Effect of chemical composition and T6 heat treatment on microstructure and mechanical properties of a hyper eutectic Al–Si alloy

Abstract

The automotive and aircraft industries’ requirements have led to increasing application of Al–Si alloys thanks to their great potential as a replacement to cast iron and steel. The current work is an investigation of the effect of chemical composition and T6 heat treatment on the microstructure and mechanical properties of a hyper eutectic Al–Si alloy. Secondary Al–Si alloy ingot was cast using the sand casting technique. Samples were prepared for microstructural examination and mechanical properties tests. One set of the samples was subjected to solution heat treatment at 530°C, quenched in water at room temperature and aged at 175°C for five hours. Microstructural examination of cast samples using scanning electron microscopy (SEM) revealed three main phases in the alloy. Primary α–Al dendritic phase, eutectic Si phase and intermetallic phases of Fe and Mg. After heat treatment, the eutectic Si phase was spheroidized and uniformly distributed, the bonding strength of the α–Al dendritic phase and Si eutectic phase were well distributed, and the Fe and Mg phases precipitated. The ultimate tensile strength and hardness improved by 37.17% and 40.38% respectively. T6 heat treatment is therefore a necessary step in the production of parts made of Al–Si alloy by sand casting.