Refill friction stir spot welding tool plunge depth effects on shear, peel, and fatigue properties of Alclad coated AA7075 aluminum joints

Abstract

This study investigates the impact of refill friction stir spot welding (RFSSW) on Alclad-coated AA7075 aluminum alloy, specifically exploring the effects of two plunge depths (g = 1.55 mm and g = 1.9 mm) on the mechanical and fatigue properties. The influence of the Alclad layer on the final joint properties is assessed. Internal flow analysis reveals a concentration of the Alclad layer at the corners of the stir zone for an increased plunge depth. Notably, the sample using a plunge depth of 1.55 mm exhibits a 32 % increase in pure shear strength compared to the sample executed with a plunge depth of 1.9 mm, emphasizing the significance of the plunge depth for achieving superior mechanical performance. SEM analysis of the fracture surface highlights deformation and dimples in the g = 1.55 mm sample, while EDS confirms the Alclad layer's presence, indicating its positive influence on mechanical resilience. Additionally, peel tests demonstrate a 41 % strength increase for the g = 1.9 mm sample. Low and high cycle fatigue tests reveal superior fatigue performance in the g = 1.55 mm sample, supported by SEM analysis illustrating crack initiation and fracture mechanisms. These findings contribute to a nuanced understanding of the interaction between plunge depth, Alclad ldistribution and resulting mechanical and fatigue properties.