Preparation And Properties Of SiC_P/Al Composites With High Volume Fraction By Powder Metallurgy Method

High volume fraction?40⁷0%?SiCP reinforced Aluminum matrix composites?AMCs?with have great application potential in electronic packaging applications,due to its high thermal conductivity,low thermal expansion coefficient,high strength and low density.In this paper,SiCP reinforced AMCs with high volume fraction was prepared by Powder metallurgy?P/M?.The effect of the volume fraction and particle size of SiC_P on the properties of the composite was systematically studied.In view of the problem of poor wettability between SiC_P and Al,the surface modification of SiC_P and the addition of Si elements in the composites powder are used to prepare high volume SiC_P reinforced AMCs,and the densification process,interfacial reaction,mechanical properties and thermal physical properties of high volume fraction SiC_P/Al composites were investigated.The SiC_P-Al powder was prepared by planetary ball milling?PBM?through a wet milling process,and the high volume fraction of SiC_P reinforced AMCs was sintered by spark plasma sintering?SPS?suing SiC_P-Al powder.The results show that the composites with good dispersion of SiC_P can be obtained with suitable ball milling and sintering process.The relative density of the composites can be over 99%.The thermal conductivity of the 56?m 52vol.%SiC_P/Al composite is 204 W/mk,the average bending strength is 392 MPa,and the average thermal expansion coefficient of 25²00°C is 11.50×10^-66 K^-1.Through the thermodynamic calculation,it is found that the composites is difficult to carry out spontaneous interfacial reaction under the present sintering process.At the same time,the Al₄C₃ diffraction peak was not found in the XRD patterns of the 52 vol.%SiC_P/Al sample.As the median diameter of SiC_P is 56?m and the volume fraction changes in the range of42⁶0 vol.%,the bending strength of the sample increases first and then decreases with SiC_P of volume fraction increases.Compared with pure Al,the addition of SiC_P can effectively improve the thermal conductivity and reduce the thermal expansion coefficient of composites.When the volume fraction of SiC_P increases,the thermal conductivity increases at first and then decreases,but the thermal expansion coefficient always decreases.When the particle size of SiC_P decreases,the bending strength of the composite increases.The average thermal expansion coefficient of composites decreases with the decrease of SiC_P particle size.Through comprehensive consideration,it is more appropriate to choose the SiC_P with a median diameter of 56?m as reinforcements.In order to improve the wettability of SiC_P and Al matrix,the surface oxidation of SiC_P was carried out at different temperatures and holding time.The results show that the thickness of SiO₂ layer increases with the increase of oxidation temperature and oxidation time,and the relative density and bending strength of the specimen remain unchanged.The average bending strength of the SiO₂ layer with the thinnest thickness reaches the maximum value of 443 MPa,which is 13%higher than that of the untreated sample.By measuring the thermal conductivity of the samples,the moderate thickness of SiO₂ layer?1100°C treat 2 h?has the least effect on the thermal diffusion rate and thermal conductivity of the sample.A small amount of SiO₂ on the surface of SiC_P has little effect on the thermal expansion of the composites.In order to reduce the thermal expansion coefficient of the composites and suppress the bad interfacial reaction during sintering,Si element was added to prepare densified 52vol.%SiC_P/Al-Si composites in the experiment.The results showed that the relative density and bending strength of the samples decreased with the rise of Si content.The bending strength of52 vol.%SiC_P/Al-1Si sample reached 427 MPa,which was 10.8%higher than that of Si samples.When Si content is less than 6 vol.%,the thermal conductivity of samples at25¹00°C are greater than the sample without Si.The average thermal expansion coefficient decreases obviously with the increase of Si content,and the average thermal expansion coefficient of 52 vol.%SiC_P/Al-8Si decreases to 9.54×10^-6 K^-1 at 25²00°C.The fracture mechanism of high volume fraction SiC_P reinforced AMCs is mainly based on the combination of brittle fracture of SiC_P and ductile fracture of Al matrix through the analysis to the SEM photos of the composites fracture.The interface between SiC_P and Al matrix is well connected,and SiC_P can effectively carry and transfer load.In the samples,the dimples on the matrix decrease and shrank with the increase of Si content,indicating that the plasticity of the matrix decreases.