Influence Of Currentdensity And Ferrous Sulfate On The Structures And Characteristics Of Micro-arc Oxidation Coated Aluminum

In this research,pure aluminum specimens were treated by a self-designed WH-1A micro-arc oxidation device in self-designed N15 electrolyte.In this way,the ceramic layer will grow on the surface of the pure aluminum.The influence of current density and Fe SO₄ in the base electrolyte on the structure and performance of ceramic coating on pure aluminum were studied,respectively.The PEO coatings were detached from the substrate by a self-developed electrochemical method to observe the effect of current density on the back and interface of the ceramic coating.The study shows that the surface roughness of the specimens and thickness of the coating increased with the increase of current density,as well as the number of holes and cracks.In addition,the interconnected discharge channels are more conductive for aggressive ions to penetrate towards the C/S interface in order to promote the corrosion process.Although most part of the PEO coatings is porous,a thin inner layer with a thickness of ¹ ?m can be identified at the C/S interface region,and the thickness of the thin inner layer basically maintains constant.This compact thin layer is composed of many inter-connected tiny globular particals.These tiny globular particals have a relatively uniform diameter of ⁰.5 ?m.The corrosion resistance of the PEO coated samples prepared in this work decreases with the current density.Among the coated samples?1.1A/dm2⁸.8A/dm2?,sample 1.1A/dm2 has a much higher corrosion resistance compared to the other three sample.Low current density of the sample preferable main reason is that the dense layer structure and stable phase.During the PEO process,The growth of the ceramic layer is due to the inner constant discharge to produce some products,ceramic layer continuously outward growth and this kind of discharge leads to the inward growth of the PEO coatings.The results show that the voltage rise significantly with FeSO₄ additive.This suggests that the FeSO₄ additive into the film in the process of micro-arc oxidation and participated in the reaction which affect the voltage time curve.The surface morphologycharacteristics can be seen on the graph that different content of Fe SO₄ additive on surface morphology has a great influence.while the surface quality of MAO coating is improved at first and then result in degradation with the increase of FeSO₄ additive,the cross-section quality of MAO coating result in degradation..But with the increase of Fe SO₄ content,the coating thickness as growth.Along with the FeSO₄ additives to join,The ?-Al2O3 appeared in the phase composition.That Fe SO₄ additives for layer of amorphous phase into crystals to transform.The ?-Al2O3 has good corrosion resistance which is conducive to the improvement of the performance of the coatings.When FeSO₄ additives content is2g/L,it can significantly improve the corrosion resistance of coatings.