Influence of AlN and eggshell-derived CaCO 3 on physical,mechanical,and tribological properties of LM26 Al-alloy hybrid composites

The present experimental study focuses on developing aluminium hybrid metal matrix composites using varying weight percentages of carbonized eggshell powder (CES_P) and a fixed 5 wt.% aluminium nitride powder (AlN_P) through powder metallurgy (P/M). The influence of CES_P content on the microstructure, density, hardness, compressive strength, and wear behaviour was systematically investigated. Field emission scanning electron microscopy (FESEM) revealed uniform dispersion of reinforcements up to 4.5 wt.% CES_P, with slight agglomeration observed at 6 wt.%. X-ray diffraction (XRD) confirmed the presence of AlN and CaCO₃ phases without any indication of brittle intermetallic compound formation. Increasing CES_P content led to a gradual decrease in relative density and an increase in porosity. A significant improvement in microhardness and compressive strength is observed up to 4.5 wt.% CES_P, achieving 55.52 HV and 366.04 MPa, respectively, followed by a decline at higher reinforcement levels. Tribological evaluation revealed a reduction in both wear loss and coefficient of friction (COF) with increasing CES_P, with optimum performance at 4.5 wt.%. Worn surface analysis indicated a transition from delamination and abrasion in the unreinforced alloy to predominantly abrasive wear in the composites. Overall, 4.5 wt.% CES_P was determined to be the optimal reinforcement level for enhancing both mechanical and tribological properties.