Nucleation mechanism of discontinuous precipitation in MgAl alloys and relation with the morphology

The nucleation rate of discontinuous precipitation in MgAl has been measured as a function of temperature, initial grain size and solute content. From these measurements, it appears that at high temperatures (T ≥ 220°C) all precipitation nodules nucleate via Fournelle and Clark's mechanism, whereas at lower temperatures (T ∼ 140°C), at least one of the mechanisms identified by Tu and Turnbull or Purdy and Lange is also active. The proportion …