Two quite different primary Mn-rich phases were observed by optical microscope and scanning electron microscope in the surface and central parts of Al-12 wt%Si-4 wt%Cu-2 wt%Mn heat-resistant alloy casting. Deep-etching observation reveals that one is as highly developed 3D-dendrites and the other is as simple 2D-laths. The results of SEM-EDS show the constituents of these two Mn-rich phases are quite different too. The results of TEM-EDS verify it further. By selected area electron diffraction pattern, the lath-shaped Mn-rich phase is identified as: Al₁₃Mn₄Si₈, simple tetragonal, a = b = 1.240 nm, c = 0.489 nm. The tension test indicates the contribution to strength from dendritic Al₁₅Mn₃Si₂ phase is larger than Al₁₃Mn₄Si₈ phase whether at room temperature or at high temperature. The reason for it is thought to be tied with the much larger difference in elastic modulus of Al₁₃Mn₄Si₈ phase with aluminum matrix than that of Al₁₅Mn₃Si₂.

通过光学显微镜和扫描电子显微镜在Al-12 wt％Si-4 wt％Cu-2 wt％Mn耐热合金铸件的表面和中央部分观察到两个完全不同的富锰主相。深蚀刻观察发现，一个像高度发达的3D树枝状晶体，另一个像简单的2D板条。SEM-EDS的结果表明，这两个富锰相的成分也完全不同。TEM-EDS的结果进一步证明了这一点。通过选择的区域电子衍射图，板条状富锰相被确定为：Al ₁₃ Mn ₄ Si ₈，简单四方，a = b = 1.240 nm，c = 0.489 nm。拉伸试验表明树枝状Al ₁₅ Mn ₃ Si ₂对强度的贡献无论在室温还是在高温下，该相都大于Al ₁₃ Mn ₄ Si ₈相。认为其原因与铝基质的Al ₁₃ Mn ₄ Si ₈相的弹性模量比Al ₁₅ Mn ₃ Si ₂的相差更大。