Abstract
This paper reports on an investigation of the modifying effects of individual additions of the rare earth elements cerium and lanthanum on the microstructural characteristics of an as-cast Al-Si-Mg alloy. The solidification process was analyzed by thermal analysis and the microstructures of the alloys were examined using conventional optical microscopy and electron probe microanalysis (EPMA) techniques. The eutectic silicon particle characteristics were evaluated using quantitative image analysis. The results indicate that modification of the eutectic silicon particles was obtained with both Ce and La additions. Depressions of 2-9C (36-48F) in the eutectic temperature were observed with the addition of rare earths. Cerium and lanthanum form mainly ternary or quaternary intermetallic compounds with Al and Si when their concentration exceeds approximately 1 wt pct. These Ce- and La-rich phases display different types of morphology, including needlelike and flat platelet-like forms.