Scandium Microalloying for Al-Cu-Mg-Mn-Ti Alloys with High Cu Content

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Increasing the Cu content is an important approach to enhancing the strength of Al-Cu alloys, but the widening of the solidification temperature range leads to deterioration in the casting performance of the alloy, significantly limiting its application. This work investigates the effect of Sc content on the microstructure and mechanical properties of Al-Cu-Mg-Mn-Ti alloys with high Cu content. The results show that the solidification path of the Al-8.5Cu-0.3Mg-0.35Mn-0.2Ti-xSc alloy changes when the Sc content reaches 0.37%. When the Sc content is less than 0.37%, the primary phase is α-Al, whereas when the Sc content is greater than 0.37%, the primary phase is Al3Sc. As the Sc content increases to 0.4%, the grain size of the alloy first decreases and then increases, with the smallest grain size occurring at a Sc addition of 0.3 wt.%. Accordingly, the tensile strength of the alloy at both room temperature and high temperature reaches the highest when the Sc content is 0.3 wt.%. Specifically, the alloy's tensile strength at room temperature reaches 327.2 MPa, an increase of 14.0% compared to the alloy without Sc, and the alloy's tensile strength reaches 103 MPa at 350 °C, an increase of 24.5% compared to the alloy without Sc. It is speculated that when Sc is added to the Al-Cu melt, it refines the grains by forming Al3Sc heterogeneous nucleation cores, and it may also form Sc-containing precipitates with higher temperature resistance, which boosts the alloy's strength.