The mechanism of silicon modification in aluminum-silicon alloys: Impurity induced twinning
Document Type
Article
Publication Date
10-1987
Department
Department of Materials Science and Engineering
Abstract
Modification of silicon by sodium in aluminum silicon eutectic alloy has been examined in detail by optical, SEM, and TEM methods. The aluminum phase is not significantly affected but the silicon becomes very heavily twinned. Modification by quenching does not involve an increase in twin density. Consideration of the atomic positions which attend the formation of growth twins on {111} planes suggests that adsorbed impurity atoms of suitable size, on the solid-liquid interface, could be responsible for changing the {111} stacking sequence, so promoting 'impurity induced twinning'; the optimum hard sphere radius ratio would be ≈ 1.65. It is proposed that this condition could be the first and principal requirement for a modifying agent to be effective in this system. It is shown further, that other reputed modifiers do also induce a higher twin density. Variations in the efficiency of individual elements to promote such an effect are discussed in terms of other relevant factors which include melting points and vapor pressures, the free energies of formation of compounds - notably of oxides, and the forms of alloy phase diagrams.
Publication Title
Metallurgical Transactions A
Recommended Citation
Lu, S.,
&
Hellawell, A.
(1987).
The mechanism of silicon modification in aluminum-silicon alloys: Impurity induced twinning.
Metallurgical Transactions A,
18(10), 1721-1733.
http://doi.org/10.1007/BF02646204
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/4402
Publisher's Statement
© 1987 The Metallurgical of Society of AIME. Publisher’s version of record: https://doi.org/10.1007/BF02646204