Kinetics and Microstructural Control

· Slow cooling from the single phase region produces an equilibrium microstructure with CuAl₂ precipitates nucleating heterogeneously on grain boundaries.
· Quenching the alloy retains the copper in the α-phase as a super-saturated solid solution.
· Further heat treatment can produce a controlled second phase micro-structure as the material moves towards a thermodynamic equilibrium state.
· The mechanical properties of the alloy depend on the final microstructure reached during this heat treatment --- the precipitation hardening process.
· If the final microstructure is not the thermodynamic state of lowest Gibbs function, high temperature use of the alloy will change its properties with time.