Microstructure evolution during refill friction spot weldingof aluminium-lithium alloy

The optical microscope, scanning electron microscope(SEM) and electron back scattered diffraction(EBSD) were used to analyze the microstructure in different reigns of refill friction spot welded(RFSW) joints. The results showed that complete dynamic recrystallization occurred in the nugget zone with fine equiaxial grains, and much finer grains existed at the bottom. The nugget zone had no obvious texture. Part dynamic recrystallization occurred in the TMAZ which contained fine equiaxial grains and partly recovery grains with deformed structure. An obvious interface existed between the nugget zone and TMAZ, and its grain was much finer than those on both sides, and the grain boundary was denser.