Microstructure, tensile properties of Ti-6Al-4V by ultra high pulse frequency GTAW with low duty cycle

• We compare the characteristics of Ti-6Al-4V titanium alloy for C-GTAW with the different duty cycle of UHFP-GTAW.
• We investigate the effects of heat input on average grain size in FZ, microstructure, tensile properties and fracture behavior.
• A lower heat input by UHFP-GTAW process will decrease the grain size and enhance the ductility.
• The microstructure and tensile properties are improved significantly under the influence of a low duty cycle.

The paper compares the characteristics of Ti-6Al-4V titanium alloy for conventional gas tungsten arc welding (C-GTAW) process with ultra high frequency pulse gas tungsten arc welding (UHFP-GTAW) on the conditions of 50% and 20% duty cycles. The effects of heat input on average intercept of grain size in the fusion zone (FZ), microstructure, tensile properties and fracture behavior were determined. These findings suggest that a lower heat input by UHFP-GTAW process was responsible for better grain size, microstructure and tensile properties except for the effect of ultra high frequency pulse current. In contrast with C-GTAW process, the average intercept of grain size in FZ decreased by 30% at most with 20% duty cycle. The morphology of basketweave structure predominated in the microstructure of FZ by UHFP-GTAW, moreover, a large density and uniform distribution of resultant basketweave were obtained with 20% duty cycle. The samples obtained by UHFP-GTAW generally displayed better ductility, in particular, when the duty cycle was reduced to 20%, the elongation and percentage reduction of area were respectively increased by 140% and 275%. The fractures with 20% duty cycle were mainly located in the base metal, such fractograph showed development of intense shear and deep dimple aggregation, which might be caused by improvement of the ductility.