Résumé:
The aluminium alloys; in particular the Al-Mg-Si alloys (6xxx series) have a great interest for their privileged uses in the automotive and aeronautical industries. The aims of this research is focused on the comprehension of the influence of the addition elements and more particularly copper and excess silicon on the microstructure, the precipitation kinetics and the mechanical properties in Al-Mg-Si alloys series. The use of the different experimental techniques such as transmission electronic microscopy (TEM), differential scanning calorimetry (DSC) and Hardness Vickers (Hv) allowed us to define the influence of the addition elements on the precipitation kinetics, and to characterize age-hardening behavior of the Al-Mg-Si alloys. The effect of artificial ageing, natural ageing and preaging heat treatments on the microstructural evolution and the mechanical properties was studied, too. The Al-Mg-Si alloys with excess silicon presents the largest density of precipitates. The alloys with an excess of silicon require larger activation energy for precipitation despite the acceleration of the precipitation by the excess of silicon. The precipitation sequence of the four Al-Mg-Si alloys depends on the concentration of the addition elements silicon and copper. It is obtained as: Formation of Guinier - Preston (G.P) zones precipitation of ’’ phase precipitation of ’ or Q’ phase precipitation of phase and/or the Si particles. The copper addition to the Al-Mg-Si alloys led to the mechanical properties improvement after the heat treatment of an artificial ageing at 185°C. The double effect of the addition copper (0,10%) and the excess silicon (0,50%) in Al-Mg-Si alloys is found to have a very significant effect on the improvement of the mechanical properties (Hardness), especially after a preaging heat treatment. Key words: Al-Mg-Si alloys, Precipitation, Transformation kinetics, Excess silicon, DSC, Activation energy,
