Etude des réactions de précipitation continue et des propriétés mécaniques des alliages à base d’aluminium.

Abstract

The Al-Mg alloys are widely used in industry especially for marine applications since they possess good properties such as general corrosion resistance, strength, weldability, weight compared to other Al alloys and formability. These properties are related to the magnesium content and to the applied heat treatments. These alloys undergo phase transitions by precipitation which improves their mechanical properties following solution heat treatments and suitable ageing ones. Although these alloys are already well studied, the questions concerning the stability of the microstructure and the effect of the various heat treatments are always asked. In this work, we present a study on the evolution of the precipitation (continuous one) reactions after quenching, more precisely the evolution of the precipitated phases (formation, coalescence, and dissolution), in Al-(12, 10 and 8)wt.% Mg alloys aged at 150 and 250 °C during different ageing times. The use of various experimental techniques as differential dilatometry, differential scanning calorimetry, scanning and transmission electron microscopy, X-ray diffraction, microhardness and internal friction measurements, shows their importance and their complementarity in the study of ageing process in these alloys. The obtained results clarified the parameters that govern the stage of β’and β particles appearance and the mechanical responses to the applied heat treatments. The ageing effect of a supersaturated solid solution on the Temperature Dependent Internal Friction (TDIF) spectra has been studied. A detailed TDIF analysis revealed the sensibility of the internal friction technique to the formation of semi-coherent and non-coherent phases (β' and β) but not enough to the formation of coherent phases (GP zones). Several observations on the nature and the shape of the precipitates are also discussed.