Question for those very experienced anodizing and aluminum

This is probably going to be a silly or basic question to most but I have very little experience actually working with aluminum. I have some purchased parts for some of my hobbies that are machined from 6061 and anodized. As the colors start to fade or wear they look like shit. Does the anodizing provide any structural integrity to the aluminum? I know there's several types ( 1, 2 # 3 and hardcoat) but excluding the hardcoat if I remove or polish the piece to bare aluminum will I be weakening the parts in any way? I also thought I read somewhere that they can heat treat aluminum. I've only HT tool steels and I know it can't be the same process. Any help or referrals to some reading is greatly appreciated. thanks

I will assume that your parts were processed as Type II with color which is very standard for anodize. This provides very little in the way of wear protection (about .00005" thk.) but you do get a lot of color choices. If you want more wear resistance then you would specify Type III. You can get up to about .004" penetration and build up. Your color choices are very limited to usually black and clear which is actually a dark grey/green. One thing to know before doing this is that it does build up so holes get smaller as well as tapped holes and OD's get larger. If you have close tolerance holes and tapped holes they will need to be masked to avoid be anodized. If you have close tolerance OD's then you have to machine the part accordingly and hope the plater follows your written instructions in regard to buildup/penetration. Hope this helps.

Wild West said:

I will assume that your parts were processed as Type II with color which is very standard for anodize. This provides very little in the way of wear protection (about .00005" thk.) but you do get a lot of color choices. If you want more wear resistance then you would specify Type III. You can get up to about .004" penetration and build up. Your color choices are very limited to usually black and clear which is actually a dark grey/green. One thing to know before doing this is that it does build up so holes get smaller as well as tapped holes and OD's get larger. If you have close tolerance holes and tapped holes they will need to be masked to avoid be anodized. If you have close tolerance OD's then you have to machine the part accordingly and hope the plater follows your written instructions in regard to buildup/penetration. Hope this helps.

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It does help and thanks. Does the anodizing add any strength? Say like shear strength or prevent it from bending easily?

It will make the aluminum more "brittle" to bend, meaning you can't form it as well after anodizing. The thicker the anodizing the less you can bend the part. Also the die will fade but that does not affect the layer of aluminum oxide.

Type III anodizing generates a layer of aluminum oxide, which is hard. This provides some wear advantages, but it is also somewhat abrasive. It doesn't really add much as far as structural strength, but can help with shock loading in certain situations. It is also a nodular surface so if you need a smooth Ra, it can be tricky. Aluminum Oxide is also an excellent insulator against heat.

I also thought I read somewhere that they can heat treat aluminum.

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Yeah you can.. However, when you get it, 95% of the time when you buy 6061 its already
heat treated.. You aren't getting any stronger than a T6xxx? If you happen to get some
6061 at a T4xx you can toss it in the oven next to your turkey next Thanksgiving and
bring it up to a T6xxx...

6061 is pretty damn "weak" as it is.. 2000 and 7000 series are about double 6061, somewhere
around a mild steel strength, they also cost double and have their own "issues"...

Here is the(one of) spec for heat treatment of most aluminums. The one at the bottom 8.75MB,
71 pages of god awful boredom and charts.... I've spent FAR too much time with that spec lately.

MIL-H-688 G HEAT TREATMENT ALUMINUM ALLOYS

Powder coat them and be done with it.

Some of the Ali alloys were a bit enigmatic, the copper bearing ones, they do thier own hardening, it's called age hardening and is a product of time and temperature, it can be slowed or halted by reducing the temperature, annealed rivets for aircraft were often color coded to aid identification and refrigerated till needed, needless to say elevating the temperature increases the speed of this process, it's generally called age hardening but more correctly it's forced age hardening, a type of precipitation hardening.
A typical treatment in an "ageing" furnace (hot air recirculating) would be 175 degrees C of 12 hours, though most plants used 7 1/2 hrs due to 8 HR shifts, it would get 75% UTS and the remainder would get there in 10-14 days I was told.
Anodising does accelerate the age hardening process, but the max temperature is the boiling water seal so it does pick up some strength but not as much as a full age harden, generally extrusions are put in the oven before they get anodised anyway.
Any bending or roller correcting gets done before ageing or anodising.
Dye finish is often added (beware of red, it fades out real quick as pointed out)
Bronze seems the most stable
Mark
(Warning will Robinson, it was 1979 when I worked in an Ali extruder/anodiser, we still use the "z" spelling and apart from the metallurgy things change!)

Bobw said:

Powder coat them and be done with it.

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Never gave that a thought! Probably cheaper too. A lot of good info. Thanks alot guys.

Tonytn36 said:

Type III anodizing generates a layer of aluminum oxide, which is hard. This provides some wear advantages, but it is also somewhat abrasive. It doesn't really add much as far as structural strength

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ALL anodizing generates a layer of aluminum oxide, as does exposure to air. only difference is the thickness. the oxide layer adds NO structural strength.

^ Very diffrent crystaline structure, even the heavier type 2 coatings tend to offer a fair degree of wear resistance, colour fade is uv break down of the dye, better dies will resist that a lot better and it also depends on how the die was sealed into the part, the old school boiling water approach to sealing locks the colour in a lot better, but its never as vivid as the chemical approach to sealing, just tends to look better down the road.

Hard anodizing will likely have micro cracks in the anodized layer, that's why you can't (you can if your a d******) hard anodize parts that are subject to fatigue.

moto367 said:

A lot of good info. Thanks alot guys.

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Yeah, we're full of it here.