Fatigue assessment of refill friction stir spot weld in AA 2024-T3 similar joints

摘要

Refill friction stir spot welding is a solid-state process technology that is suitable for welding lightweight materials in similar or dissimilar overlapped configuration. In this study, the fatigue behaviour of single overlapped spot joints of AA2024-T3 was studied. To statistically analyse the fatigue data, a 2-parameter Weibull distribution was deployed, considering several reliabilities (R_e = 0.99, R_e = 0.90, R_e = 0.5, R_e = 0.10). To obtain an optimized weld parameter according to the fatigue behaviour, 2 different weld conditions were studied, taking into account the effect of the hook formation. The microstructure analyses and microhardness profiles showed great similarity in both weld conditions. However, these conditions presented distinct interfacial hook profiles, in which the interfacial hook downward represented better fatigue life and infinite fatigue life at 15% of the maximum strength load. The fracture surfaces obtained from 3 different fracture modes were investigated by using scanning electron microscopy; the crack was tracked and described according to its fracture mechanisms from its initiation until the final failures. It was observed that the crack is initiated at hook profile.