Role of the Addition of La and Ce on the Cooling Characteristics and Porosity Formation in A356 and A413 Alloys

• Published in: International journal of metalcasting 2022-04, Vol.16 (2), p.553-572
• Main Authors: Samuel, A. M., Zedan, Y., Doty, H. W., Songmene, V., Samuel, F. H.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Materials Science; Metallic Materials; Structural Materials; Technical Paper
• ISSN: 1939-5981; 2163-3193
• DOI: 10.1007/s40962-021-00613-8

The present study was performed on A356 and A413 alloys containing (6–11) %Si. Measured amounts of high-purity La and Ce were added to the molten metal that was allowed thereafter to solidify at a slow rate (~ 0.8 °C/s). The results show that the addition of RE metals (La + Ce) up to 3 wt% leads to an increase in the freezing range through an increase in the melting point of the non-modified alloys by 12 °C, with a decrease in the Al–Si eutectic temperature, by 8 °C, respectively, at 3 wt% addition, regardless of the alloy Si content. Although 0.2% Ce is sufficient to drop the Te2 by about 6 °C, 1.5% Ce is required to raise the Tα2 by about 8–10 °C, regardless of the alloy composition. In the case of A413 alloy, eutectic undercooling was only observed in the non-modified base alloy. In the case of alloys modified with Sr, the presence of Sr neutralizes the effect of RE on the freezing range due to its reaction with RE. Addition of La up to 1.5% has no significant effect on the increase in either Tα2 or Te2 compared to that caused by the addition of the same amount of Ce. The increase in the freezing range with the addition of RE metals leads to the formation of a marked amount of shrinkage porosity, in particular in modified alloys. Due to the high affinity of Sr for oxidation, the porosity observed in Sr-modified alloys is twice as much as that in the non-modified alloys, on account of the porosity resulting from the presence of SrO films, in addition to that from shrinkage porosity resulting from the RE metal addition. The main RE-based intermetallics are: Al–RE–Ti, Al–RE–Si, Al–RE–TR–Si (TR = transition metals). In high Si-containing alloy, i.e., 413 alloy, Al–Re–Si compound was frequently observed.