Grain refinement and anisotropy improvement of arc-directed energy deposited Ti-6Al-4V with oscillating laser

Ti-6Al-4V parts fabricated by wire plus arc additive manufacturing (WAAM) usually exhibit columnar grain shapes and serious anisotropy in mechanical properties. This study aims to solve these issues by proposing a laser-assisted WAAM technique in which a vertically oscillating laser beam acts on the molten pool in WAAM. The influences of oscillation laser power on the microstructure and mechanical properties of Ti-6Al-4V parts built in WAAM are revealed and discussed. The oscillation laser can refine prior-beta grains in WAAM. As the laser power increases, the depths of laser fusion lines in deposited layers increase, the size of prior-beta grains decreases first and then increases, and both the microhardness and ultimate tensile strength (UTS) increase first and then decrease. At a laser power of 1600 W, the columnar prior-beta grains are completely transformed into equiaxed shapes. The UTS values in the vertical and horizontal directions reach 1322 and 1309 MPa, respectively, respectively 30.5% and 15.7% higher than those of the WAAM sample. Meanwhile, the indices of plane anisotropy of UTS and elongation decrease by 90.6% and 76.4%, respectively.