The copper alloy and aluminum alloy were welded by friction stir welding, and the welding technology and mechanical properties of the samples were studied. The results show that in the friction stir welding, aluminum alloy should be as a forward side, copper alloy as a return side. There are Al2 Cu and Al4Cu9 intermetallic compounds generating in the welding joint. From Al side to Cu side, the microhardness is high-low-high peak-low-high trending, and the maximum hardness is in the intermetallic compound la...