Effect Of Alloy Elements And Marine Environment On Electrochemical Performances Of Al-Zn-In-Mg-Ti Sacrificial Anode

Aluminum alloy sacrificial anode material was widely used in the protection ofsteel structure in marine environment, which was attributed to its high drivingpotential, high theoretical capacity, high current efficiency, low cost and easyconstructed. Aluminum sacrificial anodes were refined by adding moderate alloyelements to aluminum ingots. The electrochemical performances of aluminum anodesdepended on the chemical composition. With the developing of deep-sea resources,corrosion protection design of steel structure in the deep-sea gradually becameurgently. In addition, the changes of application environment played a decisive role inthe effectiveness of the sacrificial anode cathodic protection. Therefore, in the presentdissertation, Al-Zn-In-Mg-Ti sacrificial anode was chosen as research material, andalloy elements were designed by Latin orthogonal. The effects of alloy elements andmarine environment on electrochemical performances of Al-Zn-In-Mg-Ti sacrificialanodes were studied by using constant-current test, polarization curve,electrochemical impedance spectroscopy (EIS), scanning electron microscopy(SEM).The results of testing of alloy composition factor indicated that the greatestimpact for the anode electrochemical performance was the content of In, following Tiand Mg, and content of Zn had the minimum impact. Open-circuit and closed-circuitpotentials of the anode gradually became negative, in the contrast, the currentefficiency trended down and dissolution morphology got worse with increasing of thecontent of In. Therefore, the content of In should be controlled between0.020%and0.030%. According to the current efficiency, the best formula of anode (wt%) was Zn6.0, In0.020, Mg1.5, Ti0.050, the rest of material was Al, and its current efficiencywas89.85%. The anode activation mechanism was the preferential dissolution of theactive element which would deposit on the surface of the anode with electrons, and damaged the oxide film of the surface, leading the anode dissolved actively, when theactive element ions reached a certain concentration in the medium.The results of testing of marine environment factors indicated that open-circuitand closed-circuit potentials of the anode gradually became negative, while theelectrochemical capacity and current efficiency increased, and dissolved morphologybecame better with temperature decreasing in static and dynamic conditions. Theanodic dissolution morphology was worse, and the anode manifested as non-uniformcorrosion as a result of corrosion product attached to the surface of the anode. Owingto the active element ions deposited on the surface of the anode and damaged theoxide film of the surface as well as the anode dissolved actively, the electrochemicalperformances of anodes were improved in low temperature. In the same temperature,the electrochemical capacity and the current efficiency of the anode in dynamic werelower than in static. The main reason was that the flowing seawater exacerbated thescouring to the anode in dynamic leading to the metal particles which without bindingforce of the anode surface would fall out mechanically and not discharged fully. Therewas no obvious correlation between the concentration of dissolved oxygen and theelectrochemical performances of anode. With the decreasing of concentration ofdissolved oxygen, the current efficiency declined slightly and dissolution morphologybecame worse. With salinity increasing, anodic dissolution exacerbated along thegrain boundary to the anode in-depth, localized corrosion was serious andelectrochemical performances of the anode became worse, which manifested thatopen-circuit and closed-circuit potential shifted positive, current efficiency andelectrochemical capacity decreased, and dissolution morphology was worse.