# Heat Treating (T-6) Aluminum Alloys



## zonian1903 (Jun 19, 2007)

Would someone please elaborate on what "Solution Heat Treat" and "Artificial Aging" means and what process/equipment this entails for heat treating 6061 to T-6? I have a decent amount of experience heat treating steel, but I've never worked with Aluminum. Is this similar to hardening/austentinizing (via heat/oil-quenching for instance) and then tempering/normalizing (via heating & timed-controlled cooling) of steel? 

Any links with details/specs/standards on the process so that someone with a decent sized shop and some time on their hands could experiment? 

Frank


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## zonian1903 (Jun 19, 2007)

OK...

From what I've been able to find out:

If I start with 6061 T-0 stock

1) Solution Heat Treat ==
a) Heat to 990F until part has completely reached temp
b) Water Quench

2) Precipitation Harden ==
a) Heat to 320F for 18 hours
b) Air Cool

3) Artificial Aging ==
a) Heat to 350F for 8 hours
b) Air Cool

Does this sound right?


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## michigan_maniac (Dec 30, 2009)

Hi zonian1903,

I have had several Material selection classes for engineering applications, back college. 
I do not use it on an "everyday" basis ... it's more like a monthly basis.

I am not sure if a T-0 strength exisits a processed material you could purchases, however, you can change any strengthened aluminuum alloy to T-0 with heat input.

Your best resource: *ASM International *

They are the Encyclopedia Britanica for metals. (No joke, the entire series is about $3,000 for all the books). However, for $50 a year, you can subscribe to their resources pages on their website and get ALL the help, engineering, and physical chemistry your brain could ever adsorb in a lifetime. I have the ASM Aluminum alloy book here at work and another book at home (I forgot the name of that book.)

2xxx, 6xxx, & 7xxx series aluminum alloys are Precipitation hardened alloys. (These are used for High-strength / low-weight appplications.) To properly return the alloy (POST WELD) to its original (high strength) molecular phase, you MUST "resoluntinionize" the metal. This entails: 1.) heat the metal to it's austenization temperature 2.) Quench the metal faster than its critical-cooling-rate 3.) Age the material. This is usually done artifically and at a max temp for a specific amount of time.

It's the AGING that gives the aluminum it's Strength. NOT the quenching.

Checkout ASM international for detailed explanantions. I personally do not "experiment" with this as I no longer have the resources avalilable.

It would appear that user: "shovelon" has experimented with this. Shoot him a pm.

-MB


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## zonian1903 (Jun 19, 2007)

MB,
Thanks!
I went to ASM Int. and I just ordered "ASM Specialty Handbook: Aluminum and Aluminum Alloys". That should keep me busy for a while.

Frank


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## michigan_maniac (Dec 30, 2009)

Great to hear you bought it! But, I am more excitied to hear some is serious about metallurgy! For the last two years I have been in search of a processing book I borrowed once. That contained specific heat treating processes for almost any metal imagineable. That book was every bit as thick the ASM Specialty handbooks! If I get my hands on that ... I will be sure to let you know what it is.

Good Luck! You are in for some serious reading!

Have Fun!!!

-MB


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## jeffscott (May 10, 2006)

http://www.eastonbike.com/downloadable_files_unprotected/fab_instr/fab_instructions-7005_6061.pdf

This is a little more specific.


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## michigan_maniac (Dec 30, 2009)

Good Frame Building resource! I have been looking for aluminum frame building resource for some time now.

I am glad to see that Easton noted that powder coating temperatures on these aluminum alloys shall compromise strength!

-MB


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## michigan_maniac (Dec 30, 2009)

However .... regarding the 7005 not requiring solution heat treatment is all relative ... relative to the specific heat treatment desired. 

I had bad-luck with a late 90's Manitou Frame that I had sent out to be re-welded. Unfortunately it an Easton aluminum tubeset.

-MB


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## zonian1903 (Jun 19, 2007)

If my mind serves (thats an if'y proposition nowadays), when we send parts out to powder coat, the oven temp is less than 350F which is the aging temp. Also, I believe the curing times for the powder, it was less than 1.5 hours. My intuition tells me this shouldn't make a difference practical difference in the final physical properties of a 6061 weldment (mind you my experience is with alloy steels and Ti), but who knows. On the other hand powder coating always seems plane-jane to me... I'm more of a three part-silver-metallic-blue-mica-with-red-pearl-with-the-big-1-mm-flakes kinda paint geek. Haven't done that on on a bike frame but its commin'


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## shovelon (Mar 16, 2006)

zonian1903 said:


> If my mind serves (thats an if'y proposition nowadays), when we send parts out to powder coat, the oven temp is less than 350F which is the aging temp. Also, I believe the curing times for the powder, it was less than 1.5 hours. My intuition tells me this shouldn't make a difference practical difference in the final physical properties of a 6061 weldment (mind you my experience is with alloy steels and Ti), but who knows. On the other hand powder coating always seems plane-jane to me... I'm more of a three part-silver-metallic-blue-mica-with-red-pearl-with-the-big-1-mm-flakes kinda paint geek. Haven't done that on on a bike frame but its commin'


I think you are right in regard to Powdercoat. The temps would need to rise to 650F. or so in order to anneal(soften) but not take the alloy into solution. From what I remember solution heat treat means that the alloying elements free flow at mid 900sF. then are trapped when cold water quenched. See the image below how the linear grain structure 7050 commercial goes to random(solution) after heated.


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## jeffscott (May 10, 2006)

shovelon said:


> I think you are right in regard to Powdercoat. The temps would need to rise to 650F. or so in order to anneal(soften) but not take the alloy into solution. From what I remember solution heat treat means that the alloying elements free flow at mid 900sF. then are trapped when cold water quenched. See the image below how the linear grain structure 7050 commercial goes to random(solution) after heated.


Aluminium is age hardened to get higher strength (at least the heat treatable alloys 6000/7000).

Age hardening occurs anywhere from room temp up to about 400 F. Higher temp faster the time...

Aluminium heat treatable alloys can be overaged, when that happens the alloy gets harder with no increase in strength.

So if you properly age harden an alloy, then powder coat (and reheat) you may over treat that alloy.....

Best guess powder coat at heat treat temp and hold for reccomended time..

ie use the powdercoat as heat treatment.


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## shovelon (Mar 16, 2006)

jeffscott said:


> Aluminium is age hardened to get higher strength (at least the heat treatable alloys 6000/7000).
> 
> Age hardening occurs anywhere from room temp up to about 400 F. Higher temp faster the time...
> 
> ...


Well said jeffscott.:yesnod:


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