Corrosion studies on Al 7075/boron carbide/titanium/graphite hybrid composites for heat exchangers

In this study, hybrid composites of Al7075 reinforced with boron carbide (B 4 C), titanium (Ti), and graphite (Gr) were synthesized using the stir casting technique and was investigated to assess their suitability for aerospace applications. Six different compositions were prepared by varying the vol% of B 4 C and Ti and maintaining a constant vol% of graphite in all composites. The physical and structural characteristics were analyzed through density measurements, porosity evaluation, and x-ray diffraction (XRD) analysis. The experimental and theoretical density values showed a decreasing trend with increased reinforcement, Porosity values were found to decrease with higher Ti content. XRD confirmed the presence of Al matrix phases along with B 4 C, Ti, and graphite, , indicating uniform distribution and phase stability. Corrosion resistance was assessed using static immersion tests, polarization studies, Nyquist plots, and Bode plots. The base alloy demonstrated susceptibility to galvanic corrosion, with minimal passivation. Composites with boron carbide showed moderate corrosion rate (−1.479 mm y −1 ), and those with titanium exhibited remarkable improvements (−1.116 mm y −1 ). The polarization curves of the reinforced composites displayed lower current densities in the anodic region with an E corr and I corr value of 776.856 mV and 8.332 mA for composite reinforced with boron carbide and 727.265 mV and 8.001 mA for composites reinforced with titanium, indicating enhanced passivation and reduced corrosion rates. Nyquist plots revealed larger semicircular arcs for titanium-reinforced composites, signifying higher charge transfer resistance (R ct ). Among the tested compositions, the hybrid composite with 7 vol% Ti, 3 vol% B 4 C, and 2 vol% Gr exhibited improved passivation, and superior corrosion resistance.