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

摘要

The effects of thermal history on the microstructure and mechanical properties of a friction-stir-processed Al-Mg-Ti0_2 (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 urn) 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.