Investigation of mechanical and tribological properties of hybrid green eggshells and graphite-reinforced aluminum composites

Low cost, low density and good thermal stability of hens' eggshells make them a new reinforcement material. Further, eggshell (Es) is considered as a renewable eco-friendly material. Besides, its waste causes insect infestation and therefore pollution problems. Graphite (Gr) is one of the most commonly used reinforcements due to its self-lubricating properties. Hence, the current work aims to use the powder metallurgy technique to fabricate various aluminum matrix composites having different weight percentages of hybrid green particles (eggshells and graphite). Sintering additives such as magnesium and tin were used to improve the density. Firstly, the powders were manually mixed and cold compacted at 475 MPa and then sintered at 630 degrees C for 2 h. A pin-on-disk wear, Vickers hardness and compressive strength tests were used to investigate the mechanical and tribological properties. Scanning electron microscope (SEM) was used to characterize the morphology and microstructure of the produced composites as well as wear mechanisms. Energy-dispersive X-ray spectroscopy (EDX) test was used to investigate the elemental composition of the composites. The results showed that adding graphite to the aluminum matrix composite containing eggshell has a positive impact on the tribological properties of the composite up to a certain limit (1.5 wt%). However, the additional increase in graphite content has an adverse effect. Hybrid composites with 3 wt% eggshell show the best compressive strength and hardness, whereas hybrid composite with 9 wt% eggshell has the lowest compressive strength and hardness. The mass loss of the hybrid composite increases with the increase in the graphite weight percentages regardless of the eggshell weight percentages. The combination of SEM micrographs and EDX showed signs for three wear mechanisms: abrasive, adhesive and delaminated wear in the examined composites.