Influence of post weld aging treatment on microstructural features and fatigue behaviour of unnotched and notched specimens of friction stir welded AA6061-T651 aluminium alloy joints under completely reversed stress cycle

Abstract

AbstractA comparative investigation on rotating bending fatigue behaviour between unnotched and notched specimens of friction stir-welded (FSW) AA6061-T651aluminium alloy joints has been conducted under completely reversed cyclic loading (R = −1). Post-weld aging treatment was done for 8 h at 200°C on the welded joints. After post-weld aging treatment, the fatigue strength was significantly improved, while the grain size remained unchanged. Microstructural evolution before and after post-weld aging treatment was studied using orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). It was found that post-weld aging treatment decreased dislocation density and facilitated precipitation hardening through the reprecipitation of fine β″(Mg2Si) particles. Fine particles of post-weld aged specimens of FSW joints were sheared by dislocations generated during cyclic loading, resulting in difficult crack initiation and tortuous crack propagation. Fractographic results confirmed that Post-weld aged specimens of FSW joints have better fatigue resistance than as-welded specimens, owing to the presence of significant precipitates along the grain boundary.Keywords: Friction stir weldingpost weld ageing treatmentfatigue behaviorS-N curvesmicrostructure AcknowledgementsThe authors wish to record sincere thanks to the Director of Naval Materials Research Laboratory (NMRL), DRDO, Ambernath Maharashtra for the financial support rendered through a CARS project No: NMRL/MMG/0401/04/NMRL253/CARS/145/2020-21. The authors thank the Naval Materials Research Laboratory (NMRL-DRDO), Mumbai, India, for providing base materials to carry out this investigation. The authors also thank IIT Kanpur for allowing them to use their EBSD facility.Disclosure statementThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.