Patents
The development of an alternative process to conventional toxic Chromic Acid Anodization (CAA) with equivalent corrosion resistance is a challenging task. The invention provides a chromate free process for the manufacture of corrosion resistant sealed anodized coating for long term corrosion resistance of aerospace grade aluminium alloy. This method includes the steps of cleaning, chemical etching, anodizing in Tartaric-Sulphuric acid electrolyte followed by dipping the specimen in the sealing bath containing at least two water soluble either Mn and Mo or Mn and V oxyanions as corrosion inhibitors and a sufficient amount of alkali metal ion based nitrates at a temperature range between 60 and 80° C. for about 20 to 40 minutes at a pH range of 7 to 9. The sealed anodic coatings developed from this invention showed improved corrosion resistance in neutral 5% NaCl fog environment for greater than 2000 h of exposure. The sealed anodic coatings developed by this invention also showed self-healing protection in NaCl environment.