Microstructure, mechanical properties and post-weld heat treatments of dissimilar laser-welded Ti2AlNb/Ti60 sheet

Abstract

Dissimilar joining of Ti2AlNb and Ti60 rolled sheet was performed by laser beam welding. The microstructures and mechanical properties of as-welded and post-weld heat-treated Ti2AlNb/Ti60 joints were investigated by microstructure observation and mechanical properties testing. The fusion zone (FZ) of the as-welded joint consisted of B2/β matrix and small S2 balls. The heat-affected zones HAZ-Ti2AlNb and HAZ-Ti60 for the as-welded joint were characterized as α2 + B2/β + O and α′ + α + β + S2, respectively. The tensile strength and elongation of as-welded sheet were 597.5 MPa and 6.2% at 650 °C, respectively. Most of the plastic deformation was taken place at the side of Ti60 alloy. With the increase in the heat treatment temperature, the anchoring strength between each other of B2/β grains was enhanced by the precipitated lamellar α′ and O grains at the FZ. The depth of the fracture dimples increased with the heat treat temperature increasing. The heat-treated welding joint at 970 °C presented a good balance of the tensile strength and plasticity, where the tensile strength and the elongation were enhanced to 669.7 MPa and 7.1% at 650 °C, respectively.