Phase Equilibria And Solidification Of Al Rich Al Mg Cu Alloys

Author : Senlin Cui
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (979 download)

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Download or read book Thermodynamic Modeling and Experimental Study of the Al-Cr-Cu-Fe-Mg-Mn-Si System written by Senlin Cui and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Aluminum alloys are extensively used in civil engineering, ship building, automotive, and aerospace industry. The requirement of improving fuel efficiency and weight reduction of vehicle triggers a resurgence of research of aluminum in automobile industry. Al 6xxx series alloys are commonly utilized as extruded materials because of their high strength, formability and ductility, weldability, corrosion resistance, and low cost. The whole chain of Al alloy component manufacturing starts from aluminum melt refining, to casting, homogenization, rolling/extrusion, and finally heat treatment. The microstructure evolution of Al alloys is controlled by both thermodynamics and kinetics. The driving forces for each processing step basically include the chemical driving force or thermodynamic driving force, the interfacial energy, the mechanical driving force, etc. Thermodynamics related to chemical reactions and phase transformations is thus of fundamental importance.The study of thermochemical properties and phase diagram of Al alloys is helpful for new Al alloy composition design and process optimization. The CALPHAD (CALculation of PHAse Diagram) approach is one of the most efficient ways to study alloy thermodynamics systematically. With a well-developed Al alloy thermodynamic database, the phase equilibria and thermodynamic properties can be calculated for complex alloy systems. As a cornerstone for the understanding of various phenomena in Al 6xxx alloys, the current work focuses on the development of a thermodynamic database for the Al-Cr-Cu-Fe-Mg-Mn-Si system via a coupled experimental and thermodynamic modeling approach. Isothermal sections in the Al rich corner of the Al-Cr-Mg system were measured at 400, 450, and 500 °C via equilibrated alloys, diffusion couples, and differential thermal analysis (DSC). The thermodynamic optimizations of the binary Al-Cr, Cu-Cr, Cu-Mg, Cr-Si, and Fe-Si systems were newly performed, and the thermodynamic descriptions of the Al-Mn, Cu-Mn, Cr-Fe, Cr-Mg, and Cr-Mn systems were revised. The ternary Al-Cu-Cr, Al-Cu-Mg, Al-Cu-Si, Al-Cr-Mg, Al-Cr-Mn, Al-Cr-Si, Cu-Fe-Cr, Cu-Fe-Mn, Cu-Mg-Si, Cr-Fe-Si, and Fe-Mg-Si systems were thermodynamically modeled, and the Al-Cu-Mn system was revised. Moreover, the quaternary Al-Cu-Mg-Si system was remodeled. The optimization or revision of the thermodynamic descriptions of all the systems were based on the current experimental results and the critically evaluated literature data including phase diagram, enthalpy of mixing, activity, Gibbs energy of formation, enthalpy of formation, standard entropy, heat capacity, etc. The liquid phase was described using the Modified Quasi-chemical Model (MQM) in pair approximation, and the Compound Energy Formalism (CEF) was utilized for the descriptions of all the solid phases. The order-disorder transitions (bcc_A2/bcc_B2 transition and bcc_B2/bcc_D03 transition) were modeled using the split compound energy formalism. A self-consistent set of thermodynamic description for the Al-Cr-Cu-Fe-Mg-Mn-Si system was obtained by combining the currently assessed thermodynamic parameters with the thermodynamic parameters available in the literature. The obtained thermodynamic database was applied to investigate the recycling of Al alloys. The effect of each major and impurity alloying element on the types of precipitates and their amounts in both the solidification and equilibrium conditions were also systematically investigated for the Al 6xxx series alloys using the thermodynamic calculations with the present new database." --