Research On The Fabrication And Characterization Of Aluminum/graphene Composites Synthesized By In-situ Reduction Reaction Method

Compared with ceramic phases(SiC,Al2O3),graphene,with perfect mechanical and thermal properties,can enhance the mechanical and thermal properties of the aluminum matrix with rather low addition.The density of graphene is low,which makes the density of the composites lower.What's more,the difficulty of machining caused by the hard,brittle ceramic phases can be solved by the use of graphene.Based on the present situation of AI/graphene composite,we first coated graphene onto the surface of aluminum particles by the method of in-situ reduction.Then,the bulk composites were prepared by the powder metallurgy(P/M)technique.The mechanical and thermal properties of bulk composites after sintering are better than that of pure aluminum.The solution was stable when the concentration of graphene oxide was adjusted to 0.2 mg/ml.The weak acid solution with the pH value of 4.0 could remove the thin aluminum oxide layers on the surfaces of A1 powders without severely corroding the powders.The removal of aluminum oxide layers can lead to the sufficient contact between aluminum powders and solution,and in-situ reduction reaction of graphene oxide(GO)will happen on the surface of metallic aluminum.The reduced graphene oxide(rGO)can be attached to the surfaces of aluminum particles closely after in-situ reduction reaction.We found that the hydrolysis reactions occurred during the 8 hours' drying process.Al(OH)3,as the reaction products,would have bad influence on the properties of composites.In order to avoid this side reaction,the powders after reaction were washed by ethyl alcohol before drying.The composite powders without washing were synthesized as comparison.The spontaneous hydrolysis reaction occurred violently because of the high surface energy of the micro-sized Al particles.The formation of Al(OH)3 on the surface of A1 particles makes the powders heavier.The bulk samples were sintered at 600 ? for 5 h in Ar atmosphere after optimization.Pure sample,composite samples(?40×5 mm)with 0.1 wt.%,0.2 wt.%and 0.3 wt.%graphene additions were prepared.Morphology and structures of graphene coated powders and bulk samples were characterized.SEM and TEM images indicated that graphene was coated onto the surfaces of aluminum particles closely,and the lattice structure of reduced graphene oxide was obvious.Raman spectrum indicates that ID/IG ratio increases from 0.84 to 1.13 after graphene coating,which means that the graphene oxide was reduced in certain degree.No diffraction peaks of oxide or carbide were observed from the XRD pattern.The density of the bulks was measured to be 1.132 g/cm3,1.128 g/cm3,1.125 g/cm3 and 1.132 g/cm3 respectively by the Archimedes principle method,which indicates that the density decreases with the increased addition of graphene.Mechanical and thermal properties of bulk samples were characterized.The compressive strength is 207 MPa,232 MPa,249 MPa and 260 MPa for pure Al,0.1%rGO/Al,0.2%rGO/Al,and 0.3%rGO/Al,respectively.Their Vickers hardness values are 43.1 ±2.5 HV,49.2 ± 2.5 HV,50.7 ± 1.2 HV and 52.2 ± 1.9 HV.Their thermal conductivity are 143 W/(m*K),154 W/(m*K),159 W/(m*K)and1 65 W/(m*K)at 20?.And the specific heat capacity are 0.905 J/(g*K),0.921 J/(g*K),0.928 J/(g*K),0.987 J/(g*K)at 20 ?,respectively.The DSC curves indicate that the specific heat capacity of composite with 0.3 wt.%graphene is lager than that of pure A1 before melting.Copper and titanium powders were also used to prove the usability of the method of in-situ reduction reaction method for rGO coating.Ethyl alcohol should be introduced into the graphene oxide solution to improve the wettability between copper powders and solution.What's more,the oxide layers of titanium particles should be etched away by hydrofluoric acid and nitric acid.In consideration of the risk of using acid,we explored the method of coating graphene oxide layers onto powders by the mechanism of electrostatic self-assembly method,which can be used for metal powders with stubborn oxide layers,such as titanium.The method was turned out to be effective.