The effect of Ni-doping on the microstructure, hot deformation behavior, and processing map of as-cast Al–Si piston alloy

Abstract

Al–Si alloy is widely utilized in automobile pistons and cylinders due to good castability, high strength-to-weight ratio, excellent thermal conductivity, good resistance to corrosion/oxidation, and acceptable wear resistance. To increase the efficiency of engine motor, it is imperative to modify and engineer the microstructure of Al–Si alloy to enhance the high-temperature behavior. For this reason, in the current study, different concentration of Ni (0.8% and 2%) was doped into Al–Si alloy during casting to generate various Ni-rich intermetallic compounds within the alloy matrix. AlNiCu, AlCu, AlFeSi, and Mg2Si were found to be the main intermetallic compounds precipitated within the dendritic and interdendritic regions, which could enhance the thermal stability and high-temperature performance. High-temperature compression test at high temperatures ranging from 400 to 550 °C and at different strain rates ranging from 10−3 to 1 s−1 was carried out to develop high-temperature processing map and optimize the hot workability parameters of Ni-doped Al–Si alloy. The maximum power dissipation efficiency (η) was observed within the temperature range of 450–500 °C and strain rate of 0.05–0.08 s−1 (lower strain rate) for Al–Si–0.8%Ni alloy and within the temperature range of 450–500 °C and strain rate of 0.3–1 s−1 (medium to high strain rate) for Al–Si–2%Ni alloy. Dynamic recrystallization was found to be the primary softening mechanism at high temperatures (T > 450 °C).