Abstract
Mg-7Zn-(xY-0.6Zr (x = 6, 9, 12 wt.%) alloys have been designed to investigate the effects of Y content on the microstructure and mechanical properties. The results show that Y content plays a key role in the phase composition and mechanical properties of the investigated Mg-7Zn-(xY-0.6Zr alloys. With the Y content increasing from 6 to 12 %, the phase composition transformed from (α-Mg + W-phase (Mg₃Y₂Zn₃) to α-Mg + X-phase (Mg₁₂YZn). The amount of X-phase increases rapidly, and W-phase decreases accordingly. Furthermore, the W-phase distributes alternatively with the X-phase, due to the specific local Y/Zn mole ratio at the final solidifying stage. After extrusion, the phase composition and corresponding volume fraction have great influence on mechanical properties. The X-phase is in favour of high strength and the W-phase makes for good plasticity. The as-extruded Mg-7Zn-12Y-0.6Zr alloy establishes the highest strength with an ultimate tensile and yield tensile strength of 416 MPa and 302 MPa, respectively.

Key words
Mg-Zn-Y-Zr, extrusion, casting and solidification, microstructures, mechanical properties

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