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

•Addition of Y element significantly refines the grains of ZM31 magnesium alloy.•I- and W-phases are present in the extruded alloy ZM31 with low Y additions.•X-phase and Mg24Y5 are observed in the extruded alloy ZM31 with a 6% Y addition.•While I- and W-phases are dissolved after heat treatment, LPSO X-phase remains.•I- and X-phases increase compressive yield strength and hardness of the 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 (0.3wt.%) 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.