Study and Preparation of Zn-Mn Series Black Phosphating Solution at Middle Temperature

A kind of Zn-Mn black phosphating formula and process at medium temperature was studied.The best black phosphating solution formula and process conditions were obtained by using the orthogonal test method as follows: manganous dihydrogen phosphate 60.0 g/L,zinc nitrate 35.0 g/L,nickel nitrate 20.0 g/L,potassium chlorate 6.0 g/L,citric acid 1.0 g/L,manganese nitrate 20.0 g/L,sodium dodecyl benzene sulfonate 0.4 g/L,temperature 60 ℃,pH 2.5 and plating time 30 min.Corrosion resistance,hardness,thickness and morphology of the coating were investigated.The process is used for pretreatment of steel and iron surfaces before coating process,it has the characteristics of stable solution,strong adhesion,good corrosion resistance etc.