Microstructure and mechanical characterization of re-melted Ti-6Al-4V and Al-Mg-Si alloys butt weld

It is becoming increasingly difficult to improve tensile strength of dissimilar metals by controlling the formation of intermetallic compounds (IMCs) in the welding of Ti and Al alloys. In this study, a novel laser welding process based on welding-brazing process is proposed, referred to as local remelting process. Metallurgical bonding of incompatible Ti-6Al-4V and Al-Mg-Si alloys was successfully achieved and sound joint with well appearance was obtained. Tensile strength of the joint reached up to 78.6% that of Al substrate, typically the strength is lower than 70%. In order to reveal the effects of local remelting process on the microstructure and tensile strength, SEM, EDS and XRD were applied for the analysis and tensile strength was tested. In addition, FEM simulation was conducted to improve the comprehension of microstructural evolution involved in the process. The results indicate that the joint realized the metallurgical bonding by direct irradiation on aluminum sheet and heat conduction formed by welding on titanium sheet promoted the joining in the interface. Original ordered phase structure was destroyed and a thinner IMCs layer was formed. Both joints present brittle fracture characteristics, but for the joint of remelting process, parts of fracture surface were featured by dimples.