Enhancing strength and ductility synergy through heterogeneous structure design in nanoscale Al2O3 particulate reinforced Al composites

Abstract

Nanoparticle reinforced aluminum matrix composites fabricated by a high energy ball milling method showed significantly improved strength, however, their ductility was relative lower. This study proposed for the first time a heterogeneous structure strategy toward good strength and ductility synergy for Al matrix composites. Nanoscale Al2O3 particulate reinforced pure Al composites were fabricated as model materials. Three ball milling procedures were conducted to construct uniform ultrafine grain, random bi-modal grain, and heterogeneous lamella grain structures. It was shown that all composites exhibited significantly improved tensile strength. The heterogeneous lamella structure provided the composites with increased tensile strength and ductility compared to the uniform or the random bi-modal grain structure. Compared to ball milled pure Al, the heterogeneous structure composite had 160% and 121% increases in yield stress and ultimate tensile stress, respectively. Meanwhile, its elongation was as high as 8%. The results were rationalized through back stress theory. Geometrically necessary dislocations were believed to be the main reason for the good ductility without strength sacrifice.