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

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 degrees 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 (similar to 46 HV) and electrical conductivity (similar to 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.