Effect of multiple-pass friction stir processing on microstructure and tensile properties of a cast aluminum–silicon alloy

Five-pass friction stir processing (FSP), with 50% overlap, was conducted on cast A356. Overlapping FSP did not exert a significant effect on the size and distribution of the Si particles. In the as-FSP condition, the strength and ductility of the transitional zones between two FSP passes were slightly lower than those of the nugget zones. Further, in the multiple-pass material the strength of the previously processed zones was lower than that of the subsequent processed zones due to overaging from the FSP thermal cycles.