Study On Low Potential Al-alloy Sacrificial Anode Under Oil-contaminated Seawater Environment

Sacrificial anode as a kind of cathodic protection methods has a history nearly200years. Studys on sacrificial anodes for special interest areas have been undertakencontinuously as the development of the application fields. Some researches about lowpotential anodes for high strength steel or anodes for carbon steel in oil-contaminatedseawater have got some achievements, but there is little study on the combination ofthe two fields above to solve the corrosion problem on high strength steel of deckcabin caused by oil-contaminated seawater, so it has a certain significance to developa kind of anode to solve this problem.Alloys of Al-Zn-In-Bi-Si-Ce has been selected in this paper by referring torelative literatures. Some research methods as impressed current laboratory testing ofaluminum alloy anodes, polarization curves, EIS, SEM, EDS and macrometallo-graphic observation are carried out to find the active mechanism of alloying elements.Orthogonal analysis based on current efficiency has been taken on16set of anodessamples to find the admirable chemical composition.8set of anode have beenproduced by2chemical compositions, one is the mentioned above and another israndom selected within orthogonal scope, in4different heat treatments. Effectsanalysis of electrochemical properties and microstructure caused by heat treatments isalso carried out.The results show that the grain would be refined when Si<0.4%or Ce<0.3%.Hydrogen evolution reaction may be occurred if the element Si is added in excess andcorrosion products would be attached to anode surface if the content of Ce added to0.5%. Uniform dissolution of alloy could be caused by adding alloying element Bi to0.5%, adding too much could have poor effect on dissolving uniformity. The potentialof anode moves towards negative direction remarkably, and the current efficiencyimproves greatly by increasing the Zn percentage composition. The results meet themechanism of spinel destruction of oxide film. It is showed by range analysis that the influence on current efficiency ofelements is R_Zn=21.54%>R_Si=13.73%>R_Ce=13.67%>R_Bi=9.4%>R_In=4.81%,Al-0.5%Zn-0.018%In-2%Bi-0.4%Si-0.2%Ce is the optimize compositon. The EDSindicates that element In meets the “Dissolution-Redeposition” mechanism bydepositting on the surface of anode. Fe exists in the transition zone of corrosion pit,which reduces the current efficiency by causeing grain fall in advance. The grain sizeof two kinds of chemical composion anodes under4heat treatment isannealing<quench<normalizing<solid solution, and the quench technic has the mostbrillent electrochemistry property. So the optimized composition could be treatedmerely by quench technic without any other expensive heat treatment. Throughanalyzing EIS of the optimized composition alloys, the corrosive mechanism can becharacterized by the equivalent circuit of R_S（R_PC）（QR_DR_A）.