The butt joints of dissimilar materials（1060-O aluminum alloy

T2 copper）were welded by two kinds of friction stir welding. The effects of two different rotation speeds on the mi crostructure and mechanical properties of the joint were studied by means of metallographic observation

microhardness test

tensile test and SEM fracture scanning

and the microstructure of fracture was also analyzed. The results show that the cross section macromorphology of the dissimilar FSW joint is characterized by the interpenetrating and mixing of the two base metals. The copper alloy particles are dispersed in the aluminum alloy matrix in the nugget zone（NZ）

and the aluminum copper intermetallic compound（IMC）forms at the interface of the two metals in the NZ. The embedded layer depth of copper in the NZ of higher-speed aluminum copper welding joint is larger

the microstructure of the TMAZ on the aluminum side is stirred more violently

and the grains are elongated and twisted more obviously. The mechanical properties of high-speed joints are better than those of lower-speed joints

which have higher joint hardness and tensile properties.