Local mechanical properties, microstructure, and microtexture in friction stir welded Ti-6Al-4V alloy

Abstract

Local mechanical properties of Ti-6Al-4V butt joints produced by friction stir welding (FSW) were investigated using the shear punch testing and correlated with the global mechanical properties, microstructure, and microtexture evolution of the joint. The conditions for obtaining defect-free joints, under high heat input conditions were determined for the investigated alloy. The shear punch results revealed important differences in yield and ultimate strength between the base material (BM), the heat affected zone close to the BM (HAZ1), the heat affected zone close to the nugget (HAZ2) and two distinct regions in the stirred zone (SZ1 and SZ2). Electron microscopy examination indicated that the microstructure of the BM was converted from equiaxed and elongated α grains with an average size of about 20 µm and a basal transverse texture to a very fine, less than 1 µm diameter, equiaxed microstructure at the center of the SZ, while bimodal structures with lamellar and equiaxed grains were found elsewhere. The analysis of the local mechanical properties indicated that HAZ1 had the lowest mechanical properties of the joint and the obtained results are interpreted in terms of transition texture evolution from the BM to the HAZ using misorientation analysis of high resolution EBSD maps.