Experimental Investigation And Thermodynamic Modeling Of The Na-X (X=Si, Ag, Cu, Cr) And Al-Fe-Ni-Si Systems In Al Alloys

CALPHAD technique is an effective and widely utilized method for assessment and calculation of phase diagrams. It provides a thermodynamic basis for materials kinetics and the computational simulation of the microstructure evolution. Furthermore, it can be widely applied to the design and synthesis of new materials. Al-based alloys are widely used in aviation, aerospace, automotive, machinery manufacturing, shipbuilding and chemical industries. Fe、Cu、Ni、Cr、Si、Ti and Nb are the important alloying elements in the Al-based alloys. To effectively improve the performance of aluminum alloy, design alloy’s composition, optimize the synthesis process, an accurate knowledge of the phase diagram and thermodynamics of the multi-component Al-based system is needed. This work was involved in the investigation of the binary Na-X (X=Si, Ag, Cu, Cr) system and quaternary the Al-rich of Al-Fe-Ni-Si system. The main research results obtained in this work are shown as follows:(1) A thermodynamics modeling of the Na-X(X=Si, Ag, Cu, Cr) system has been carried out by CALPHAD. A self-consistent set of parameters has been obtained. The agreement between calculation and experiment is reasonable.(2) The phase relationship and phase transition temperature of the Al-rich corner of the Al-Fe-Ni-Si system have been determined by means of scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), electron probe X-ray microanalysis (EPMA), differential thermal analysis (DTA), transmission electron microscope (TEM). With the DTA analysis of the equilibrium alloys and the analysis of the as-cast alloys, the solidification process were preliminary stuied. No quaternary compounds have been observed in this work. Two three-phase regions,(Al)+(Si)+Al9Fe2Si2and (Al)+(Si)+Al9FeNi have been determined. Based on the experimental data from both the present work and the literature, a thermodynamic description of the Al-rich corner of the Al-Fe-Ni-Si system has been carried out by fitting the phase equilibria, and a self-consistent set of parameters has been obtained. The agreement between calculation and experiment is reasonable.(3) The nano-size particles were determined by the TEM technique. It is important to use the TEM technique in this work. And it has an important role in the material research.