In recent years, many aluminum parts have been used for the higher performance and weight reduction of automobile engines. Wear resistant iron plating on aluminum parts is important technology to apply to automobile engines. However, conventional hard iron process had some problems such as the low deposition rate and solution instability, which affected the productivity. Therefore, we have developed a new iron plating process which has a high deposition rate and uses insoluble anodes. The results are summerized as follows;
Hard Fe-N coating was electrodeposited from a ferrous sulfate bath containing urea at a deposition rate of more than 10mm/min. Urea had a remarkable advantage not only to harden coatings but also to buffer the pH of the bath. Additionally, urea stabilized Fe³⁺ produced on the insoluble anode in continuous plating. However, Fe³⁺ concentration must be kept below 2g/L in order to maintain good plating condition. A Fe³⁺ ion sensor was developed to measure the Fe³⁺ concentration in real time, and fine-metallic Fe powders were applied to reduce Fe³⁺ to Fe²⁺. As a result, the reduction was carried out rapidly and efficiently to put the powders in the bath. By both methods, we could keep the Fe³⁺ concentration in the bath below 2g/L.

The wear resistance of the coating which has a hardness of Hv500 to 700 was better than that of the conventional Fe-P plating.

This coating is expected to be applied to various sliding parts in non-corrosive environment.

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