Influence of Y on the phase composition and mechanical properties of as-extruded Mg-Zn-Y-Zr magnesium alloys

The influence of Y on the microstructure, phase composition and mechanical properties of the extruded Mg-6Zn-xY-0.6Zr (x = 0, 1, 2, 3 and 4, in wt%) alloys has been investigated and compared by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and tensile testing. The increase in Y content has shown grain refinement effects on the microstructure morphologies of the extruded alloys. However, when the content of Y exceeds 2.2 wt%, the grain refinement effect of the Y is not obvious any more with the increase of the Y content. The quasicrystal I-phase (Mg3YZn6), face-centred cubic structure W-phase (Mg3Y2Zn3) and a long period stacking ordered (LPSO) X-phase (Mg12YZn) can precipitate in different ranges of Y/Zn ratio (in at.%) when the Y content in the Mg-Zn-Y-Zr alloys is varied. Comparison of the mechanical properties of the alloys showed that the different ternary Mg-Zn-Y phases have different strengthening and toughening effects on the Mg-Zn-Y-Zr alloys in the following order: X-phase > I-phase > W-phase > MgZn2.