PNNL

Abstract

Friction stir lap welded (FSLW) joints have weight-saving potential in aluminum-intensive automotive assembly. However, FSLW also modifies the material microstructure close to the joint. Optimizing the FSLW process requires understanding the relationship between the strength and the joint's microstructure. In previous studies, efforts have been dedicated to determining the effects of local softening, the shape of the oxide line, and porosity. However, the impact of changes to the fracture properties on the joint's strength has not been studied. In this work, strength testing, and simulations, aided by material characterization, were used to determine the role of fracture properties on the shear strength of a 3-sheet (aluminum alloys 7055-7055-6022) lap joint. Characterization involved testing for fracture properties in the weld region. This data was then implemented into finite element simulations. As a result, the joint strength was predicted with a deviation of less than 6% from the experimental value. Comparison with strength prediction using only the base metal properties indicates that fracture property in the nugget region determines the strength of AA7055 FSLW.