Strengthening mechanisms of graphene- and Al2O3-reinforced aluminum nanocomposites synthesized by room temperature milling

Powder metallurgy (PM) is a widely used processing method to synthesize ultrafine and nanometric grain-sized alloys and composites. While most previous work on synthesizing nanocrystalline (NC) metal-matrix nanocomposites (MMNCs) has used cryomilling technique with liquid nitrogen and stearic acid followed by high temperature/high vacuum drying, we employed an advanced room temperature method that involves milling in ethanol followed by low temperature atmospheric drying – a much less expensive process. To understand the strengthening mechanisms of MMNCs, pure NC Al was reinforced with varying concentrations of Al2O3 nanoparticles (NPs) and graphene nanoplatelets (GNPs). The results show that i) room temperature milling in ethanol followed by a relatively low temperature drying treatment can produce NC Al and NC Al MMNCs with grain sizes comparable to materials produced by cryomilling, ii) grain boundary strengthening as described by the Hall–Petch relation accounts for the strength of Al‐Al2O3 MMNCs, and iii) grain boundary strengthening and solute strengthening seem to account for the strength in Al‐GNP MMNCs.