| Aluminum coating is one of the most effective methods for surface protection of steel. The aim of this study was to establish the optimum working conditions for aluminum coatings on steel in molten chloride salts. Electrolytes used were chloride mixtures of AlCl₃ and KCl. The working temperatures were 300℃ in chloride salts. Experiments were carried out in argon-gas atmosphere and electrolytes were pre-electrolyzed to remove residual impurities. In chloride system, effects of NH₄Cl as a surface active and electrochemically active substance were investigated. Influences of the co-deposition elements, manganese and copper on the coating were also investigated. Characteristics of deposit layer was analyzed by means of SEM, EPMA and XRD. Optimum conditions for the coating were found to be the bath temperature, 300℃ and the current density, 150 mA/ ㎠. In chloride electrolyte, more promising electrodeposition of aluminum was obtained with addition of NH₄Cl as surface active substance. Compact and fine aluminum coatings were obtained with 1.5wt.%NH₄Cl at 300℃ and the current density, 150mA/㎠. Addition of MnCl₂as a co-deposit element also significatly improved the quality of deposit layer. By addition of CuCl, however, the layer had better quality than that of MnCl₂. Metalliding didn`t occur at bath temperature lower than 500℃. Optimum current density for the metalliding of aluminum in chloride electrolyte containing 1.5wt.% NH₄Cl was found to be 150Al/㎠. Deposit layer formed was identified as an aluminum-iron alloy. |
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