess materials around the weld. Polish the repair welding area and the casting base material to achieve a smooth transition.

[0030] (6) Heat treatment: Place the repaired casting in a heat treatment furnace for aging treatment at a temperature of 250°C for 3 h.

[0031] (7) X-ray inspection: Use X-ray to inspect the weld fusion zone of the casting to observe the internal quality.

[0032] Example 2

[0033] 1. A method for repairing defects in large ZM6 castings, comprising the following steps:

[0034] (1) Preparing the welding wire: Use a magnesium alloy rod made by extrusion from cast ZM6 as the welding wire, with a diameter of 5 mm and a surface roughness of 12.5 μm. Grind the active agent powder particles to a size of 25 μm by thoroughly mixing 30% ZnCl2, 30% CdCl2, 30% TiO2, and 10% CaO. Mix 98% anhydrous ethanol with 2% active agent powder to form a suspension, and evenly apply the suspension to the surface of the welding wire. Place the wire in a drying box and heat to 45°C until the alcohol evaporates completely.

[0035] (2) Cleaning: Use an angular grinder to make a groove with a diameter of 15 mm, a cutting angle of 60°, and a depth of 3 mm at the casting defect. Polish the surface with sandpaper and a steel wire brush until the metal luster is exposed. Remove oil stains with acetone.

[0036] (3) Preheating: Cover the casting with asbestos board and place it in an oven. Heat to 150°C and maintain for 2 h. After preheating, use a copper plate as a backing plate for the back of the casting defect repair welding.

[0037] (4) Repair welding: Repair welding is performed by using manual AC tungsten argon arc welding, with welding parameters of current 120 A, tungsten electrode diameter 5 mm, argon purity 99.99%, argon flow rate 8 L / min, arc striking and staying time 3 s, and welding layer number 1.

[0038] (5) Cleaning: The oxides, welding slag and other excess materials around the weld are cleaned, and the repair welding part and the base material of the casting are polished to smooth transition.

[0039] (6) Heat treatment: The casting after repair welding is quickly placed in a heat treatment furnace for aging treatment at a temperature of 200°C for 4 h.

[0040] (7) X-ray inspection: The X-ray is used to inspect the fusion zone of the casting welding to observe the internal quality.

[0041] Example 3

[0042] 1. A method for repairing defects of a large ZM6 casting, comprising the following steps:

[0043] (1) Preparing welding wire: A magnesium alloy rod formed by extrusion from a cast ZM6 is used as the welding wire, with a diameter of 6 mm and a surface roughness of 6.3 μm. The active agent powders of 20% ZnCl2, 30% CdCl2, 20% TiO2 and 30% CaO are ground and mixed to a particle size of 5 μm. 99% anhydrous ethanol and 1% active agent powder are mixed to form a mixed solution, which is uniformly coated on the surface of the welding wire, and then placed in a drying box for heating at 40°C until the alcohol is completely volatilized.

[0044] (2) Cleaning: An angular grinder is used to form a groove with a diameter of 25 mm, an opening angle of 45° and a depth of 5 mm at the defect of the casting. The surface is polished with sandpaper and a steel wire brush until the metal luster is exposed, and then the oil stains are removed with acetone.

[0045] (3) Preheating: The casting is covered with aluminum silicate cotton and placed in an oven, and heated to 200°C for 3 h. After preheating, a stainless steel plate is used as a backing plate for repair welding on the back of the casting defect.

[0046] (4) Repair welding: Repair welding is performed by using manual AC tungsten argon arc welding, with welding parameters of current 160 A, tungsten electrode diameter 6 mm, argon purity 99.99%, argon flow rate 10 L / min, arc striking and staying time 2 s, and welding layer number 1.

[0047] (5) Cleaning: The oxides, welding slag and other excess materials around the weld are cleaned, and the repair welding part and the base material of the casting are polished to smooth transition.

[0048] (6) Heat treatment: The casting after repair welding is quickly placed in a heat treatment furnace for aging treatment at a temperature of 200°C for 6 h.

[0049] (7) X-ray inspection: X-ray is used to inspect the fusion zone of the castings to observe the internal quality.

[0050] Example 4

[0051] 1. A method for repairing defects of large ZM6 castings, comprising the following steps:

[0052] (1) Preparation of welding wire: A magnesium alloy rod of ZM6 castings is used as the welding wire by extrusion forming, with a diameter of 5 mm and a surface roughness of 12.5 μm. The active agent powder particles of 40% ZnCl2, 40% TiO2 and 20% CaO are ground to a particle size of 35 μm. A mixture of 96% anhydrous ethanol and 4% active agent powder is prepared, and the mixed suspension is uniformly coated on the surface of the welding wire. The coated welding wire is placed in a drying oven and heated to 35°C until the alcohol is completely volatilized.

[0053] (2) Cleaning: An angular grinder is used to make a groove with a diameter of 30 mm, a groove angle of 60° and a depth of 10 mm at the defect of the casting. The surface is polished with sandpaper and a steel wire brush until the metal luster is exposed. The acetone is used to remove the oil stains.

[0054] (3) Preheating: The casting is covered with a ceramic fiber cloth and placed in an oven, and heated to 250°C for 3 h. After preheating, the graphite plate is used as a backing plate for the repair welding of the back of the casting defect.

[0055] (4) Repair welding: The repair welding is performed by manual alternating tungsten electrode argon arc welding, with the welding parameters as follows: current 250 A, tungsten electrode diameter 5 mm, argon purity 99.99%, argon flow rate 15 L / min, arc striking and staying time 3 s. The welding is performed in 3 layers, and the slag is removed before welding the next layer.

[0056] (5) Cleaning: The oxides, slag and other excess materials around the weld are cleaned, and the repair welding part and the casting base material are polished to smoothly transition.

[0057] (6) Heat treatment: The casting after repair welding is quickly placed in a heat treatment furnace for aging treatment, with a temperature of 300°C and a holding time of 2 h.

[0058] (7) X-ray inspection: X-ray is used to inspect the fusion zone of the castings to observe the internal quality.

[0059] Example 5

[0060] 1. A method for repairing defects of large ZM6 castings, comprising the following steps:

[0061] (1) Preparation of welding wire: ZM6 castings were used as welding wire by extrusion forming, the diameter of the wire was 5 mm, and the surface roughness was 6.3 μm. The active agent powder particles of 40% ZnCl2, 20% CdCl2 and 40% TiO2 were ground to 20 μm. The mixed solution of 95% anhydrous ethanol and 5% active agent powder was prepared, and the mixed suspension liquid was uniformly coated on the surface of the welding wire, and then the welding wire was placed in a drying oven at 50°C until the alcohol was completely volatilized.

[0062] (2) Cleaning: the defects of the castings were made into a groove with a diameter of 10 mm, a groove angle of 45° and a depth of 8 mm by using an angular grinding machine. The surface was polished with sandpaper and steel wire brush until the metal luster was exposed. The oil stains were removed with acetone.

[0063] (3) Preheating: the castings were covered with asbestos board and placed in an oven, and the temperature was raised to 150°C and kept for 2.5 h. After preheating, the back of the castings was repaired with stainless steel plate as backing plate.

[0064] (4) Repair welding: manual AC tungsten argon arc welding was used for repair welding, and the welding parameters were as follows: current 180 A, tungsten electrode diameter 6 mm, argon purity 99.99%, argon flow rate 10 L / min, arc starting and staying time 2 s. Two layers of welding were performed, and the slag was removed before welding the next layer after the upper layer of repair welding.

[0065] (5) Cleaning: the oxides, slag and other excess materials around the weld were cleaned, and the repair welding part and the base material of the castings were polished to smooth transition.

[0066] (6) Heat treatment: the castings after repair welding were quickly placed in a heat treatment furnace for aging treatment at a temperature of 250°C for 1 h.

[0067] (7) X-ray inspection: X-ray was used to detect the weld fusion zone of the castings to observe the internal quality.

[0068] Example 6

[0069] 1. A method for repairing defects of large ZM6 castings, comprising the following steps:

[0070] (1) Preparation of welding wire: ZM6 castings were used as welding wire by extrusion forming, the diameter of the wire was 6 mm, and the surface roughness was 12.5 μm. The active agent powder particles of 30% ZnCl2, 10% CdCl2, 30% TiO2 and 30% CaO were ground to 10 μm. The mixed solution of 99% anhydrous ethanol and 1% active agent powder was prepared, and the mixed suspension liquid was uniformly coated on the surface of the welding wire, and then the welding wire was placed in a drying oven at 35°C until the alcohol was completely volatilized.

[0071] (2) Cleaning: Use an angle grinder to make a bevel with a diameter of 30mm, a cutting angle of 60°, and a depth of 4mm at the defect of the casting. Grind the surface with sandpaper and wire brush until the metal luster is exposed. Remove the oil stains with acetone.

[0072] (3) Preheating: Cover the casting with aluminum silicate cotton, place it in an oven, heat it to 250℃, and keep it at that temperature for 1 hour. After preheating, use a copper plate as a backing plate to weld the defective parts on the back of the casting.

[0073] (4) Repair welding: Manual AC tungsten inert gas welding is used for repair welding. Welding parameters: current 140A, tungsten electrode diameter 6mm, argon purity 99.99%, argon flow rate 15L / min, arc dwell time 4s, number of welding layers 1.

[0074] (5) Cleaning: Clean up oxides, slag and other excess materials around the weld, and grind the repaired weld area to make a smooth transition with the base material of the casting.

[0075] (6) Heat treatment: The welded casting is quickly placed in a heat treatment furnace for aging treatment at 250°C for 4 hours.

[0076] (7) X-ray inspection: X-rays are used to inspect the weld fusion zone of the casting to observe the internal quality.

[0077] Comparative Example 1

[0078] (1) Preparation of welding wire: Magnesium alloy rods formed by extrusion of cast ZM6 are used as welding wire with a diameter of 4mm.

[0079] (2) Cleaning: Make a pit with a diameter of 25mm and a depth of 3mm at the defective part of the casting, polish the surface with sandpaper and wire brush until the metal luster is exposed, and remove the oil stains with acetone.

[0080] (3) No preheating required.

[0081] (4) Repair welding: Manual AC tungsten inert gas welding was used for repair welding. Welding parameters: current 150A, tungsten electrode diameter 4mm, argon purity 99.99%, argon flow rate 12L / min.

[0082] (5) Cleaning: Clean up oxides, slag and other excess materials around the weld, and grind the repaired weld area to make a smooth transition with the base material of the casting.

[0083] (6) Heat treatment: The welded casting is quickly placed in a heat treatment furnace for aging treatment at 250°C for 3 hours.

[0084] (7) X-ray inspection: X-rays are used to inspect the weld fusion zone of the casting to observe the internal quality.

[0085] Comparative Example 2:

[0086] (1) Preparation of welding wire: Magnesium alloy rods formed by extrusion of cast ZM6 are used as welding wire with a diameter of 6mm.

[0087] (2) Cleaning: Make a pit with a diameter of 30mm and a depth of 5mm at the defective part of the casting, polish the surface with sandpaper and wire brush until the metal luster is exposed, and remove the oil stains with acetone.

[0088] (3) Preheating: Place in an oven and heat to 250℃, keep warm for 2 hours.

[0089] (4) Repair welding: Manual AC tungsten inert gas welding was used for repair welding. Welding parameters: current 230A, tungsten electrode diameter 6mm, argon purity 99.99%, argon flow rate 15L / min.

[0090] (5) Cleaning: Clean up oxides, slag and other excess materials around the weld, and grind the repaired weld area to make a smooth transition with the base material of the casting.

[0091] (6) No heat treatment.

[0092] (7) X-ray inspection: X-rays are used to inspect the weld fusion zone of the casting to observe the internal quality.

[0093] For defects on a large ZM6 casting with an external profile of 650mm × φ400mm, the aforementioned process methods from the comparative examples and embodiments were used for defect repair. The test results for porosity and slag inclusion defects at the repaired weld areas of Comparative Examples 1, 2, and Embodiments 1-6 are shown in Table 1. During the inspection process, no cracks were found in Embodiments 1-6, and no defects such as incomplete penetration or lack of fusion were observed at the repaired weld areas.

[0094] Table 1. Defect test results at the weld repair area

[0095]

[0096] Test results of defects in the repaired weld areas showed that the embodiment significantly reduced porosity and slag inclusions, had smaller maximum diameters, and only a maximum of two porosity defects with relatively large average spacing. The improvement in defects was significantly better than that of Comparative Example 1 and Comparative Example 2. This demonstrates that the welding process for repairing defects in large ZM6 castings of the present invention can reduce defects such as porosity, slag inclusions, and cracks in large ZM6 castings, meeting the requirements for welding repair technology.

Claims

1. A method for repairing defects in large ZM6 castings, characterized in that, It comprises the following steps: (1) preparing the welding wire: using cast ZM6 extruded magnesium alloy rod as the welding wire, fully grinding and mixing the active agent powder to a particle size of 5-35 μm, then mixing anhydrous ethanol and the active agent powder in a ratio of 95-99%:1-5% by mass percentage to form a suspension, and then uniformly coating the suspension on the surface of the welding wire and heating in a drying oven until the ethanol is completely volatilized; (2) cleaning: using an angular grinding machine to make a groove with a diameter of 10-30 mm, a groove angle of 45° or 60°, and a depth of 3 mm-10 mm at the defect of the casting, polishing the surface with sandpaper and a steel wire brush until the metal luster is exposed, and removing the oil stains with acetone; (3) preheating: covering the casting with asbestos board, aluminum silicate cotton or ceramic fiber cloth, and placing it in an oven and heating to 150-250℃ for 1.5-3 h; (4) repair welding: using manual alternating tungsten electrode argon arc welding to perform repair welding, welding 1-3 layers, and removing the slag after the upper layer of repair welding and then welding the next layer; (5) cleaning: cleaning the oxides and slag around the weld, and polishing the repair welding part and the casting base material to a smooth transition; (6) heat treatment: quickly placing the casting after repair welding in a heat treatment furnace for aging treatment, at a temperature of 200-300℃ for 1-6 h; (7) inspection: using X-ray to detect the weld fusion zone of the casting and observing the internal quality; The welding wire in step (1) has a diameter of 4-6 mm and a surface roughness of 6.3 μm or 12.5 μm; The active agent powder consists of the following substances by mass percentage: 20-50% ZnCl2, 0-30% CdCl2, 20-50% TiO2, and 0-30% CaO; The repair welding has the following welding parameters: current 120-250 A, tungsten electrode diameter 4-6 mm, argon purity 99.99%, argon flow rate 8-15 L / min, and arc starting and staying time 2-5 s.

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