ZM6稀土镁合金铸件荧光线性缺陷形成机理

Formation Mechanism of Fluorescent Linear Defects in ZM6 Mg-RE Alloy Castings

摘要:

当前稀土镁合金作为一种新型高强轻合金材料在航空航天领域的应用日益广泛，但其铸造缺陷问题日益凸显。荧光线性缺陷是该类合金典型缺陷，其形成机制尚不明确，缺乏精准调控方法。本工作以砂型低压铸造ZM6（Mg-Nd-Zr）合金机匣构件为研究对象，系统表征荧光线性缺陷的成分、形貌与微观结构，结合充型流场数值模拟揭示缺陷演化规律。结果表明，该合金荧光线性缺陷由具有多尺度、多形态特征的双层氧化膜形成。氧化膜以疏松MgO为基体，包含Nd₂O₃颗粒。膜体韧性差，易破碎，在氧化膜周围形成小尺寸氧化夹杂。充型流场分析表明，熔体充型过程中存在的汇流与回流现象造成熔体表面氧化膜折叠并卷入熔体，进而产生双层氧化膜，导致荧光线性缺陷。

Abstract:

Rare-earth magnesium alloys, as a new type of high-strength lightweight structural material, have become increasingly widespread in the aerospace industry. However, issues related to casting defects have grown more prominent. Fluorescent linear defects are a typical defect found in this class of alloys. Nevertheless, their formation mechanism remains unclear, and there is a notable lack of precise control methods to mitigate them. This study systematically characterized the composition, morphology, and microstructure of fluorescent linear defects in a sand-cast low-pressure ZM6 (Mg-Nd-Zr) alloy casing component, and revealed the defect evolution mechanism through numerical simulations of the filling flow field. The results show that fluorescent defects are formed by multi-scale and multi-morphology double-layer oxide films. Meanwhile, the oxide film in ZM6 consists of porous MgO as the matrix, containing Nd₂O₃ particles. This film exhibits poor toughness and is prone to fragmentation, resulting in the formation of small-sized oxide inclusions around the oxide film. Combined with the analysis of the casting structure and filling flow field, it is found that the convergence and backflow of the melt during the filling process cause the oxide film on the melt surface to fold and be incorporated, thereby generating double-layer oxide film that can be displayed by fluorescent inspection.