Browsing by Author "Azizi, Assia"

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    Artificial Aging Effect On Precipitation And Age-hardening In An Al-zn-mg-cu Alloy
    (Oum-El-Bouaghi University, 2019) Boumaza, Leila; Hadjadj, Lakhdar; Belamri, Zahira; Azizi, Assia; Benmelit, Rabia; Hamana, Djamel
    In the present work, the influence of heat treatment on the mechanical properties and precipitation of the different phases in Al-Zn-Mg-Cu alloy was studied. The precipitation sequence and the mechanism of structural hardening have been followed using the differential scanning calorimetry (DSC), the microhardness measurements, the X-ray diffraction (XRD) and the scanning electron microscopy (SEM). Five calorimetric effects have been recorded and correspond to the different phases precipitating in this system of alloys and which are: the GPI zones and / or VRC (or GPII), the intermediate η' phase and the equilibrium η phase with a suspicion concerning the existence of T and S phases. Microhardness measurements of the aged state at 226 °C confirm the existence of two types of phases: the metastable η’ phase and the equilibrium η phase (MgZn2). The appearance of the first precipitates was followed by SEM. The fine precipitates become larger (holdings at 243 and 266 °C) and the equilibrium η phase continues to grow inside and on the grain boundaries to become a large spherical and/or lamellar precipitate. The X-ray diffraction confirmed that only the equilibrium η phase was observed in this type of alloy.
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    Study Of The Microstructural Evolution Of Precipitation In Az91 Alloy
    (Oum-El-Bouaghi University, 2019) Azizi, Assia; Hamana, Djamel; Boumaza, Leila; Belamr, Zahira; Toubane, Mehdia; Medjemedj, Warda
    Magnesium-based alloys have been the subject of several scientific research projects. Their excellent mechanical properties have allowed their use in various fields such as aeronautics and automotive. Phase transformations play a crucial role in the mechanical properties improvement; therefore the understanding of structural hardening due to the precipitation reaction is important. The main objective of this work is to study the influence of the aging temperature on the precipitation mechanism in AZ91 () alloy. It has been found that at high aging temperatures continuous precipitation is appeared and characterized by fine precipitates, however, discontinuous precipitation is observed under cellular form at low temperatures. With increasing ageing time continuous precipitates can be also observed and they block the growth of discontinuous precipitates. This phenomena influence directly the mechanical properties of such alloys, for that microhardness measurements are done to evaluate the mechanical properties variations as function of temperature, ageing time and so on.