Anodise hurt by baking?

[outrageous]

Well, I'm looking for some solid information to disprove my theory that a once anodized product can be baked and it not hurt the Al.

Heres a link to the majority of the discussion. Anyone have any ideas?

[Geof]

I read through most of the posts in your link and did not find anything that I would consider terribly wrong. Anodizing is simply a method of electrochemically increasing the thickness of the natural oxide layer that is present on all aluminum. As someone mentioned in one of the posts the anodizing bath is a sulfuric acid solution and after the anodizing process the surface is porous: I have seen scanning electronmicrographs of the surface of freshly anodized aluminum and it has a hexagonal structure; someone mentioned that the surface 'grows' during the anodizing which is correct, it sort grows to form a honeycomb-like surface (very tiny honeycomb). The dye molecules in the dyeing step simply enter the hexagonal pores by diffusion, then the sealing step locks them in. Actually the sealing simply converts the aluminum oxide to hydrated aluminum oxide; all that happens here is that some water molecules become incorporated into the aluminum oxide structure and this causes a swelling which closes off the top of the pores trapping the dye molecules inside. Another name for aluminum oxide is sapphire and it is clear like glass which is why the dye is visible; 'dirty' sapphire is corundum which is an abrasive. Someone mentioned that aluminum oxide is a ceramic which is kinda right but not completely; aluminum oxide is a metal oxide, ceramics are normally mixtures of metal oxides. This is a bit of a picky point, not worth worrying about; aluminum oxide is hard, very hard, and brittle and doesn't have the same coefficient of expansion as aluminum metal so it is likely that significantly heating anodized aluminum will cause micro-cracking, 'crazing', of the surface which could produce a somewhat irridescent effect. Also the heating could cause changes to the dye molecules, for brightly colored anodized aluminum the dyes are nearly always organic compounds and these can be unstable at moderate to high temperatures; architectural aluminum is often colored with inorganic dyes that are much more stable but are also normally rather drab browns and bronzes. And to finally get to the point; does baking anodized aluminum hurt it? The answer could be maybe; how is that for evading a direct answer. If the part in question is subject to a siginificant cyclic load it may be more susceptible to fatigue failure. Aluminum is a metal that is susceptible to fatigue failure...guaranteed. It does not matter how small the cyclic load is on aluminum it will eventually fail from fatigue. Anodizing aluminum can increase the susceptibility to fatigue failure because the anodized surface is brittle so when the aluminum distorts elastically the anodized surface cracks and the crack grows into the body of the aluminum. Strongly heating anodized aluminum could create many cracks and simply accelerate the onset of fatigue failure.

[destroyer125]

I am the one that posted most of the negative effects of placing your anodized parts in an oven to turn them brown on that forum. I am an anodizer dealing mainly in paintball gun anodizing and re-anodizing and have been doing it for over 4 years now. The problem here lays with the crowd of people that is doing it, mainly teenagers feeling the need to ignorantly mod their paintball equipment without knowing or caring to comprehend the damage that is being done here. Ive did tests myself and with enough heat and or time, the anodizing was damaged enough that you could scrape it off with a fingernail.

[Geof]

.....Ive did tests myself and with enough heat and or time, the anodizing was damaged enough that you could scrape it off with a fingernail.

That is certainly logical given that significant thermal cycling would produce crazing. And if it has been heated to this extent I think flaky anodizing is one of the less important things to worry about: I didn't mention it although it was mentioned in the discussion, heating aluminum alloys will change the temper; go too high and you will probably finish up annealing it, conversely if it is held for a long time at a temperature that is not high enough to cause annealing it could do just the opposite, take the temper up and make the alloy more brittle.

I think could be the most important reason to steer clear of heating any aluminum alloy parts anodized or not.

[outrageous]

Thank you for the information geoff.

However I would like to know the steps you took and went through for the ano to "scrape off" with your fingernail 125. Mine isn't even close to being like that which makes me think you did something different. And another thing would the alloy of the aluminum change the way it heats and cools with the ano on the gun?

[Geof]

.....However I would like to know the steps you took and went through for the ano to "scrape off" with your fingernail 125.....

.....And another thing would the alloy of the aluminum change the way it heats and cools with the ano on the gun?

It is destroyer125 who mentions scraping anodizing off.

Rour question about the alloy type: Different alloys anodize differently, I think some are difficult to anodize, also they are different in the way they anneal or harden, so there could be some differences. I think you are most likely dealing with 6061 on paintball guns and cannot imagine what other alloys may be used; 2011 or 2024 possibly but I think these are difficult to anodize and dye effectively. I cannot give you any definite answers and it might be difficult to get definite answers; I was simply pointing out some of the technical details related to anodizing. I have no idea what type of stresses a paintball gun is under, but for any aluminum part that is subject to significant stress I would be very wary of heating it to temperatures high enough to create dye color changes.

[destroyer125]

My Test was done on 7075 and 6061 parts. With the correct amount of time, baking them til they turn a nice crispy brown, you can actually scratch the anodizing off. You heated your gun until it crazed but not discolored. Lurker from PBN has did alittle research and has found you can change 6061 with a temper of T6 down to a T4 at 350-400 degree's in an oven. Most of the concern here comes with not the function of the marker, but the weakening of areas where threads and thinly milled spots are. Ive seen Egos and DM's bend and rip apart when someone takes a nasty dive. So if a gun can be destroyed by a 250 lbs guy falling on it, Id imagine baking your gun down to a T4 would weaken it to where a smaller guy would do just as much damage.