The systems described here are real assessments, most of which have been published and the reference is given; but the descriptions here include some of the mistakes made when solving the problems leading to the publication. Such things are never included in the final publication. Discussing such problems does not mean that the assessment technique described here is bad or wrong, only that learning from mistakes is the only way to become a successful assessor, in the same way as many mistakes are inevitably made before one can learn how to be a good experimentalist.

A complete assessment of the Cu–Mg system

The Cu–Mg system published by Coughanowr et al. (1991), shown in Fig. 9.2 later, is very simple but offers some interesting examples of modeling. Assessments with two different software packages will also be discussed.

Physical and experimental criteria for solution model selection

There are five phases in the system, the liquid phase, the Cu phase with fcc lattice with some solubility of Mg, the Mg phase with hcp lattice and hardly any solubility of Cu, and two intermetallic phases:

• CuMg2, a stoichiometric phase, and

• Cu2Mg, with some range of homogeneity, having the cubic Laves-phase structure, C15 in the Strukturbericht notation.

The Laves phase Cu2Mg

The range of homogeneity of the Laves phase is very well determined experimentally; it deviates on both sides from the ideal composition of 66.7% Cu.