Detailed Structures and Formation Mechanisms of Well-Known Al₁₀RE₂Mn₇ Phase in Die-Cast Mg–4Al–4RE–0.3Mn Alloy

Abstract

The detailed structures and the corresponding formation mechanisms of the well-known Al₁₀RE₂Mn₇ phase in the conventional die-cast Mg–4Al–4RE–0.3Mn alloy were thoroughly investigated using transmission electron microscopy (TEM). The results indicate that the Al₁₀RE₂Mn₇ phase ordinarily contains both normal $(11\overline{2} 1)$ twins and orientation twins. Both detailed TEM observations and density functional theory calculations indicate that the Al₁₀RE₂Mn₇ phase is transferred from the Al₈REMn₄ phase following an orientation relationship as $[010]_{{{\text{Al}}_{ 8} {\text{REMn}}_{ 4} }} / /[\overline{1} 101]_{{{\text{Al}}_{ 1 0} {\text{RE}}_{ 2} {\text{Mn}}_{ 7} }}$ and $(101)_{{{\text{Al}}_{ 8} {\text{REMn}}_{ 4} }} / /(11\overline{2} 0)_{{{\text{Al}}_{ 1 0} {\text{RE}}_{ 2} {\text{Mn}}_{ 7} }}$. Moreover, forming orientation twins in the Al₁₀RE₂Mn₇ phase is attributed to the blurry regions at incoherent twin boundaries in the Al₈REMn₄ phase. Finally, these formed orientation twins result in the $(11\overline{2} 1)$ twins in the Al₁₀RE₂Mn₇ phase.