Secondary phases in quasicrystal-reinforced Mg–3.5Zn–0.6Gd Mg alloy

•Secondary phase evolution for Mg–Zn–Gd alloy during extrusion is studied.•Orientation relation between dendritic I-phase and Mg matrix is determined.•A new orientation relation is found between nanoscale I-phase and Mg matrix.

The secondary phases in quasicrystal-reinforced Mg–Zn–Gd alloys are investigated by transmission electron microscopy. The orientation relationships between the dendritic I-phase and the Mg matrix are identified to be [11 2¯ 0]Mg ∥[2-fold]I-phase and (0001)Mg ∥(5-fold)I-phase. We also find that the dendritic I-phase is brittle along 2-fold, 5-fold, and 3-fold atomic planes during hot extrusion. Moreover, new orientation relations [1¯ 101]Mg ∥[mirror 2-fold]I-phase and (0 1¯ 11)Mg ∥(5-fold)I-phase are found between nanoscale I-phase and Mg matrix. The findings have implications for our understanding of excellent mechanical properties of the I-phase-strengthened Mg alloys.