PNNL

Abstract

Friction stir welding (FSW) produces a gradient microstructure with distinct metallurgical zones. The present study focuses on characterizing the fracture behavior during uniaxial loading across thick-section FSW joint in non-heat-treatable 5083 aluminum alloy. The hardness variation was linked to microstructural features across the weld zones through correlative microscopy. Notably, the heat-affected zone (HAZ) exhibits a lower hardness of 75 HV, while the thermo-mechanically affected zone (TMAZ) and stir zones (SZ) display a hardness of around 79HV. A marginal difference in hardness in HAZ prompts strain localization in HAZ on the advancing side of the weld resulting in offset in fracture from the SZ, which is captured through in-situ monitoring of the tensile test. Further, the post-deformation analysis reveals crack propagation along the maximum shear stress plane due to the coalescence of micro-voids resulting from the fracturing and debonding of second-phase particles. Overall, this study provides valuable insight for optimizing the FSW process of AA 5083 alloy for thick-section applications.