Influence of MAO Treatment on the Galvanic Corrosion Between Aluminum Alloy and 316L Steel
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JMEPEG DOI: 10.1007/s11665-017-3037-4
Influence of MAO Treatment on the Galvanic Corrosion Between Aluminum Alloy and 316L Steel Yuanhang Yang, Yanhong Gu, Lei Zhang, Xiangdong Jiao, and Juntie Che (Submitted December 25, 2016; in revised form October 4, 2017) To slow down the galvanic corrosion of aluminum alloy and 316L stainless steel in subsea water, a micro-arc oxidation (MAO) coating was prepared on the surface of the Al alloy, and no treatment was performed on the surface of the 316L. The surface morphology of MAO-coated Al alloy was evaluated using a scanning electron microscope (SEM) before and after corrosion. A micro-hardness tester was used to measure the micro-hardness. Corrosion behaviors were evaluated by open-circuit potential (OCP), potentiodynamic polarization (PDP) and electrode impedance spectroscopy (EIS) tests in a 3.5 g/L NaCl solution. The results of PDP testing show that the corrosion potential of the MAO-coated galvanic pair was more positive than that of the uncoated galvanic pair and that the corrosion current density was smaller than that of the uncoated galvanic pair. EIS results show that the impedance of the galvanic pair increased after MAO coating. SEM images show that the corrosion damage of the uncoated Al alloy was more severe than that of the MAO-coated one, and the post-corrosion images of the surface of the 316L connected with MAO-coated Al alloy were more compact than those of the 316L connected with uncoated Al alloy. A physical model was developed to discuss the influence of MAO treatment on the galvanic corrosion process and corrosion mechanism. Keywords
corrosion model, galvanic corrosion, MAO, 316L
1. Introduction Al alloy and 316L stainless steels are the most commonly used materials in marine industrial applications due to their excellent mechanical properties (Ref 1-3). Al alloy is mainly used in the shipbuilding industry and oil applications. For example, Halliburton Subsea has developed a system made of Al alloy for pipeline and spool protection (Ref 4) because of its high strength/weight ratio (Ref 5, 6). 316L stainless steel is mainly used in offshore gas storage platforms and subsea pipelines. For example, it has been widely used in Persian Gulf seawater due to its high corrosion resistance resulting from the formation of a protective oxide film and passive film on its surface (Ref 7, 8). Many marine oil systems are made of Al alloy and 316L stainless steel, especially for the corrosion protection in welding dissimilar materials (Ref 9-12). When two dissimilar metals are in contact in the presence of an electrolyte, the difference in the electrochemical potential of the two metals can lead to galvanic corrosion, which will accelerate the deterioration of the metal that is more active, shorten the service life, and result in security risks and significant financial losses in marine engineering (Ref 2, 13). Therefore, prevention Yuanhang Yang, Yanhong Gu, Xiangdong Jiao, and Juntie Che, School of Mechanical Engineering, Beijing Institute of Petrochemical Technology,
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