Optimization of Mn-Al-P Chemical Conversion Coating for a Process Sequence Adjusted Low Sn-Coated Steel

Abstract

In recent years, in the field of tinplate production, it has become a trend to use lower tin coating mass to lower production costs. However, the preparation of low Sn-coated steel must face two significant problems: toxic chromate post-treatment and low corrosion resistance. In this work, we developed an Mn-Al-P chemical conversion coating using a process sequence-adjusted tinplate of 0.5 g/m2 tin coating mass as an alternative to the chromate treatment. Meanwhile, by adjusting the subsequence of the reflowing process and the post-treatment process, the wash water and electricity consumption were effectively reduced. The influence of reflowing time on the microstructural appearance, phase composition, surface element distribution, and corrosion resistance of this new brand tinplate was studied. Moreover, the composition was determined by x-ray photoelectron spectroscopy, and further discuss the formation mechanism of this coating. The results show that this mutielement coating could effectively fill tin-free zones on the surface of the tinplate and improve the corrosion resistance when the reflowing time is properly set up to 3.5 s after the process adjustment. However, continually extending the reflowing time would cause the phosphate coating to fall off, leading to the corrosion resistance deterioration. The coating was mainly made up of a series of amorphous phosphate compounds and metal oxides, which was suitable for a tinplate with low tin coating mass.