Multi-objective optimization of silicon carbide-reinforced 7075 aluminium composite for military-grade firing pin applications

Abstract

This research investigates the development and performance optimization of silicon carbide (SiC)-reinforced 7075 aluminium matrix composites for high-stress military applications, with specific interest in general-purpose machine gun (GPMG) firing pins. Building upon the previously optimized base alloy (Al7: 6.1% Zn, 2.9% Mg, 1.2% Cu, 0.18% Cr), SiC particles were introduced at varying weight fractions (0–10 wt.%) and processed via squeeze casting to produce dense, high-integrity composite samples. A four-factor, four-level Taguchi L16 orthogonal array was employed to investigate the influence of process parameters, stirring speed, squeeze pressure, reinforcement preheat temperature, and SiC content on mechanical and tribological properties. Grey Relational Analysis (GRA) was used to perform multi-response optimization with a focus on maximizing hardness, tensile strength, and wear resistance. Results show that the addition of 10 wt.% SiC under optimized processing conditions significantly improved Brinell hardness (127.4 BHN), tensile strength (206.1 MPa), and wear resistance (reduced from 0.6334 mm³/min in the unreinforced alloy to 0.417 mm³/min in the composite). ANOVA results confirmed that stirring speed was the most influential factor, followed by squeeze pressure. Microstructural analysis using optical microscopy and SEM revealed uniform particle dispersion and a refined grain structure with reduced porosity. The optimized composite was used to fabricate a prototype firing pin, which was then subjected to dimensional analysis and preliminary functional assessment. This study demonstrates the viability of low-cost, high-performance aluminium matrix composites (AMCs) for critical defense applications and offers a replicable framework for the development of custom-engineered components in resource-constrained settings.