On the Al-Al₁₁Ce₃ Eutectic Transformation in Aluminum-Cerium Binary Alloys

The solidification behavior of Al-Ce alloys remains poorly understood, particularly regarding the eutectic transformation involving Al and Al₁₁Ce₃. While prior research has documented general eutectic structures in aluminum-rich systems, the precise coordinates of the eutectic point in Al-Ce alloys have been inconsistent across studies. Existing literature lacks clarity on the morphology and coherency of Al₁₁Ce₃ in different alloy compositions. Additionally, the mechanical properties of eutectic structures in these alloys remain understudied. This uncertainty limits the design of Al-Ce alloys for structural applications. The need for precise thermal and microstructural data motivates further investigation. The role of Ce concentration in influencing eutectic morphology is not fully resolved. Understanding these factors could improve alloy performance. However, no prior work had resolved the exact eutectic composition and its impact on microstructure.

This study aimed to clarify the eutectic transformation in Al-Ce alloys by determining the exact coordinates of the eutectic point. Researchers focused on alloys with Ce concentrations between 5 and 20 wt.%. The goal was to resolve discrepancies in the literature regarding the eutectic temperature and composition. The team also sought to analyze the microstructure of the solidified eutectic product. They examined how Ce concentration affects the morphology of Al₁₁Ce₃ in both hypo- and hypereutectic compositions. The study aimed to identify orientation relationships between Al and Al₁₁Ce₃ in the eutectic structure. Additionally, the mechanical properties of the eutectic phase were evaluated. The findings could inform the development of Al-Ce alloys with tailored microstructures.

The researchers used thermal analysis to determine the eutectic transformation temperature and composition. Metallographic techniques were employed to examine the microstructure of solidified alloys. Electron microscopy was used to observe the atomic-scale faceting of Al₁₁Ce₃. The study involved analyzing alloys with varying Ce concentrations, from hypo- to hypereutectic compositions. The team assessed the morphology of the eutectic phase in each composition. Orientation relationships between Al and Al₁₁Ce₃ were determined using diffraction methods. The mechanical properties of the eutectic structure were measured through hardness tests. The combination of thermal and structural analyses provided a comprehensive view of the eutectic transformation.

The eutectic point was determined to occur at 644.5 ± 0.6 °C with 10.6 wt.% Ce. Hypoeutectic alloys showed a regular lamellar morphology typical of non-faceted systems. In lamellar eutectics, atomic-scale faceting of Al₁₁Ce₃ was observed. Hypereutectic compositions exhibited a complex morphology influenced by proeutectic Al₁₁Ce₃. The Al₁₁Ce₃ phase lost coherency with Al during solidification. Partial coherency was present only at early stages of lamellae growth. Orientation relationships between Al and Al₁₁Ce₃ were identified as _Al ║ _Al11Ce3 with _Al ║ _Al11Ce3. The eutectic structure formed an in situ composite with Al₁₁Ce₃ acting as reinforcement.

The study clarified the eutectic transformation in Al-Ce alloys by identifying the exact coordinates of the eutectic point. The morphology of Al₁₁Ce₃ varied between hypo- and hypereutectic compositions. The observed lamellar structure in hypoeutectic alloys contrasts with the complex morphology in hypereutectic compositions. The Al₁₁Ce₃ phase exhibited partial coherency with Al at early growth stages. Orientation relationships were determined to be _Al ║ _Al11Ce3 with _Al ║ _Al11Ce3. The eutectic structure formed an in situ composite with Al₁₁Ce₃ acting as a reinforcement. However, the coarse and incoherent Al₁₁Ce₃ phase provided limited strengthening. The 100% eutectic alloy achieved a yield stress of about 70 MPa at room temperature.