Microstructure and Residual Stresses in a Friction Stir Welded Butt Joint of as-cast ZK60 Alloy Containing Rare Earths

The effect of a travel speed of 200 mm/min as well as a tool rotational speed of 1200 rpm on butt joint quality of friction stir welding (FSW) ZK60 magnesium casting alloy containing 1.5 wt.% rare earths (ZK60-1.5RE) was investigated to determine microstructure and residual stresses. FSW results in the generation of heterogeneous metallurgical structures consisting of the base material (BM), stirred zone (SZ) and thermo-mechanical affected zone (TMAZ). The stirring action also produced a non-uniform distribution and segregation of intermetalics. The transversal distribution of the longitudinal welding stresses exhibits a M-like shape with mostly tensile stresses under the shoulder region and only one compressive stress peak in the advancing side of the SZ and TMAZ. It could be demonstrated that FSW of ZK60-1.5RE alloy was successful in the welding conditions applied during the present work.