Precipitation in AlCu4.3 and AlCu4Mg alloys studied by dilatometry and calorimetry

Abstract

The precipitation kinetics of a laboratory alloy (AlCu4.3) is compared with that of a commercial alloy AW2024 (AlCu4Mg) by continuous and isothermal dilatometry and differential scanning calorimetry (DSC). The precipitation and decomposition sequence are demonstrated by means of DSC. Precipitation of θ causes an accelerated thermal expansion of AlCu4.3 complemented by retarded expansion in the dissolution temperature range. Dilatometry results from several temperature scan rates are analysed by the Kissinger method to give apparent activation energies and rate constants for the precipitation of θ in AlCu4.3. The activation energy of formation varies from 80 to 100 kJ mol −1 , while that for dissolution amounts to 200 kJ mol −1 . The sequence of precipitation of the S phase in solutionized 2024 aluminium is more complex, but shows only little effect on the thermal expansion.K e y w o r d s : Al-Cu alloys, precipitation kinetics, dilatometry, differential scanning calorimetry (DSC), activation energy

Investigation of Thermophysical Properties of AW-2024-T3 Bare and Clad Aluminum Alloys

“…In the case of the AW-2024-T3 clad alloy, there was an overlap in the process of forming θ and S precipitations (overlapping formation of θ and S ). For both alloys, i.e., bare and clad AW-2024-T3, a similar activation energy was obtained, i.e., 137.1 kJ•mol −1 for the bare alloy and 131.0 kJ•mol −1 for the clad alloy [13,39].…”

“…As can be seen in the Al–Cu phase diagram the solubility limit of Cu in Al is 2.48 ± 0.5 at.% (5.65 wt.%) at a temperature of 548.2 °C (eutectic point on Al-Cu equilibrium diagram), whereas at lower temperatures (below 200 °C), it reduces down to 0.1 at.% [ 13 , 18 ]. For precipitation-strengthened alloys, there must be a terminal solid solution that has a decreasing solid solubility as the temperature decreases.…”

“…The GP2 zone is sometimes called (Al 3 Cu-θ") [19]. During heating, GP zones dissolve and Cu atoms diffuse to the growing semi-coherent and metastable nuclei of θ" precipitates and θ platelets [13]. At the end, the stable equilibrium θ-Al 2 Cu phase forms.…”

“…For commercially available AW-2024 alloy, the precipitation sequence differs from the one for the binary system, mostly because of the addition of Mg. According to the work of Semnani et al [13], this sequence can be written as…”

“…However, in the relevant body of literature, there are few works concerning the thermophysical properties of the AW2024 aluminum alloy. An example of this is the work of Mohammadian Semnani and Degischer [13], in which the authors compared the precipitation kinetics of laboratory AlCu4.3 and commercial AlCu4Mg alloys using differential scanning calorimeter (DSC) analysis and the dilatometry technique.…”