heat treating aluminum

[gt40]

I have been playing around with some 6061 and it seems soft. I read that you can "harden" or strengthen aluminum by two methods:

The first one is called solution heat treating. You heat the part at 990 F for adequate time to allow for thorough heating and then water quench.

The second one is called precipitation hardening. It is done at 320 F for 18 hours and air cool, followed by 350 F for 8 hours and air cooling. I got this from the 6061 aluminum material property data sheet on the metal suppliers online site. I wonder if it is worth the trouble and how it might affect thread cutting and finishing. I have a computer controlled kiln so it is easy to hit a temp and maintain it for specific periods of time. Just wondering if anyone else has tried it. Any thoughts or feedback would be appreciated if you have experience or info on this.

 

[Kestrel]

I have been playing around with some 6061 and it seems soft.

Unusually soft 6061 could be -O (and won't respond to aging treatments) or T0 but most commercially available 6061 is (already hardened) -T6.
A little bit of related info: http://webcache.googleusercontent.c...58522/+hardened+6061&cd=6&hl=en&ct=clnk&gl=us

The first one is called solution heat treating. [...]
The second one is called precipitation hardening.

The usable hardening techniques vary based on the aluminum alloy - the alloying elements that the Al contains will dictate what hardening procedures can be used.

My two lumens, if it's not working for you I wouldn't bother trying to heat-treat it correctly. Heat-treated 6061-T6 stock is good-to-go and should be relatively inexpensive.

Edit: But maybe I'm in the wrong forum? :whoopin: The CPF answer?? Go for it!

 

[gt40]

Thanks for the info. I know a lot more about about steel than aluminum. I guess I should just focus on T or 7075 alloys. I got a bunch of scrap 6061 really cheap. I guess I will try treating some for the cost of the electricity firing the kiln and to satisfy my curiosity

 

[Kestrel]

I guess I will try treating some for the cost of the electricity firing the kiln and to satisfy my curiosity

You could do the following on a piece of the 6061 stock for a (very approximate) indentation hardness comparison test:

• Get a small circular bar of steel, maybe 1-2 foot long
• Position it near-vertically on one end so that when you let go, the higher end will fall & create an indentation near the end of a piece of the 6061 which is sitting on the floor in the appropriate location.
• Try some sort of heat treatment on the 6061
• Do the same test, but slightly further down on the 6061 stock.
• Now you have two indentations relatively close together, one from the untreated condition, and one after your heat-treatment. If your second indentation is considerably smaller, :goodjob:
• Repeat as necessary. :shrug:

Edit: you could even 'calibrate' this 'test' with some known Al stock to see if your 6061-Tgt40 is at least approaching your considerably harder 7075 or some known 6061-T6.

 

[Chauncey Gardner]

Good advice from Kestrel.
Both T6 & the 7075 are pretty hard. Both have been used in in higher end aluminum bike frames (more so 7075 now) and are durable with much higher fatigue resistance than lesser al that has not been also properly heat treated.

 

[warren55]

One guy i knew used a pizza oven to HT a bicycle frame he built.
Seems his TIG joints softened too much around the welds.
The oven was available.....

 

[warren55]

Both T6 & the 7075 are pretty hard. Both have been used in in higher end aluminum bike frames (more so 7075 now) and are durable with much higher fatigue resistance than lesser al that has not been also properly heat treated.

Last I knew you couldn't weld 7075. Something about the copper in it.
It is hard, but everything needs to be cast, I don't think bicycle frames are made with that ...