AVS 50th International Symposium
    Applied Surface Science Wednesday Sessions
       Session AS-WeA

Paper AS-WeA9
The Role of Hexafluorozirconate in the Formation of Chromate Conversion Coatings on Aluminum Alloys

Wednesday, November 5, 2003, 4:40 pm, Room 324/325

Session: Fuel Cell & Battery Materials/Corrosion
Presenter: C.R. Clayton, State University of New York at Stony Brook
Authors: D. Chidambaram, State University of New York at Stony Brook
C.R. Clayton, State University of New York at Stony Brook
G.P. Halada, State University of New York at Stony Brook
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Alodine 1200S® process is widely used to form chromate conversion coatings (CCCs) on aluminum alloys. Potassium hexafluorozirconate (K2ZrF6) forms a major component of Alodine. Although the roles played by most of the other components of the treatment bath are known, there is no knowledge about the interaction of hexafluorozirconate with aluminum alloys. Electrochemical and surface analytical techniques have been employed to study the nature of interactions between hexafluorozirconate and constituents of aluminum alloy AA2024-T3. AA2024-T3 is widely used in the aerospace industry. Studies on the interactions between major components found in Alodine® with aluminum alloys showed maximum activation to occur in the case of hexafluorozirconate pretreatment. This is contrary to the belief that sodium fluoride, another major component of Alodine®, acted as an activator. Contact angle measurements have also been performed. Hexafluorozirconate was found to decrease the interfacial tension besides leading to increased surface wetting. The results obtained from electrochemical techniques have also been compared with similar studies conducted using other fluoride components found in Alodine such as sodium fluoride and potassium fluoborate. X-ray photoelectron spectroscopy (XPS) has been used to study the surface chemistry of the alloys after exposure to hexafluorozirconate, thereby giving an insight into the mechanism of activation and surface wetting. The results indicate hexafluorozirconate to play an important role in the formation of chromate conversion coatings on aluminum alloys. This will be useful to the development of coatings based on benign components. Acknowledgements The U. S. Air Force Office of Scientific Research under contract F49620-96-1-0479 supported this work. Lt. Col. Paul Trulove, Ph.D. served as the contract officer.