Double-peak ageing behavior of Mg–2Dy–0.5Zn alloy

Ageing behavior of Mg–2Dy–0.5Zn alloy was investigated during isothermal ageing at 180 °C. Two significant ageing peaks were observed at 36 h and 80 h, respectively. Examination of microstructure evolution during ageing revealed that 14H long period stacking ordered (LPSO) phase forms in the α-Mg matrix and its volume fraction increases, (Mg, Zn)xDy particle phases precipitate and their size, distribution and amount vary, as ageing time increases. The LPSO strengthening and the precipitation strengthening are two main mechanisms responsible for the double-peak ageing behavior observed for the Mg–2Dy–0.5Zn alloy. The first ageing peak is mainly attributed to the precipitation strengthening of a large amount of the fine (Mg, Zn)xDy particle phases. The second ageing peak arises mainly from the LPSO strengthening of a high volume fraction of the 14H LPSO phase.

► The ageing behavior of Mg–2Dy–0.5Zn alloy was investigated at 180 °C.
► Two significant ageing peaks were observed at 36 h and 80 h, respectively.
► The double-peak ageing behavior is explained by the microstructure observation.