Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The nucleation and transformation of L12-Al3Zr and DO22-(Al,Si)3Zr dispersoids in Al–Mg–Si 6xxx alloys were studied using interrupted quenching and transmission electron microscopy. Spherical L12-Al3Zr dispersoids precipitated preferentially along  〈001〉Al in early stages of nucleation, coinciding with the same sites and orientation of β′ precipitates that dissolved during heating. Two nucleation mechanisms were suggested to explain this preferable precipitation. At a relatively low heat treatment temperature (400 °C), the L12-Al3Zr dispersoids were predominant, and no transformation occurred. With further increase in temperature to 550 °C, the L12-Al3Zr dispersoids started to transform into DO22-(Al,Si)3Zr. At high temperatures, elongated DO22-(Al,Si)3Zr dispersoids, which were formed through the transformation of pre-existing L12 dispersoids rather than the direct precipitation from the supersaturated aluminum solid solution, became the dominant phase.