Development and performance evaluation of AA6061-SiC-graphite hybrid composites for lightweight automotive structural applications

This study focuses on the development and performance evaluation of AA6061-based hybrid metal matrix composites (MMCs) reinforced with silicon carbide (SiC, 5 μm) and graphite (Graphite, 25 μm) particles for lightweight automotive structural applications. The composites were synthesized using the stir casting method, with reinforcement content varying from 0 to 4 wt% (equal parts SiC and Graphite). The effect of reinforcements on structural, mechanical, and corrosion behavior was systematically investigated. The results revealed a 3.33 % reduction in density (from 2.70 to 2.61 g/cm³) and a progressive improvement in Brinell hardness, which increased by approximately 80 % (from 30.71 BHN to 55.27 BHN). The compressive strength improved significantly by 36.76 %, rising from 322.83 MPa for the base alloy to 441.6 MPa for the composite with 4 wt% reinforcement. A slight decline in impact strength was observed with increasing reinforcement dropping from 9.45 N·m to 8.1 N·m attributed to the brittle and lubricating nature of graphite particles. Corrosion resistance was enhanced, with a 21.57 % reduction in corrosion rate after 168 h in 3.5 wt% NaCl solution, due to the formation of a protective oxide layer and the electrochemical stability of the reinforcements. Microstructural analysis (SEM, EDX, XRD, FTIR) confirmed homogeneous dispersion of reinforcements and absence of unwanted intermetallic phases. These findings demonstrate that the developed AA6061-SiC-Gr hybrid composites offer a superior combination of strength, corrosion resistance, and reduced weight making them well-suited for structural applications in the automotive sector. The novelty of this work lies in the combined use of SiC and graphite reinforcements in a micron-sized hybrid system, evaluated through integrated mechanical and corrosion testing an area not fully addressed in earlier AA6061 composite studies. These findings establish a performance-optimized composition suitable for automotive structural applications.