Interfacial Bonding Mechanism Of Graphene/Aluminium Matrix Composites Formed By Selective Laser Melting

The study of graphene?Gr?reinforced AlSi10Mg composite is of great significance for the development of new aluminum matrix composites and the application of aluminum matrix composites.With the support of the National Natural Science Foundation of China?No:51775521?and Research Project Supported by Shanxi Scholarship Council of China?No:2017-095?,a new Gr/AlSi10Mg composite with excellent tensile strength and hardness was prepared by selective laser melting?SLM?.It was found that there are multiple phases in the composites and the internal composition is relatively chaotic.The graphene added into the composites formed a two-phase interface with the matrix,which brought instability to the strength of the composites.Moreover,the graphene reacted with the aluminum atom,forming the Al₄C₃ phase.The influence of this new phase on the matrix material also needs to be further explored.To this end,based on experimental results,the first-principles calculation method was used to study the effect of Al₄C₃ on the nucleation of aluminum atom and the bonding strength of the Mg₂Si/Gr interface in the Gr/AlSi10Mg composites.The conclusions are as follows:?1?The interfacial bonding between graphene and matrix in the SLM formed Gr/AlSi10Mg composite was studied.The distribution of graphene in composites is uniform,a stable metallurgical bonding area was formed between the graphene and matrix.During the selective laser melting,the high-energy laser destroys the structure of graphene added into the composite,resulting in the formation of some hole defects with different sizes on the surface of graphene.This phenomenon leads to an increase in the reactivity of the carbon atoms at the edge of graphene,and some unstable carbon atoms react with aluminum atoms to form the Al₄C₃.?2?The elastic modulus and elastic anisotropy of Al,Al₄C₃ and Mg₂Si which were presented in the SLM formed Gr/AlSi10Mg composites were studied and the lattice mismatch of Gr/Al,Gr/Mg₂Si and Al₄C₃/Al interfaces was calculated.The results show that the elastic modulus of these three phases are anisotropic.According to the two-dimensional lattice mismatch theory,?0001?_Al4C3/?111?_Al orientation has the smallest lattice mismatch between Al₄C₃ and Al,and a semi-coherent interface may be formed between Al₄C₃ and Al;?0001?_Gr/?011?_Al orientation is beneficial to form a coherent interface between graphene and aluminium;graphene and Mg₂Si can form a completely coherent interface with low interfac ial energy under?0001?_Gr/?001?_Mg2Si orientation.?3?The stability of Al/Al₄C₃ interface was studied and nucleation analysis was carried out.The simulation results show that the interfaces composed of three low-index surfaces Al?001?,Al?011?,Al?111?with Al₄C₃?0001?have stable structures.For C-termination interfaces,there is an interaction between the electronic orbits of Al atom and that of C atom,which caused the formation of Al-C covalent bond at the interface.For Al-termination interfaces,Al-Al metal covalent bond is formed at the interface.The analysis of interfac ial energy and thermodynamics shows that Al₄C₃ can be palyed as the heterogeneous nucleation substrate of?-Al in Gr/AlSi10Mg composite.?4?The stability of Mg₂Si/Gr interfaces were studied.The simulation results show that the interfaces constructed with low-index surfaces Mg₂Si?001?,Mg₂Si?011?,Mg₂Si?111?and Gr?0001?have smaller interface adhesion work and larger interfac ial energy,and the interfacial spacing of the stable interface were larger than the length of the chemical bond.After analysed the charge density difference and the partical density of states,it was concluded that there is no chemical bond at the Mg₂Si/Gr interfaces,only strong Van der Wals forces.The interfacial energy of Mg₂Si/Gr is much greater than that of?-Al/Al melt?0.15 J/m²?.When the Gr/AlSi10Mg composite is deformed under stress,the Mg₂Si/Gr interface in the composite is easy to separate and become the crack growth source.Therefore,the formation of Mg₂Si/Gr interface should be avoided in the preparation of Gr/AlSi10Mg composite.