Influence of heat treatments on microstructural and mechanical properties of Grade 5 titanium friction welds

Abstract

Titanium and its alloys are extensively used in automobile, aerospace and biomedical applications. There are many problems associated with the fusion welding of titanium. Thus, friction welding is an alternative technique for joining titanium without defects. In this study, Ti-6Al-4V (Grade 5 -Titanium alloy) rods were welded using a rotary friction process. Before welding, pre-heat treatments were carried in α-β and β conditions followed by stress relieving on Grade 5 -Titanium alloy rods and some rods were stress relieved after welding. After several trials, friction welding at rotational speed, 1500 rpm and 5 kN upset force obtained defect-free joints. α-β heat treatment enhanced ductility as compared with β heat treatment. α-β heat treatment lead formation of bimodal microstructure in the base metal and β heat treatment produced lamellar Coarse β grains with colonies of α within β grains. Among different heat treatment conditions, high hardness was observed in the α-β heat treatment condition with stress-relieving. Stress-relieving of the welds resulted in an improvement in the hardness because of β precipitates. Fracture morphology is brittle in β treated conditions and ductile in α-β conditions. All welded samples failed away from the weld region irrespective of heat treatments applied, this shows that the weld region is much stronger than the base region due to acicular α and β phases. Mechanical properties were correlated as evidenced by microstructural features.