Zn-Mn System Phosphating Solution at Room Temperature Improved by Baric Ion

The Zn-Mn system phosphating solution was composed of H3PO4,ZnO,Mn(NO3)2,Ba(NO3)2,(NH4)6Mo7O24·4H2O and so on.The washing-free color phosphating film could be formed quickly in the phosphating system on Q235 steel after drying for more than 3 h at room temperature.The morphology and element contents of the film were analyzed by SEM and EDS.The results showed that the washing-free phosphating film was composed of phosphate of Fe,Zn,Mn and Ba and a little of molybdate.The crystalline size of phosphating film was smaller than or equal to 3 μm.The phosphating film was continuous and compact with weightiness of 1.1 g/m2,and was not corroded in 3% NaCl solution for about 2.5 h.Its adhesion force reached 1st grade after spraying epoxy resin with iron oxide red.