Microstructure evolution and deformation resistance of heavy-thickness Ti-6Al-4V narrow-gap welded joints

Abstract In this work, 60 mm thick Ti-6Al-4V plates were joined by narrow-gap multi-pass gas tungsten arc welding (GTAW) technology to investigate microstructure and deformation resistance of joints. Depending on cooling condition, mixed weld microstructure consists of stable α phase, martensite α′ phase and few retained β phase. Hardness of joined parts is higher than base metal (BM) mainly contributed by martensite strengthening. A simplified model was established to reveal microstructure evolution during welding thermal cycle. It can also demonstrate that different thermal action effect is responsible for distinct microstructure forms especially martensite α′, which varies hardness in different regions of joints.