THE EFFECT OF HEAT TREATMENT ON MECHANICAL PROPERTIES OF ALUMINIUM-SILICON ALLOY

Aluminium-Silicon (Al-Si) alloys are among the most widely used engineering materials due to their excellent castability, lightweight nature, and good mechanical properties. They are applied extensively in automotive, aerospace, and marine industries. However, their as-cast condition often exhibits coarse microstructures and non-uniform distribution of silicon particles, which limits their mechanical performance. Heat treatment, particularly quenching, is a proven technique to improve these properties, but the effectiveness largely depends on the choice of quenching medium. In this research, Aluminium-Silicon alloys were produced by sand casting and heat-treated by quenching in four different media: water, air, engine oil, and sodium chloride solution. The as-cast specimen served as a control. Mechanical tests including tensile strength, hardness, and impact resistance were conducted on all samples. Metallographic examinations were also performed to study the grain structure and silicon particle distribution before and after heat treatment. The findings revealed that heat treatment significantly improved the mechanical properties of the alloy. Water-quenched samples recorded the highest hardness and tensile strength due to rapid cooling and grain refinement. Oil-quenched specimens exhibited superior toughness and impact resistance, making them ideal for applications subjected to sudden loads. Air-quenched samples showed moderate improvements, providing a balance between strength and ductility. Sodium chloride solution quenching produced results comparable to water quenching but slightly lower. Microstructural analysis confirmed refinement of grains and uniform distribution of silicon particles in the heat-treated specimens compared to the as-cast sample. The study concludes that the choice of quenching medium plays a critical role in determining the mechanical properties of Al-Si alloys. Water quenching is most suitable for applications requiring high strength and wear resistance, oil quenching for components exposed to impact, and air quenching for general-purpose applications. This work validates heat treatment as an essential processing step in tailoring Al-Si alloys for engineering use.