Thermal and corrosion behavior of as cast Al-Si alloys with rare earth elements

Aluminum silicon based alloys are the most important commercial casting alloys. Their cast microstructure is strongly related to their technical properties. By adding other selected alloying elements, the alloy microstructure is known to be modified, thus improving its desired properties. Rare earths (RE) can be used as alloying elements to achieve better technical performance of Alsingle bondSi based alloys. In this work, the effects of individual RE (La, Pr, Nd, Sm, Gd, Tb, Dy or Er) addition on a hypoeutectic as cast Alsingle bondSi alloy were studied. In order to investigate the correlation between microstructure changes and thermal and corrosion behavior, the microstructure of the samples and of the intermetallic phases was examined by scanning electron microscopy, electron microprobe analysis, and X-ray powder diffraction. Differential thermal analysis was performed to determine ternary eutectic reaction temperature. A similar decrease in eutectic temperature was recorded for all Alsingle bondSi-RE samples. Decreased hardness due to RE addition was shown by Vickers hardness measurements. DC polarization potentiodynamic measurements showed that RE addition increased corrosion resistance in 3.5 wt% NaCl solution.