Spontaneous Aryl Diazonium Treatment of Exposed Carbon Fiber Surfaces for Reducing Galvanic Corrosion at Composite-Aluminum Alloy Joints during Cyclic Accelerated Degradation Testing

The treatment of exposed carbon surfaces in a carbon fiber reinforced epoxy composite (CFRP) with a spontaneously formed adlayer of 4-nitroazobenzene (NAB) diazonium was applied to inhibit galvanic corrosion on a mechanically joined and conversion-coated aluminum alloy 7075-T6. The adlayer was formed by immersion in acetonitrile under open circuit conditions for 24 h. The NAB adlayer bonds the exposed carbon surface and attenuates the rate of galvanic corrosion on a joined alloy specimen (lap joint configuration) during a 14-day cyclic accelerated degradation test. The NAB adlayer blocks surface sites, which slows the rate of dissolved oxygen reduction thereby slowing the rate of galvanic corrosion on the nearby alloy. The galvanic corrosion damage on the trivalent chromium process (TCP) conversion-coated alloy was significantly reduced near the composite edges and importantly in the fastener through-hole region. The spontaneously formed NAB adlayer provides better cathodic protection than does the electrochemically formed NAB adlayer, due to more complete coverage with fewer defects (i.e., better blocking layer).