Reactive friction-stir processing of nanocomposites: Effects of thermal history on microstructure–mechanical property relationships

Abstract

The effects of thermal history on the microstructure and mechanical properties of a friction-stir-processed Al–Mg–TiO₂ (3 vol.-%, 20 nm) nanocomposite were studied. It is shown that, with increases in peak temperature, a more uniform distribution of nanoparticles in the metal matrix, and a refined grain structure, are attained. Transmission electron microscopy indicated that the mechanism of grain refinement is influenced by the hard inclusions, changing from discontinuous to continuous dynamic recrystallisation. A fine-grained nanocomposite (average grain size of 3 µm) with a uniform distribution of nanoparticles is obtained after four fully-overlapping passes at 1200 rev min⁻¹ and 100 mm min⁻¹. Under these circumstances the mechanical properties, including yield stress (95%), tensile strength (36%) and hardness (72%) are significantly enhanced relative to the untreated alloy.