Galvanic corrosion of the anodized 7050 aluminum alloy coupled with the low hydrogen embrittlement Cd[sbnd]Ti plated 300M steel in an industrial-marine atmospheric environment

Abstract

The industrial-marine atmospheric corrosion behavior and mechanism of anodized 7050 Al alloy coupled with low hydrogen embrittlement CdTi (LHE CdTi) plated 300M steel were investigated by means of morphology observations, corrosion product analysis and mechanical property testing. The results showed that the CdTi coating reduced the potential difference between the cathode and the anode, and greatly weakened the galvanic corrosion. Therefore, the self-corrosion of anodized 7050 Al and LHE CdTi plated 300M steel dominated the corrosion process. The pitting and intergranular corrosion (IGC) of the anodized Al were severe, and significantly reduced the strength and elongation. The corrosion products composed of AlOOH, Al(OH)3 and Al2(SO4)3 distributed non-uniformly on the surface. The high concentration of Cl− in the industrial-marine atmosphere destructed the anodized films and induced the pitting corrosion of the Al alloy. Due to the pitting and the micro-galvanic corrosion at the grain boundary, the IGC initiated and propagated. In addition, the sulfide dissolved into the thin electrolyte film and aggravated the pitting and IGC. For the LHE CdTi plated steel, the sacrificial CdTi coating was preferentially corroded, and the further corrosion was inhibited due to the corroded surface composed of cadmium hydroxides, chlorides and sulfates.