Research On Selective Laser Melting Forming Of Aluminum Matrix Composites Reinforced By SiC And TiB₂

Ceramic reinforced aluminum matrix composites are widely used in aerospace,automobile and other fields for their light weight,high strength,good heat and abrasion resistance,high dimensional stability.The traditional processing routes generally in a low processing temperature,as a result,the problems such as the aggregation of the reinforcing phase and the weak combination of the matrix and the reinforcing phase are easy to occur.Selective laser melting technology has strong applicability of forming different materials systems,and has unique advantages in forming complex structure and high-performance metal components.In this paper,SiC powder and TiB₂ powder were well studied.These two kinds of ceramic powders were uniformly mixed with AlSi10Mg powder.The ceramic particles reinforced aluminum were successfully fabricated by Selective Laser Melting（SLM）technology.The action of laser parameters on the densification level,phase,microstructural characteristics,hardness and tensile performance has been researched.In addition,the strengthening mechanism of the reinforcing phase in aluminum matrix composites was discussed.Based on the combination of finite element numerical simulation and experimental investigation,quantitative thermal behavior during SLM of SiC/AlSi10Mg composites was performed.Under the action of a Gaussian distributed laser heat source,the temperature gradient inside the molten pool is different,which causes the microstructure evolution in the molten pool.The differences in microstructure and mechanical performance inside the molten pool were further studied.Through the analysis of the nano-hardness and elastic modulus at different positions of the melting pool,the results show that the nano-hardness of the composites prepared by SLM is more than twice that of the as-cast AlSi10Mg alloy.The micro-TiB₂/AlSi10Mg composite was successfully fabricated by SLM.The sample has a high density and can reach a maximum of 99%or more.The individual molten pool can be divided into three typical characteristic zones:center zone,boundary zone of a molten pool,and heat-affected zone.The characteristic morphologies of molten pool in three different regions are fine cell crystal,coarse cell dendrites,and Si particles,respectively.In the laser forming process,the TiB₂ powder particles and the AlSi10Mg do not undergo an interfacial reaction,and the bonding between the two interfaces is good.The addition of the TiB₂ particles can refine the grains.Thereby,the hardness and tensile properties of the TiB₂/AlSi10Mg composite are improved effectively.Grain refinement makes the composites have higher strength,so that the strength of TiB₂/AlSi10Mg composite fabricated by SLM is higher than that of AlSi10Mg alloy without adding reinforcing phase under the same preparation conditions.With the decrease of TiB₂ particle size,the submicron TiB₂/AlSi10Mg composites were fabricated by SLM.The density of the formed sample was higher,reaching a maximum of 99.5%.Due to the addition of small TiB₂ ceramic particles,the grain size of the composite was refined,and the solidification mode of Si precipitates in the matrix changed from cellular structure to directional linear structure.SLM-processed submicron TiB₂/AlSi10Mg composites have tensile strength of⁴37MPa and elongation of⁴.6%.It is significantly higher than the micron TiB₂/AlSi10Mg composite and AlSi10Mg alloy under the same SLM processing condition.