Improving mechanical properties of quasi-continuous-wave laser beam welded 7075 aluminum alloy through microstructural refinement and homogenization of the fusion zone

Laser beam welding of aluminum alloy is challenged by poor mechanical properties of weld joint. Here we employ a quasi-continuous-wave laser beam welding to join 7075-T6 aluminum alloy sheets. High cooling rate, unconstrained multi-directional solidification and high overlapping factor of the quasi-continuous-wave laser beam welding produce a dense fusion zone with homogeneous, refined, and equiaxed grain and dendrite structures. The tailored fusion microstructure is beneficial for improved yield strengthen, enhanced plastic deformation and relieved strain concentration of the weld. A 78.56% strength efficiency and a 26.39% elon-gation efficiency are achieved. The results demonstrate that the microstructural refinement and homogenization of the fusion zone are effective to improve mechanical properties of weld joint.