Microstructures and mechanical properties of Ti6Al4V alloy repaired by the technology of point-mode forging and laser repairing

Abstract

In this experiment, the technology of point-mode forging and laser repairing (PF-LR) has been employed for the repair of rolled Ti6Al4V Alloy. Three subtransus heat treatment regimes were used to investigate the microstructure and mechanical properties of the Ti6Al4V repaired parts before and after heat treatment. The results showed that the macrostructure of the repaired zone (RZ) of PF-LRed Ti6Al4V repaired part was equiaxed prior β grains with an average size of 150–350 μm, while the microstructure consistsed of basketweave microstructure. The yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of PF-LRed Ti6Al4V repaired part with 50% repair volume fraction in X-axis direction and Z-axis direction samples exceeded the ASTM B381-2013 standard. After heat treatment 550 °C/4h/air cooling (AC), the microstructure of the RZ and RSZ did not change significantly, but the mechanical properties tended to be similar. After heat treatment at 850 °C/2h/AC, the α laths in the RZ were coarsened or spheroidized, and the EL in the RZ and RSZ decreased dramatically. After heat treatment 940 °C/2h/AC + 550 °C/4h/AC, the microstructure of the RZ was trimodal structure consisting of globular α, lath α and transformed β, the EL of the RZ and RSZ almost disappeared. PF-LRed Ti-6Al-4 V repaired parts are not supposed to choose a heat treatment regime with too high temperature. The 50% PL-LR (i.e. the volume fraction of the RZ was set to 50%) tensile specimen sampled in the Z-axis direction was prepared and the phenomenon for its EL reduction was discussed and analyzed.