On the fatigue and fracture behavior of keyhole-free friction stir spot welded joints in an aluminum alloy

Abstract

The target of this research study was to evaluate the shear-tensile and fatigue behavior of aluminum 6061 alloy welds, in two different heat treatment conditions, joined by the recently developed intermediate layer friction stir spot welding (FSSW) technique. The keyhole, which is the disadvantage of the conventional FSSW process, was avoided using an additional intermediate layer (IL) accompanied by a simple tooling. Shear-tensile experiments demonstrated acceptable mechanical performance of IL-FSSW joints in comparison with that obtained using alternative methods. Fatigue behavior of the joints revealed a dependency to pre-processing temper especially at high cyclic load levels with improved life for the aged condition. Observations on the failure regions under shear-tensile experiments exhibited plug type and shear-plug type fracture modes for the aged and annealed conditions, respectively. In contrast, the fracture mode showed variation with respect to the load level but not to the type of temper during cyclic loading.