Research On Electrochemical Performances Of Aluminium Alloy Sacrificial Anode Materials

Aluminum alloy sacrificial anode materials are widely used for protecting steel structures in oceanic environment, due to its high driving potential, high theoretical capacities, high current efficiency, low cost and easy constrion. At present, Al-Zn-In series sacrificial anode materials were widely used because of its good electrochemical performances without heat treatment, but there are still many problems, such as positive shift of the potential, uneven dissolution of the surface and decreased current efficiency for long-term application. Therefore, in the paper, taking Al-Zn-In-Si sacrificial anode materials as research objects, the effects of oxide inclusion, content of Fe impurity, chemicial composition and microstructure on their electrochemical performances of Al-Zn-In-Si sacrificial anode materials are systematically studied to increase the electrochemical performances of the sacrificial anodes mentioned above. At the same time, the effects of content of Fe impurity on electrochemical performances of Al-Zn-In-Cd sacrificial anodes were also studied in this paper.The open circuit potential, the working potential, dissolved morphology, current efficiency, polarization degree, activation-dissolution behavior of sacrifical anodes were measured using constant current testing, self-discharge testing, electrochemical impedance (EIS) etc. in artificial seawater. The microstructure of sacrificial anodes was analyzed by metallography, scanning electron microscopy (SEM) and X-ray energy dispersive analysis (EDX) and the distribution form, size, the phase composition and phase content of second-phase of precipitation in anodes were determined. The role of the second-phase was discussed. The dissolution products of anodes were analyzed by X-ray diffraction (XRD) to determine phases of oxide inclusion, the loss of reason of the current efficiency and main products of dissolution from anodes were analyzed at the same time.The testing results of Al-Zn-In-Si sacrificial anodes indicated that oxide inclusion phase mainly include Al2O3and AlO in lack of refining process; the dissolved products of anode were Al(OH)3, Zn(OH)2and a small amount of Al of mechanical exfoliation due to intergranular corrosion; the presence of oxide inclusion cause positive shift of the potential and decreased current efficiency, but not obvious for the morphology of anodes.An optimal way to remove oxide inclusion is mixed solid solvent refined (hexachloroethane+cryolite). Dissolved products of Al-Zn-In-Si anodes were Al(OH)3and Zn(OH)2through this refined way. Less mechanical loss and increased content of the appropriate Si make the anodes current efficiency higher. Extra Zn and Si added to Al-Zn-In-Si sacrificial anodes can form a"claw-like" AlFeSiZn phase that changes the phase composition and Fe content, therefore, improves the electrochemical performances of anodes. A16.0ZnO.025In0.13Si anode has good overall electrochemical properties, and tolerance of the Fe impurity can be increased to its theoretical content0.14%.The testing results indicated that Al-Zn-In-Cd sacrificial anodes have smaller polarization, stable working potential and larger output current, but the current efficiency is not high enough. The loss of the current efficiency is mainly owing to Cd added to anodes, which caused high activation of anodes. With the increase of Fe content in anodes, the second phase of precipitation increase in the number, much larger in size, uneven in distribution, which cause positive shift of the potential, uneven dissolution morphology of anodes and slightly decreased current efficiency. The second-phase of precipitation in anodes is mainly FeAlZn phase. The contents of Fe and Zn increased in the precipitation phase with the increasing Fe content.