Effect Of Graphene On Microstructure And Properties Of Aluminum Alloy Formed By Selective Laser Melting

Graphene/aluminum composite are widely used in transportation,aerospace,energy and power fields due to their advantages of high strength,good wear resistance and small thermal expansion coefficient.Supported by the National Natural Science Foundation of China(No.: 51775521)and the scientific research support project for returned overseas students of Shanxi Province(No.: 2017-095),the research on graphene/aluminum composite was carried out.In this paper,AlSi10Mg-0.5wt.% graphene composite powder was prepared by vacuum mechanical ball milling,then High-quality AlSi10Mg-0.5wt.% graphene composite is formed by Selective laser melting(SLM).The SLM forming process of AlSi10Mg-0.5wt.% graphene composite was optimized,and the structure and properties of AlSi10Mg-0.5wt.% graphene composite material were analyzed.The research results are as follows:(1)The effect of graphene on the microstructure of AlSi10Mg-0.5wt.% graphene composite was studied.When the laser power is 220 W,the defects in the composite material are the least,and the forming quality is the best.The laser power is less than 220 W,the composite is warped,and the laser power is greater than 220 W,the defects in the composite material increase.The main defects in the composite materials are: 1)The oxide film on the surface of the AlSi10 Mg powder absorbs the moisture in the air.During the SLM process,the moisture decomposes to generate hydrogen,forming hydrogen pores in the composite.2)If there are graphene agglomerations in the composite powder,graphene pores will be formed in the composite;3)If the laser power is too high,intergranular cracks,liquefying cracks will be formed in the composites.And If the laser power is too low,irregular holes will be formed in the composites.Using proper method to pretreat powder and optimize SLM forming process can effectively reduce the probability of defects.(2)The effect of graphene on the microstructure of AlSi10Mg-0.5wt.% graphene composite was studied.The addition of graphene can effectively refine the cell of the composite and promote the dispersion distribution of eutectic Si phase in cell.Graphene can be used as the nucleation sites in the composite to improve the nucleation rate of Al matrix.At the same time,graphene can block the grain boundary movement to inhibit the crystal cell growth.Graphene can improve the cooling rate of the composite to refine the crystal cell and eutectic Si phase.(3)The effects of graphene content,sliding speed and temperature on the wear resistance of AlSi10Mg-0.5wt.% graphene composite were studied.The results show that the formation of graphene film and mechanical mixed layer is the main reason for the improvement of wear resistance of the composite.At room temperature,sliding speed is 5m/min,the wear mechanism of AlSi10Mg-0.5wt.% graphene composite is abrasive wear,mixed with adhesive wear,the wear mechanism of AlSi10 Mg alloy is adhesive wear,the wear mechanism of AlSi10Mg-1wt.% graphene composite is abrasive wear,mixed with fatigue wear.At room temperature,the sliding speed is 2m/min,the wear mechanism of AlSi10Mg-0.5wt.% graphene composite is adhesive wear,mixed with abrasive wear.At high temperature,the wear mechanism of AlSi10Mg-0.5wt.% graphene composite and AlSi10 Mg alloy is adhesive wear,the wear surface of the composite is smoother,the friction coefficient curve of the composite is more stable,which shows that the composite can still maintain good wear resistance at high temperature.(4)The compressive deformation behavior and conductivity of AlSi10Mg-0.5wt.% graphene composite were studied.The maximum compressive strength of AlSi10 Mg alloy is 19.76 KN,and that of AlSi10Mg-0.5wt.% graphene composite is 27.58 KN.The main reasons for the improvement of compressive strength of composite are as follows: 1)the cell size of composite is small,which plays the role of fine grain strengthening;2)the size of eutectic Si phase in the cell of composite is small and dispersion distribution,which can high-efficiency pinning position;3)graphene is well combined with the matrix to ensure the efficient transmission of load and play the excellent mechanical properties of graphene.The fracture mode of composite is ductile fracture.