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"Corrosion observed in Sulphuric anodised Aluminium Component"

April 5, 2016

Q. We are Manufacturing & supplying Anodized aluminium component (Sheet metal) to European customer but from past some days we are getting complaint from customer that they are facing corrosion on the anodised aluminium component after some time.
Also note : To this Anodized aluminium component we have assembled Zinc blue passivated screws as per the customer requirement...which passes 120 hours of salt spray.
Packaging will be Export quality.

On this issue need assistance to resolve the crisis.

Naveen Kumar
Product Designer - Bangalore , Karnataka & India

April 2016

? Hi Naveen. People would like to help you but we don't know the alloy, the nature of the corrosion, whether it occurs after a day or after two years, whether it is everywhere or just at the point of contact of the zinc plated screws, the thickness of the anodizing, the sealing method, the environment the corrosion is occurring in, etc. We don't know if the anodizing is done in house or farmed out. We don't have any pictures.

Unfortunately, getting anodizing to not corrode requires doing a hundred things right, and we have no way to know which one or several things aren't right. I think you should address "the crisis" by retaining an anodizing consultant; but lacking that, please give us some info so we can try to help. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

April 29, 2016

A. My big questions are:
-What is your seal, and are you sure it's working? Is it being tested and changed on a regular schedule?
-Are the holes drilled before or after anodizing, if that is the corrosion site?
You say that you are passing salt spray and I assume you are salt spray testing the Aluminum, but I have to ask anyway, are you referring to the screws or the sheet metal? That is unclear.
-During the process of inserting the screws, are you damaging the anodized layer?

Then of course there's the question of what conditions in the field are causing corrosion. Also I don't know enough about galvanic corrosion to be of much use here but maybe someone will chime in with some info about whether the contact between two different metals, in the presence of a potentially corrosive solution in the field (such as seawater), might be contributing.

Rachel Mackintosh
Plating Solutions Control Specialist /
Industrial Waste Water Treatment - Brattleboro, Vermont


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