Effect of ball milling on the ageing response of Al2618 composites reinforced with SiC and oxide nanoparticles

High-energy ball milling was carried out to disperse SiC nanoparticles (ex-situ reinforcement) and fragments of oxide (in-situ reinforcement) in an Al2618 alloy matrix. Nanocomposite powders were consolidated by hot rolling at 600 °C. Samples produced using ball milled powder showed a weak response to ageing treatment as demonstrated by thermal and microstructural analyses and by hardness tests. Repeated plastic deformation of powder induced by ball milling led to high density of crystal defects which are believed to be responsible of an extension of solid solubility, thus reducing the driving force for precipitation during ageing. Tensile tests were performed at room temperature and at 120 °C on solution treated and peak-aged samples. The nanocomposites showed a remarkably high yield strength and an impressive ability in keeping high mechanical properties even at high temperature. Serrations were noticeable in stress-strain curves both before and after ageing, which are ascribed to the dynamic strain ageing mechanism.