Superplastic deformation mechanism and mechanical behavior of a laser-welded Ti–6Al–4V alloy joint

The mechanical behavior and superplastic deformation mechanism of a laser-welded Ti–6Al–4V alloy joint were investigated. Uniaxial tensile tests were performed on welded specimens at 870–920 °C temperature and 10−3 to 10−1 s−1 strain rate. The microstructural evolution of the weld zone was observed under the strains of 43%, 143%, 229%, and 387%. The laser-welded joint was found to have good superplasticity under a suitable strain rate; the highest joint elongation reached 397%. Superplastic deformation in the weld zone accompanied the globularization of the as-welded microstructure. Continuous globularization ensured a good superplasticity of the laser-welded joint. As a major cause of the globularization of lamellar structures in the weld zone, the stress activated the diffusion of Al atoms by changing the chemical potential at the boundaries of the α phase. Consequently, α → β phase transformation occurred. The globularization of the as-weld microstructures was considered to be governed by this transformation and the development of grain boundary sliding.