PNNL

Abstract

We utilized friction extrusion (FE), a novel solid-phase processing technique, to fabricate aluminum metal matrix composites (Al-MMCs) with hierarchical microstructures and exceptional properties, highlighting its scalability potential. In this study, alumina (Al2O3) particles were dispersed within an aluminum alloy 6061 (AA6061) matrix, and precursor pucks containing 0–15 vol% Al2O3 particles were extruded into fully dense composite rods. The FE process induced a distinctive arrangement of Al2O3 particles, forming concentric rings of alternating particle-rich and particle-lean layers radiating outward from the rod’s center creating a tree-trunk like structure. Grain sizes in the particle-lean regions were approximately twice those in the particle-rich regions. Tensile testing revealed an increase in tensile strength with the incorporation of Al2O3 particles, while maintaining uniform ductility above 12%. The magnesium in 6061 selectively reacted with the alumina particles to form nodes of spinel on the surface of alumina particles resembling a virus -like structure. The formation of a ‘virus-like’ structure of Al2O3 particles enhanced the wettability and promoted the accumulation of geometrically necessary dislocations (GNDs) at the interfaces, thereby enhancing strain hardening. The development of the hierarchical microstructure through FE played a crucial role in overcoming the conventional strength-ductility trade-off, demonstrating the method’s potential for producing advanced composite materials.