Phase Diagrams And Microstructure Evolution Of Al-Cu-RE (RE=Y,Nd,Gd,Dy,Er,Yb And Ti) Alloys

Interest in aluminum alloys is increasing continuously due to their properties such as the low density, high strength, high corrosion-resistance as well as their potential applications in the automotive and aerospace industries. Microalloying has been used to improve the high temperature strength of the selected age hardening aluminum alloys. Rare earth elements are benefit to casting process in the conventional aluminum alloys resulted in improving tensile strength, heat resistance and corrosion resistance, etc. for many years. The invesitagiation on the glass forming ability (GFA), especially on the thermodynamic modeling of amorphous forming system, is an important issue on the amorphous alloys research. The key to the thermodynamic modeling of GFA of alloys is the reliable binary and ternary phase diagram and thermodyniac properties. Associated with a project entited "Investigation of phase diagram and microalloying of Al-Cu based alloy systems" supported by National Science Foundation of China (No. 50771106), partial phase equilibria of Al-Cu-Y-Nd-Gd-Dy-Er-Yb-Sb-Ti have been investigated by means of experimental determination and CALPHAD method. Based on these results, the relationship between the GFA and the driving forces of crystalline phases was further investiagated. Also a materials design method based on phase diagram and thermodynamic was established in this work. With the help of this new method, A US patent was analyzed. The major work of this study is as following:(1) By means of annealing method, metallography, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), the phase relations of Cu-rich region at 1073 K and phase constitution of the electric-arc melted cast-state sample of Cu-RE (RE=Y, Nd, Gd and Dy) systems were determined. The experimental result showed that Cu7RE phase form in the Cu-rich region of Cu-Y and Cu-Dy binary systems, and in Cu-Y and Cu-Dy binary systems the Cu-rich compounds are Cu6RE phases. It was shown that Cu7Dy phase was only stablized at high temperature, this phase was decompced to Fcc(Cu)+Cu5Dy_L in low temperature.(2) Based on the experimatal results and literature information, the Al-Yb, Cu-Gd, Cu-Dy, Cu-Er and Sb-Y binary systems were performed by means of CALculation of PHAse Diagram (CALPHAD) technique. The thermodynamic parameters of these binary systems have been obtained. The calculated phase diagrams were in good agreement with available experimental data.(3) Using metallography, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), the isothermal section of Al-Cu-Nd at 673 K were determined. Six ternary compounds (τ1-Al8Cu4Nd,τ2-Al9Cu8Nd2,τ3-Al6Cu7Nd,τ4-Al2.4Cu8.6Nd,τ5-Al3CuNd andτ6-AlCuNd) were determined in this work. Based on the experimental phase relations and literature results, the Al-Cu-Nd ternary system was critically assessed using the CALPHAD method. A series of vertical sections and isothermal sections were calculated and compared with experimental data.(4) With the help of X-ray diffraction analysis (XRD), the partial isothermal section of Al-Cu-Er at 673 K was determined. A ternary compounds(τ1-Al8Cu4Er) was determined in this work. Based on the experimental phase relations and literature results, the Al-Cu-Er ternary system was critically assessed using the CALPHAD method. A series of isothermal sections were calculated and compared with experimental data.(5) Combined with reasonable binary systems, the ternary systems, Al-Cu-Y,Al-Cu-Gd,Al-Cu-Dy,Al-Cu-Yb,Al-Cu-Ti and Al-Sb-Y have been optimized using CALPHAD method on the basis of available experimental data. Finally, the self-consistent thermodynamic parameters formulating Gibbs engeries of various phases in these six ternary systems have been obtained, and the thermodynamic database of Al-Cu-Y-Nd-Gd-Dy-Er-Yb-Sb-Ti system has been also developed.(6) Using metallography, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), the the electric-arc melted cast-state sample of Al-Cu-RE (RE=Y, Nd, Gd, Dy, Er and Ti) were determined. Based on thermodynamic database of Al-Cu-Y-Nd-Gd-Dy-Er-Yb-Sb-Ti system, the equilibrium solidification and the solidification according to the Scheil model were calculated for the alloys. The calculated results were successfully applied to understand the experimental microstructures of the above mentioned alloys in Al-Cu-MM (MM=Y, Nd, Gd, Dy, Er and Ti) system.(7) Based on the thermodynamic database of Al-Cu-Y-Nd-Gd-Dy-Er-Yb-Sb-Ti system, the relationship between the GFA and the driving forces of crystalline phases was investigated. It was revealed that the alloys with good glass forming ability in the Al-Cu-RE system have the low driving forces of crystalline phases. These minimum driving forces are the criterion for selecting the composition for formation of Al-Cu-MM amorphous alloys. Based on the above information, A US patent was analyzed.