Abstract
In this paper, fatigue behaviour of friction stir spot welded joints in Al-Mg-Si aluminium alloy was investigated. Fatigue tests were conducted using lap-shear specimens at a stress ratio R = 0.1. It was found that fatigue fracture morphology was dependent on load level. When high load was applied, debonding and opening deformation took place along the boundary between the upper and lower sheets around the weld nugget. The opening deformation caused stress concentration, which resulted in fatigue crack initiation at the edge of the nugget followed by crack growth through the mixed zone (MZ) until final fracture. When low load was applied, fatigue crack initiated at the edge of the nugget and propagated through the sheet thickness and grew to the width direction. Based on experimental observation of the weld zone, fatigue fracture mechanism of friction stir spot welded joint was discussed.
