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

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 heataffected zones HAZ-Ti2AINb and HAZ-Ti60 for the aswelded joint were characterized as α2+B2/β+O andα’+α+β+S2,respectively.The tensile strength and elongation of as-welded sheet were 597.5 MPa and 6.2% at650℃,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 at970 ℃ 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℃,respectively.