Influence of Superheating Melt Treatment on Microstructure of Gd-Modified Al-15wt.% Mg2Si In-Situ Composite

Abstract

The influence of melt superheating treatment with different superheating temperatures (750, 800, 850, and 900°C) on the microstructure of Al-15wt. % Mg₂Si composites before and after addition of Gd (1.0 wt.%) were studied. Microstructure characterisation was carried out via optical microscopy (OM) and x-ray diffraction (XRD).The results showed that in the unmodified composite, when the temperature of superheating raised from 750°C to 900°C, the primary Mg₂Si experienced a decrease of the average grain size from 40 to about 32 µm, while, in the Gd-modified composite, the particle size was refined considerably from 27 to 13 µm by increasing the temperature from 750°C to 850°C. Furthermore, with a further increase in temperature to 900°C, the particle size slightly increased to about 15 µm which might be due to the burning loss of Gd in the melt. Nevertheless, for both unmodified and Gd-modified composites, the superheating temperature exhibited minor influence on the Mg₂Si crystals morphologies. It is believed that compiling of Gd addition and superheating melt treatment is efficient to improve the composite properties that could encounter the application requirements.