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.
