Dry sliding wear characteristics, corrosion behavior, and hot deformation properties of eutectic Al–Si piston alloy containing Ni-rich intermetallic compounds

Abstract

Al–Si eutectic alloys could be an alternative for gray and compacted graphite cast iron engine blocks due to their excellent thermal conductivity, low density (resulting in weight reduction and fuel efficiency), and good combination of strength and ductility. However, microstructural softening at service temperature (170–250 °C) due to coarsening/coalescence of metastable precipitates and low wear resistance are a stumbling block limiting their usage in engine components. To meet endless demands for fuel-efficient car engine (i.e. higher temperature and pressure in combustion chamber), optimization of current chemical composition seems to be essential. For this reason and in the present study, different concentration of Ni (from 0.8% to 3.5%) was doped into a eutectic Al–Si alloy to investigate tribological, corrosion, and hot deformation properties. It was pointed out that Al–Si eutectic alloy containing 2–2.6% Ni had the highest wear resistance due to uniform dispersion, skeleton-type morphology of Ni-rich intermetallic compounds, and their better bonding with the matrix. Oxidation and delamination of oxide layer was shown to be the main wear mechanism. The presence of (Ni,Cu)-rich intermetallic compounds increased the corrosion rate by ≈ 60%; however, the repassivation potential was found to be slightly higher in 2.6%Ni sample indicative of easier repassivation of micropits. To better understand the high temperature behavior of Ni-containing Al–Si alloy, hot compression test was carried out within the temperature range of 400–550 °C and strain rates of 0.001 to 1s−1 and constitutive equations were used to develop hot deformation processing maps. The presence of Ni-rich intermetallic compounds enhanced the hot deformation behavior and increased the activation energy for hot deformation. Dynamic recrystallization was found to be the main softening mechanism during hot deformation. At true strain of 0.6, the maximum power dissipation efficiency (≈54%) was obtained at 400 °C and a strain rate of 0.01s−1.