An investigation of the structure and corrosion resistance of a permanganate conversion coatings on AZ91D magnesium alloy

摘要

Conversion coatings for magnesium havetraditionally been based on immersion treatment in the solutioncontaining hexavalent chromium compounds. The excellentperformance of these coatings as paint bases has beenestablished in a broad range of application. However, thereplacable surface treatment has been strongly emphasized bypresent environmental needs to eliminate hexavalent chromium.The development of a chemical conversion coatings inpermanganate bath on magnesium alloys have been studiedusing mass gain measurements, measurements of corrosionpotential, X-ray diffraction, X-ray photoelectron spectroscopy,glow discharge spectroscopy and microscopic examination.Chemical conversion coatings obtained from HF addition inbath consisted of the film that was composed mainly ofmanganese oxides and magnesium fluoride. It was found thatthese films formed amorphous composite coating. Corrosionresistances of permanganate chemical conversion coatings werecomparable with that for chromating.