Double-sided laser welding of dissimilar titanium alloys with linear variable thickness

Double-sided laser welding of Ti-6Al-4V and BTi6431S dissimilar titanium alloys with linear variable thickness was investigated. Relationships between penetration depth and the laser power at different welding speeds were first studied utilizing single pass laser welding, and optimized parameters for double-sided laser welding were obtained. The effects of overlap rate on the formation of porosity as well as microstructures and properties of the weld bead were investigated. It is shown that the welding speed and overlap rate play a key role in the formation of porosity. Porosities were found at both welding passes during the double-sided welding, while more porosities with bigger diameter were observed in the second pass. Porosities were minimized by the combination of higher welding speeds (1.5 to 2.5 m/min) and smaller overlap rates. Precipitations and a hard Widmannstatten structure were formed in the heat-affected zone (HAZ) in the BTi6431S side, which results in increase in hardness in this region. In comparison, fine interlaced acicular Martensite alpha' was found in the HAZ of the Ti-6Al-4V side. A hard Widmannstatten structure was also observed in the overlap zone of the double-sided welded bead, which leads to a higher microhardness in this region. The double-sided laser welds exhibited excellent property, and the tensile strength at room temperature and at high temperature (500 A degrees C) was more than 1090 and 750 MPa, respectively.