Tailoring the microstructural hierarchy and strength-ductility synergy in a Mn-microalloyed Al-Cu alloy via a modified thermomechanical protocol

In this work, two representative thermal/thermomechanical/protocols, denoted as HT (heat-treated) and TMT (thermomechanical treated), respectively, were utilized to tailor the microstructural hierarchy of constituents, dispersoids and nanoprecipitates in an Mn-microalloyed Al-Cu-based alloy, with the goal of optimizing the mechanical properties. On the one hand, the modified thermomechanical TMT protocol, merely with extra rolling processes compared to the HT counterpart, is found to greatly refine the constituents and thus improve the ductility. On the other hand, the TMT protocol encourages the precipitation of Mn-rich dispersoids and, surprisingly, highly accelerate the precipitation transition of θ″→θ′. As a result, the age-hardening response of the TMT-treated alloy is remarkably enhanced, leading to yield strength increased by ∼100 MPa compared to the HT-treated counterpart. Theoretically, the most significant strengthening increment in the TMT-treated alloy is contributed by the predominant θ′ precipitates, as clarified by the strengthening model.