Mechanical property and anisotropy of as-extruded Mg–Zn–Y–Mn alloys with different volume fraction of long-period stacking ordered (LPSO) phase

Effects of different volume fraction of long-period stacking ordered (LPSO) phase on the microstructure, mechanical property and anisotropy of the as-extruded Mg-xZn-yY-0.1Mn (x = 1 wt%, 2 wt%, 4 wt% and y = 2 wt%, 4 wt%, 8 wt%) alloys were studied by an optical microscope, a scanning electron microscope, texture analysis, a transmission electron microscope and tensile testing. The results reveal that the volume fraction of LPSO phase increases from ZW12 to ZW24 to ZW48 alloys with the elevating Zn and Y content but constant Y/Zn value, and the mechanical strength of the LPSO-containing Mg–Zn–Y–Mn system is gradually improved when increasing LPSO phases. With the highest volume fraction of LPSO phase, ZW48 alloy presents the highest ultimate tensile strength (UTS) of 427 MPa along the extrusion direction (ED) when compared with those of ZW12 alloy with the UTS of 307 MPa and ZW24 alloy with the UTS of 347 MPa. Moreover, the elongation ratio of ZW48 alloy is maintained to moderate 9.9%, which is also the highest among three studied alloys. On the other hand, texture analysis demonstrates that the basal texture of the α-Mg phase in the ZW48 alloy is significantly weakened by the generation of more LPSO phases. On the contrary, a high texture intensity of α-Mg phase and obvious mechanical anisotropy can be observed for the ZW12 alloy. However, mechanical anisotropy still exists in the ZW48 alloy containing massive LPSO phases, which is attributed primarily to the zonal distribution of large LPSO along the ED.