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 tu ngsten arc welds (GTAW) of aluminium-lithium alloy 8090 (2 mm thick ro lled sheets) was studied using cathodic hydrogen charging. To stimulat e an increased amount of hydrogen into welds, the charging current den sity was increased through a galvanostatic circuit. The deleterious ef fect of hydrogen on ductility is documented in terms of degradation in tensile ductility (reduction in area and elongation-to-failure). Micr oscopic analysis was performed to characterize the microstructure and grain morphology of the weldments. Hardness measurements revealed an i ncrease in hardness of the charged welds over the uncharged counterpar t. Scanning electron microscopy observations of uncharged welds reveal ed 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 ne ar the outer surface of the uncharged welds. The change in fracture mo de from the outer surface to the central portion of the charged welds is attributed to intrinsic differences in hydrogen densities. An attem pt has been made to rationalize the role of hydrogen on tensile proper ties and quasi-static fracture behaviour of the GTAW welds.