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Chromic Acid Anodizing Is Not Passing Salt Spray Test

September 24, 2008

We are carrying out chromic acid trials of AA2024-T3 with Hot water sealing. The panels are not withstanding the salt spray corrosion test for 336 hrs. We followed the parameters as:
Anodizing Ramping cycle:
0 to 22 V for 11 minutes
22V for 45 minutes
22V to 0 V for 1minute.
Hot water Sealing:
98 Deg C for 25 minutes.
We would like to know the cause for failure of test panels at salt spray test.

RAMADASS VENKATRAMAN
SENIOR MANAGER - Bangalore, KARNATAKA & INDIA

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Ramadass,

What investigations have you carried out? What were the results of the investigation?

From the information you have given us no-one could make an intelligent guess at the problem.

What are the cleaning methods used? Do you caustic etch or use a proprietary acid etch? Do you etch even? Have you checked the panels are free from corrosion before you start? Have you checked your chloride and sulphate levels in the anodise? Have you checked the conductivity of your sealing water? What is the failure mode? Is it on the edges, is it all over? Are there a few spots or is it a complete breakdown of the anodic layer?

Once you answer a few of these questions you may even solve the problem yourself, otherwise it will give the experts here more of a chance of getting to the root of your problem.

Brian Terry
Aerospace - Yeovil, Somerset, UK
September 26, 2008

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