The effects of zinc coating layer upon steel substrates on corrosion properties of weldable prepainted steel sheets are investigated by means of salt spray test and galvanic coupling test.
As the sacrificial corrosion prevention effect of zinc powders in the paint film is poor, it is difficult to completely prevent red rust if steels are used as substrates. In case that zinc coated steels are used, both zinc coating and zinc powders in the paint film sacrificially prevent corrosion of steel substrates, resulting in delaying red rusting to some extent depending upon the type of paint applied.
If the paint containing zinc, stainless steel and aluminium powders in ratio of 43 : 37 : 20 is applied onto zinc coated steel, it is proved that corrosion resistance is superior in wide range of powder contents between 20 and 35 vol%. Based on these results, the weldable prepained steel sheet having excellent corrosion resistance, formability and weldability has been developed by applying 10 μm of paint film containing totally 30 vol% of zinc, stainless steel and aluminium powders onto 20 g/m² of zinc coated steel sheet.