Effect of Pulse Current on Grain Refinement in Ti6Al4V Welds during Pulsed Plasma Arc Welding

Titanium alloys are widely applied in the aerospace field owing to their exceptional properties, but coarse grains can easily form during the welding process, seriously diminishing the mechanical properties of the welded joint. To address this problem, a pulsed current was introduced to refine the grain structure of titanium alloy welds. In this study, we investigated the effect of varying the pulsed current frequency on grain refinement in titanium alloy welds and explored the mechanism of grain refinement using the “overlap welding” method. The results showed that the grain refinement improved with increasing pulse current frequency, particularly at the original β and α grain boundaries. Compared to non-pulsed welding, the original β grain boundary decreased from 305 to 158 μm, and the maximum α grain size decreased from 93.236 to 46.693 μm when the pulse frequency was 100 Hz. Moreover, dendrite fragmentation was identified as the primary mechanism of grain refinement in pulsed plasma arc welding of the Ti6Al4V alloy. The repeated heating of the molten pool by application of the pulsed current caused the dendrite tip to remelt in the pasting region, promoting dendrite fragmentation.