Abstract:The microstructure and mechanical properties of Mg₉₄Zn₂Y₄ extruded alloy containing long-period stacking ordered structures were systematically investigated by SEM and TEM analyses. The results show that the 18R-LPSO structure and α-Mg phase are observed in cast Mg₉₄Zn₂Y₄ alloy. After extrusion, the LPSO structures are delaminated and Mg-slices with width of 50-200 nm are generated. By ageing at 498 K for 36 h, the ageing peak is attained and β′ phase is precipitated. Due to this novel precipitation, the microhardness of α-Mg matrix increases apparently from HV108.9 to HV129.7. While the microhardness for LPSO structure is stabilized at about HV145. TEM observations and SAED patterns indicate that the β′ phase has unique orientation relationships between α-Mg and LPSO structures, the direction in the close-packed planes of β′ precipitates perpendicular to that of α-Mg and LPSO structures. The ultimate tensile strength for the peak-aged alloy achieves 410.7 MPa and the significant strength originates from the coexistence of β′ precipitates and 18R-LPSO structures.

Key words: Mg₉₄Zn₂Y₄ alloy; long-period stacking ordered structure; precipitation; ageing; tensile property