Effect of arc pulsing in gas tungsten arc welding on microstructure and mechanical properties of Ti–6Al–4V-2.5Cu

Abstract

In the present study, a copper modified titanium alloy (Ti–6Al–4V–2.5Cu) was prepared by using vacuum arc re-melting and processed successfully by hot forging and rolling. The alloy was subjected to solution treatment (ST) at two temperatures, viz. 900 °C and 1010 °C followed by low temperature ageing at 500 °C. The weldments were fabricated from the alloy by using gas tungsten arc welding (GTAW) in continuous current (CC) and pulsed current (PC) modes. The effect of heat treatment and welding mode with and without post weld heat treatment (PWHT) on microstructure, hardness and tensile properties has been studied and compared. Pulsing of current during GTAW prompted in refinement of grains. While CC weldments showed coarser columnar grains, PC weldments reveal finer equiaxed β grains. Ageing and PWHT caused the formation of Ti2Cu intermetallic precipitates in the base alloy as well as in weldments. While the grain refinement in PC weldments manifested in higher strength and percent elongation relative to that of CC weldments, the higher improvement of strength in PWHT condition is due to the combination of both grain refinement and presence of Ti2Cu precipitates. However, the base metal evidenced the better strength properties in both heat treatment conditions than the weldments.