Hypereutectic Aluminum Alloys and Composites: A Review

Fast development of automotive industry increases demands in terms of fuel efficiency, reduction of weight and increased reliability of constructions. Nowadays major materials for production of pistons are cast iron, Aluminum-Silicon (Al-Si) alloys and some composites. Use of hypereutectic Al-Si alloys is increasing in automobile and aerospace industry. Application of hypereutectic Al-Si alloys with more than 12wt.% of Si is due to their properties like good thermal and electrical conductivity, high strength to weight ratio, good corrosion resistance and others. Higher Si content in the alloy can affect its properties; it increases size of primary Si and hardness but reduces machinability. In order to improve their properties and meet the high requirements of the industry, usually, grain refinement of these alloys is needed. Some of the ways to obtain grain refinement and potentially improve hypereutectic Al-Si alloys' properties are different manufacturing technologies, heat treatments and/or addition of grain refiners like Ni, Mg, Sr, Sn and many others. There is a large amount of manufacturing technologies used for hypereutectic Al-Si alloys, and in this paper will be considered most of them, as well as their influence on microstructure, mechanical and tribological properties of hypereutectic Al-Si alloys and composites. Also, the effect of higher Si content in the hypereutectic Al-Si alloy on its properties will be considered, as well as addition of modificator/refiner or reinforcement. Liquid state processes are usually used for hypereutectic Al-Si alloys, but some newer (semi-solid and solid processes) have emerged that give better microstructure, mechanical and tribological properties, and those are tixocasting, rheocasting and selective laser melting. Based on available investigations tixocasting gives promising results, the only drawback is the price and in the future, investigations should be oriented to finding ways for its reduction.