Enhanced age-hardening response in Mg-Zn-Co alloys with Bi additions

Effects of Bi additions on age-hardening response and precipitation of Mg-2.31Zn-0.31Co (at.%) alloy have been investigated. The addition of Bi can substantially promote the age-hardening response at 200 degrees C. The precipitates microstructure is characterized using high-angle annular dark-field scanning transmission electron microscope, and the results show that the remarkable improvement is attributed to a much higher number density of beta'(1) rods and the formation of prismatic Mg3Bi2 plates. At the early stage of ageing, Mg(3)Bi(2 )precipitates out first and then Zn segregates to the Mg3Bi2/Mg interface, which could provide chemical environment and heterogeneous nucleation sites for the subsequent precipitation of the beta'(1) phase. (C) 2019 Elsevier B.V. All rights reserved.