Fabrication And Mechanical Properties Of Copper Coated Graphene Nanoplatelets Reinforced Al-Si Alloy Matrix Composites By Stir Casting Method

The stir-casting method is considered as a breakout in mass production of graphene reinforced aluminum matrix composites,due to its advantages like low cost,simple operation process,and large-scale output.On account of the poor wettability and large density mismatch between graphene and liquid aluminum,when directly added into the molten aluminum,it is easy for graphene to float on the surface of the liquid aluminum and difficult to uniformly disperse into the matrix.Moreover,the poor wettability between graphene and Al matrix caused by the large difference in surface tension of them makes it difficult to achieve a good interfacial bonding between graphene and the matrix,resulting in poor strengthening efficiency and poor elongation of the composites.Therefore,it is very difficult to successfully introduce graphene into molten Al matrix directly.Exploring a new graphene synthesis method to improve the wettability between graphene and aluminum thereby achieving fabrication of graphene reinforced aluminum matrix composites by stir casting is of great significance to the application of the new matetials in industry in the future.In this work,Cu nanoparticles coated graphene nanoplatelets(Cu-NPs@GNPs)were synthesized by the spray drying method with the assistance of Na Cl templates and used for reinforcing Al-10Si composites through stir casting process.The effect of the ratio of precursors of Cu-NPs@GNPs on the quality and morphology of graphene was explored.The effects of mixing parameters during stirring process on the mechanical properties of composites were studied.The effects of Cu-NPs@GNPs on the structure and mechanical properties of composites were investigated.The roles of Cu nanoparticles and graphene in strengthening mechanism were discussed.The results showed that the ratio of raw material and water content of Cu-NPs@GNPs precursor had a significant effect on the quality of graphene,and the optimization of process parameters could achieve stable and efficient preparation of high-quality Cu-NPs@GNPs.Shift-speed ball milling process can disperse Cu-NPs@GNPs evenly in aluminum powders.Cu-NPs@GNPs was effectively added into Al-Si melting by using Al-(Cu-NPs@GNPs)master alloy.The mixing time during stirring melting stage had an important effect on the dispersion effect of graphene in Al-Si matrix,and then affected the mechanical properties of composites.GNPs showed refining effect on Si phase and?-Al.The coating of Cu-NPs can not only reduce the density difference between GNPs and the matrix to hinder the upward floating of GNPs in molten Al Si alloy,but also helped to protect the structure of GNPs and promote the Al/GNPs interfacial bonding through reacting with Al matrix to form Al₂Cu on the interface.As a result,the as-prepared 0.5 wt.%Cu-NPs@GNPs/Al-10Si composite exhibited tensile strength of 251 MPa(45%enhancement compared to Al-10Si)with a total elongation of 15%.