Achieving synergistically enhanced corrosion resistance and hardness in nano-ZrB₂/Al composites through friction stir based solid-state additive manufacturing

Aluminum matrix composites (AMCs) hold significant potential as lightweight structural materials for aerospace applications. However, achieving a simultaneous enhancement in both hardness and corrosion resistance remains a longstanding challenge. In this work, nano-ZrB₂ particle-reinforced AMCs were fabricated via solid-state additive friction stir deposition (AFSD), which enables uniform dispersion of nanoparticles through severe plastic deformation and mechanical stirring at low processing temperatures. With the incorporation of 6 vol% ZrB₂, the composite exhibited a 35.62% increase in hardness and a 14.42% improvement in ultimate tensile strength compared to the unreinforced AFSD-processed alloy. These enhancements are attributed to the combined effects of high-hardness ZrB₂ nanoparticles and a dual grain refinement mechanism: dynamic recrystallization induced by AFSD leads to fine equiaxed grains, while ZrB₂ particles serve as heterogeneous nucleation sites and effectively pin grain boundaries, resulting in further microstructural refinement. More importantly, the 6% ZrB₂-reinforced composite demonstrated optimal corrosion resistance, exhibiting a low corrosion current density of 0.196 ± 0.025 μA/cm². This improvement is ascribed to the redistribution of precipitates during the solid-state process: Mg-Si phases preferentially encapsulate ZrB₂ particles to form a core-shell structure, while the fraction of cathodic Al-Fe-Si intermetallics is significantly reduced. Such microstructural modifications alleviate electrochemical heterogeneity and suppress micro-galvanic coupling, leading to significantly enhanced corrosion performance. This study provides an effective solid-state additive manufacturing strategy for tailoring microstructures and breaking the conventional hardness-corrosion resistance trade-off in AMCs.