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Improvement and stabilization of the electrochemical properties of zinc alloys during casting

The main reasons for the appearance of electrochemical heterogeneity of cast sacrificial galvanic anodic alloys in the “metal–electrolyte” system are internal factors related to the nature of the metal, its composition, structure, etc. Obviously, when developing the technology for manufacturing of cast anodes, special attention should be paid to ensuring the structural homogeneity of the alloys. The main role in the formation of the structure and basic properties of cast anodes is played by thermal processes that affect the conditions for solidification of the melt in the mould. The results of studies of the structure and basic electrochemical properties of cast zinc sacrificial alloys (ZSA) depending on the cooling conditions are presented in this paper. The analysis of the temperature fields of the solidifying metal (when the metal is cooled) and the shape (when the mould is heated) at different cooling intensities has made it possible to optimize the duration of the casting cycle. This takes into account the cooling conditions determined by the initial temperature of the mould, which ensures a homogeneous structure and stable electrochemical properties of the material over the entire thickness of the tread. For example, it is established that for the casting of zinc alloys treads weighing 18 kg, the temperature of the mould before casting should be 120–160°C. In these conditions, the necessary quality of cast sacrificial anodic alloys is achieved: Current Capacity–Efficiency 93–96%; Corrosion Potential –Ec = 815–820 mV vs. SHE. The required duration of the casting cycle is 10–14 min. Similar data was obtained for sacrificial anodes of various shapes and sizes. Based on the results of studies of the thermal interaction of zinc anodes with a casting mould (sandy-argillaceous, cast iron and steel water-cooled) using numerical simulation methods, the expediency of casting anodes into water-cooled moulds is provided, providing the most favorable conditions for heat removal and obtaining a homogeneous structure of cast treads. Based on the results obtained, a technology has been developed for casting zinc anodes of various sizes, which provides high and stable electrochemical properties.