Effect Of The Porosity Of Perform On Microstructure And Performance Of The SiC/Al Composite Materials

High content SiC/Al composites materials have many excellent properties such as low density,high strength,well wear resistance,high thermal conductivity and low thermal.Therefore it has extensive potential applications materials in electronic packaging and wear-resistance.Now there have some questions of high sintering temperature of SiC preform,complex process of infiltration and low productivity in making SiC/Al composites materials.In this paper,a vacuum pressure infiltration method for making of SiC/Al composites was investigated.Study the effects of forming pressure,binder content,pore-forming content,glass powder content and sintering temperature on the porosity,bulk density and compressive strength of SiC preform.Study a controllable method for the porosity of SiC/Al preform.Study the microstructures and phases of SiC/Al composites and the effects of preforms with different porosity on the strength and thermal expansion of SiC/Al composites.Discuss the fracture mechanism of SiC/Al composites.The results are useful for the production and application of SiC/Al composites with high SiC content.The main results are as follows:(1)With the increase of the amount of Al(H2PO4)3,the porosity of the preform decreases and the bulk density and compressive strength increase gradually.With the increase of the glass powder content,the porosity of the preform decreases,the bulk density and the compressive strength increase and then decrease.With the increase of phenolic resin,the porosity of the preform gradually increased and the bulk density decreased.The sintering temperature of SiC preform can be reduced from 1000℃ to 700℃ and the SiC preform can meet the requirements of infiltration,when the forming pressure is 45 MPa,the mass percent of Al(H2PO4)3 is 10%and the mass percent of glass powder is 7%.The porosity of SiC preform can be controlled by controlling the amount of phenolic resin.(2)The SiC/Al composites were maded by vacuum pressure infiltration method are mainly composed of Al and SiC phases.The microstructure of the composites shows that the SiC particles are uniformly distributed in the aluminum alloy and the interface between the SiC particles and the aluminum alloy is well bonded.Al4C3 brittle phase is not formed at the interface,which is mainly due to the addition of glass powder to suppress the formation of Al4C3 brittle phase.With the increase of the porosity in the SiC preform,the flexural strength of the composites firstly increases and then decreases,and the compressive strength decreases gradually.When the porosity of the SiC preform is 45%,the flexural strength and compressive strength of the composites are 358.83 MPa and 354.03 MPa,respectively.(3)From the fractures of SiC/Al composites,it can be seen that the SiC particles are mainly brittle cleavage fracture while the aluminum alloy is dimple fracture.With the increase of the porosity in the SiC preform(the increase of the aluminum content in the composite),the dimple fracture characteristic of the composite gradually increases.Fracture crack source of SiC/Al composite from the preform in the process of forming SiC particles broken crack,fracture cracks along the SiC and aluminum alloy interface and SiC brittle fracture surface to expand.(4)The coefficient of thermal expansion of the composites increases with the increase of the porosity in the preform,and the thermal expansion coefficient decreases by 0.7 × 10-6 K-1 for every 2%decrease in the porosity.Aluminum alloy is the main reason for the increase of the expansion coefficient of the composite.