Exploring differences in irradiation-induced defects between Mg2Si and Si-rich precipitates in Al-alloys

The interfaces of precipitates serve as strong defect sinks that interact with irradiation defects, affecting the microstructure of materials. Under transmutation effects, Al-alloys in nuclear systems continuously form Mg₂Si and Si-rich precipitates. Yet, the mechanisms by which these precipitates respond to irradiation-induced self-interstitial atoms (SIAs) and vacancies, as well as the role of interfaces, remain insufficiently elucidated. In this work, the evolution of SIAs and vacancies in a 5xxx-series Al-alloys, pre-prepared with Mg₂Si and Si precipitates, was investigated through in-situ transmission electron microscopy during 400 keV Al⁺ and 30 keV He⁺ irradiation at room temperature and 523–603 K. Significant differences in defect evolution near Mg₂Si and Si-rich precipitates were observed under similar irradiation damage and He implantation. Unlike the Si precipitates, the Mg₂Si precipitates exhibited preferential nucleation and aggregation of dislocation loops on their surfaces and in surrounding regions. The differences in the behavior of SIAs and vacancies induced by the strain field and orientation relationships contributed to the variations in loop evolution for the two precipitates. After annealing, in contrast to Si-rich precipitates, Mg₂Si precipitates exhibited a stronger absorption of released vacancies, leading to pronounced faceted growth of bubbles within the precipitates. This is attributed to differences in their interfacial properties and vacancy mobility.