Many Aluminium alloys use the precipitation of metastable phases to generate optimum
properties. The effect of including additional structures such as θ’ and GP zones is described in the
context of a hierarchy of metastable structures. Extending a Thermodynamic data base that has been
designed solely to deal with equilibrium conditions is a vital prerequisite to handling the heattreatment
of aluminium alloys. It is then possible to generate TTT and CCT diagrams, using the
Johnson-Mehl-Avrami treatment previously applied in to other materials providing provision is
made for the presence of supersaturated quenched-in vacancies. Calculations using JMatPro are
given for the expected behavior of commercial aluminium alloys of increasing complexity,
including AA319, AA6061 and AA7075.