Microstructures and mechanical properties of laser rapid repaired Ti-6A1-4V alloy

Laser rapid forming has been used to repair three kinds of mis-machining defects in Ti-6Al-4V alloy forgings: the milling groove, the milling surface and the milling rib, respectively. There is dense metallurgical bonding between laser repaired zone and forging matrix. The Al and V elements were uniformly distributed without fluctuation and segregation from the matrix to the laser-repaired zone. The laser-repaired zone exhibited the typical Widmanstaten microstructure consisting of prior huge columnar β grains, in which fine acicular α and α+β basket weave were distributed. In the heat affected zone, the microstructure changed from equiaxed grains to Widmanstaten structure gradually. The results of hardness and room temperature tensile test show that the mechanical properties of repaired samples reached the forging standards of HB5224-1982, and hardness of laser-repaired zone is higher than that of the forging matrix, meanwhile, the plasticity is lower than that of the forging matrix. Therefore, the laser-repaired zone and the forging matrix can be treated as a combination of 'strong + weak', corresponding to the different microstructures of laser-repaired zone and the forging matrix, respectively.