Influence of melting current pulse duration on microstructural features and mechanical properties of AA5083 alloy weldments

Abstract

The formation of intermetallic particles and dislocation structure play a vital role in strengthening aspects of non-heat treatable aluminium alloy weldments. In this work, the effect of melting current pulse duration (McT) on grain boundary characteristics, dislocation structure, size and distribution of intermetallics on AA5083-H111 aluminium alloy weldments processed by pulsed gas tungsten arc welding are investigated. The mechanical responses of the weldments are evaluated by impression creep test, tensile test and microhardness measurements. The results suggest that at both lower and higher current level, the use of shorter McT (40%) had retained a considerable amount of Mg at fusion zone and assisted in nucleation of β-phase precipitates at various sites of grain boundaries whereas the change in McT from 40% to 60% produced grain boundaries free of β-phase precipitates. Also, the longer McT (60%) at a lower current level produced rod-like finer (~50–400 nm) Mn-rich intermetallics at grain boundaries and distributed uniformly at grain interiors. It caused a rise in activation energy which leads to an increase in pinning pressure during plastic deformation and resulted in higher tensile strength and creep resistance. In contrast, the longer McT (60%) at a higher current level encouraged the formation of plate-like coarser (~527 nm length and 419 nm width) Mn-rich intermetallics at random locations allowed the grain boundaries to slide at various points during deformation and resulted in lower mechanical properties. This study shows that the change in McT caused significant variations in mechanical properties by altering the microstructural features of weldments.