Similar and dissimilar joining of AA6061-T6 and copper by single and multi-spot friction stirring

Similar and dissimilar friction stir spot welding (FSSW) between AA6061-T6 aluminum alloy and copper with single and multi-spots are prepared with pinless tool and variation of joint lap shear, cross tensile strength are investigated and presented. Finite element models for lap shear and cross tensile loading conditions are created considering the stir zone, thermo-mechanically affected zone, base metal, shoulder penetration and flash region. For similar FSSW joints, failure from joint circumference is mostly observed under lap shear test whereas plug type and interface fracture is observed in cross tensile test. Finite element results predicted maximum stress and strain near these regions. In dissimilar joints failure and separation of the sheets are mostly observed from the joint interface. Formation of intermetallic compound is observed in dissimilar joints having maximum thickness near the joint periphery. Significant amount of grain refinement as compared to the base metal is observed in stir zones due to the dynamic recrystallization. Observation of failure surfaces showed presence of numerous dimples all thought out the surface in similar joints and presence of micro-cracks, rupture in dissimilar joint.