Influence of Tool Offset on Performance of Thin Al-Cu Dissimilar Metal Friction Stir Butt Welded Joint

The 1-mm-thick Al to Cu friction stir welding is successfully performed at the tool offsets toward Al side ranging from 0 to 2 mm. With increasing tool offset, the phenomenon of material sticking to tool shoulder surface is restricted and the area of Al-Cu mixing zone is reduced progressively. As the tool offset is increased from 0 to 1 mm, the weld shows a variation of intermetallic phases from CuAl2 + Cu(9)Al(4)to CuAl(2)and exhibits a lowering in hardness and tensile properties. The 2-mm-offset weld without intermetallic phases discernible exhibits the highest hardness due to the thinness of Cu lamellar and Al-rich compound layers, and the joint featured by a failure at the relatively soft region adjacent to harder Al-Cu mixing zone in a ductile pattern shows the best tensile strength equivalent to 80% of that of the base material.