Microstructure and mechanical properties of Al/Cu-SS hybrid composite via ball milling and friction stir processing

To balance aluminum matrix composites' (AMCs) strength and ductility, this study used hybrid micron-sized Cu/316L stainless steel (SS) particles, fabricated via ball milling (BM) and multi-pass friction stir processing (FSP). Cu mainly enhances strength through load transfer, while the addition of SS further promotes the pinning effect and dynamic recrystallization (DRX). The <i>in situ</i>-formed Al₂Cu further strengthens fine grain strengthening, dispersion strengthening, and load transfer efficiency. Al-5Cu AMCs showed 185.2 MPa ultimate tensile strength (UTS, +104.4% vs. matrix) but 13.8% elongation (-9.2%). Al-10SS AMCs had milder UTS (143.3 MPa, +58.2%) but better ductility (19.3%, +27.0%). The optimal Al-5Cu-10SS AMCs exhibited 183.6 MPa UTS (+102.6%), 58.96 vickers hardness (HV, +96.5%), and 20.3% elongation (+33.6%), with fracture dimples correlating to its performance. This hybrid reinforcement synergizes particle mechanisms, offering an effective route for high-performance AMCs.