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How do I expose weld cracks prior to anodizing?

We are welding 1/8" 5052 aluminum for the Navy and have had a problem with hot cracks being exposed after type II anodizing. We built some test panels (2 each from 5052 and 5086). No cracks were found after a good visual inspection prior to anodizing, but several were found in each test piece after anodizing. Is the anodizing exposing/making worse existing cracks? Is there a good compound (dilute NaOH?) that we can use to etch the welds prior to anodizing to find and repair the cracks?

Thanks for your help.

Eric Tyalor
Mechanical Engineer - Louisville, Kentucky, USA
January 18, 2011

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I would be more interested in finding out what the problem with your welder/equipment is. You should not have cracks in Mil Spec welding.

Spray on dye penetrate and a cheap black lite will do what you asked for.

James Watts
- Navarre, Florida
January 19, 2011

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Aluminium can be prone to smearing which could cover cracks or porosity in welds if they are being dressed back prior to anodising.
For this reason many aerospace companies requires you to etch the surface prior to inspection. (particularly fluorescent dye penetrant). You are right about NaOH. Swab etching is commonly 20% solution for around 30 seconds.

Ciaron Murphy
Aerospace - South Wales, United Kingdom
January 21, 2011