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.