Fatigue Performance and Strength Assessment of AA2024 Alloy Friction Stir Lap Welds

This work experimentally studied the weld-seam cross section characteristics and the fatigue performance of AA2024 aluminum alloy friction stir linear welded joints. The Vickers hardness values on the cross section of the weld-seam have a tendency of being lower than those of the upper sheet, whereas in the lower sheet there is a significant downward profile across the nugget, like a “V” shape. The grains in the welded nugget are finer than those of the base material. Within low-cycle regime, the fracture always occurred at the hook vertex on the loading-carrying upper sheet, while on the loading-carrying lower sheet within relatively high-cycle regime. The typical SEM fractographs of the upper and lower sheets are observed and compared accordingly. The fatigue lives of these specimens were assessed by fictitious notch radius approach and two local damage equations, Morrow’s modified Manson–Coffin damage equation and the Smith–Watson–Topper damage equation, combined with stress and strain at the weld-seam periphery obtained from finite element analyses. Results showed that both the Morrow’s modified Manson–Coffin damage equation and fictitious notch radius approach can give more reasonable results.