Heat treating and ageing cast aluminum

[Doug Schwochert]

Hi all

I cast a pulley and now want to heat treat it and artificialy age it.Does any one have the procedure such as temps and time for first heat treating and temps and times for ageing. I have searched around and come up with nothing definite for a procedure. any good links.

Thanks Doug s

[JerryFlyGuy]

Do you know what 'type' of aluminum you've cast. They are not all equal on how to heat treat.. if you have an idea of what kind of aluminum it is I can look it up and give you the Kauser recommended treating proceedure..

Also what 'condition' are you looking to take the aluminum to?

[Geof]

Do you know what 'type' of aluminum you've cast. They are not all equal on how to heat treat.. if you have an idea of what kind of aluminum it is I can look it up and give you the Kauser recommended treating proceedure..

Also what 'condition' are you looking to take the aluminum to?

Excuse a semi-hijack, please.

Jerry can you provide a link to the Kaiser information or answer this question?

I have heard of a process to take 6061 T65 back to zero temper in a manner that keeps it stable provided it is held at -18 C. or lower, but which allows it to revert to T65 within a few hours after it has come up to room temperature.


To sort of answer Doug's question.

For most of the sand casting alloys the heat treatment is something like bringing it up to about 80% of the melting point, (does around 500 degrees F. sound close?). Quenching in water and then reheating to something like 50-60% of melting temperature for around 12 hours.

This takes me back a few years, almost fifty; I did my time in a place that made aluminum fire hose fittings and several times helped load and unload the big baskets that the castings were heat treated in. I remember one time the thermostat on the oven malfunctioned and all the castings melted. The initial annealing temperature was very close to the softening point and often the castings at the bottom of the load were slightly distorted.

[JerryFlyGuy]

Geof, long time no chat..

The Kaiser info I have is in a book from them. They used to publish it years back but now you can only find it used.. and they are getting tough to find..

I've never heard of this proceedure for T65 I'l have a look at the book this weeked and see if it mentions anything..

Most aluminums the proceedure [temp varies] is to take the casting to Eutetic which means you heat it to w/in 30-50deg of melting [900 to 1200deg] and hold it there for 6hrs [time varies] then quench it in boiling water.. [or other liquids]

The trick is to get the copper and other metals to re-flow back into the aluminum and then slam it back down through their melt points very quickly.. this keeps the alloying metals more evenly dispersed and improves both strength and machinability.

But I'm sure you all know that

[Geof]

....to Eutetic which means you heat it to w/in 30-50deg of melting [900 to 1200deg] and hold it there for 6hrs [time varies] then quench it in boiling water.. [or other liquids]....

Oooh BIGwords.

I was a bit low on my temperatures; maybe we used C back then not F?

But we did not use boiling water, just room temp. I am sure on that because the water tank was made of wood and just sat on the concrete floor. Mind you it was damn close to boiling after 600 lbs of hot aluminum was dropped in.

[JerryFlyGuy]

Not really.. it's only.. 7 letters long.. nothing like stoimetric or Sublimation

I can imagine that the water would get hot pretty quick.. I think they recommend boiling water because it reduces the number of degrees that the alum must fall before leveling off.. The farther it goes at a rapid rate, the more chance there is for other issues..

I'm currently building a foundry in my backyard so I'll be playing w/ this more next summer i hope

J

[Geof]

Not really.. it's only.. 7 letters long.. nothing like stoimetric or Sublimation ...J

Which would be a better response if you could spell stoichiometric.

The thing is do you know what it means?

[JerryFlyGuy]

ok Mr Smarty Pants

Funny thing is I wrote it.. and it didn't look right.. so I searched it on Google.. and low and behold.. I'm not the only person who spells it wrong!

Anyway, yes I know what it means.. It's what my airplane is operating at when I'm at Take-off power.. leaned for best power w/ Altitude compensation included

[lukewarm]

From what I understand (I am by no means a metallurgist so take it with a grain of salt, and feel free to correct) there are two important types of heat treatments to increase strength in alloys. The first is precipitation hardening (age hardening) and the second is solid solution hardening. Both work on the principles of solubility. Another hardening process is work hardening which also works by limiting dislocation movement. Dislocations are defects in the crystalline lattice, rips or tears if you will, where the molecular bonds have been disturbed between the surrounding atoms. These are sites of weakness, and plasticity stems from them as they allow the surrounding atoms to shift and move, and allow further dislocations to form.

Precipitation hardening is essentially where you raise the temperature of your alloy and hold it at the Eutetic temperature. This increases the alloys solubility and all the alloying elements dissolve within your parent metal. Quickly quenching the alloy locks those elements in the metal solution and create a supersaturated solution. Reheating, also called artifically aging, the alloy slowly to a certain temperature for a certain amount of time allow a controlled amount of the alloying elements to precipitate out of solution (like sugar precipitating out of cool cup of coffee that was mixed too sweet). These evenly spaced particles of the alloying elements act as anchors to pin dislocations that form within the metal which are largely responsible for metal plasticity.

Solid solution hardening is nearly the same but the alloying elements aren't in as high of percentages and are able to remain in solution at room temperature. The atoms of these elements can either replace one of the parent metals atom in crystalline lattice (if the atoms are near the same size and form the same sort of crystal) or if they are much smaller the atoms will crowd between the parent metals atom and cause a localized stress field. Either way they both work the same by causing stress fields within the parent lattice work that impede dislocations.

[Eurisko]

That's why I love CNCZone.

Not only have I discovered why my aluminum castings are terrible to machine, but I've also added at least 5 new words to my vocabulary.