Simulation Of Diffusion Coefficients And Microstructure Evaluation In Al Alloys

Multi-component Al alloys are of great commercial value. Al alloys are extensively utilized in aviation and civil industries. The understanding of the relationship among microstructure, processing and properties is critical for the design of advanced Al alloys. Microstructure simulation based on first-principles calculation, thermodynamic and kinetic databases, and phase field method can be an effective approach to gain insight in the relationship among microstructure, processing and properties of alloy systems. Diffusion is an important factor which can seriously affect the reliability of phase field simulation. Thus, the establishment of an atomic mobility database for multi-component Al alloys is of vital importance for the development of Al alloy industry.A key senary system, Al-Ag-Cu-Mg-Ni-Zn, in the multi-component commercial Al alloy was chosen as the target in the present thesis, aiming at the simulation of diffusion coefficients and microstructure evolution. Based on the critically reviewed available experimental diffusion information on the fcc Al-Ag, fcc Al-Zn, fcc Ag-Zn, fcc Cu-Zn, fcc Ni-Zn, fcc Al-Ag-Zn, fcc Al-Cu-Zn, fcc Al-Mg-Zn, and fcc Cu-Ni-Zn alloys, the atomic mobility parameters for these systems were accurately assessed by using DICTRA (Diffusion Controlled TRAnsformations) software. By combining the corresponding thermodynamic database, the obtained atomic mobilities were applied to predict various diffusion phenomenons, such as concentration profiles, diffusion paths, and Kirkendall effect, etc. In conjunction with the reported atomic mobility parameters and thermodynamic descriptions for other sub-ternary systems, one set of self consistent atomic mobility and thermodynamic database were established for fcc Al-Zn-Mg-Ag and fcc Al-Zn-Mg-Cu alloys. The database can predict the concentration profiles of diffusion couples in fcc Al-Zn-Mg-Ag and fcc Al-Zn-Mg-Cu alloys with a high accuracy.By coupling the atomic mobility database and thermodynamic database, the MICRESS (MICRostructure Evolution Simulation Software) software developed on the basis of multi-phase field method was used to conduct two dimensional simulations for the microstructure evolution of γ’ phase precipitate in the γ Al-Ni matrix. The data input for the simulation are experimentally determined ones from the literature. In addition, the effect of coherency stress on the shape of precipitates and the coarsening process was also considered. The simulated microstructure evolution process was in agreement with the experimental observation.