GALVANIC CORROSION OF ALUMINUM-MATRIX COMPOSITES

The galvanic corrosion current density (CD) of Al-matrix composites in 0.5 M NaSO4, and 3.15 wt% NaCl was measured. Galvanic couples of Al with graphite fiber, SiC, and TiB2 were investigated. The galvanic corrosion CD was highest (approximately 10(-4) A/cm2) for Al coupled to graphite fiber in aerated 3.15 wt% NaCl. Results indicate that the galvanic corrosion rate of Al should be approximately 30 times less when coupled to SiC or TiB2. Oxygen reduction was the primary cathodic reaction in the aerated solutions. In deaerated 0.5 M Na2SO4 and 3.15 wt% NaCl, galvanic corrosion was negligible. The galvanic corrosion CD was determined using the zero-resistance ammeter technique and from potentiodynamic polarization diagrams of ultrapure Al, 6061-T6 Al, graphite fiber, SiC, TiB2, and a commercial graphite fiber/6061-T6 Al metal-matrix composite.