Microstructural evolution and thermophysical properties of hypereutectic Al-22Si-xNi alloys prepared by sub-rapid solidification

Abstract

Al-22Si-xNi (x = 0, 5, 10, 15, 20) alloys were prepared by sub-rapid solidification in the present study. Their microstructures were observed and thermophysical properties were tested. Solidification reactions of the alloys changed with the increase of Ni content. Al3Ni compounds with different morphologies were formed in different solidification stages. The eutectic Al3Ni and primary Al3Ni phase assumed fiber-like and fishbone-like, respectively. Al3Ni–Si binary eutectic structure appeared when Ni content reached 15wt.%. After annealing, the eutectic phase was spheroidized and coarsened. The thermal conductivity decreased with the increasing Ni content. Annealing could enhance the thermal conductivity of the alloys. With the increase of Ni content, the thermal expansion coefficient of the alloys decreased linearly. The as-annealed Al–22Si–15Ni alloy had good comprehensive performance in thermal properties, i.e., the thermal conductivity at 25 °C was 107.09W/(m·K) and coefficient of thermal expansion at 100 °C was 13.04 × 10−6/K. The predicted linear coefficient of thermal expansion values by Turner model agreed well with the experimental values.