Anodize ASTM B580 Inspection for defects under 500-600X magnification

A. Anodizing, like etching & electropolishing, reveals defects smeared over by mechanical finishing. If the customer is willing to pay for quality parts for a critical application, the requirement is achievable for a 6000 series alloy in T6 condition. Pre-anodizing inspection (after any etching and deox/desmut) may be useful in identifying material & machining problems.

Of course, crazing of hard anodizing may require negotiation and/or modified procedures. Use an additive that allows higher anodizing temperature, and avoid hot water rinses!

A. I personally hated tumbled parts because the manufacturer of those parts rarely rinsed properly, resulting in adherent material that was very very difficult to remove.

A. Paul, the problems are due to foreign material (e.g., lubricant, burnt or dirty surfaces of folded over burs, abrasive fines) embedded into the aluminum. Anodizing can act as QC in revealing these defects (see DEF STAN 03-24 (3) Chromic Acid Anodising).
Do a systematic examination after machining, cleaning, and tumbling steps. Examine parts both with and w/o etching. Liquid penetrant inspection may help, especially after a little etching to remove smearing.

Possible remedy: Machine to a lower Ra, degrease, then lightly etch. This removes contamination and weaken burs prior to tumbling. Avoid alumina or silica tumbling media, as fines of these materials easily embed into aluminum. A light, post-tumbling etch should also help.

Work hardening shouldn't be a problem except perhaps secondarily, by causing high residual stress in folded-over burs.

A. Paul

In response to your initial post, do the parts that exhibit the pitting, cracks, and non-bonded regions of anodize pass performance or process control testing, i.e. salt spray?

A. Paul

I do not have the ASTM B580 spec but I would think that if the anodize truly had pits, cracks and areas of non-bonded anodize, your coupons would not pass the SS test. Unless the specification or your PO/contract specifies to inspect at that level, I would think your parts should be acceptable.

Bottom line- do your parts meet the criteria specified by the PO/contract?

A. Paul,
It would have to be a very, very good customer to remake the parts or even rework the parts IF they met the contract language.
Examination at 500 X is virtually unheard of and should have been reflected in the PO since ist is so grossly unusual. 40 X is the max that I have ever heard of with 3X check the most common if any X was used.