Study On Microstructures, Properties And Welding Processes Of 2195 Al-Li Alloy

Due to its high specific strength and well properties in low temperature conditions, Al-Li alloy has been widely used in aerospace industry. But after welding process, it has several problems such as low weld strength coefficient and joint weakness which have bad influence on Al-Li alloy using properties. At present, only limited research on 2195 Al-Li alloy welding process have been published. In this paper, two processing methods have been applied to traditional weld process and a new weld process has been investigated. Microstructures and properties of 2195 Al-Li alloy welds during different welding processes have been researched.Single-pulsed MIG and synergic-pulsed MIG weld experiments have been carried on 5mm thick 2195 Al-Li alloy. The result shows that when synergic-pulsed MIG happening, the pulse current which changed periodically stirred the molten pool liquid. By enhancing the stir effect, synergic-pulsed MIG deduced the pore tendency, refined weld microstructures and enhanced the weld mechanical properties. The strength is 308.54 MPa compared with 165.78 MPa after Single-pulsed MIGLognitudinal magnetic field is employed in traditional MIG, the molten pool is stirred by the electromagnetic force and the solidification process was changed, the crystal grain is refined, eutectic phase distributed evenly, tensile strength and elongation were improved. The weld properties are enhanced greatly after heat treatment. Heat treatment included 510℃×1h solution and 150℃×11h aging.Friction Stir Welding (FSW) experiment is carried on 2195 Al-Li alloy. The results indicates that the welded joint is composed of three distinctive zones:welded nugget zone (WNZ),thermo-mechanically affected zone (TMAZ),heat affected zone (HAZ). When welding speedν=100 mm-min-1, the rotating speedωis between 700rpm and 1300rpm, the tensile strength of the welded joints decreases with the rotating speed improves; when rotating speedω=1000rpm, the welding speedνis between 60mm·min-1 and 140mm-min-1, the tensile strength of the welded joints raises with the welding speed increases.73% joint strength coefficient is obtained atω=1000rpm,ν=140 mm-min-1. The welded joint weakened obviously after weld process, the lowest hardness was located in the retreat thermo-mechanically affected zone.