Evolution of Microstructure in Friction Stir Processed Dissimilar CuZn37/AA5056 Stir Zone

Dissimilar friction stir processing on CuZn37/AA5056 was performed to study structural and phase evolution of a friction stir zone. Formation of 5-10 μm intermetallic compounds (IMCs) such as Al₂Cu was the main type of diffusion reaction between copper and aluminum. Other alloying elements such as Mg and Zn were forced out of the forming Al₂Cu grains and dissolved in the melt formed due to exothermic effect of the Al₂Cu formation. When solidified, these Zn-enriched zones were represented by α-Al+Al₂Cu+Zn phases or α-Al+Al₂Cu+Zn+MgZn regions. Eutectic Zn+MgZn was undoubtedly formed the melt after stirring had stopped. These zones were proven to be weak ones with respect to pull-off test since MgZn was detected on the fracture surface. Tensile strength of the stirred zone metal was achieved at the level of that of AA5056.