Abstract:

In order to accelerate the coating formation and improve the corrosion resistance of Ce-Mn conversion coating on aluminium alloy at room temperature,six additives including H₃BO₃,Zr（SO₄）₂,NaF,HF,NaBF₄ and Na₂ZrF₆ were respectively added in the mixed solution of Ce（NO₃）₃ and KMnO₄,and the effects of these additives on the behaviours of Ce-Mn conversion coating were investigated.Then,the metallographic structure and thickness of the coating were analyzed by using an optical microscope and an eddy current thickness meter,respectively,and the corrosion resistance of the coating was discussed by dropping corrosion test,Tafel polarization curves and electrochemical spectroscopy（EIS）.Finally,the effects of NaF on the morphology and composition of the coating were analyzed by means of SEM and EDS.The results indicate that,with the help of NaF,Ce-Mn conversion coating can be prepared at room temperature with a time consumption of only 9min,the thickness,anti-corrosion time,co-rrosion current density and impedance of the coating are respectively 3.3,3.0,1/3 and 4.9 times that of the coating without any additives,and the Ce and Mn contents of the coating increase from 5.14% to 8.59% and from 7.70% to 14.42%,respectively.It is thus concluded that NaF is an optimal additive for the formation of Ce-Mn coating.

Key words: aluminium alloy, film-forming accelerator, Ce-Mn conversion coating, cerium nitrate, potassium permanganate, corrosion resistance