Electroless Fe-P film was prepared from a chemical bath by connecting an aluminum foil to the brass substrate during deposition. The deposition mechanism of electroless Fe-P film was discussed and proposed. It is found that, due to the Al dissolution, the Fe film firstly deposited on the substrate keeps the substrate surface active, thus assures the chemical reduction of iron ions by hypophosphite continuously during the whole deposition process. The Fe-P film results from a superimposition of the electrochemical process due to the galvanic cell with Fe film deposition and Al dissolution and the chemical process due to the reduction of the Fe cations by H2PO2- anions, accompanied by phosphorus co-deposition. We also investigated the effects of bath component and process parameters on the electroless Fe-P deposition. The results show that the bath component and process parameters obviously effect the formation and the composition of Fe-P film. The effect of hypophosphite on the deposition rate is more pronounced than that of FeSO4 due to the higher polarization resistance of anodic reaction, indicating that the rate-determining step for the chemical iron reduction is the oxidation of hypophosphite. The understanding of Fe-P deposition mechanism is beneficial for development of new electroless Fe-based alloy films.
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