The similarity between continuous and discontinuous precipitation

Precipitation mechanisms in Al-8 wt % Mg and Cu-15 wt % In alloys have been studied, using X-ray diffraction and optical microscopy. Usually, discontinuous (cellular) and continuous precipitations are observed in Cu-In and Al-Mg systems respectively. A new lattice parameter variation a(t) containing characteristics of both precipitation types, the continuous variation and the simultaneous existence of two values of a is found for Al-8 wt % Mg alloy. On the other hand, a discontinuous coarsening followed by spheroidization of lamellar structure in Cu-15 wt % In alloy lead to more homogeneous precipitation identical with that observed in the last stages of ageing in Al-8 wt % Mg alloy.