Microstructure And Properties Of SiC_p/AlSi₁₀Mg Composites By Selective Laser Melting

Selective Laser Melting(SLM),as a new preparation process of top-down layer by layer forming,has the advantage that complex structural parts difficult to achieve by traditional manufacturing methods can be processed.Metal powder can be fully melted to form high quality and high density parts;Rapid cooling can effectively refine the microstructure and significantly improve the mechanical properties,which is expected to solve the problems encountered by traditional manufacturing methods.In this paper,SiCp/AlSi10Mg composites were successfully prepared by SLM technique.With the final forming sample quality as the main criterion,The effects of different laser treatment processes and parameters on the properties such as phase,compactness,microstructure,mechanical properties,friction and wear of SLM SiCp/AlSi10Mg composites,and the effects of different oxidation and heat treatment processes on the microstructure and mechanical properties of SLM forming parts were analyzed.The main results are as follows:(1)The variation of density,microstructure and physical properties of SLM forming samples with forming process were revealed.With the increase of scanning speed and scanning spacing,the density of SLM forming parts increases firstly and then decreases.When the scanning strategy is 67° deflection scanning,the SiC particles are uniformly distributed and have high density.The optimal process parameters are:scanning speed 1100 mm/s,scanning spacing 0.11 mm,scanning power 340W,powder layer thickness 30 um.The energy of high-energy laser beam makes the microstructure of SiCp/AlSi10Mg composites prepared by SLM have fine equiaxed ?-Al base and lattice Si eutectic distributed between matrix,and the in-situ reaction between SiC particles and Al matrix produces Al4SiC4 reinforced phase.The final SLM can be divided into central zone,pool boundary zone and part of heat affected zone in the microstructure.The maximum microhardness is 189HV and the friction coefficient and wear rate are relatively low,which are 0.44 and 3.38×10-5mm3N-1m-1 respectively.The maximum tensile strength is 365 MPa and the elongation is 2.2%.(2)High temperature oxidation of SiC particles can improve the interface bonding between SiC particles and Al matrix and improve the properties of composites.When the oxidation temperature of SiC is maintained above 1200? and the oxidation duration of SiC is 2h-6h,the SiC surface eventually presents crystalline SiO₂ with high temperature quartz.SiC particles are passivated at the edges and corners after oxidation.The distribution of SiC particles in SLM-formed composites gradually improves with the change of oxidation degree and the interfacial bonding of composites also improves with the change of oxidation degree.The SiO₂ produced by the oxidized SiC particles formed a new interfacial structure between Al matrix and SiC particles,which realized a good wettability.The maximum relative density and tensile strength of the composite were 98.36%and 376MPa when the composite was oxidized at 1200? for 6h.The wear resistance is improved when the wear rate decreases,and the wear mechanism is changed to abrasive wear.(3)The effect of heat treatment on microstructure and properties of SiCp/AlSi10Mg composites formed by SLM was clarified.When T6 heat treatment,the net-like eutectic Si is completely decomposed and converted into separated large Si particles during solution,and the tensile strength and hardness of the formed samples are significantly reduced and the ductility is increased.After the completion of T6 heat treatment,Si precipitates from the matrix and is no longer connected and acicular AlFeSi intermetallic compound precipitates from the Al matrix,which increases the hardness and tensile strength and decreases the ductility.After heat treatment,equiaxial dimples appeared at the tensile fracture of the specimen,and the fracture mode turned into typical ductile fracture.