Optimization of mechanical properties of fine-grained non-combustive magnesium alloy joint by asymmetrical double-sided friction stir welding

The asymmetrical Double-sided Friction Stir Welding (DFSW) technique was applied to the fine-grained non-combustive AMX602 (Mg-6%Al-0.5%Mn-2%Ca) magnesium alloy in order to tailor the appropriate crystallographic texture in the joint and maintain its mechanical properties. The diverse material flows caused by the different welding parameters affected the macrostructure of the DFSW joints. As the travel speed increased, the larger flash and the internal cavity disappeared, and the prior interface residue composed by a linear array of Ca oxide and adjacent coarse grains with lacking of Ca solute, which is a kind of joint defect due to excess heat input, became shorter. The complicated material flows caused by the asymmetrical layout of the double-sided tools produced a relatively weaker texture in the DFSW joint. In addition, compared with the one-sided FSW joint, the asymmetrical DFSW joint shows a relative higher strength since the microstructure in the joints maintains a fine grained structure with slight crystallographic isotropy.