Aluminium-based Protecting Coatings On Magnesium: Fabrication, Microstructures, And Molecular Dynamics

Coatings on magnesium have been studied widely to provide a reliable protection to the base magnesium metal. Especially, a method of Al diffusion coating has been developed in recent years. In the other hand, fluidised bed reactor was studied in a lot of applications for the surface treatment of metals. Fluidised bed reactor can provide a dynamics environment for the reaction of solid state materials. However, there is no study on the fabricating Al diffusion coating in a dynamics environment yet. To study the diffusion behaviour of Al and Mg on an atomic scale, it is necessary to establish models to simulation this phenomena. Molecular Dynamics method is a widely used modelling tool for simulating different systems from metals to biomacromolecules. There is no any report on the study of diffusion behaviour of Mg-Al diffusion system using Molecular Dynamics simulations.In this work, the study includes two major parts:a) experimental study using a fluidised bed reactor, b) numerical modelling of diffusion behaviour using Molecular Dynamics method. In experimental work, Al powders are used to fabricate diffusion coatings on the surfaces of pure Mg cube substrate. All diffusion treatment procedures are carried on in a fluidised bed reactor. The effects of temperature and fluidisation are studied in fabrication of Al diffusion coatings. After metallographic preparation, microstructure of prepared coatings is analysed under an optical microscope to investigate the quality of fabricated coating. XRD test is carried on to study the composite of fabricated coatings.Meanwhile, Molecular Dynamic method is adopted to simulate the diffusion behaviour of Al-Mg system in this work. A model of Cu-Ag system using Molecular Dynamics method is employed to check the suitability of Molecular Dynamics and LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) software. Furthermore, models for Al-Mg system were established. Simulations are carried on using computing resource available in Victorian Partnership for Advanced Computing (VPAC). The post-processing of simulations are carried on with Atomeyes software, VMD software and some homemade programs. Sets of simulations were carried on to study the correction of models and effects of parameters. Different potential functions, including 1 pack of parameters with EAM potential function and 4 packs of parameters with MEAM potential function are applied to verify the suitability of different potential function parameters for Al-Mg diffusion problems. Visualisation of simulation results is carried on to present the diffusion process of Al-Mg system vividly. Sets of simulations with different temperatures and different pressures are carried on to study the effects of these parameters. The accuracy of models is discussed to verify the numerical modelling results to the experimental results. Qualitative analysis is carried on to compare the numerical modelling results with the experimental results.