Precipitate evolution and mechanical properties of Si-modified A286 alloy aged at 510 °C

Si-modified A286 alloy was designed to be compatible with liquid lead-bismuth eutectic (LBE) metal. The addition of Si resulted in a distinct microstructure compared to A286 alloy. In this study, we investigated the microstructure and mechanical properties of the experimental alloy after 510 °C isothermal aging for 5000 h. The results showed the presence of two types of G-phase in the alloy before aging: one with a core-shell morphology, the other with a chain-like morphology. After long-term aging, the Si-modified A286 alloy maintained the same refined grains as in the SAT(solid solution and aging treatment) specimen, with minimal changes observed in the two G-phases even after 5000 h of aging. However, a newly precipitated submicron spherical-like G-phase was observed on the grain boundaries after 500 h of aging, leading to a significant decrease in impact toughness. These spherical-like G-phases gradually coarsened with increasing aging time and eventually stabilized after 2000 h. The reduction in impact toughness in the Si-modified A286 alloy was attributed to the precipitation of the spherical-like G-phase.