Corrosion-resistant aluminum matrix for graphite-aluminum composites

Graphite-aluminum (Gr-Al) metal matrix composites (MMC) possess several attractive mechanical and thermal properties, but use of these materials has been limited, partly because they are extremely susceptible to corrosion. Corrosion-resistant Al alloys that contained nonequilibrium concentrations of molybdenum (Mo) were developed as the matrix for Gr-Al composites using co-sputter deposition. Corrosion testing included potentiodynamic polarization and galvanic coupling of as-sputtered (AS) and heat-treated (HT) alloys. Polarization behavior of the AS and HT alloys measured in sodium chloride (NaCl) solutions was improved greatly over that of pure Al and traditional Gr-Al matrix alloys such as type 6061 Al (UNS A96061). Galvanic current density values for as-deposited and HT Al-18% Mo and Al-23% Mo alloys coupled to equal areas of pitch-based graphite from Amoco P75 Gr fibers were found to be up to 3 orders of magnitude lower than for pure sputtered Al-to-Gr couples. Galvanic diagrams for the Al-Mo alloys indicated corrosion was controlled by the anodic reaction irrespective of the cathode-to-anode area ratio.