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

In recent years, in the field of tinplate production, it has become a trend to use lower tin coating mass to lower production cost. 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 a Mn-Al-P chemical conversion coating using for process sequence adjusted tinplate of 0.5g·m^-2 tin coating mass to alternative the chromate treatment. Meanwhile, by adjusting the subsequence of the reflowing process and the post-treatment process, the wash water and electricity consumption was 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 XPS, and further discuss the formation mechanism of this coating. The results show that this muti-element coating could effectively fill tin-free zones on the surface of tinplate and improve the corrosion resistance when the reflowing time is properly setup to 3.5 s after the process adjustment. However, continually extended the reflowing time would cause the phosphate coating to fall off, which lead to the corrosion resistance deteriorate. The coating was mainly made up by a series of amorphous phosphate compounds and metal oxides, which was suitable for tinplate with low tin coating mass.