| Adhesion strength is of vital importance for the coating performance in surface engineering,and the poor adhesion usually dues to the lack of proper surface pretreatments.The key of the pretreatments is the removal of oxide film on the surface.And the high electrochemical activity of reactive metals makes it so difficult to perform suface pretreatments.Ionic liquid is a kind of new electrolyte,which shows its unique advantages in surface pretreatments of reactive metals.It can remove the oxide film on the surface effectively through anodic electrolytic etching in ionic liquid.And this method makes it possible to study the effect of oxide film on reactive metals on the adhesion strength.In the present paper,the effect of oxidation parameters on the adhesion strength of A1 electrodeposited from acidic AICl3-EMIC(2:1)was studied with the method of removing the natural oxide film on 430 stainless steel with anodic electrolytic etching,followed by controlled oxidation in air atmosphere,which could help to explain the mechanism about the influence of oxide film on the adhesion strength.Spectroscopy ellipsometry and XPS were used to measure the thickness of natural oxide film of 430 stainless steel.Linear sweep voltammetry was carried to understand the anodic behavior of samples with and without oxidation.Morphologies and compositions of samples were characterized by SEM and EDS.Surface roughness of samples was measured with surface roughness tester.Adhesion strength of Al coatings was measured with pull-off adhesion tester.The results showed that the degree of oxidation of samples can be judged according to the characteristics of linear voltammetric curve,including the initial potential and the current of anodic peak.For the linear voltammetric curve of mirror-polished sample,there was a small anodic peak between 2.5-2.8 V,which could be attributed to the general breakdown of the oxide film.However,when 430 stainless steel was oxidated at 300?,the small anodic peak disappeared,which was related to the increase thickness of oxide film after oxidation.And when 430 stainless steel was polished with emery paper,the small anodic peak turned to be an unsmooth curve,which was concerned with the unevevn of oxide film after polishing.The natural oxide film of 430 stainless steel could be removed with anodic electrolytic etching for the first time or second time,and the current density had little effect on it.Compared to the original sample,the adhesion strength of Al coatings on samples after anodic electrolytic etching was improved observably.In the atmosphere of 25?,35%RH,when the oxidation time was less than 60 s,the adhesion strength of Al coatings was pretty good,which was higher than 18.8 MPa.However,when the oxidation time was more than 90 s,it decreased with the increase of oxidation time. |
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