Mechanistic Origin of Ductility in Precipitation Hardening AlMgScZr Alloys

Abstract

Precipitation hardening is the most effective strategy to enhance the mechanical properties of metals. Dislocation mechanisms to control strengthening during precipitation have been demonstrated extensively. However, owing to the complexity of different precipitates in alloys, variations in ductility caused by precipitation are very complex and have not been clarified so far. In this study, the effects of precipitation on ductility in precipitation hardening aluminium alloys are investigated based on a modified dislocation-based approach and experimental characterisation. The AlMgScZr alloy with spherical Al3(Sc, Zr) precipitates is used as a model alloy system to understand the effects of precipitation on ductility. Via heat treatment, shearable and non-shearable Al3(Sc, Zr) precipitates are introduced in the AlMg matrix. The results show that the ductility of AlMgScZr alloy decreases when shearable precipitates occur, while it increases during the shearable–non-shearable transition. The variation in ductility is mainly controlled by the dynamic recovery rate of the dislocations. This dislocation mechanism is supported by analysing the different precipitation–dislocation interactions and evaluating the dislocation density evolution during deformation. This study reveals the dislocation mechanism for controlling ductility during precipitation, which can provide a theoretical foundation for the design of high-performance structural materials.