Galvanic Corrosion of Low-Hydrogen-Embrittlement Cd-Ti 300M Steel Coupled with Composite-Coated TC4 Titanium Alloy in an Industrial-Marine Atmospheric Environment

The atmospheric exposure test of low-hydrogen-embrittlement Cd-Ti plated (LHE Cd-Ti) 300M steel coupled with TC4 titanium alloy of different surfaces was conducted in Qingdao industrial-marine atmospheric environment. The corrosion behavior and mechanism of LHE Cd-Ti 300M steel in the galvanic couples were investigated by means of morphology observation, corrosion product analysis, electrochemical measurement and mechanical property tests. The results show that the composite coating of epoxy polyamide primer and acrylic polyurethane topcoat on the surface of TC4 titanium alloy can significantly reduce the galvanic corrosion behavior of LHE Cd-Ti 300M steel and TC4 titanium alloy, and delay the corrosion process of anode LHE Cd-Ti 300M steel, thus reducing the loss of its mechanical properties. The corrosion of LHE 300M steel in the industrial marine atmosphere of Qingdao is induced by pitting corrosion. After Cd-Ti coating layer gradually dissolves, the corrosive medium reaches the substrate-plating layer interface, and the generated corrosion products accumulate and overflow the surface. The Cl- in Qingdao atmospheric environment severely destructs the surface oxide film, which induces pitting corrosion. In addition, the corrosive media containing sulfate ions can directly participate in the reaction and further aggravate the corrosion.