Towards strength-ductility synergy in bimodal-grained 7075Al matrix composites reinforced with high-content n-SiC by regulating coarse-grained components

Abstract Owing to the inherent strength–ductility trade-off and complex changes in precipitation behavior, the design of 7xxxAl composites with high n-SiC content has long been a formidable challenge. Here, we fabricated a bimodal n‑SiC/7075Al composite in powder metallurgy route and investigated the role of coarse-grained (CG) microstructures in mechanical responses. The spatially alternate arrangement of ultrafine-grained (UFG) zones with high-content (10 wt%) n‑SiC and CG zones without n‑SiC delivers superior mechanical properties: yield strength (YS) of 538.4 MPa, ultimate tensile strength (UTS) of 662.0 MPa, elongation (El) of 5.7% and a strain hardening exponent of 0.078. Compared with 7075Al, the suppressed intragranular nanoprecipitates by dispersive n-SiC/Al interfaces facilitate the hetero-deformation-induced (HDI) stress as dominant strengthening contribution rather than Orowan mechanism. The improved ductility is attributed to the synergy of both intrinsic and extrinsic toughening mechanisms. The former origins from the enhanced HDI strain hardening capacity by means of strain gradients and nanoprecipitates; while the latter derives from the delocalized nucleation and growth of microcracks.