Improving mechanical properties of 2219 aluminium alloy GTA welds by scandium addition

The effect of scandium additions to 2219 aluminium alloy weld metal has been investigated. At low levels (0·16%) of scandium, in spite of grain refinement in the weld metal, improvement in the mechanical properties has been nominal. At higher levels of scandium (0·37%), a substantial improvement in the tensile properties has been obtained. Further improvement in mechanical properties has been achieved by adding small amounts of magnesium. Transmission electron microscopy revealed the presence of fine precipitate particles in the scandium containing weld metals. Electron probe microanalysis (EPMA) and SEM–EDX revealed extensive copper segregation to grain and subgrain boundaries. The presence of scandium reduces the severity of segregation by producing fine equiaxed grains in the weld metals and also by refining the grain substructure. The morphology and size of the high copper eutectic phase at grain boundaries and sub-boundaries have been found to be finer and well distributed in the case of scandium containing weld metals. EPMA linescans and quantitative analyses proved that the depletion of copper in the matrix is minimised as a result of the fine grained structure.