INFLUENCE OF HYDROGEN CHARGING ON MECHANICAL-PROPERTIES OF GAS TUNGSTEN ARC WELDMENTS OF ALUMINUM-LITHIUM ALLOY-8090

The effect of hydrogen charging on the mechanical properties of gas tungsten arc welds (GTAW) of aluminium-lithium alloy 8090 (2 mm thick rolled sheets) was studied using cathodic hydrogen charging. To stimulate an increased amount of hydrogen into welds, the charging current density was increased through a galvanostatic circuit. The deleterious effect of hydrogen on ductility is documented in terms of degradation in tensile ductility (reduction in area and elongation-to-failure). Microscopic analysis was performed to characterize the microstructure and grain morphology of the weldments. Hardness measurements revealed an increase in hardness of the charged welds over the uncharged counterpart. Scanning electron microscopy observations of uncharged welds revealed a mixed mode failure with predominantly ductile rupture. Although, the charged welds exhibited a near similar mode of failure to that of the uncharged welds, extensive planar slip deformation was observed near the outer surface of the uncharged welds. The change in fracture mode from the outer surface to the central portion of the charged welds is attributed to intrinsic differences in hydrogen densities. An attempt has been made to rationalize the role of hydrogen on tensile properties and quasi-static fracture behaviour of the GTAW welds.