The Voice of the Finishing Industry since 1936

  • PF Youtube
  • PF Facebook
  • PF Twitter
  • PF LinkedIn
2/1/2010 | 1 MINUTE READ

Dichromate Sealing and Fatigue Life

Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

We are looking for some references that show that dichromate sealing restores the loss in fatigue life caused by hard anodizing aluminum alloys.

Q. We are looking for some references that show that dichromate sealing restores the loss in fatigue life caused by hard anodizing aluminum alloys. R.R.


A. To my knowledge, there is no such thing as complete restoration of fatigue life by dichromate sealing of anodized aluminum. It is a fact that dichromate sealing does somewhat reduce loss in fatigue strength. The effect is different for different alloys, and individual situations and conditions vary somewhat. For example, a hard, thick anodic coating on 6061 lowers the endurance or fatigue strength appreciably. On 7075 alloy, the loss of fatigue strength is somewhat less than on 6061. When dichromate sealing hard anodic coatings, the seal can be shortened somewhat to minimize loss of hardness caused by sealing. However, care must be used in sealing if superior corrosion resistance is also required. Coating thickness has little affect on loss of strength. Loss of fatigue strength is usually only a significant factor when high stresses are induced. Anodizing affects fatigue strength very little at low levels of stress.

If loss of fatigue strength is a critical factor in a project, I would recommend comparative testing to see just what the difference in performance is for your parts. You can read more about it in The Surface Treatment and Finishing of Aluminum and its Alloys, by Wernick, Pinner and Sheasby, Fifth edition, Vol 2, pp 718–720. I believe the latest printing of this reference is Edition Six. You can also do an on-line search for various papers on the subject. They may, or may not, be applicable to your situation. 

Related Topics


  • Test Methods For Evaluating Anodized Aluminum

    Benefits of anodizing include durability, color stability, ease of maintenance, aesthetics, cost of initial finish and the fact that it is a safe and healthy process. Maximizing these benefits to produce a high–performance aluminum finish can be accomplished by incorporating test procedures in the manufacturing process.  

  • Aluminum Surface Finishing Corrosion Causes and Troubleshooting

    In this paper, a review of several process solutions, examining coolants, solvent cleaning, alkaline clean/etch and deoxidizing/desmutting, listing intended and unintended chemical reactions along with possible mechanisms that would favor corrosion formation.

  • Chromium-free Etching and Palladium-free Plating of Plastics

    Plastics are replacing metals in the manufacture of many parts, and quite often there is a need for metallic coatings on the plastics and other non-conductors. This paper will describe new processes of preparing ABS plastic substrates for subsequent metallization.