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 CaCO 3 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.