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Tuckerfan
01-11-2007, 11:49 AM
Anybody know what the standard (if there is one) test for hydrogen embrittlement in aluminum castings is?

Evan
01-11-2007, 12:03 PM
What environment have these castings been used in?

Tuckerfan
01-11-2007, 12:15 PM
Cast in a high humid environment and would be used in military applications.

Steve Stas
01-11-2007, 12:22 PM
Yeah, if it breaks when you use it, it's got it! :rolleyes:


Seriously, I do believe the only sure way is a destructive test (and expensive) to cross-section it and photomicrograph it, or a spectrometer test.

In the aviation trade, it's been attempted to detect hydrogen embrittlement by eddy current inspection, x-ray. or ultrasonic. However, it takes an experienced technician in a good test shop and a known-good piece to compare against. Any of these approaches don't detect hyd embrittlement directly, they will just detect changes in the crystaline structure as compared to a sample. Not something that can be done in the average shop to my knowledge.

steve stas

Evan
01-11-2007, 12:36 PM
Use degassing tablets when casting and there should be no problems.

Tuckerfan
01-11-2007, 01:45 PM
Use degassing tablets when casting and there should be no problems.
Unfortunately, they weren't used when the stuff was cast.

WORMgearster
01-11-2007, 08:55 PM
I am not sure you see true hydrogen embrittlement in a Aluminum die casting. Hydrogen embrittlement is more often a concern in certain high strength steels. Ferritic stainless steel seems to be more prone to having it. Aluminum die castings or sand castings, permanent mold, and extruded shapes are very susceptible to high humidity. The hydrogen usually ends up as a gas or a porosity issue with the product. This can be easily identified through radiographic and liquid penetrant testing.

The degassing tablet, such as chlorine has been replaced in most Aluminum operations with inert gas. Such as Argon or Nitrogen. Nitrogen mixed with a percentage of Sulfur Hexafluoride(5%-15% contained) is released at the bottom of the molten aluminum bath, holding tank or crucible, sometimes through a lance. As the nitrogen floats to the top it bonds with the hydrogen and "degases" as they dissipate into the atmosphere. The die caster we use than takes a sample from the moltent holding tank pulls a vacuum around this small round ceramic button holding the test sample of Aluminum till the sample solidifies. They then cut the sample in half a visually check the cross section for any gas to verify the degas operation worked.

You would think if the part you have is critical it would be x-rayed and FPI for soundness. You may want to send it out and have it x-rayed or even have some mechanical test pieces machined from the part and get them tested
before you use the parts.

Hope this helps!!


Die Dulci Freure

CCWKen
01-11-2007, 11:12 PM
I've never had any problems with hydrogen embrittlement with aluminum or die cast (or heard of it concerning aluminum). Unless it's some high-tech alloy, I think Wormgearster is right that it's more applicable to steels. The biggest problem with aluminum is oxide entrenchment that causes pockets and crystaline fractures. I don't use gas controlled melts but with some careful melts and chemical additions, some control of the oxide inclusions are possible.

If you're concerned enough to want to do tests, I'd suggest you seek out the services of a metallurgist. Not that we're idiots. We're just wannabe machinists here. :D

WORMgearster
01-11-2007, 11:18 PM
I am an idiot... just ask my wife or the X- wife!!

The Worm

Tuckerfan
01-12-2007, 03:21 AM
WORMgearster, that helps a bunch. I'm assuming that a visual inspection like you described is not an absolute certainty that the parts are free from embrittlement? These castings were investment jobs, and I'm certain that at least some of them were exposed to high humidity, since the aluminum on some occassions was wet when it was thrown into the the furnace. (Certainly explains why some of them would shatter when I hit them with a hammer.)

Evan
01-12-2007, 04:14 PM
Put the castings in a kitchen oven at maximum temp for 4 hours (500 to 700f). This will help to drive out any gasses and will stress relieve and anneal them making them much more ductile. Let them cool in the oven after turning it off.

WORMgearster
01-12-2007, 06:44 PM
Evan is right, annealing will help and the parts will naturally age harden over time. You need to be carefull if you are melting wet stock. A aluminum burn is far more dagerous then steel. If you are melting in your shop be sure your stock is dry even if you have to pre-heat it in your oven.

Good luck!

topct
01-12-2007, 07:37 PM
Someone I know wants to know what alloy you might be using.

They also want to know about the hammer test.

Tuckerfan
01-13-2007, 03:32 AM
Put the castings in a kitchen oven at maximum temp for 4 hours (500 to 700f). This will help to drive out any gasses and will stress relieve and anneal them making them much more ductile. Let them cool in the oven after turning it off.
By the time I've whacked on them, they've already been heat treated.

topct, T6 I do believe, and hitting them with the hammer is to straighten the castings out.

topct
01-13-2007, 08:56 AM
T-6 is a temper number not the alloy.

What is your meaning of "heat treated"?

WORMgearster
01-13-2007, 10:14 AM
Hitting your castings with a hammer will most likely crack Aluminum whether or not they have hydrogen trapped. I have read that you can anneal some Al Alloy @900 f and then straighten them. You only have a short window of time to perform the straightening or bending before the Al will age harden. This AMS book states 72 hours.

T-6 has two stages; first it is annealed then it is aged. Tucker if you are given an aluminum part that has been T-6 to straighten with a HAMMER then the cracking you have is more likely mechanical than hydrogen.


WORM;)

Orrin
01-13-2007, 10:21 AM
These castings were investment jobs, and I'm certain that at least some of them were exposed to high humidity, since the aluminum on some occassions was wet when it was thrown into the the furnace. (Certainly explains why some of them would shatter when I hit them with a hammer.)

It could be that the aluminum was contaminated with iron. A minuscule amount of iron will greatly reduce the strength of aluminum. Mere contact with iron and the molten aluminum is enough to do the damage.

No amount of annealing, etc. will be able to get rid of the effects of iron contamination.

Orrin

Tuckerfan
01-13-2007, 10:42 AM
T-6 is a temper number not the alloy.

What is your meaning of "heat treated"?
Then 6061, that's the only other thing I was told. As for heat treating, again, I was told by the folks who're supposed to know these things that they were heat treated properly. I wasn't there when it was done, so I don't know how long the parts were stuck in the oven, nor how hot the oven was.

WORMgearster
01-13-2007, 11:16 AM
Tucker, I don't think that 6061 is a die cast or investment cast alloy. It may be a plate or bar?? I am not sure but these other guys can help.

Worm

topct
01-13-2007, 11:23 AM
Then 6061, that's the only other thing I was told. As for heat treating, again, I was told by the folks who're supposed to know these things that they were heat treated properly. I wasn't there when it was done, so I don't know how long the parts were stuck in the oven, nor how hot the oven was.

Normal 6061 does funny things when you try to cast it. As it cools from molten uneven structural changes take place. That combined with heat treating could make it very brittle.

It is not one of the "common" casting alloys. I believe it requires some kind of additive? to keep it from doing the above.

Evan
01-13-2007, 12:52 PM
6061 is not a casting alloy. Casting alloys have much larger amounts of silicon usually with 4 to 15 percent being common. The silicon greatly improves fluidity so the metal runs into the mold properly. Also, as 6061 is a heat treatable alloy if it is cast it must be properly solution heat treated after casting. That isn't a matter of just tossing it in an oven, time and temperature control are critical.

Also, alloys such as 6061 are very sensitive to even slight changes in alloy constituents so any contamination can dramatically change the properties. Casting alloys are not so sensitive as the large amount of silicon swamps out small changes in other constituents.

topct
01-13-2007, 06:27 PM
Billets and/or ingots are cast of 6061. And there are methods used to help insure it's structure while doing so.

What I seem to be finding is related to the continious casting procedures used for the making of above billits and ingots out of 6061.

I seem to remember that while watching them cast ingots at Kaiser, that a reel of something that appeared to be metalic was fed into the mix as it was poored. The guys said it was to help the metal flow better. I think they called it flux, but that was not what it was. It was something that helped the metal maintain a consistant granular structure as it cooled. They stired it in there at the last second.

6061 is not an alloy that would be used in your situation.

Why would a caster that supposidly knew what they were doing suggest or even use that alloy?

Tuckerfan, we seem to have a consesis here.

Very wrong alloy. If it really was 6061.

I have at this point lost all confidence in your caster. And also their camber and their toe in. :D