Investigation Of Phase Diagrams Of Mn-Ni-B, Cu-Mn-Ni, Cu-Ni-Si Systems Of Al Alloys And Phase Field Simulation Of Solidification And Aging Process Of Al Alloys

Description of materials microstructure is important for materials design. The thermodynamic and kinetic databases established by CALPHAD method provide accurate thermodynamic and kinetic data for quantitative simulation of microstructure. The phase field method based on accurate thermodynamic and kinetic inputs has been an effective method for simulation of microstructure evolution in recent years.Cu, Mn, Ni, Si and B are important alloying elements or additives in Al-based alloys, their phase relationships have influence on the phase equilibria of multicomponent Al alloys. The microstructure evolution of Al alloys in the preparation process can be obtained by phase field simulation. However, quantitative phase field simulation of multi-component Al alloys is rare. In the present work, a hybrid approach of experiments, first-principles calculations and CALPHAD is used to investigate the phase diagrams of Mn-Ni-B, Cu-Mn-Ni and Cu-Ni-Si systems, which are important sub-systems of multi-component Al alloys. The thermodynamic parameters obtained in the present work improve the thermodynamic database of Al alloys. Moreover, by coupling to the thermodynamic and kinetic databases of Al alloys, the multi phase field method is used to simulate the microstructure evolution of A1356.1(Al-0.46Fe-0.3Mg-0.32Mn-6.97Si, wt.%) alloy in the solidification process and the Al-Ni alloy in the aging process. The major research achievements of the present work are:(1) The NiB)2and NiB2are demonstrated to be unstable phases at950℃by XRD. The invariant temperatures in the Ni-B system are measured. The enthalpies of formation of all compounds are calculated by first principles calculation to assist the thermodynamic calculation. The thermodynamic parameters of Ni-B and Mn-B system are obtained by thermodynamic calculation and the calculated results agree with the experimental data. By combining the parameters of Ni-B, Mn-B and Mn-Ni systems, the thermodynamic calculation is performed on the Mn-Ni-B system. The liquidus projection and Scheil reaction scheme of Mn-Ni-B system are constructed using the obtained parameters.(2) The isothermal section of Cu-Mn-Ni system at600℃is measured. The three-phase equilibrium of cbcc_A12, cub_A13and fcc_Al is observed. The fcc_Al phases in binary systems form continuous solid solution in the ternary system. The solubility of Cu in Ll0-MnNi phase is up to16at.%。 A set of thermodynamic parameters is obtaind and the calculated results generally agree with the experimental data.(3) The isothermal section of Cu-Ni-Si system at700℃is measured. The line ternary compound Cu45.8Ni2.5Si29.2is observed for the first time. The ternary compound Cu56.8-63Ni10.4-16.1Si26.6-27.3reported in literature is demonstrated. The solubities of all compounds at700℃are accurately measured. The Ni2SiH phase stable above820℃in the binary Ni-Si system can be stable at700℃and dissolve12.7-20.6at.%Cu in the ternary system. A set of thermodynamic parameters for this system is obtained and the calculated results agree with the experimental data. The current set of parameters can successfully extrapolate to high order Al-Cu-Ni-Si system and predict the phase type and molar fraction of precipitates formed in the aging process of Cu based Corson alloy.(4) The solidification process of A1356.1alloy is simulated by multi phase field method. The simulation involves five components and five phases. The concentration distribution of alloying elements Fe, Mg, Mn and Si in the primary (Al) phase is quantitatively obtained. The simulation result is reasonable and better than the result of Scheil model. Two sets of diffusion databases of liquid phase are used, and it is found that the diffusion coefficients of liquid have significant influence on the simulation of microstructure evolution in the solidification.(5) The precipitation, growth and coarsening process of γ precipitate in y1matrix in the Al-Ni system is simulated. Under the effect of interfacial energy and elastic stress, the shape of y precipitate evolves from sphere to cubic and finally plate like shape. In addition, the splitting behavior is observed as to minimize the total energy in the system.There are84figures,21tables and246references in this thesis.