Microstructure Evolution and Shaping of Friction Stir Lap WeldedDissimilar Magnesium Alloy Joint

Abstract

Friction stir lap welding (FSLW) experiment has been conducted on 3mm thick AZ80 extruded sheet and 2.3mm thick AZ31B rolled sheet. The influence of the shape of the taper thread mixing head on microstructure has been discussed. Pores forming, hooked defects, interface migration, tissue distribution have been analyzed. The organization of both sides of nugget zone (NZ) is arranged diagonally above, due to the corresponding resultant force along the thread of pin. NZ was collided to form a cascade "onion ring" by plastic microstructure rotating with thread of the pin and dropping from concave of mixing head conical body. Cavity defect was concerned with the poor deformation of AZ80 magnesium alloy placed underneath and relevant organization collision.