Comparative study on microstructure and mechanical properties of Ti and Zr micro-alloyed AlMgSc alloy deposits fabricated via wire-arc directed energy deposition

Microalloying can potentially enhance the uniformity of the microstructure and mechanical properties of AlMgSc alloys. In this study, wire-arc directed-energy deposition (WA-DED) was performed to prepare AlMgScZr and AlMgScTi alloy deposits with self-developed wires, followed by a comparative analysis of their microstructure and mechanical properties to investigate the effects of two microalloying elements, Zr and Ti. The microstructure of the AlMgScZr and AlMgScTi alloy deposits were analysed using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The mechanical properties of the deposits were tested and the burning tendencies of Zr and Ti were evaluated. The AlMgScZr alloy exhibited a significant number of columnar grains, whereas the AlMgScTi alloy exhibited the microstructure predominantly composed of fine equiaxed grains. No Al₃(Sc, Zr) phase was observed in the AlMgScZr alloy, while Al₃(Sc, Ti) phase was identified in the AlMgScTi alloy. The AlMgScTi alloy exhibited superior hardness and tensile properties compared with the AlMgScZr alloy. The substantial burning of Zr and minimal burning of Ti contributed to the differences in the microstructure and mechanical properties between the AlMgScZr and AlMgScTi alloys. This study provides novel insights into the selection of microalloying elements for AlMgSc alloys fabricated via WA-DED.