Co-stabilization of θ′-Al2Cu and Al3Sc precipitates in Sc-microalloyed Al–Cu alloy with enhanced creep resistance

As to the increasing demands for the light materials in weight-sensitive fields, scandium (Sc) is arguably known as one of the most attractive and effective microalloying elements to develop high-performance aluminum-based alloys applied at elevated temperature. This report exemplifies how the Sc microalloying effect can be fully utilized to seek for the synergetic stabilization between dual precipitates, more than simply forming the well-known Al3Sc nanoprecipitates. Two sets of precipitation protocols are introduced to create a coexistence of θ′-Al2Cu and Al3Sc precipitates in an Al–Cu–Sc alloy, and the thermal stabilization of the two precipitates is found to be closely correlated. In the case of θ′-Al2Cu precipitate decomposed because of an invalid protection from weak interfacial Sc segregation, the Al3Sc precipitates will coarsen much quickly, which induces a simultaneous loss in thermal stability and strengthening effect of the dual precipitates. In contrast, a sensible approach is proposed to induce a strong Sc segregation at the θ′-Al2Cu/matrix interface to greatly stabilizes the θ′-Al2Cu precipitates even crept at 300°C and concomitantly suppresses the coarsening of Al3Sc precipitates, leading to extremely high creep resistance. The acceleration effect of the Cu on the Al3Sc coarsening is illustrated and can be alternatively prohibited by modified Sc partitioning to stabilized θ′-Al2Cu precipitates as Cu storage and thus provides a much stronger coupling precipitate strengthening as well as creep resistance at elevated temperatures. This strategy is broadly applicable to other high-temperature alloy containing Sc together with primary elements such as Si, Mg, and Zn via the creation of precipitate co-stabilization.