ABSTRACT

Material selection for various engineering purposes have been the challenge for engineers in design and manufacturing as there are many materials available. A combination of one or more materials can alter the property of the main element (as in case of alloys) depending on what purpose the material will serve. Aluminium alloys have been mostly desirable in many engineering applications with Al-Si cast been the predominant. The reason for its (aluminium-silicon) dominance is due to excellent improvement in properties that silicon offers such as, low melting temperature, improved strength, ease of casting, abrasion resistance amongst others.

The aim of this study is to determine the effect of silicon on the tensile strength, hardness and microstructure of aluminium scrap using sand casting method. This was carried out in the foundry workshop in the Department of Production Engineering, University of Benin, Benin City and involved preparation of the sand mold and pattern which was done using a cylindrical rod and cylindrical flask. Microstructural examination was done at Engineering Materials Development Institute, Akure, Ondo State where the samples prepared by sectioning, mounting, grinding, polishing and etching. The microstructure was well studied using a light optical microscope and micrographs of 50x and 100x magnification were taken. Tensile strength test and hardness tests were carried using Avery universal testing machine and Avery Brinell hardness testing machine out at the Department of Mechanical Engineering Laboratory of University of Benin, Benin City respectively. Hypothesis testing was carried out on the research study result using one way ANOVA to know if there is enough statistical evidence to reject/ accept a certain hypothesis about a given parameter.

The results from the microstructural examination shows the presence of primary rich aluminium matrix and the silicon phase. The hypoeutectic phase forms a 3-D eutectic silicon network of interconnected particle embedded in aluminium matrix. This is found to be responsible for the increase in the tensile strength and hardness property of Al-Si alloys. In the hypereutectic, the silicon particles tend to form coarse polyhedral shaped primary silicon in the eutectic. Also, it was found in this study that the tensile strength of the Al-Si alloy increased with increasing silicon content. Same can be said of Brinell hardness number which indicates a materials ability to resist plastic deformation. It was observed that the Brinell hardness number increased with increasing silicon content. The result of the ANOVA shows that they don’t have enough evidence to reject the null hypothesis so cannot accept the alternative hypothesis.