Aluminium metal matrix composites have gained a lot of attention because of their outstanding properties making them useful for aerospace, automobile and marine applications. Composites are replacing metals as structural materials, and a detailed study of the relationship between hardness and Young's modulus becomes essential. In this paper, the correlation between hardness and elastic modulus of discarded aluminum pistons reinforced with zirconium diboride and snail shells is presented. The theoretical hardness was determined from the ratio of indentation hardness to indentation modulus while elastic modulus was evaluated based on composite equation. The results indicated that hardness and elastic modulus increased with the weight percentage of the composites while the resistance to plastic deformation H 3 / E 2 increased with H. The wide discrepancy between the theoretical and experimental Young's modulus is attributed to the fact that theoretical elastic moduli were obtained from perfect/single crystal materials while experimental values are obtained from polycrystalline/imperfect crystals. The calculated Young's moduli obtained through mixture rule range from 64 to 92 GPa which are higher than 69 GPa of aluminium alloy. It is therefore evident that the composite materials can be used for engineering applications.
This paper presents the relationship between the Young’s modulus and hardness of composites developed from recycled aluminium pistons reinforced with alumina and snailshells. The percentages of alumina and snailshells were kept within the range of 0-30 and 0-10 wt.%, respectively. Experiments were designed using response surface methodology (RSM) to evaluate the influence of the reinforcements on the tensile, hardness and Young’s modulus of the composites. The theoretical hardness was analyzed from the ratio of indentation hardness to indentation modulus while the Young’s modulus was evaluated from the composite equations. The results indicate that an increased fraction of the hybrid reinforcement does not necessarily translate to higher hardness value and Young’s modulus. The sample with the best characteristics has a tensile strength of 172.5 MPa, modulus of resilience of 28.28 GPa and hardness value of 44.9 RHN. The average experimental Young’s modulus of the samples is about 30% of the theoretical value of 86.5GPa while experimental hardness value of 44.90 is about twice that of the theoretical value. The discrepancy between the experimental and theoretical modulus is due to the assumption of a perfect crystal for the former as against polycrystalline crystals. The two samples with the highest modulus of resilience were chosen and further characterized. Scanning Electron Microscope images showed that the fillers in the two samples were well bonded with the aluminium matrix. Keywords - Mechanical Properties, Casting, Aluminum composite, Alumina and Snailshells
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