Effect Of Oxidized SiC On Microstructural And Properties Of SiC/Al Composites By Selective Laser Melting

SiC/Al composite is a new preferred material for fabricating high reflectivity and light reflectors due to its low density,high specific strength,high specific modulus and high thermal conductivity properties,which can be widely used in aerospace,fire control,laser guidance and space optical remote sensing fields.However,the SiC particle content increases,the hardness of the material various.As a result,the SiC/Al composite mirror prepared by traditional technology possesses disadvantages,such as high processing difficulty,complex process,long processing cycle and high energy consumption.Fortunately,Selective Laser Melting(SLM)technology is suitable to produce thin-walled parts and other abnormal structure components through melting metallic powders layer-by-layer,it also can be combined by advanced design technology with high precision,high density and good mechanical properties.Therefore,it has received extensive attention at home and abroad.In this paper,the influence of SLM process parameters(laser power(P),scanning speed(V),scanning spacing(S))on the relative density of SiC/Al composites was systematically studied by using AlSi10Mg powder and SiC particle as raw materials.The SiCp/AlSi10Mg composites with volume fraction of 10%were prepared by the optimal process.In order to improve the wettability and bonding strength of the solid/liquid interface between SiC particle and Al matrix,the high temperature oxidation pretreatment of SiC particle was carried out to obtain a compact and uniform oxide film.The effects of high temperature oxidation of SiC on the microstructure,phase composition,microhardness,compression property and corrosion resistance of SiCp/AlSi10Mg composites were studied.The results are as follows:(1)The oxidation reaction of SiC particles starts at 800?,and the optimal oxidation process is 1200? for 4 hours.The amorphous SiO2 film can reach 347.6 nm on the surface of SiC particles.Meanwhile,the edges and corners of SiC particles are passivated and round,the cleavage surface platform is weakened and blurred,and the mechanically mixed SiCp/AlSi10Mg composite powder has certain fluidity.(2)The optimal deposition parameters of SiCp/AlSi10Mg composites is obtained when the laser power is 250 W,scanning speed is 1200 mm/s,the hatch space is 0.1 mm,and the highest relative density can reach 97.72%.The three parameters increase the relative density of SiCp/AlSi10Mg composites firstly and then decrease.According to the Box-Behnken response surface method,The relationship model between deposition parameters and the relative density of the SLMed composites is as follows:RD=90.6826-0.0053P+0.0032V+86.4484S+1.19×10-5PV+0.0459PS-0.0528VS-4×10-5P2+1.17×10-6V2-160.153 × S2 Where,P is the laser power(W),V is scanning speed(mm/s),S is scanning spacing(mm),RD is relative density(%).The results show that the influence reduces successively of scanning speed,laser power and hatch space on the relative density of the SiCp/AlSi10Mg composites,which is consistent with the results of orthogonal analysis of variance.(3)The microstructure of SiCp/AlSi10Mg composites is composed of a mixture of ?-Al matrix,eutectic Si phase,in-situ reaction Al4SiC4 reinforced phase and SiC particles.The microstructure of SiCp/SiO2/AlSi10Mg composites pretreated by high temperature oxidation of SiCp has a clear and bright SiO2 transition layer,and the interface bonding is smooth.The microstructure is the same as SiCp/AlSi10Mg composites,and the surface quality of the formed samples is high.(4)The high load transfer mechanism of SiCp/SiO2/AlSi10Mg composites formed by SLM is better than that of SiCp/AlSi10Mg composites with fine grain strengthening,solid solution strengthening and dispersion strengthening.Therefore,the microhardness,compression performance and corrosion resistance of SiCp/AlSi10Mg composites are higher than those of SiCp/AlSi10Mg composites.The microhardness in the horizontal plane and vertical plane is 246.25 HV and 184.67 HV,respectively,the yield strength reaches 481.9 MPa,and the elongation is 12.2%.The SiC particles in the fracture morphology are passivated and better bonded with the interface.The results of AC impedance and polarization curves also show that the corrosion resistance of SiCp/SiO2/AlSi10Mg composites is higher than that of SiCp/AlSi10Mg composites.