Influence of Silicon Content On the Microstructural, Thermal and Tribological Behavior of Cast Al–Si Piston Alloys

This study investigates the influence of silicon content (10, 15 and 20 wt.%) on the microstructural, thermal and tribological behaviour of cast Al–Si piston alloys. The microstructure transitioned from hypoeutectic (Al-10Si) to near-eutectic (Al-15Si) and hypereutectic (Al-20Si) with a progressive increase in primary Si particle volume. Hardness improved with increasing Si due to the combined strengthening from eutectic and primary silicon phases. In contrast, thermal conductivity and diffusivity decreased with higher Si content, while specific heat increased. Tribological testing at 3.0 m/s demonstrated that wear rate rose with load for all alloys; however, the Al-15Si alloy showed the lowest wear rate owing to its optimally distributed silicon phases. The Al-10Si alloy exhibited the highest wear rate, while Al-20Si showed intermediate performance due to micro-cracking around coarse primary Si particles. Overall, Al-15Si offered the best balance of thermal–mechanical properties and wear resistance, indicating its suitability for high-load piston applications.