铝基体中溶解度较低的 Sn 元素，在含量变化下会引发枝晶取向演变。 本研究利用 OM 与 EBSD，对不同成分 Al-Sn 合金定向凝固过程中的枝晶取向演变进行分析，试样纵截面的宏观组织呈现出单一典型的规则柱状晶、扇状组织或两者共存的特征。 不同截面的 EBSD 晶粒重构图及其对应的极图可揭示枝晶实际生长方向。 结果表明，低 Sn 含量 Al-Sn 合金的定向凝固微观组织中不存在孪生枝晶，仅存在柱状晶；而当 Sn 含量达到 4%(质量分数)时，发生两种关键转变：部分枝晶的晶体学生长方向由 <100> 转变为 <110>，并开始形成以{111}面为孪晶界的孪生枝晶。 柱状晶宏观生长方向与温度梯度方向平行，而孪生枝晶虽保持 <110> 晶体学取向，但其宏观生长方向偏离温度梯度。结果表明枝晶取向演变与界面能各向异性的变化相关，在合适的凝固条件下，Sn 含量超过临界阈值，会通过改变界面能各向异性，同时导致枝晶生长模式与择优生长方向的改变。

The presence of tin, which has a low solubility in an aluminium matrix, can affect the evolution of dendritegrowth with different contents. The evolution of the dendrite orientation during the unidirectional solidification of Al-Snalloys with different contents is investigated by optical metallography (OM) and electron back-scatter diffraction (EBSD).The macrostructure of the longitudinal section of the sample exhibits a single typical fan-like structure, regular columnargrains or both. The EBSD grain reconstruction maps and corresponding poles of different sections can demonstrate theactual dendrite growth directions. The results show that only columnar grains but no twinned dendrites are present in thedirectional solidification microstructures of low-tin-content Al-Sn alloys. When the Sn content reaches 4 wt.%, the preferredgrowth direction of some dendrites changes from <100> to <110>, and twinned dendrites with {111} as the twin boundarystarts to form. The macroscopic growth direction of the columnar crystals is parallel to the temperature gradient, whereasthe twinned dendrites, despite maintaining the <110> crystallographic orientation, have a macroscopic growth direction thatdeviates from the temperature gradient. The results indicate that the evolution of the dendrite orientation is related to thechange in the anisotropy of the interfacial energy. Under suitable solidification conditions, when the Sn content exceeds thecritical threshold, it can simultaneously cause changes in the growth pattern of dendrites and the preferred growth directionby altering the anisotropy of the interfacial energy.