TITLE:
Structural Modification of Sand Cast Eutectic Al-Si Alloys with Sulfur/Sodium and Its Effect on Mechanical Properties
AUTHORS:
Chikezie W. Onyia, Boniface A. Okorie, Simeon I. Neife, Camillus S. Obayi
KEYWORDS:
Aluminum-Silicon Alloy; Sand Casting; Modification; Morphology; Mechanical Properties
JOURNAL NAME:
World Journal of Engineering and Technology,
Vol.1 No.2,
August
12,
2013
ABSTRACT: In the present study, the
structural modification of sand cast Al-12wt%Si alloy with sulfur/sodium and
its effect on mechanical properties were investigated. Different addition
levels of sulfur and sodium were used to modify and produce castings of the
same shape and size from the alloy. The results indicated that the addition of
sodium or sulfur to eutectic Al-Si alloy can modify the Al-Si eutectic
morphology from needle-like eutectic silicon structure to fine-scale eutectic
silicon structure with significant improvement in mechanical properties of the
alloy. The optimum levels of modification by sodium flux (60% NaF and 40% NaCl)
and sulfur were found to be 0.6% - 1.0% and 0.02% - 0.05% of the weight of the alloy respectively.
The alloy modified with 0.6% Na flux had the best mechanical properties closely
followed by the one modified with 0.02% sulfur. Over modification of the alloy
with sodium produced over modification band which consisted of aluminum
dendrites and coarse silicon particles in the microstructure of the alloy.
Increase in concentration of sulfur decreased the degree of fineness of the
eutectic silicon structure with significant decrease in mechanical properties
of the alloy and this is suggested to be as a result of the presence of a
brittle sulfur compound at the grain interfaces of the alloy.