Preparation And Properties Of Fe-Cr-Al Electrothermal Alloy Anodized Films

Fe-Cr-Al alloy is the most widely used electrothermal alloy in China,it has good thermal stability and high resistivity.In the production practice,it is economical and input power stability.But if this electrothermal alloy works in the reducing atmosphere,it will be corroded,in this case,surface treatment of the alloy is required before the use of the alloy to produce a layer of dense alumina protective film on the surface.Common method is heat treatment to oxidize the surface of the alloy to form a dense film,but this method consumes a lot of energy,and in the process of coating,it is necessary to pull the electric resistance wire out of a certain gap,the construction is difficult,the cost a lot,and the film layer can be damaged easily in the process of use.In our experiment,we use alkaline electrolyte,constant current anodic oxidation at low current density.characterized the surface of Fe-Cr-Al electrothermal alloy a good anodic oxide film,which is compact,insulating,corrosion-resistant and mechanical,then,use different varies of sealing treatments to improve its corrosion resistance.Compared with the traditional technology,the method adopted in this experiment is more efficient and energy-saving.We use SEM,EDS and XRD,the electrochemical impedance and polarization curves,Mechanics performance testing,immersion test to characterization and test the structure and properties of the film layer,in the process of oxidation and the influence of different factors on the film performance is analyzed and discussed.The experimental results show that the optimal oxidation process is electrolyte composition NaOH 150 g/L,KNO₃ 75 g/L,ethylene glycol 100 m L/L,current density0.8 A/dm²,oxidation time 1h.Under this condition of the preparation of anodic oxide film on macroscopic homogeneous density,excellent insulation and corrosion resistance,good mechanical performance,and to recycle the electrolyte after tests found after repeated use electrolyte prepared by the oxidation film comprehensive performance has no obvious drop,therefore the application to production is feasible.The results of SEM,EDS and XRD showed that the microstructure of the anodized film was compact,mainly composed of Fe,Cr and Al oxides,and the distribution of the elements was even.After sealing treatment,the corrosion resistance of anodic oxidation film has been further improved.After the Al?OH?₃ sol gel sealing method,anodized film's impedance is the highest in 3.5 wt.%NaCl solution,and the corrosion current has been reduced by an order of magnitude,both in acidic alkalinity and in the neutral 3.5 wt.%NaCl solution.although the corrosion resistance of the membrane layer was improved after the use of potassium dichromate seal,NiF₂ cold seal and boiling water seal,there was a gap between the treatment of Al?OH?₃ sol gel method.After 7 days of immersion test,There is less hydrogen in the anodic oxidation film after Al?OH?₃ sol gel sealing treatment.,the pH change smaller,and after immersion the layer integrity is good,but not closed area of the oxide film appeared damaged,show sealing treatment processing to further improve the corrosion resistance of anodic oxidation film.