Abstract

    In recent years the use of thermodynamic modelling via the CALPHAD method has been extensively applied to industrial alloys of many types. Although pertaining to equilibrium conditions, valuable information can be gained for a variety of practical applications where equilibrium is not reached, for example, in solidification. The purpose of the present paper is to provide a review and examples of the practical application of the CALPHAD method to commercial industrial alloys. A further purpose of the paper is to present new results for the modelling of metastable hardening phases, such as GP zones, θ′, S′, MgxSiy based phases, and show how CALPHAD modelling can be extended to calculate relevant TTT and CCT diagrams for their formation.

1. Introduction

    For many years the prime sources of information regarding phase equilibria in Al-alloys have been the compendia of Philips [1] and Mondolfo [2]. These books provide extensive information concerning the behaviour of binary and ternary systems and, to a certain degree, higher order systems. Such work enables a reasonable understanding of many known alloys. However, while providing broad information on particular alloy systems, equilibrium phase diagrams fall short in providing detailed information on how multi-component alloys behave, particularly for the case of new alloys and in understanding what may happen as compositions vary within the composition specification of known alloys.

    Recently, the use of thermodynamic calculations via the CALPHAD method [3] has demonstrated that high quality calculations can be made for complex alloys of many types, including Al-based alloys. In particular, phase formation in numerous types of Al-alloy is well matched [4,5] and the approach is readily extendable to use in solidification modelling [4,6]. The aim of the present paper is to review past work and present the present status of CALPHAD calculations to Al-alloys and their extension to modelling of solidification. It will also present new work concerning the modelling of metastable phases and their transformation kinetics.

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