Study On Multi-fuctional And Environmental Phosphating Solution

The multifunctional phosphating solution is one of the most promising chemical conversion processes on the surface of steel,which combines oil removal,rust removal,phosphating and passivation.At present,there are few detailed reports on the multifunctional phosphating,the existing technology is not mature and perfect,and the effect of rust removal and rust prevention is difficult to meet the demand at the same time.In view of this,composition and,process parameter optimization,were conducted by single factor variables and the orthogonal experiment.Anticorrosion mechanism of multi-functional phosphating solution was studied.The main research contents are as follows:Through the sample characterization,the surface morphology and the mechanism of phosphoric acid rust removal were studied before and after the rust removal.On this basis,the phosphoric acid with the concentration of 14 wt%was selected and the temperature was40?.The effect of single accelerator on phosphating was studied by means of potential-time curve and CuSO₄ drop test,and the appropriate promoter was selected,Though orthogonal test,the composition of phosphating was optimized.BTA:0.1 wt%?Zn?NO₃?₂:5 wt%?Zn?H₂PO₄?₂:6 wt%?Na₂MO₄:0.5 wt%?citric acid:2 wt%?OP-10:0.1wt%.The effects of phosphoric acid concentration,phosphating temperature,phosphating time,ultrasonic phosphating and post treatment process on Phosphating effect were studied by means of SEM,potentiodynamic polarization curve and salt spray test.The final determination of the concentration of phosphoric acid:14 wt%,phosphating treatment time:35 min,the optimum temperature range of phosphating:30⁴0?.The rate of phosphating was improved by ultrasonic phosphating,but the corrosion resistance of the surface was reduced after ultrasonic treatment.The corrosion resistance of the sample by natural drying is better than the sample by air drying.The corrosion resistance of the sample by air drying is better than the sample of washing immediately after phosphating.The films were characterized by SEM,XPS,EIS and potentiodynamic polarization curves.The SEM observation of phosphating film showed that a conversion coating was formed on the surface after phosphating.Through EDS and XPS analysis,the main components of the film include MoO₃,MoO₂,ZnO,Fe₂O₃,Zn₃?PO₄?₂·nH₂O and FePO₄.The corrosion resistance of the specimen is greatly improved by comparation with the bare steel.The time of CuSO₄ drops is 110 s.The corrosion current density after phosphating is reduced from 1.58×10²uA·cm^-2to 2.05 uA·cm^-2.From the fitting results of electrochemical impedance experiments,charge transfer resistance of phosphate film increased from 331.6?·cm^-22 to 10346?·cm^-2.