Microstructure Evolution of Ti-6Al-4V Laser Weld Joint Fusion Zone in Superplastic Deformation Process

Microstructure evolution of Ti-6Al-4V laser weld joint fusion zone was studied by observing the microstructure during the superplastic deformation process. The results suggested that the fusion zone microstructure first was composed of short lamellars. With the increase of deformation, the microstructure of fusion zone, heat-affected zone and weld was mingle penetrated and the width of the fusion zone was increased. When the sample was breaking, the sample tissue was completely equiaxed and the grain of fusion zone was evenly equiaxed. The deformation process of the fusion zone can be divided into the following three processes:the first microstructure transformation, the second microstructure transformation and the microstructure homogenization.