A Study On The Microstructures And Properties Of Al-27%Si Alloy Prepared By Rapid Solidification Powder Metallurgy Process

High silicon aluminum alloys for electronic packaging, which combine the high conductivity of aluminum matrix and low thermal expansion coefficient of silicon reinforcement, fully meet the requirements of electronic packaging technology due to their excellent mechanical and thermal properties that play very important roles in electronic packaging materials enduring high frequency fatigue.In this paper, the Al-27%Si alloy powders are manufactured by rapid solidification gas atomization technology. The effects of powders size and heat treatments on their microstructure are studied. Then the hot-extrusion method is used to fabricate the Al-27%Si alloy, whose thermal shock properties such as mechanical strength and thermal conductivity, thermal expansion coefficient of variation are investigated. The main results are as follows:1) The Al-27%Si alloy powders were manufactured by rapid solidification gas atomization technology, the internal construction is composed of α-Al phase, primary Si bulk phase and dendritic structure eutectic silicon phase. With the size of the powder getting smaller, the amount of β-Si bulk phase and dendritic structure eutectic silicon phase decreases and the roughness of the surface also decreases.2) During heat treatments, the primary Si bulk phase is coarsened and the eutectic silicon phase is transformed into bulk phase and then coarsened with roughness even larger than that of the primary Si bulk phase.3)The hot extruded Al-27%Si alloy had small uniform microstructure, the small Si particles uniformly dispersed in the Al matrix, dendritic structure eutectic silicon phase disappears. Alloy has higher strength level, the mechanical strength declines and the extensibility increases with a rising temperature. At300℃, the alloy still maintains a certain strength, and its tensile stress is102Mpa, elongation is13%.4) rapidly solidified Al-27%Si alloy had a good mechanical or thermophysical stability and a strong ability to survive thermal fatigue. After400times of thermal shocks, the tensile stress of the alloy was170Mpa, the thermal expansion coefficient was16.48×10-6/K, the thermal conductivity was148W·(m·K)-1, which is still a satisfactory value.