Threaded cast Al seized into threaded cast Al

Hi Everyone,
After flipping through my old engineering textbooks, I thought I'd ask you guys for a quick and dirty practical answer.
I have two pieces of cast aluminum with mating machined threads. They've been together for 49 years, in a damp environment, and now they're seized into each other. Alloys are unknown. Penetrating oil, heat, pounding, and very long "persuaders" have been attempted.
Unfortunately, they have to come apart to service a bearing. I'm unwilling to cut either piece because they're going to be very hard to replace.
Application? 1954 Maytag washing machine that I'm restoring. (It's a family heirloom now...)
Anyone know of any chemicals (preferably household) which will penetrate small cracks and dissolve aluminum oxide? Any galvanic methods (I have large high-current DC power supplies)?
Thanks for any suggestions, advice or commiseration.
Lawrence Wade www.glowingplate.com
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Dear Lawrence;
You could consider trying this:
Try to cool the inner piece with dry ice, and at the same time, heat the outer piece with a hot water bath (if that's possible). Wear work gloves when handling the dry ice / aluminum part. Should you hear small 'cracking' sounds, that would be the time to start applying the twisting force to get the parts loosened. The outer and inner parts will try to reach thermal equilibrium quickly, but hopefully there is enough corrosion between the joints to allow for some small insulation between the two.
The powers of thermal expansion and contraction almost always win out over other mechanical forces.
The household chemical that dissolves Aluminum is "Red Devil Lye" diluted with water. -- 10% by weight is strong enough for Aluminum.
Aluminum Oxide is difficult to dissolve. Hot Phosphoric acid works to some extent, but we are talking about 150 Centigrade, and it will dissolve the Aluminum like crazy - and it etches glass at that temperature. (I now have several beakers etched on the bottom as a result)
I am assuming that you don't have access to Liquid Nitrogen, but that would be my choice for cooling the inner part.

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If the two parts were quite clean at the time of mating, then interfacial diffusion of Al atoms is a possibility. This would constitute solid state welding at the interface. Al2O3 has a very high negative Gibbs Free Energy of formation, so breakdown will be very difficult.

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Thanks to everyone who replied.
Yeah, with over 1/2 ton of force pulling orthogonal to a 12" pipe wrench and liberal blasts from an air hammer on the back of the wrench, it still isn't free.
49 years threaded into each other and presumably they were clean when they went together...
I haven't tried liquid nitrogen yet. :)
I'm afraid I'll have to cut one casting and chisel out the remains; fortunately, a former Maytag repairman tells me that they still use the same brake design on their top-load laundromat washers so the part I'd have to cut is very expensive but still available.
Lawrence
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I'll throw in my 2.
YEARS ago my father gave me an aerosol product.
Sexauer "Easy-off" Nut Loosener
It sprayed on as a kinda soapy/foamy stream. Let it sit for a while, tapping parts lightly with a hammer or wrench. parts would come apart.
My can dried up & I tried to buy some more recently at Ace Hardware where everyone thought I was nuts.
I searched the web & found:
http://www.sexauer.com/listing.html
Cleaners, Lubricants & Sealers Nut Loosener
I have not purchased any but if its the same stuff its awesome......much better than Liquid Wrench (which is pretty good itself).
The Sexauer "Easy-off" Nut Loosener seems to work especially well with plumbing parts that have been together for a long time is wet environments.
good luck
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