EWI Proposal No._Date: February 21, 1997

High-strength aluminum alloys are of increasing interest to the aerospace and automotive industry for critical high-strength components. B-pillars and door beams being of particular interest to the automotive industry Refill friction stir spot welding (RFSSW) offers an attractive means of joining these difficult-to-weld alloys since bulk melting is avoided and no exit hole is left. In this study, an aluminum-copper-lithium alloy and AA7075-T6 were refill fiction stir spot welded. The effects of welding parameters on mechanical properties and fracture behavior were examined. Lap shear and cross-tension testing were performed to determine effect of parameters on mechanical strengths. Metallography was used to examine weld morphology. Cross tension and lap shear strengths on the order of 0.6 and 6.7 kN, respectively, were obtained in the Al-Cu-Li material. Cross tension and lap shear strengths on the order of 2.1 and 6.4 kN, respectively, were obtained in 7075-T6. While the Al-Li-Cu material in the T3 temper is lower in cross tension, it is expected that the T8 temper of the Al-Cu-Li material would exhibit similar performance as the AA7075-T6 material. Mixed mode failures including button pull and interface failures were noted across both alloys at identical parameter sets. Fracture surfaces of failure types were characterized via scanning electron microscope.