Influence of Titanium on the Microstructure and Wear Properties of Spray-Formed Hypereutectic Al-Si Alloys

The present study explored the development of hypereutectic Al-Si alloys such as Al-15Si (SF1), Al-15Si-0.5Ti (SF2), Al-15Si-1.0Ti (SF3), and Al-15Si-2Ti (SF4) alloys by spray forming, a technique that yields refined microstructures with minimal segregation, and examined the effects of titanium (Ti) on the microstructure and wear properties of alloys at various temperatures. Microstructural analysis revealed equiaxed aluminum (Al) matrices with distributed silicon (Si) phases and Al₃Ti intermetallics in Ti-containing alloys. The addition of Ti refined the microstructure and enhanced the refinement of Si particles. The hardness increased as Ti content increased in the alloy, with spray-formed alloys (SF) exhibiting 30-35% higher hardness than their as-cast (AC) counterparts at all temperatures. The SF alloys demonstrated improved wear resistance, with 50-65% lower wear rates than AC alloys at 25 °C and 68-82% lower at 250 °C. Specifically, the Al-15Si-2Ti SF alloy exhibited 62% and 82% lower wear rates than Al-15Si-2TiAC alloy at 25 °C and 250 °C, respectively. The coefficient of friction (COF) decreased with load for both AC and SF alloys, while COF values increased as the temperature increased. The AC alloys exhibited a 21-35% increase in coefficient of friction (µ) per unit rise in temperature, while SF alloys showed a significantly lower increase of 0.18-0.29%. The SF4 alloy demonstrated the lowest COF across the entire load and temperature range. Spray-formed hypereutectic Al-Si-Ti alloys demonstrate a high potential for aerospace and automotive applications due to their refined microstructure and enhanced wear resistance, achieved through addition of Ti, making them suitable for high-performing applications.