Structural evolution during non-isothermal ageing of a dilute Al–Cu alloy by dilatometric analysis

Non-isothermal ageing of an Al–4, 5% Cu alloy has been studied by using differential dilatometry, differential scanning calorimetry (DSC) and high-temperature X-ray diffraction (HTXRD). Six anomalies have been detected on the differential thermodilatometry curve (DTD). The GP zones formation and dissolution are traduced by two small contractions followed by one expansion. The precipitation of θ′-phase induces a big expansion and its dissolution reaction produces an important contraction. Moreover, θ-phase formation accompanies the precipitation, as well as the dissolution reactions of the θ′-phase. The θ-phase dissolution which dissolves the Cu atoms in the Al lattice is accompanied by a thermal dilatation of the Al lattice. The obtained values of the activation energy associated to the main precipitation reaction, by using Kissinger and Ozawa methods, are similar to that found for the precipitation reaction of θ′-phase.