Tailoring precipitation strategy to optimize microstructural evolution, aging hardening and creep resistance in an Al-Cu-Sc alloy by isochronal aging

Sc microalloying has been regarded as one of the most effective methods to improve the high-temperature resistance of Al-based alloys via additional Al3Sc precipitation. However, synergetic precipitation of Al3Sc and some conventional precipitates (i.e. theta'-Al2Cu) is usually difficult in traditional series Al alloys due to the huge temperature gaps between their formation, which limits the Sc microalloying effect in multicomponent systems. Here, an optimized isochronal aging strategy was illustrated in an Al-Cu-Sc alloy to achieve better ambient- and high-temperature properties in comparison to the artificially aged counterparts. A series of microstructural characterizations reveal that, upon isochronal aging, the Sc-rich entities preferentially form in regions adjacent to theta'-Al2Cu precipitates at relatively low temperature stage (similar to 250 degrees C) and are responsible for refining the theta'-Al2Cu precipitation in Al-Cu-Sc alloy. At higher aging temperature (similar to 300 degrees C), the preferentially formed Sc-rich entities will be collected by adjacent pre-existing theta'-Al2Cu precipitates, accompanying with additional Al3Sc formation in matrix. The coexistence of theta'-Al2Cu and Al3Sc precipitates realized by isochronal aging contributes to the improved aging hardening behavior as well as better creep resistance at 300 degrees C in Al-Cu-Sc alloy compared with its Sc-free or isothermally aged counterparts.