New orientations between β′ 2 phase and α matrix in a Mg-Zn-Mn alloy processed by high strain rate rolling

Highlights: • Spherical precipitates have a hexagonal structure and can be defined as β′₂ phase. • Most spherical precipitates have common orientation relationship to the matrix. • New orientation relationships between spherical particles and matrix were observed. • The formation mechanism of the new orientation relationships was discussed. Strengthening precipitates in a Mg-Zn-Mn alloy, processed by high strain rate rolling, have been characterized by transmission electron microscopy. Precipitations involve a few (0001)_α plates and spherical precipitates. All the precipitates have a hexagonal structure of MgZn₂ and can be defined as β′₂ phase. The (0001)_α plates and a portion of the spherical precipitates have a common orientation relationship of ${\left[\overline{2}110\right]}_{{\text{β}}_2^{\text{'}}}//{\left[01\overline{1}0\right]}_{\text{α}}$, ${\left(0001\right)}_{{\text{β}}_2^{\text{'}}}//{\left(0001\right)}_{\text{α}}$ and ${\left(01\overline{1}0\right)}_{{\text{β}}_2^{\text{'}}}//{\left(\overline{2}110\right)}_{\text{α}}$ to α-Mg matrix. New orientation relationships (for example, ${\left[\overline{2}110\right]}_{{\text{β}}_2^{\text{'}}}//{\left[01\overline{1}0\right]}_{\text{α}}$ and ${\left(01\overline{1}5\right)}_{{\text{β}}_2^{\text{'}}}\sim //{\left(\overline{2}110\right)}_{\text{α}}$) between the spherical precipitates and α-Mg matrix were firstly observed, and the formation mechanism was systematically discussed.