Investigation On Microstructure And Properties Of 5A06 Aluminium Alloy Joints Welded By TIG Repair Welding

The application of 5A06 aluminum alloy in can effectively reduce the weight.Welding is one of the main methods to joining aluminum alloy.But the defects,such as pores,fatigue cracks and corrosion,are easily produced in aluminum alloy welded structures during welding or service,which will bring serious safety hazards in operating aircraft.As an indispensable technology in practical applications,repair welding can eliminate aircraft safety hazards and reduce the occurrence of flight accidents.Therefore,it is significant to study the microstructure and properties of welded joints after repair welding for practical applications.In this paper,the influence of different welding currents on the performance of5A06 aluminum alloy welded joints is studied.Under the optimized welding current,the effects of different repair times?0,1,2,3?on the weld shaping,microstructure,mechanical properties and corrosion properties were discussed.The main results are as follows:?1?The welding current has an obvious influence on the joint shaping.There are pores in the joint under low welding current,which seriously affects the mechanical property of the welded joints.As the welding current increases,the number of pores in the joint gradually decreases.While reaching 70A and 75A,almost no pores were distributed in the joint.Under the currents of 70A and 75A,the tensile strength of the welded joint is significantly increased,which is higher than that under the currents of 60A and 65A.Therefore,70A is regarded as the optimized welding current in this research.?2?Due to the the number of repair welding increased,the diffusion Al₃Mg₂enhanced-phase in welded joint is gradually aggregated into a network distribution.So the mechanical properties of the welded joint are reduced.As the number of repairs increases,the grains in the welded joints gradually grow up.At second and third repair welding,the average grain size is reduced on the retained tissue at the weld because of the recrystallization.However,the large grain is still dominant in weld,so the mechanical properties of the joint continuously deteriorate.?3?During repair welding,the distribution of substructures on the retained structure at the weld is not obvious,as well as the hardness.However,the proportion of substructures in this area increased significantly at second repair welding.Since the substructure is proportional to the degree of softening,the hardness tends to decrease sharply.Both the weld heat affected zone and the retained structure at the weld experience significant thermal deformation during second repair welding.The thermal deformation enhances with the number of repair welding increasing,and the residual stress in the welded joint also increases.?4?There are significant differences in tensile properties under different repair times.With increasing the number of repairs welding,the elongation and tensile strength of welded joints gradually decrease,as well as the fatigue performance.The fatigue strength of the welded joint at median fatigue strength of 2×10⁶ cycles under different repairing times?0,1,2,3?is 96.5 MPa,61.5 MPa,34.3 MPa and 22.2 MPa.?5?Since the Al₃Mg₂ phase precipitates inside the crystal grains as the repairing number increases,the potential difference between the crystal grains and the grain boundary is weakened,so that the intergranular corrosion resistance of the heat-affected zone is gradually improved.The Al₃Mg₂ phase in the grain on the retained structure at the weld is solid solution,the potential difference between the grain and the grain boundary is enhanced,so that the intergranular corrosion resistance is gradually weakened.In this paper,the microstructure,mechanical properties and corrosion properties of thin-plate aluminum alloy welded joints under different repairing times are systematically studied.The research results have a significantly directive effect on promoting the application of repair welding technology in thin-plate aluminum alloy.