The impact of heat input on the microstructures, fatigue behaviors, and stress lives of TIG-welded 6061-T6 alloy joints

Abstract

This work shows that heat input is an important parameter that influences microstructural changes in the heat-affected zones (HAZs) of TIG-welded 6061-T6 alloy joints and their fatigue behavior. Double-shielded TIG samples were welded using various heat input parameters and a gas mixture of 50% He and 50% Ar was used to produce an improved weld penetration, their mechanical properties and microstructures of the samples were compared to those of the unwelded alloy. The mechanical properties of the aluminum alloys and the welding zones were evaluated by performing tensile and fatigue tests. The fatigue behaviors of the 6061-T6 joints welded with different heat inputs were assessed by performing cyclic fatigue experiments. Their microstructures were examined via optical microscopy and scanning electron microscopy (SEM). Grain coarsening was observed in the fusion zones (FZs), and heat input during TIG welding made the HAZs larger. Applying the lowest heat input value yielded samples with poor ultimate tensile strength, which was attributed to partial penetration and the presence of pores in the welded joints. The oxygen content of the weld pool depended directly on the shielding method and the surface temperature distribution.