A CALORIMETRIC STUDY OF THE PRECIPITATION HARDENING MECHANISMS IN AN Al–Cu–Mg–Si ALLOY

Abstract

The precipitation phenomena and the related hardening in an Al – Cu – Mg – Si alloy were studied by calorimetry, X-ray diffraction analysis and microhardness measurements. The main calorimetric peaks were identified to be due to β′′, θ′ and Q′ phases precipitation. The hardening during aging at room temperature and 160°C, was respectively, explained by atomic clusters and GP zones formation and by GP zones and β′′/θ′ phases coprecipitation. Although the mechanical properties variation during aging at 200°C is simple, the corresponding microstructural evolution is complex: on the basis of the DSC results, the increasing of microhardness values, is mainly due to the coprecipitation of GP zones and β′′/θ′ phases, however, the maximum hardening is explained by the coexistence of β′′/θ′ and θ′′ phases. Another important conclusion is that during aging at 160°C and 200°C, the θ′ phase is essentially developed from GP zones.