Formation of β-related composite precipitates in relation to enhanced thermal stability of Sc-alloyed Al-Mg-Si alloys

The Al-Mg-Si alloys added with trace Sc demonstrates an improved thermal stability, as compared with that without Sc-addition. But the microstructural origin of the enhanced property is unclear. In the present study, the precipitates formed in an Al-Mg-Si-Sc alloy were studied in detail by atomic-resolution scanning transmission electron microscopy. It is shown that the dominant precipitates formed at the peak-aging condition are the disordered beta precipitates consisting of Sc-free beta sub-units and Sc-containing disordered regions, rather than the well-ordered beta. Upon further aging, these disordered beta precipitates will evolve to beta/beta'/B '/U2 composite precipitates. The formation of the composite precipitates is probably associated with the strong binding between Sc and Si atoms, and with the non-preference for Sc atoms to occupy the atomic sites of the beta-structure. Our study reveals the following: It is the formation of stabilized beta-related composite precipitates that enhances the thermal stability of the Sc-added Al-Mg-Si alloy. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study analyzed the precipitates formed in Al-Mg-Si alloys added with trace Sc using atomic-resolution scanning transmission electron microscopy, and found that the enhanced thermal stability is attributed to the formation of stabilized beta-related composite precipitates.