Study On The Preparation And Electrochemical Property Of Mg-Al Composite Sacrificial Anode

The sacrificial anodes are applied to various of areas such as offshore platform, petroleum pipeline and city pipe network, and have attained good social and economic benefits. As well as the widely application of cathodic protection technology, the required standard for sacrificial anodes becomes higher and higher. The common sacrificial anodes can't meet the demands of cathodic protection thoroughly. Then, the composite sacrificial anodes emerges because of demand.In this paper, four groups of Mg-Al composite sacrificial anodes with different thickness ratios and two groups of common sacrificial anodes are prepared in the way of vacuum melting and machining, which coated with Mg-6Al-3Zn-Mn alloy and in-lined with Al-3.5Zn-0.02In-0.01Cd alloy.The open-circuit potential and working potential of the composite sacrificial anode samples are tested with the galvanostatic method. The current efficiency of the composite sacrificial anodes was calculated by the way of anode weight-loss. The solution treatment is carried out on the composite anode parallel sample which owns the best electrochemical properties. The microscopic constitution of the sample is observed. The electrochemical properties of composite sacrificial anode are tested and compared with the anode without solution treatment. The effect of heat-treatment on electrochemical properties is studied. The corrosion surfaces are photographed by digital camera and the corrosion feature is observed and compared too.It finally comes to the conclusion that: all the electrochemical perperties of four groups of composite sacrificial anodes have reached or surpassed surrelevant national standards. The open-circuit potential becomes higher as the thickness of magnesium coat increases; the current efficiency falls accordingly; the consumption rate of the anode grows accordingly; the working potentials are both stable. Under this test conditions, the optimum thickness ratio of magnesium coat and aluminum core is 3:7. This type of composite sacrificial anode has an enough negative working potential in the early period, so it can afford good protection effectiveness to the cathode construction. When the magnesium coat is consumed out, it just right finished the cathodic polarization to the protected construction. It degrades the request for working potential, and then the aluminum core can afford an effective protection to the cathode construction.The solution treatment can reduce the quantity of the second-phase in grains and nodularize them, then make them distribute evenly in grains. It can avoid the occurrence of intercrystalline corrosion or degrade the level of intercrystalline corrosion. So, solution treatment can improve the solution property of the surface of anode sample. The solution treatment can shuffle both the open-circuit potential and working potential of the composite sacrificial anode samples slightly. Meanwhile, it can enhance the current efficiency and degrade the consumption rate of anode. Generally, solution treatment can improve the electrochemical properties of composite sacrificial anode.