Effects of Si on the Electrical Conductivity, Microhardness, Microstructure and Hot Tearing of Al–0.8Fe–0.5Mg–0.4Ni Alloys

Abstract

Electrified automotive powertrains require new Al alloys with high castability and high electrical conductivity . This research presents the effects of Si on the electrical conductivity , microhardness , microstructure and hot tearing of Al–0.8 wt% Fe–0.5 wt% Mg–0.4 wt% Ni–x wt% Si alloys. The Al–Fe–Mg–Ni–Si alloys were prepared by mixing pure Al, Fe, and Ni, as well as Al–50 wt% Mg and Al-50 wt% Si master alloys at 720 °C. Silicon contents of 0.15 and 0.30 wt% were examined. The alloys were characterized using microhardness testing, optical and electron microscopy , X-ray diffraction, electrical conductivity measurements and hot tearing susceptibility testing. The microstructure of the Al–Fe–Mg–Ni–Si alloys contained fibrous as well as elongated or rounded Al₃Ni and Al₉FeNi intermetallics, with Mg and Si contained in the Al solid solution. Increasing Si content from 0.15 to 0.30 wt% in the Al–Fe–Mg–Ni–Si alloys resulted in more rounded intermetallics but nearly constant microhardness (~46 HV) and electrical conductivity (~50 %IACS). The hot tearing susceptibility of the Al–Fe–Mg–Ni–Si alloys was more severe than a modified A380 alloy but did not result in a complete separation of the casting .