Effects Of Oxidation Of Si Particles On Microstructure And Properties Of SiAl Composite

Si/Al composite was fabricated by pressureless infiltration. The effect of oxidation of Si particles on composite was investigated. The oxidation characteristics of Si particles and the microstructure of Si/Al composite were investigated by X-ray diffraction, scanning electron microscope, spectrum analyzer and optical microscope.The effect of oxidation of Si particles on microstructure formation mechanism of Si/Al composite was discussed. Combined with the microstructure of composite,thermal conductivity, the thermal expansion coefficient and the bending strength were tested by laser thermal conductivity meter, thermal expansion instrument and a universal testing machine. The effect of oxidation of Si particles on corrosion resistance of Si/Al composite was investigated by corrosion weight loss,electrochemical test and the microstructure after corrosion.The results show that Si particles can be obviously oxidized above 1000 ℃.The SiO2 layer comes into being on the Si particles after oxidation. The microstructure of Si/Al composite which is prepared by original Si particles is reticular.With the oxidation time increasing, the microstructure of Si/Al composite which is fabricated by oxidated Si particles will gradually transform into granular.Both the primary crystal Si which is precipitated in the Al alloy liquid and the eutectic Si which is produced by the eutectic reaction in the Al alloy liquid will attach to the coessential Si phase to grow in the cooling course after the pressureless infiltration of Si/Al composite which are fabricated by the original Si particles. This phenomenon is similar to separate-eutectic. However, in the cooling course after the pressureless infiltration of Si/Al composite which is fabricated by the oxidated Si particles, the SiO2 layer on the Si particles can hinder the dissolution of Si particles.With the increasing of oxidation time, the microstructure of Si/Al composite which is prepared by oxidated Si particles will gradually transform into granular. The increasing of Al matrix’s continuity can improve the thermal conductivity of Si/Al composite. But when the SiO2 layer on the Si particles are too thick to be consumed by the Al alloy liquid during the infiltration, the SiO2 will be thermal resistance which can reduce the thermal conductivity of Si/Al composite. The reticular Si phase can inhibit the expansion of composite. The oxidation of Si particles can increase the coefficient of thermal expansion and the bending strength of Si/Al composite.With the increasing of oxidation time, the interface of Si/Al composite will increase. Compared with the Si/Al composite which is fabricated by original Si particles, the corrosion resistance of Si/Al composite which is fabricated by oxidated Si particles is not well.