Abstract
The development in electronics and semiconductors industry requires better packaging materials. Among the candidates is silicon particle reinforced Al-base composite material, which has high thermal conductivity, low thermal expansion and relatively low density. It is of great value both theoretically and commercially to investigate into this composite
The solidified Al-Si composite is an in-situ composite. It is valuable to study the microstructure of primary Si phase solidified under different cooling conditions for better understanding and control of the primary Si phase in the composite.
The microstructure of Al-50%Si, Al-60%Si and Al-70%Si (weight percent) composites solidified under different cooling rates were studied to investigate the influence of Si content and the cooling rate on the size and shape of primary Si. It was found that the Si content controls only the size of the primary Si in the composite. The size of primary Si phase increases with the adding of Si content in the composite. While the cooling rate controls both the size and the shape of the Si phase. With the increase of the cooing rate, the primary Si in the composite changes from huge acicular (under 10K/s) to refined acicular(under 20K/s) and even equiaxed fine grains(under 106K/s).There is a critical cooling rate between 10-103K/s at which the shape of the Si changes suddenly.
A new fabrication method of Al-Si composite containing high silicon was indicated in this research. The composite was prepared by quasi-rapid solidification progress in vacuum. Microstructures and properties were studied and the results showed that the particle size of the primary Si could be refined to 10 μm ~30 μm, and the CTE of the Al-50%Si composite is 8.40×10-6/ K.
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