Abstract: Aviation aluminum alloy 2A12 containing the prefabricated 0.8mm deep and 0.5mm horizontal cracks was repaired by the friction stir method， and the microstructure evolution and mechanical properties of the healing zone were observed and analyzed in details. The results showed that the crack repairing is realized in the reasonable healing process， and the tensile strength R_m and the yield strength R_eL can reach 90.1% and 92.2% of the base metal. The healing zone consists of three different evolution zones， and in the core zone the cracks are repaired by grain fragmentation， growth and recrystallization. The structural softened zone consists of the thermo-mechanically affected zone with obvious plastic deformation and the heat affected zone with obvious grain growth. The surface hardness is similar to that of the upper cross section with the upper section being harder than that of the lower section. The healing core zone consists of many small angle crystals with dislocated lines inside and tiny strengthening phases around.

Key words: friction stir, aluminum alloy 2A12, crack repairing, microstructure, mechanical property