Influence of micron and nano SiCp on microstructure evolution and mechanical properties of laser metal deposition AlSi10Mg alloy

In this work, laser metal deposition (LMD) technique was applied to fabricate SiCp/AlSi10Mg composites. Innovatively, the effect of SiCp of different scale (micron, submicron and nano scale) on the microstructure and mechanical properties was studied. With the decrease of SiCp size, the reaction between SiC and aluminum matrix was more intense, and the volume fraction of Si precipitates and grain boundary Al-Si eutectic phase increased. Few micro-SiCp and agglomerated nano-SiCp were all unevenly distributed in the aluminum matrix, which caused the bimodal distribution of grain size in varying degrees. The mechanisms of defect formation, phases evolution and mechanical property enhancement were also discussed. Due to the agglomeration of nano-SiCp and its decomposition under laser irradiation, the seriously uneven microstructure of nano-SiCp/AlSi10Mg limited the mechanical properties. Moreover, the addition of SiCp increased the Marangoni flow instability of molten pool, leading to the high porosity and reducing the tensile strength of composites, which was more prominent in the samples containing micron and nano SiCp. Submicron-SiCp/AlSi10Mg presented uniform equiaxed crystals and the best comprehensive mechanical properties (microhardness 118.37HV, wear rate 1.60 x10(-3) mm3N- 1m- 1 and UTS 269.08 MPa). Based on the experimental results, adding multi-scale reinforcements will be more conducive to the performance optimization of composites. This study provides theoretical guidance for the engineering application of SiCp/Al composites.