Need help Anodizing aluminum lower. I think.

[Archbishop]

I have a raw aluminum lower that I'm working on. I want to finish it before I continue my build. I guess that means anodize. Are there other options that I should consider?
I found this website. Seems pretty straight forward. Home Aluminum Anodizing
Anyone got any suggestions for me?
I think I'd like to end up with a color. Blue, green, whatever just something that makes it stand out. If I really get what I want, I'd love to have some sort of design work around the mag, but that might be more than I want to bite off.
Any help from folks who have done this would really help.

 

[engineerpower]

Go for the DIY anodizing. You'd be surprised how good of a result you can get, and it's another tool to put in your trickbag.

Anodizing aluminium isn't just for cosmetics; you really need it as Al is a soft metal and the AlO3 layer you build up is much, much harder.

I'm a chemist, mechanical engineer, and avid DIY'er; I may be able to help out any technical questions you have.

 

[Archbishop]

If don't mind looking at the link. Does this look like a reasonable way to do it? If so, I can probably follow those instructions.

Go for the DIY anodizing. You'd be surprised how good of a result you can get, and it's another tool to put in your trickbag.

Anodizing aluminium isn't just for cosmetics; you really need it as Al is a soft metal and the AlO3 layer you build up is much, much harder.

I'm a chemist, mechanical engineer, and avid DIY'er; I may be able to help out any technical questions you have.

 

[engineerpower]

Yes it does, but you should use a much larger cathode than this guy does. Your reaction is based on the surface area of your anode and cathode, so the more area you use the better. I forget the rule of thumb right off, but you want the cathode to be a multiple of your anode. If it gets going to fast, dial back the amperage, increase distance from the cathode, water down the solution, etc.

 

[Archbishop]

Thanks. I'm gonna try this in a couple of weeks. Gotta get all the stuff together first and then get a free Satureday afternoon.

Yes it does, but you should use a much larger cathode than this guy does. Your reaction is based on the surface area of your anode and cathode, so the more area you use the better. I forget the rule of thumb right off, but you want the cathode to be a multiple of your anode. If it gets going to fast, dial back the amperage, increase distance from the cathode, water down the solution, etc.

 

[engineerpower]

Check instructables, they have good instructions on there too!

 

[30calmachinegunner]

Don't just anodize, HARD COAT anodize, there is a difference

 

[engineerpower]

I believe Type II is practical for home use, while Type III (hard coat) is not. Both will give you a hard outer layer of AlO3, and the distinction between the two is the oxide layer thickness.

Here's a description from a professional website: http://www.anodizeusa.com/anodizing-systems-hard-coat.php

"Type III (Hardcoat) anodizing differs from the typical Type II room temperature anodizing in a number of ways:

The anodizing bath parameters for Type III (hardcoat) anodizing are similar to type II (room temperature) anodizing in that the acid and aluminum concentrations can be virtually the same. The difference becomes apparent when you consider the other operating parameters.


-Type III anodizing is performed in a sulfuric acid bath containing 180-200 grams per Liter of acid and a small amount of dissolved aluminum. The operating temperature is controlled between 28-32º F but in some instances an acceptable oxide can be achieved at slightly higher temperatures. Current densities can range from 24-40 amps per square foot (ASF), but commonly are run at 24-30 ASF.

-The power supply is a DC rectifier. The aluminum part being anodized is made the anode (or positive pole) in the system. The most efficient cathodes (or negative pole) are 6063t6 aluminum."

The problem I see is the power. While a chilled bath is not hard to do, 24 ASF is pretty high as a minimum. Most DIY write-ups I've read that measure their current are in single-digit, and the outputted current is much less than the setting of their power supply (i.e. 2.5 amps from a charger set to 10 amps). Following this math, if we assume a lower is 1 square foot of surface area, we're looking at 10 automotive battery chargers hooked up in parallel to get the minimum ASF.

If you can imagine a tank with 10 chargers hooked up to a conductive fluid, that's not something I want in my garage or that I'm working with personally. I think it's best to stick with the DIY arrangement and go for a thicker layer in the Type III range.

 

[rockhopper46038]

Buy a waste piece of aluminum (same composition) to test on.

 

[Archbishop]

good call. Also, where can I find random pieces of aluminum, including aluminum wiring? Going to need that to get this whole project going.

Buy a waste piece of aluminum (same composition) to test on.

 

[BroodXI]

service entrance wire Service Entrance Wire - Wire - Electrical at The Home Depot
125" 1 8" x 12" x 9" 6061 Aluminum Sheet Plate | eBay

you could use the lcd method but then you'd have to buy the power supply to control the amperage. I did mine the old fashioned way and used a manual battery charger. i really didn't care if i achieved type III as ceracoat is on the market now. Back in the day we did our paintball markers this way. Never had an issue with the hardness. I've also read of using sodium bisulfate instead of acid, but i havent tried it yet.

Good luck

 

[CathyInBlue]

I'm a chemist, mechanical engineer, and avid DIY'er; I may be able to help out any technical questions you have.

I'm taking classes at IVYTech right now to become a designer/fabricator/machinist. I just finished the chapters in Metallurgy Fundamentals on aluminum and copper metallurgy. I noticed in the book's discussions of techniques to harden aluminum, there was a distinct lack of any mention of anodizing. The book just mentioned alloy hardening, cold working, solution heat treating/precipitation hardening. My question for you, oh seer, sage, soothsayer of central Indiana, is how do the foregoing hardening methods get along with anodization?

Can you anodize after you precipitate harden? I'd say, of course. Can you precipitate harden after you have anodized? I'd say, prolly shouldn't.

And then there's my favourite hardening method never mentioned in polite company, cryogenic annealing: chill the material down to -321°F in liquid nitrogen slowly enough to avoid distortion, then let the material cold soak like that for a couple of days, then let the material slowly warm back up to room temp as the liquid nitrogen is drawn off back to its dewar, assuming the chamber was sealed well enough to keep it all from evapourating off.

Slight aside, anyone know the recipe for the perfect Magpul foliage green from Rit dyes?

https://www.ritstudio.com/color-library/how-to-mix-colors/

I'm thinking X parts Kelly Green or Dark Green + Y parts Pearl Gray, but which green and what are X and Y?

Even further aside, this aluminum bronze stuff, anyone made receivers out of it? How well would it take an anodizing?

 

[engineerpower]

I'm taking classes at IVYTech right now to become a designer/fabricator/machinist. I just finished the chapters in Metallurgy Fundamentals on aluminum and copper metallurgy. I noticed in the book's discussions of techniques to harden aluminum, there was a distinct lack of any mention of anodizing. The book just mentioned alloy hardening, cold working, solution heat treating/precipitation hardening. My question for you, oh seer, sage, soothsayer of central Indiana, is how do the foregoing hardening methods get along with anodization?

Your book didn't mention anodization in the metallurgy chapter because it's not a process that alters the grain structure of your bulk material; it's only a surface treatment. You can anodize away all you want, and the oxide layer will still be measured in mils with the rest of the metal unaltered. While you are converting the outside surface of your workpiece from elemental aluminum or an alloy to aluminum oxide through an electrochemical process, anything not within the anodic layer is untouched. The hardening done to the metal through the aforementioned methods will remain unchanged, just as bluing steel doesn't change its properties either.

I read a write-up on a rust-bluing process, and the author stated that boiling steel might embrittle it, but baking at 300*F will anneal it back. Wow, clearly not a metallurgist there...

Can you anodize after you precipitate harden?

Sure, no worries. Most electrochemical processes don't give a damn about whatever hardening or heat treatment we've done to metal, only the chemical makeup of the material.

Can you precipitate harden after you have anodized?

I'm going to say yes. It takes elevated temperatures to alter the grain structure, and you're not going to get hot enough in a simple anodizing process to affect it.

And then there's my favourite hardening method never mentioned in polite company, cryogenic annealing

Hardening and annealing are two separate and different processes with opposite goals. Cryogenic treatment is primarily to relieve internal stresses within the part due to manufacturing processes. Here's a white paper that looks at the effect on 7075 AL and notes that other than Charpy impact, the properties remained pretty much unchanged before and after treatment.
Paper: The effect of cryogenic treatments on 7075 aluminum alloy - ResearchGate

Slight aside, anyone know the recipe for the perfect Magpul foliage green from Rit dyes?

Rit has a library of colors: https://www.ritstudio.com/color-library/color-archive

Green 1 #267 looks like a close match, made from:
1 tsp Dark Green
1/8 tsp Lemon Yellow

1 cup water

Even further aside, this aluminum bronze stuff, anyone made receivers out of it? How well would it take an anodizing?

Somebody does make it: https://www.vbd.com/noc/shop/products_detail.asp?CategoryID=29&ProductID=127
It won't anodize, though. The allow is less than 12% aluminum, and 88% bronze won't anodize to AlO3 no matter how hard you try.

 

[CathyInBlue]

Your book didn't mention anodization in the metallurgy chapter because it's not a process that alters the grain structure of your bulk material; it's only a surface treatment. You can anodize away all you want, and the oxide layer will still be measured in mils with the rest of the metal unaltered. While you are converting the outside surface of your workpiece from elemental aluminum or an alloy to aluminum oxide through an electrochemical process, anything not within the anodic layer is untouched. The hardening done to the metal through the aforementioned methods will remain unchanged, just as bluing steel doesn't change its properties either.

It's less a metallurgy chapter and more a metallurgy book. http://www.amazon.com/dp/1605250791 Chapter 15 is all about surface hardening, as opposed to full hardening, at least for ferrous metals. Chapter 17 is all about aluminum and aluminum alloys. Neither mentioned anodizing in any fashion.

I'm going to say yes. It takes elevated temperatures to alter the grain structure, and you're not going to get hot enough in a simple anodizing process to affect it.

That still sounds like you're thinking anodizing after precipitate hardening, not the other way around. I'm wondering how precipitate hardening temps (350°F) might muck up a fresh anodizing color job, which only takes place at sub boiling water temps (212°F).

Anodized coatings have a much lower thermal conductivity and coefficient of linear expansion than aluminium. As a result, the coating will crack from thermal stress if exposed to temperatures above 80 °C (176°F). The coating can crack, but it will not peel.[SUP][6][/SUP]

Seems if a crackle finish is what you want on your anodized surface, then precipitate hardening after anodizing would do that just fine, but if you want to keep your clean anodized finish, then do it after precipitate (or any other) hardening process is well completed.

Hardening and annealing are two separate and different processes with opposite goals. Cryogenic treatment is primarily to relieve internal stresses within the part due to manufacturing processes. Here's a white paper that looks at the effect on 7075 AL and notes that other than Charpy impact, the properties remained pretty much unchanged before and after treatment.
Paper: The effect of cryogenic treatments on 7075 aluminum alloy - ResearchGate

My understanding of cryogenic treatment was that it just tightened up the crystalline structure so that when it returned to room temp, it lost internal stresses without losing any hardness, which thermal annealing would cause, which seems to jive with what you're describing. I used the term "cryogenic annealing" because the temperature curves more resemble full annealing than any quenching process. Maybe if the parts are plunged into the LN, but since it's gonna return to room temp eventually, I don't see making a cryo treatment emulate a quenching treatment having much utility. Will definitely read that whitepaper.

Rit has a library of colors: https://www.ritstudio.com/color-library/color-archive

Cool. I tried navigating around the Rit website, but I think Firefox is getting sluggish in its old age. Still wondering about Dark Green and Pearl Gray mixes. Sounds like I have some experimenting to do.

Somebody does make it: https://www.vbd.com/noc/shop/products_detail.asp?CategoryID=29&ProductID=127
It won't anodize, though. The allow is less than 12% aluminum, and 88% bronze won't anodize to AlO3 no matter how hard you try.

Cool! I thought maybe the copper reacted the same way to form CuO3 in the same dendritic forms to take the dye.

 

[engineerpower]

That still sounds like you're thinking anodizing after precipitate hardening, not the other way around. I'm wondering how precipitate hardening temps (350°F) might muck up a fresh anodizing color job, which only takes place at sub boiling water temps (212°F).

Ah, could be! Haven't heated up any anodized Al to 350*, that would be an interesting, easy, and worthwhile experiment to do. Throw a cheapie carabiner into the oven after you bake your next cake, and see if it's still GTG.

Anodized coatings have a much lower thermal conductivity and coefficient of linear expansion than aluminium. As a result, the coating will crack from thermal stress if exposed to temperatures above 80 °C (176°F). The coating can crack, but it will not peel.[SUP][6][/SUP]

That doesn't make much sense to me since the color sealing process is done at higher temps than 80*C.

I tried navigating around the Rit website, but I think Firefox is getting sluggish in its old age.

I'm considering dumping Firefox due to Mozilla's anti-1st Amendment stance. Good thing I don't use Dropbox, either...

Cool! I thought maybe the copper reacted the same way to form CuO3 in the same dendritic forms to take the dye.

I've seen exactly one reference to anodizing Aluminum Bronze, but no details. It may be possible, but you won't get the same results. AlO3 is one of the hardest substances, hence the usage of anodization. Copper oxides aren't as hard or impervious to chemical attack, so it won't be an equivalent treatment, if it's practical at all.

 

[Archbishop]

OK, people smarter than me. Looking at this for my reference, Home Aluminum Anodizing does the wiring to the aluminum plates have to be aluminum as well? Why not copper? Which I have plenty of.
Where can I find aluminum wiring if needed?
I got the battery acid. I have a plastic tub and battery charger. I'm going to get aluminum plates I think at a lowes. Now for the wiring?....

 

[engineerpower]

Copper can go into solution and contaminate your process. All you want is Aluminum, water, and acid in your system; anything else will much things up.

For Al wire, you can get it in the welding section of your local hardware store.

 

[Doug B]

Remember to plug any threaded holes you may have in your parts before anodizing. Use rubber plugs to keep the anodize out of the threads. The oxidation process will alter any un-masked thread enough that the screws normally won't go into the holes. And, anodize is very hard, and if you try to re-tap an anodized threaded hole, you will be surprised at how difficult it is.... The anodize will chew up your tap.

 

[Archbishop]

Thanks for clarifying. I'll see if I can find some aluminum wiring at Lowes when I'm picking up the other stuff. Hope to get this part of the project done in the next couple of weeks.

Copper can go into solution and contaminate your process. All you want is Aluminum, water, and acid in your system; anything else will much things up.

For Al wire, you can get it in the welding section of your local hardware store.