Abstract:
Although it is sufficiently understood for many years, the comprehension of various aspects closely related to precipitation process in Al-Mg-Si alloys is often required crucial for mastering the technology and the development of new alloys. In this context, the work
undertaken as part of this thesis is focused on the study and characterization of Al-Mg-Si-(Cu) sheets. The particular interest of this work is to understand the reactions precipitation in sheets and their kinetics on the one hand, and to elucidate the effect of the Mg : Si, the influence of ageing and pre aging treatment on the response of alloy hardening , the effect of copper on the aging curves on the other hand. Furthermore, we wished to assess the corrosion behavior of sheets in chloride solution. In this regard, analysis and experimental techniques very complimentary, has been used, ie, differential scanning calorimetry (DSC), X-ray diffraction, scanning electron , transmission electron microscopy, micro hardness Hv and electrochemical analysis. The study indicated the existence of precipitates of type α-AlFeSi, α- AlFe(Mn)Si frequently present in the Al-Mg-Si alloys and remaining stable at high temperatures. Equally, it
is clear from this study it is always possible to combine the strength properties of the intrinsic properties of a material. Indeed, the hardening caused by precipitation in studied alloys is certainly due to the predominance of very fine typical precipitates β' and β'' as rods and needles developed during aging with and without preageing. The silicon in excess increases the hardening, by favoring the appearance of metastable phases in fine dispersion of precipitates. The effect of pre ageing just after homogenization and quenching is to correct the undesirable effect of aging at ambient temperature by making faster alloy hardening during artificial aging. The addition of 0.10 wt % copper has allowed to refine and to enhance the precipitation hardening after quenching. The artificial ageing treatment at temperature 180 ° C doses not affects the corrosion parameters but enhances consequently the electrochemical performance of samples due to the presence of Mg2Si, Al3Mg2 precipitates which are more corrodible than the α- aluminum matrix. The addition of 0.10 wt % copper doses not changes the corrosion resistance.
