Characterization of precipitates in a hot-deformed hypereutectic Al–Si alloy

Abstract The mechanical properties and precipitates of a hot-deformed Al–17.5Si–4.5Cu–1Zn–0.7Mg–0.5Ni alloy have been investigated by examining samples aged for periods of 4–16 h at temperatures of 120, 150 and 180 °C. The ultimate tensile strength of the alloy aged at 150 °C increases with the increase of aging time and achieves peak value of 396 MPa after 16 h of aging. High resolution transmission electron microscopy (HRTEM) observation and energy dispersive spectroscopy (EDS) were carried out to investigate the morphologies and compositions of the precipitates. It is proposed that the precipitation sequences of the alloy are likely to be as follows: supersaturated solid solution → GP zones → θ″ phase → θ′ phase → θ phase; supersaturated solid solution → GP zones → Q″ phase → Q′ phase → Q phase. The appearance of peak-strengthening can be attributed to the homogeneously distribution of the fine plate-shaped θ″ phase within the matrix.