Corrosion Beehavior Of Zn/Al Based Sacrklficial Anode Coatings In Simulated Low-temersture Sea Environment

Metal coating made by thermal spraying or sacrificial anode was widely used in the fieldof seawater corrosion protection area. However, the relatively harsh corrosive seaenvironment and the lackness of relevant experience make people choose corrosion protectiontechnology without adequate theoretical support. The high costs and the unimplementation ofconstruction and detection and maintenance in deep water require the more reliable assurance.Therefore, we have to reduce costs and maximizing the reliability of cathodic protection. Thismeans that we should ensure corrosion protection requirements and reducing the weight ofsacrificial anode in the proper way, or a reasonable substitute for sacrificial anode has animportant engineering significance.This paper attempts to use aluminum coating,Zn-15Al coating, aluminum sacrificialanode+aluminum coating and aluminum sacrificial anode+Zn-15Al coating to replace thealuminum anode in order to achieve the purpose of reducing the weight of the anode. Throughthe accelerated corrosion test simulate the deep-sea , discuss the corrosion resistance, analysethe corrosion behavior, study the corrosion rates of aluminum coatings of in different kinds ofcathodic protection, and try to set up the life-assessment system.The results show that protective effectiveness of aluminum alloy anode + Zn / Al coatingare exellent in a variety of atmospheres. In the environment saturated with oxygen, thealuminum coating and Zn-15Al coating have relatively good corrosion protectioneffectiveness. In the absent of oxygen environment, the Zn-15Al coating could meet therequirements. Thermal spray coatings can greatly improve the service life of the sacrificialanode, and the method of anode + coating has the best anticorrosion effects.The corrosion morphologies of the sample observation show that in oxygen saturatedenvironment the polarization time of the aluminum sacrificial anode is short in early stage of cathodic protection, a larger corrosion current,and short-lived; aluminum coating continuouspassivation, has the longer life ; anode + coating, the corrosion current becomes smaller, morepassive coating, further extension of life. In the anoxic environment, the anodic polarizationtime is longer, the corrosion current is small, longer life expectancy; The corrosion current ishigh because the coating is uneasy to passivate, life expectancy was short; anode + coatingtogether to protect, the corrosion current reduced, the anode and coating has received betterprotection. Zn-15Al coating in oxygen saturation in the good corrosion protection, combinedwith the anode under the action of zinc and aluminum coated with aluminum anode galvaniccorrosion exists, with the deposition of corrosion products, to ensure the life of the coating. Inthe anoxic environment, the Zn-15Al coating with electrochemical protection and anode +coating life are relatively extended.Therefore, the thermal spray Zn / Al coating or aluminuium sacrificial anode + Zn / Alcoating are effective alternatives of sacrificial anode, and both of them can extend the life ofcathodic protection.