Development and Properties Characterizations of Shea Nutshell Ash (SNSA) Reinforced Aluminium Metal Matrix Composite

Abstract

Growing interest in sustainable and low-cost engineering materials has encouraged the use of agricultural waste as reinforcement in aluminium metal matrix composites. In this study, shea nut shell ash (SNSA), an abundant agro-waste material was used as reinforcement in AA6061 aluminium alloy to develop an environmentally sustainable composite. The composites were produced using the stir casting technique with SNSA additions of 0, 5, 10, 15, 20, 25 and 30 wt%. Microstructural and phase characterisation were carried out using scanning electron microscopy with energy dispersive spectroscopy and X ray diffraction, while mechanical properties were evaluated through tensile, hardness and impact tests in accordance with ASTM standards. The results showed that SNSA is predominantly carbon based with 88.15 wt% carbon and 7.75 wt% oxygen, while minor elements such as Fe 2.18 wt%, Si 0.36 wt% and Ca 0.31 wt% were also detected. X ray diffraction revealed the presence of hard phases including Fe₃C and MnO together with graphite. In addition, the Mechanical properties revealed that the unreinforced AA6061 alloy exhibited the highest tensile strength of 119.77 MPa and elongation of 12.91%. With increasing reinforcement content, tensile strength decreased to 83.04 MPa at 5 wt% and further to 32.32 MPa at 25 wt%, before slightly recovering to 66.56 MPa at 30 wt%. Conversely, hardness increased from 7.6 HRB for the base alloy to a maximum of 13.5 HRB at 30 wt% SNSA. However, the impact energy improved from 2.64 J for the matrix alloy to 8.33 J at 10 wt% reinforcement and remained above the base alloy for all reinforced samples. Furthermore, the results indicate that moderate SNSA additions of 5 to 15 wt% provided the most balanced combination of hardness, strength and impact resistance. Therefore, the study demonstrates that SNSA is a promising sustainable reinforcement for aluminium matrix composites suitable for cost sensitive engineering applications.