Age strengthening behavior and mechanical properties of Mg-Dy based alloys containing LPSO phases

A unique age strengthening behavior of a Mg-2.2Dy-1Cu (at%) alloy containing long-period stacking order (LPSO) phases has been observed during the heat-treatment process for the first time. The results show that both microhardness and compression properties are improved simultaneously. The phase composition and phase transformation have been identified by a transmission electron microscope. The results reveal that the first strengthening peak at 535 °C for 4 h is mostly associated with the phase transformation from an 18R-type LPSO phase in the grain boundaries to a 14H-type LPSO phase in the grain interiors. However, the secondary peak (535 °C for 4 h followed by 575 °C for 6 h) is mainly related to the formation of some nano-sized Mg(Cu, Dy)2 particles, coupling with the decomposition of the 14H-LPSO phase simultaneously.