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Crazing problem on welded assemblies made from 5052 H32 aluminum

Our anodizer (in Tecate, BC, Mexico) is having crazing problems on most of our welded assemblies. The welded assemblies are made of 5052 H32 aluminum and are large enclosures (cabinet) app. dimensions are 48"w x 36"d x 55" tall. The crazing is apparently isolated to an external front surface where there is another part that is welded in the rear surface. The anodizing specification is MIL-A-8625F with a minimum anodizing thickness of .7 mils as specified by a customer requirement - Caltrans spec.

Does anyone have any idea why this is happening and how can we prevent it.

Another question I have - is it correct that the plating thickness is an average. Meaning that the plater has the liberty of going over the .7 mils in some areas (where crazing doesn't occur) and going under the .7 mils in areas where the crazing does occur? Is this acceptable per MIL-A-8625F? The reason I ask, is that to my experience with anodizing, it is okay to take multiple readings (using a De Felsko plating thickness gauge) throught every external surface and taking an average. If the average reads a minimum of .7 mils then the product is okay, right?

Martin Magana
QA Manager - Anaheim, California, USA
November 18, 2008

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Anodizing in an inside 90 degree angle will crash into itself as the coating grows perpendicular from the two 90 degree sides. That is why the Mil Spec calls for a radius.

5052 is high magnesium, which tends to migrate with heat, and may be migrating in the areas that have been twice heated. If so, the craze would show a white color.

Try to get us more information.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

November 21, 2008