Abstract:
Three kinds of alloys, Al-11Si-5Ni, Al-22Si-10Ni and Al-33Si-15Ni, were prepared by ordinary solidification, water-cooled copper mold sub-rapid solidification and water-cooled copper mold sub-rapid solidification combined with heat treatment (520 ℃×6 h). The microstructures and thermal properties of the alloys were studied. The results show that only Al-Si-Al
3Ni ternary eutectic reaction occurred in the solidification process of Al-11Si-5Ni eutectic alloy, and the microstructure was ternary eutectic structure composed of α-Al, eutectic silicon and eutectic Al3N phases. The Al-22Si-10Ni and Al-33Si-15Ni alloys were hypereutectic alloys, the microstructure consisted of primary silicor phase, primary Al
3Ni phase and ternary eutectic structure, and the solidification process was divided into three stages: the primary silicon phase precipitation, the primary silicon and Al
3Ni phase co-precipitation, and Al-Si-Al
3Ni ternary eutectic reaction. With the simultaneous increase of Ni and Si content, primary silicon and Al
3Ni phases were coarsened. Compared with the ordinary solidification process, the water-cooled copper mold sub-rapid solidification process could refine the alloy structure, and the heat treatment made the eutectic silicon phase and the eutectic Al
3Ni phase spheroidize. With the simultaneous increase of the content of Ni and Si, the alloy's thermal conductivity and the thermal expansion coefficient decreased. The water-cooled copper mold sub-rapid solidification combined with heat treatment could effectively improve the thermal conductivity of the alloy. Al-22Si-10Ni alloy prepared by the water-cooled copper mold subrapid solidification combined with heat treatment had the best comprehensive performance with the room temperature thermal conductivity of 129.9 W · m
−1 · K
−1, the thermal expansion coefficient at 100 ℃ of 13.8×10
−6 K
−1, and the average thermal expansion coefficient in the temperature range of 25–100 ℃ of 12.9×10
−6 K
−1.