Effects of phase composition and content on the microstructures and mechanical properties of high strength Mg–Y–Zn–Zr alloys

In this work, the microstructures and mechanical properties of nine different Mg–Y–Zn–Zr alloys have been investigated. The investigated Mg–Y–Zn alloys mainly contain four types: W-phase, W − + X-phase and X-phase + Mg24Y5 alloys, which should be determined by both the Y/Zn mole ratios and the total alloying content. The phase compositions and content play a fatal role on the mechanical properties of the as-extruded Mg–Y–Zn–Zr alloys. However, the Mg–Y–Zn–Zr alloys received almost no aging hardening response, except for the alloy containing X-phase and Mg24Y5. This is because a supersaturated matrix was not available to these alloys containing only the stable ternary X- or W-phase. Nevertheless, the as-extruded Mg–12Y–5Zn–0.6Zr alloy could still own extraordinary high strength, whose ultimate tensile strength and yielding tensile strength were 429 MPa and 351 MPa, respectively. It should be attributed to the X-phase strengthening effects. After peak-aging, the Mg–12Y–3Zn–0.6Zr alloy established an ultimate tensile strength and yielding tensile strength of 440 MPa and 350 MPa, respectively. The effects of phase compositions and content on mechanical properties have been discussed in detail.