The spherical-like θ-Al₄₅(Mn,Cr)₇ particle having a monoclinic structure is observed in an Al–Mg alloy using TEM. Two types of twins with different twin directions are found in these θ-Al₄₅(Mn,Cr)₇ particles. One type is shown to be a $\left(\bar{1}11\right)$ twin with $\left(\bar{1}11\right)$ plane serving as the twinning plane and the shear direction is η₁ = $\left[1\bar{2}3\right]$; the other type is seen to be a $\left(\bar{1}10\right)$ orientation twin with $\left(\bar{1}10\right)$ plane acting as the coherent plane. At least six different orientation relationships between the θ-Al₄₅(Mn,Cr)₇ particles and the α-Al matrix are observed. These relatively complicated orientation relationships are attributed to the pseudo ten-fold symmetric building block of the θ phase viewed along the [101] axis. The possible formation mechanisms of these twins are discussed based on a crystallographic consideration.

球面状的θ-Al系₄₅（锰，铬）₇具有在利用TEM的Al-Mg合金中观察到颗粒上的单斜晶结构。两种不同的双孪晶的方向在这些θ-Al系中发现₄₅（锰，铬）_7个颗粒。一种类型显示为$（\stackrel{〜}{\mathrm{1个}}11）$ 与双胞胎 $（\stackrel{〜}{\mathrm{1个}}11）$平面作为孪晶面和剪切方向为η ₁  = $\left[\mathrm{1个}\stackrel{〜}{\mathrm{2个}}3\right]$; 另一种类型被认为是$（\stackrel{〜}{\mathrm{1个}}10）$ 定向孪生与 $（\stackrel{〜}{\mathrm{1个}}10）$作为相干平面的平面。的θ-Al系之间的至少六个不同的取向关系₄₅（锰，铬）_7个颗粒和α-Al基体中观察到。这些相对复杂的取向关系归因于沿[101]轴观察到的θ相的伪十倍对称构造单元。这些双晶的可能的形成机理是基于晶体学的考虑进行讨论的。