Study On Microstructure Regulation And Properties Of NANO-SIC Reinforced Aluminum Matrix Composites By Selective Laser Melting

SiC reinforced aluminum matrix composites(AMCs)exhibit wide application prospects in aerospace,automotive lightweight and other fields due to its high specific strength and modulus,good electrical and thermal conductivity,as well as excellent fatigue resistance and impact resistance.In recently,with the development of AMCs preparation technology,selective laser melting(SLM),as a new process for forming high-performance AMCs with complex shape,has attracted extensive attention due to its near net shape,the fine grains of as-fabricated sample,uniform distribution of reinforcement,and good interface between reinforcement and matrix.However,micron-sized SiC particles with irregular shapes would seriously impede the powder spreading,cause local stress concentration and particle cracking during tensile loading,resulting in a significant decrease in the plastic toughness of the material.The strengthening effect of SiC particles is difficult to effectively exert.These factors have become the main bottleneck restricting the performance improvement of SiC reinforced AMCs.To solve these problems,near spherical nano-SiC particles were selected as reinforcement in this study.Firstly,SiC/Al Si10Mg composite powder was prepared by low-energy planetary ball milling(LEPBM)and then the composites were fabricated by SLM,the influence of scanning speed and heat treatment on the microstructure and properties of AMCs were studied.In view of the existing problems nano-SiC reinforced AMCs prepared by SLM,the optimal process window was obtained by optimizing the powder mixing process and SLM parameters.Based on the analysis of densitifacation,phase composition,microstructure evolution,interface structure,tensile/compressive mechanical properties and hardness of AMCs,the influence of laser energy density(E_V)on the interfacial bonding evolution between Al matrix and SiC particles and its effect on the mechanical properties of AMCs were discussed.The results showed that it is difficult to obtain composite powders with uniform dispersion of nanoparticles by direct ball milling.When the scanning speed is 1000 mm/s,the maximum relative density(97.94%)was obtained,as well as the hardness(121 HV_0.2)and tensile strength(387 MPa)were also reach the maximum value,but it is still lower than pure Al Si10Mg alloy.Microstructure showed that there were many pores existed in the samples,and low energy input leads to the formation of a large number of Al₄C₃ brittle phase and?-Al Fe Si phase.Under the action of tensile stress,Al/Al₄C₃ interface is easy to debond,which is unfavorable to the improvement of strength and ductility of AMCs.After annealing at 300?for 2 h,the hardness and strength decreased to 74 HV_0.2 and 254 MPa,respectively.The eutectic network were broken and Si precipitated from the supersaturated?-Al matrix during annealing.It is obvious that the weaken solution strengthening effect,the destruction of network structure and the coarsening of grains decresed the hardness and strength of AMCs.Based on the above experimental exploration,this study further realized the uniform dispersion of SiC nanoparticles in Al based spherical powder through the combination of solvent assisted dispersion(SAD)and low-energy planetary ball milling(LEPBM).In the process of SLM process optimization,it is found that when?is fixed as 250 mm/s,AMCs samples with nearly full density can be prepared at laser power(P)above 150 W;SiC nanoparticles were distributed uniformly along sub-grain boundaries,and the matrix grains were refined significantly.With the increase of E_V,the eutectic structure gradually changed from thick flakes to network shapes,and finally tended to disperse.Meanwhile,SiC particles are partially dissolved and reacted with the matrix during SLM.The increase of molten pool temperature promoted the transformation of the reaction product into Al₄SiC₄,thus strengthening the interface bonding strength between Al/SiC.It is suggested that the superior strength and elongation to failure were obtained at high laser-energy-input,which is mainly attributed to uniform microstructure,strong metallurgical/interface bonding and the effective load-bearing.The optimum mechanical performance(131.7 HV_0.1 for hardness,101 GPa for modulus,440 MPa for strength)is obtained at 210 W,which are increased by 9.1%,2.8%and 10%respectively compared with pure Al Si10Mg alloy,while maintaining a good ductility(7.4%).