The effect of scandium on the microstructure, mechanical properties and weldability of a cast Al–Mg alloy Original Research Article

The microstructure, mechanical properties and weld hot cracking behaviour of a cast Al–Mg–Sc alloy containing 0.17 wt.% Sc were compared with those of a Sc-free alloy of similar chemical composition. Although this level of Sc addition did not cause grain refinement, the dendritic substructure appeared to be finer. There was a significant increase in the yield and tensile strength and the microhardness of the Al–Mg–Sc alloy relative to its Sc-free counterpart. A discontinuous precipitation reaction was observed at the dendritic cell boundaries. Microchemical analysis revealed segregation of Mg and Sc at these interdendritic regions. No improvement was observed in the resistance of the alloy to weld solidification cracking or heat affected zone (HAZ) liquation cracking. This is explained in terms of the inability of this level of Sc addition to refine the solidification structure and to influence the liquation of solute-enriched dendritic cell boundaries of the cast material.