Galvanic Corrosion of Aluminum-Matrix Composites

The galvanic corrosion current density (CD) of Al-matrix composites in 0.5 M Na₂SO₄, 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.