Microstructure and Mechanical Properties of Ti-6 Al-4V Alloy Joints Welded via the Cold Metal Transfer Method

Abstract

Titanium and titanium alloys have several advantages, such as high specific strength and good corrosion resistance. To improve the stability and welding efficiency of titanium alloy cold metal transfer (CMT) welding, the CMT plus pulse (CMT + P) welding process, which is suitable for the welding of medium- and thick-plate titanium alloys, was first developed. This study aims to investigate the microstructure and mechanical properties of Ti-6Al-4 V alloy joints produced via CMT welding. These results indicate that the CMT + P welding mode is suitable for titanium alloys. The microstructure of the weld metal was composed of acicular α’ martensite, massive α, and Widmanstätten α + β. The microstructures of the fusion zone were composed of acicular α and a large amount of fine α’ martensite. The heat-affected zone consists of acicular martensite, a residual β phase, and an α phase. The maximum microhardness was observed in the fusion zone, the microhardness of the heat-affected zone decreased gradually, and the microhardness of the weld metal was equivalent to that of the base metal. The tensile strength of the joint was almost equal to that of the base metal, and the fracture locations of all the tensile samples were in the base metal, which was related to the element content and microstructure. The impact toughness of the welded joint of the CMT was 33% greater than that of the base metal. The fracture surface of impact toughness is typically ductile with many dimples.