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ABSTRACT
Composites are one of the best-known engineering materials for their advanced and excellent properties like improved mechanical properties, and chemical compositions. In this study, aluminium-silicon composites were produced by sand casting using a crucible furnace. The effects of silicon on specific mechanical properties such as hardness and tensile strength as well as the microstructure of the composites were examined. The widespread use of aluminium alloys in various applications in industry requires that the alloys have certain desirable properties hence the need for alloying.
Scrap automobile pistons were washed and melted to produce the aluminium ingots, which were then heated in the crucible furnace with addition of silicon ranging from 4%wt-14%wt. The sand casting method was used to create the mounds, while the patterns used were cylindrical hollow pipes. Tensile and hardness tests were carried out on the specimens to see how varying the composition of silicon impacts on the strength and overall hardness of aluminium. Also, the microstructure was examined at different magnifications at different levels of silicon compositions.
It was evident that significant increase in the hardness values was observed with a silicon concentration of approximately 4%wt. This was due to the small spherical and evenly distributed silicon particles in the aluminum matrix. The tensile strength followed similar pattern and there was a noticeable increase as soon as the concentration was approximately 4%wt. However, there was a decrease in the tensile strength when the silicon concentration was in excess of 12%wt as a result of the appearance of the silicon particles as coarse polyhedral crystals. Also, It was inferred that the foundry practice impacted on the microstructure of the cast composite as there was noticeable pores and cracks on the specimen when observed under an electron microscope. This can be avoided by choosing the right casting process, preferably permanent mould castings and also closely control the mould design.
