Preparation and Properties of Room Temperature Washing-Free Mn Phosphate Film

A washing-free colourful manganese phosphate film was prepared on the surface of Q235 steel specimen at room temperature in manganese phosphate solution containing manganese dihydrogen phosphate, manganese nitrate, sodium molybdate, sodium fluoborate by phosphating and then natural drying for 3 hours. The effect of pH value of phosphating solution, phosphating time, phosphating temperature on the properties of phosphating films were investigated. The morphology and composition of phosphating film were analysized through SEM and EDS. The results show that continuous and compact phosphate film was generated when the specimen was phosphated for 5~12 min at 5~40 ℃ in phosphating solution with pH value of 2.3~3.1. This film can resist the corrosion of 3wt% sodium chloride solution for over 90 minutes. The paint film sprayed with iron-red epoxy primer possessed impact resistance of 50 cm and adhesion force of 1 grade.