INFLUENCE OF SODIUM CHLORIDE MODIFIER ON THE PROPERTIES OF ALUMINIUM-SILICON ALLOY

Abstract

Solidification of aluminium-silicon alloy produces coarse eutectic microstructures consisting of

large and brittle plates in aluminium matrix. This result lowers the mechanical properties of alloy.

Chemical modification was applied to improve the properties of aluminum-silicon (Al-Si) alloy.

The Aluminium-silicon alloy was developed and modified with sodium chloride salt using sand

casting technique. The amount of salt used was calculated stoichiometrically. The percentage

variation of sodium content in sodium chloride was 0.005%, 0.01%, 0.015%. Aluminium ingot,

aluminum-silicon ligand and magnesium metal were melted in the furnace at varying temperatures

(750oC, 800oC and 850oC) to form the hypoeutectic alloy conforming to AA354 alloy. The modified

salt was introduced into the molten metal, mixed and then cast into molds. The cast samples were

subjected to Characterization such as microstructural analysis, X-Ray Defraction and thermal

conductivity analysis and mechanical properties such as tensile, impact and hardness tests. The

X-Ray Diffractometer analysis was conducted on the cast sample to determine the grain refinement

and the crystallinity of the modified alloy. The microstructure revealed the brake down. The tensile

strength of the unmodified alloy was 80.54MPa. The addition of sodium chloride was discovered

to have increased the tensile strength to 189.51MPa. The hardness value increased from

60.87HRB for the unmodified to 82.1HRB for sodium chloride modified alloy. The impact strength

of the alloy decreased from 2.03J for the unmodified alloy to1.68J for the modified alloy. The

modifying salt (NaCl) changed the eutectic structure of the aluminium-silicon alloy. The changes

in the structure were reflected in the outcome of the various tests conducted on the developed

samples. The modified aluminium-silicon alloy was used successfully for the casting of an

automobile brake disc.