Enhanced intragranular precipitation strengthening in Sc-microalloyed ultrafine-grained SiCp/Al-Cu-Mg composites via retrogression and re-ageing heat treatment

• A elaborately designed retrogression and re-ageing heat treatment was applied to achieve the simultaneous precipitation of Al 2 Cu and Al 3 Sc in ultrafine-grained Al-Cu-Mg matrix composites. • Compared to the T6 treatment, RRA heat treatment exhibits a significant strengthening effect in Sc-microalloyed composites, attributed to enhanced intragranular precipitation strengthening and dislocation strengthening. • The plastic deformation mechanisms were analyzed by thermal activation analysis. Ultrafine-grained Al matrix composites suffer from the insufficient dislocation accumulation capability and intragranular precipitation strengthening due to their length-scale dependent precipitation behaviors. In this work, a combination of Sc-microalloying and a retrogression and re-ageing (RRA) route was applied on the SiC p /Al-Cu-Mg composites to achieve well-balanced strength and ductility. Compared to the T6 treatment, RRA heat treatment exhibit a significant strengthening effect in Sc-microalloyed composites with only a slight loss in ductility. The yield strength and ultimate strength of the Sc-RRA samples reach up to 686.4 MPa and 734.5 MPa, respectively. The plastic deformation mechanism was analyzed by thermal activation analysis and TEM observation of deformed microstructure. The plastic deformation of UFG composites, both with and without Sc, is primarily governed by a dislocation-grain boundary interaction mechanism. As confirmed by the observed stacking faults, the Sc-microalloyed composite subjected to T6 treatment suffers from poor dislocation storge capacity and insufficient intragranular precipitation strengthening. In contrast, the RRA treatment promotes the formation of intragranular Al 3 Sc precipitates and GP zones, which improve the dislocation accumulation capability and precipitation strengthening of ultrafine-grained composites by pinning dislocations. This work provides an accessible pathway to exploit aluminum matrix composites with advanced strength-ductility balance.