Chromate-free passive films made by Manganate and waterborne polyurethane on galvanized steel sheets

摘要

In order to develop an environmental friendly passive films on galvanized steel sheet, a chromium-free passive solution based on waterborne polyurethane (WPU) and Manganate was studied. The results show that the optimized compositions in passive solution are KMnO_4 6g/L, (NH_2)_2CS 5g/L and WPU 150g/L. The passive films were prepared by dipping steel substrates into the passive solution for 10 seconds and drying at 120 °C for 30 seconds. SEM observation shows that the film's thickness is about 1.5 μm. XRD patterns indicates that the chromate-free passive films mainly consisted of MnO_2 and K_2MnO_4. Anticorrosion tests indicate that the chromate-free passive films can provide an excellent barrier to corrosive agents.