On the Al–Al(11)Ce(3) Eutectic Transformation in Aluminum–Cerium Binary Alloys

The L ↔ Al + Al(11)Ce(3) technologically important eutectic transformation in Al–Ce binary alloys, containing from 5 to 20 wt.% Ce and ranging from hypo- to hypereutectic compositions, was examined along with the microstructure and properties of its solidified product. A combination of thermal analysis and metallography determined the coordinates of the eutectic point at 644.5 ± 0.6 °C and 10.6 wt.% Ce, clarifying the existing literature ambiguity. Despite the high entropy of melting of the Al(11)Ce(3) phase, in hypoeutectic alloys the eutectic was dominated by the regular morphology of periodically arranged lamellae, typical for non-faceted systems. In the lamellar eutectic, however, the faceting of Al(11)Ce(3) was identified at the atomic scale. In contrast, for hypereutectic compositions, the Al(11)Ce(3) eutectic phase exhibited complex morphology, influenced by the proeutectic Al(11)Ce(3) phase. The Al(11)Ce(3) eutectic phase lost its coherency with Al; it was deduced that a partial coherency was present only at early stages of lamellae growth. The orientation relationships between the Al(11)Ce(3) and Al in the eutectic structure, leading to partial coherency, were determined to be [Formula: see text] (Al) ║ [Formula: see text] (Al11Ce3) with [Formula: see text] (Al) ║ [Formula: see text] (Al11Ce3) and [Formula: see text] (Al) ║ [Formula: see text] (Al11Ce3) with [Formula: see text] (Al) ║ [Formula: see text] (Al11Ce3). The Al(11)Ce(3) phase with a hardness of 350 HV and Al matrix having 35 HV in their eutectic arrangement formed in situ composite, with the former playing a role of reinforcement. However, the coarse and mostly incoherent Al(11)Ce(3) eutectic phase provided limited strengthening and the Al–Ce alloy consisting of 100% eutectic reached at room temperature a yield stress of just about 70 MPa.