Study On The Characteristics Of Vppa Welding For 2060 Aluminum-lithium Alloy

The 2060 Aluminum Lithium alloy has received much attention for components of aircraft because of its low density high strength and superb damage tolerance, as the present of third-generation Al-Li alloys. It is necessary to investigate the welding properties of 2060 Al-Li alloy. The problems such as the high input heat, large deflection and poor mechanical properties in the Al-Li alloy sheet welding process have influenced the adhibition of Al-Li alloy. The VPPA welding is beneficial to deal with such difficulties due to its high energy concentration and little defection.In this study, the VPPA welding of 2060-T8 alloy 2.0mm thick sheet by ER4043 wire of 1.6mm in diameter was adopt and the butt joint was used. Compared with different parameters, the optimum parameters were that positive current was 70 A, negative current was 110 A, the proportion of time was 19:4, wire feed rate was 1.76m/min and a travel speed of about 330mm/min.We characterized the microstructure and mechanical properties of 2060 alloy VPPA joint and insure the relationships of both sides above compared with the AC TIG joint. The reason of the VPPA joint improvement was also analyzed and the weld joint contained weld metal and HAZ. The constitutions of weld were EQZ, columnar zone and equiaxed dendrite zone. The base metal was consisted by α-Al and T phase but the T phase, T2 phase, TB phase and Si crystal were appeared in weld metal with the disappearance of T1 phase. The T1 phase was replaced by the TB phase and δ’ phase in the HAZ. The changes in weld joint made a reduction in hardness and tension properties. The dissolution of T1 phase in AC TIG joint HAZ was higher than VPPA joint although the constitutions of two weld joints were similar. The distribution of EQZ was different between VPPA joint and AC TIG joint and it influenced tensile properties deeply. The EQZ was enriched in lower weld joint nearby fusion line in VPPA joint but was found along with the fusion line thin in AC TIG joint. The formation of EQZ was related to the heterogeneous nucleation of Al3 Zr but its distribution was influenced by the fluid flow of molten pool. The ultimate strength of VPPA joint was 401.7MPa higher than the AC TIG joint. Both two joints fractures had mixed-rupture characteristics of quasi-cleavage and dimples but the rupture of VPPA joint was influenced by second-phase particles and blow holes, the deformation difference between EQZ and columnar zone was the main reason for the break of AC TIG joint.The PWHT involved a solution treatment(510℃ for 1 hour and water quenched) and artificial aging(180℃ for 10 hour and air cooled). The main strengthening phase was T phase and both hardness and tension strength improved to 469.3MPa. The rupture was in central weld and the fracture also had quasi-cleavage and dimples mixed characteristics.