Preparation Of Aluminized Graphene/Aluminum Matric Composite Powder And The Selective Laser Melting

In this paper,the surface of graphene was aluminized by chemical reduction of organic aluminum,and the aluminized graphene/aluminum matric composite powder was prepared by vacuum ball milling.Then selective laser melting(Selective Laser Melting,SLM)was used to form the aluminized graphene/aluminum matric composites.The reaction mechanism and thermodynamics of aluminum plated on the graphene surface was studied.The process parameters of vacuum ball milling aluminized graphene/aluminum matric composite powder was optimized,and the microstructure and properties of SLM formed aluminized graphene/aluminum matric composites were analyzed.The following conclusions were drawn:(1)The microstructure evolution of aluminum plated on graphene surface and the effects of process parameters on aluminum plated on graphene surface were obtained.During aluminum plated on graphene surface,the Al formed by alkyl aluminum decomposition was nonuniform nucleation on the surface of graphene,and grown up with layer growth and three dimensional crystal growth mechanism,which forming lamellar and columnar aluminum particles on the surface of graphene as the reaction process.With the increase of reaction temperature,the thermal decomposition of triethyl aluminum was intensified,make the content of aluminum particles in the coating increase and tend to be evenly distributed.After adding the reducing agent NaH,the reaction of NaH and two ethyl aluminum bromide promoted the formation of two ethyl aluminum hydride,cause the content of aluminum particles in the coating increase obviously and the distribution of aluminum particles was more uniform.When the reaction time was 1.5h,the reaction temperature was 100?,and NaH was used as reducing agent,the aluminized graphene powder with uniform distributionof aluminum particles on the graphene surface was obtained.(2)The thermodynamic properties of aluminum plated on graphene surface were obtained.At 298.15 K,the ?H of the reaction of half substance preparation was-160.77kcal/mol,the ?G was-139.83kcal/mol,the ?S was-70.2cal/mol·K,and the reaction was exothermic.The ?H of the reaction of triethyl aluminium(AlEt3)preparation was10.64kcal/mol,the ?G was 19.87kcal/mol,the ?S was-30.9cal/mol·K,and the reaction was endothermic.The ?H of the reaction of AlEt3 thermal decomposition was-20.21kcal/mol,the?G was-54.822kcal/mol,the ?S was 116.08cal/mol·K,and the reaction was exothermic.The?H of the reaction of two ethyl aluminum bromide thermal decomposition was-15kcal/mol,the ?G was-47.36kcal/mol,the ?S was 108.54cal/mol·K,and the reaction was exothermic,which was corresponded to the experimental phenomenon.(3)The effects of process parameters on the dispersivity of aluminized graphene were obtained.As the ball to powder weight ratio increase,the impact and shear effect of powder were strengthened due to the increase of ball milling media,which cause the dispersion of aluminized graphene increase.But when the ball to powder weight ratio was too large,the effective space occupied by ball milling media increased,which was not conducive to the dispersion of powder.With the increase of ball milling speed,the impact and shear force of powder were increased,and the dispersity of aluminized graphene increaseed.Meanwhile,the deformation of aluminum alloy powder occurred.With the increase of ball milling time,the aluminized graphene dispersed evenly,and when the ball milling time was too long,the deformation of aluminum alloy increased.When the ball to powder weight ratio was 8:1,the ball milling speed was 230 rmp and the ball milling time was 2h,the composite powder with better dispersion of aluminized graphene was obtained.(4)The influence of laser power on the forming quality of composites was obtained,and the microstructure and properties of composites were gained.With the increase of laser power,the forming quality of composites was getting better.However,when the power increased to a certain value,there were significant defects on the surface.When the laser power was 300 W,the composites with better forming quality and less internal defects was obtained.The maincontents of the composites were Al,Si and graphene.The distribution of graphene in the composites was more uniform,and there was good interfacial bonding between graphene and Al matrix,which improved the mechanical properties of the composites.The microhardness of the composites was 169 Hv,which was 40.8% higher than that of AlSi10 Mg material.