Research On Forming Mechanisms And Properties Of Multiphase Reinforced Aluminum Matrix Composites By Selective Laser Melting

The multiphase reinforced aluminum matrix composites were successfully fabricated by selective laser melting technology in the present paper from the mixed powder materials of SiC powders with different particle sizes and AlSi10 Mg powders. The influence of laser process parameters on the phase, densification level, microstructure characteristics, microhardness and wear performance of SLM-process AMCs samples was studied. The influence of SiC particle size on the microstructure and properties of SLM processed composites was discussed. The in-situ reaction process and the growth mechanism of the in-situ reinforcing phase were analyzed.SiC particles reacted with Al melt in the molten pool, leading to the producing of Al4 Si C4 reinforcing phase. The reinforcement of SLM-process multiphase reinforced AMCs included SiC particles, plate-structured Al4SiC4 reinforcement and particle-shaped Al4SiC4 structure. When the laser energy input was relatively low, the extent of in-situ reaction was limited and the growth of Al4SiC4 phase was insufficient, resulting in the low microstructural homogeneity, densification level and properties. When the laser energy density was 1000 J/m, the reaction was accelerated, promoting the consuming of SiC particles and full growth of plate-structured Al4SiC4 reinforcement. Particle-shaped Al4SiC4 reinforcing phase was dispersed uniformly throughout the matrix. In this instance, the SLM-processed composite exhibited high densification of 96 % of the theoretical density and high microhardness of 214 HV0.1, with reduced coefficient of friction of 0.39 and wear rate of 1.56 ×10-5 mm3 N-1 m-1.As the particle size of the applied SiC powders decreased, the densification level and microstructural homogeneity of SLM-processed multiphase reinforced AMCs increased gradually, leading to the increasing of the microhardness and wear performance. When the fine SiC powders(D50=5 ?m) were used, the residual SiC particles were dispersed in the matrix with small size, enhancing the densification level of the composites. The growth of plate-structured Al4SiC4 reinforcement was sufficient and the size of particle-shaped Al4SiC4 reinforcement was near nano scale. Meanwhile, the microhardness of the composite reached 218 HV0.1, with an 80 % increase than the composite using coarse SiC particles, and the coefficient of friction and wear rate were just 0.34 and 2.94 ×10-5 mm3 N-1 m-1, respectively.The growth of the in-situ reinforcing phase of SLM-processed multiphase reinforced AMCs was influenced by the applied laser parameters. The plate-structured Al4SiC4 phase was formed based on the Si C particles and grew up as the laser energy increased. The growth of particle-shaped Al4SiC4 reinforcing structure was related with the laser energy input and the melt viscosity in the molten pool. With low energy input, the viscosity of melt in the molten pool was large and the rearrangement of the Al4 SiC particles was limited, resulting in the nouniform distribution and agglomeration of small particles. As the laser energy input increased, the viscosity of the melt decreased and the Marangoni convection was enhanced. The enhanced Marangoni convection accelerated the uniform distributio of the Al4SiC4 particles, resulting in presence of of the reinforcing particles with nano size.