The microstructure and mechanical properties of 0.6 mm thick LY12 aluminum alloy were studied by using the refill friction stir spot welding. According to the characteristics of welded joints

it is divided into the stir zone

thermo mechanically affected zone

heat affected zone and base metal. The results showed that there was no obvious deformation of the specimen after welding

the stir zone formed fine equiaxed grain

TMAZ formation of fibrous tissue

some grains during recovery and recrystallization

the stir zone of maximum hardness

the minimum value of the thermo mechanically affected zone

the rotational speed and welding time increased respectively

and the shear force increased first and then decreased

the shear fracture mode was brittle fracture

the crack started at the boundary and expanded along the thickness of the plate

the distribution of dimple tissue was uniform at the center of fracture

the optimum welding parameters for rotating speed 2 000 r/min

press amount 0.2 mm

the welding time of 3.5 s with the depth of 0.8 mm.