Influence of yttrium content on phase formation and strain hardening behavior of Mg-Zn-Mn magnesium alloy

The aim of this study was to identify the effect of yttrium (Y) addition on the phase development and strain hardening behavior of an extruded Mg-Zn-Mn (ZM31) magnesium alloy. The addition of a small amount (0.3 wt.%) of Y in the alloy led to the formation of icosahedral quasicrystalline I (Mg3YZn6) phase. Both I-phase and W-phase (Mg3Y2Zn3) were present in the extruded ZM31+3.2Y alloy, while long period stacking ordered (LPSO) X-phase (Mg12YZn) and Mg24Y5 were observed in the extruded ZM31+6Y alloy. The Y addition significantly refined grains in the extruded state. The presence of I-phase in the extruded ZM31+0.3Y alloy increased hardness, compressive yield strength, and Stage B strain hardening rate. The extruded ZM31+3.2Y alloy exhibited a lower hardness and Stage B hardening rate due to the formation of W-phase. Both extruded ZM31+0.3Y and ZM31+3.2Y alloys showed a yield point phenomenon with an initial negative strain hardening rate. The extruded ZM31+6Y alloy had a high hardness and compressive yield strength without Stage B hardening, suggesting a change of major deformation mode from twinning to slip mainly due to the role of LPSO X-phase. After solution treatment and aging, the hardness and compressive yield strength gradually increased with increasing Y content, while the strain hardening exponent and the extent of Stage B strain hardening decreased due to the dissolution of I- and W-phases and the presence of LPSO X-phase.