The authoritative public forum
  for Metal Finishing since 1989
-----

Will a small fissure in hard coat anodizing compromise the integrity of the base aluminum?

2005

I am a novice to the science & terminology of metallurgy, so please forgive me if I sound stupid.

I own an aluminum firearm frame that is mil. spec. hard coat anodized. Problem is that at some point this frame was struck with a sharp blow, which produced a small fissure in the anodized surface. I guess my question is will the small crack in the anodizing compromise the integrity of the base Aluminum? Will time & use cause the surface fissure to spread to the metal underneath, and if so, can I prevent this from happening by buffing or sanding away the anodized layer before the crack has a chance to spread?

Thank you.

Tim Hughs
hobbyist - Troytown, New Jersey

---

Sulfuric anodizing can decrease the fatigue strength of aluminum due to precisely (at least, according to some) the issue you are worried about. Whether or not it would lower the fatigue strength enough to ever cause you any problems would be another question entirely.

Removing the anodizing in that specific spot should prevent the problem from arising, but then you will have corrosion issues in that area (and, if hard anodized, the part will be 2 tenths thinner plus whatever aluminum you removed in the process - probably not worth worry about, but worth mentioning). The most common solution then would be to put a chromate conversion coating on the part - this can be done by a lot of different job shops for a very reasonable fee, doing it yourself involves carcinogenic and highly regulated chemicals and is not recommended. The other solution would be to paint the part or just keep it nice and clean to prevent corrosion or to keep it oiled (this works on steel, I presume it works on aluminum also. And, it being a gun frame, you're going to be keeping parts oiled anyhow).

All of that being said, the biggest question, for me, would be whether or not it is worth worrying about. I'm not familiar with how much the fatigue strength is reduced, nor am I familiar with how high the fatigue strength needs to be on your firearm, but I would say it is highly likely that your probably fine without worrying about it. A lot of firearms take a lot of damage without issues arising. Your best bet would be to take the piece to a gunsmith or knowledgeable gun shop or firing range operator and ask their opinion; you might be worrying for no reason at all.

Good luck.

Jim Gorsich
Compton, California, USA
2005