Microstructure and properties of Al-60wt.%Si composites prepared by powder semi-solid squeeze

Abstract

Al-60wt.%Si composites were successfully prepared by semi-solid squeezing powder mixture of Al and Si at 700 °C. The appearance of about 50wt.% Al-Si metal liquid results that less than 4–5 MPa pressure can squeeze the Al-Si powder mixture to near full density at vacuum condition. The effects of Si particle size on the microstructure and properties of Al-60wt.%Si were investigated. The results show that the composites are consisted of only Si and Al. Si particles distribute evenly in aluminum matrix. Al matrix exhibits a certain preferred orientation under the condition of directional solidification. Si particles with 5 μm size tend to be aggregated into locally interconnected particles and can be effectively passivated. As Si particle size ranges from 10 to 20 μm, the corner passivation effect for Si particles is gradually suppressed. The fracture morphology of Al-60wt.%Si is composed of cleavage platforms of Si grains and fine tearing ridges of Al which tightly wraps Si grains. With the increase of Si particle size from 5 to 20 μm, the flexural strength of Al-60wt.%Si decreases from 270 MPa to 223 MPa, the thermal conductivity increase from 128 to 136 W·m−1·°C−1, and the average coefficient of thermal expansion from ambient temperature to 400 °C ranges from 9.49 to 9.97 × 10−6 °C−1.