Akademik Veri Yönetim Sistemi
Journal of Thermal Analysis and Calorimetry, cilt.148, sa.20, ss.10713-10725, 2023 (SCI-Expanded)
In this work, the impacts of shallow cryogenic (−40 °C) and natural ageing treatments on the precipitation of the second phases in a 7xxx alloy were investigated. Using the differential scanning calorimetry (DSC) analysis technique, transformation temperatures of the phases both in standard natural aged and naturally aged after cryogenic treatment were determined. As a result of the analyses made, the activation energies of the precipitates formed in the material were calculated with the Kissinger, Takhor and Augis-Bennett equations and their effects on diffusion were considered. With DSC analysis, nucleation characteristics of the η′ phase (MgZn2) were determined by the Avrami parameter from the Ozawa equation. Also, features and distributions of different types of precipitates were analysed by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD) techniques, respectively. Particularly, during the cryogenic and natural ageing processes, dislocation densities, strain values of the planes, texture coefficients and so subsequent after effects on the crystal structure were assessed. It was anticipated that excess dislocations generated during sub-zero treatment preferably settled on suitable planes to subside the strain energy. Finally, it was noticed that compared to natural aged samples, application of the cryogenic treatment before ageing upsurged the hardness of the material on the average by15%. This was possibly because of the η′ precipitates nucleated mainly on dislocations. Graphical abstract: [Figure not available: see fulltext.].