6082 aluminium heat treating, help?

[dusse123]

Hey everybody,

I've done a fair bit of mild steel welding but now I am making an aluminium project for the first time. I'm making a ski bike, it will be a bit like a north legion smx if anyone is interested.

I will be buying 6082 box section aluminium and it comes in a T6 condition. I know from my research that this type of aluminium will lose a lot of its strength when welded so I should get it heat treated to get it back to T6 condition.

But here is my problem, as I said earlier the metal will already be in T6 and when I weld it only a small part of the aluminium will lose its T6 temper, is it possible to heat treat to aluminium normally without changing the metal that is already in T6 condition?

Sorry if my wording is a bit hard to understand, I tried my best but if you dont understand the question please say.

Thanks for the help

Angus

[Jigantor]

Send it to a heat treatment company. They will heat treat the frame to T6.
Ji

[dusse123]

Yeah, I'm going to send it off but what I was wondering was if getting certain sections back to T6 temper will affect the rest of the metal that is already in T6 temper.
Thanks

[Jigantor]

The temper process will not damage the aluminium.
It is a process that the aluminium has already been through.
If you have designed your frame correctly you would have checked bending, shear, tensile strength and deflection. T6 makes the tensile strength much stronger than non tempered ali. And if you have designed this unit correctly you would know that temper does not help deflection, aluminiums greatest weakness a part from fatigue which is due to repeated flexing.

Ji

[Jigantor]

If the frame shape is like a push bike than it will consist of triangles where all the centroids or nodes line up. To work out the stresses involved you would employ truss analysis. This means that there is no bending moments just tension & compression acting on the members. Deflection will not be a problem in this case. That said it would be very difficult to make a frame that is a perfect truss without eccentric loading.

Ji

[dusse123]

sorry I'm not being very clear, what i'm asking is that when i get it heat treated in a furnace the entire frame will be affected and if i'm trying to get certain parts to t6 will the sections that already are t6 change to another temper?

[snowbird]

NO. Your heat treater will provide you what you want.

Some basic infos here: http://www.matweb.com/reference/aluminumtemper.aspx

Don't beleive everything you find on the internet. BUT if jiganitor suggested me to pay attention to design details when using alu alloys i would take good note of it before spending money on h.t.

good luck.

[dusse123]

Ok thanks, I'm a complete newbie when it comes to alumnium. How do you do I work out all of the things you said?

"If you have designed your frame correctly you would have checked bending, shear, tensile strength and deflection."

I've done quite a bit of research but couldnt find anything along those lines. I've talked to a fabricator who is going to teach me how to weld alu and supervise me doing it, he said 2mm thick would be enough, I'm using 50mm x 50mm 6082 tubing.

Any help would be appreciated!

[Jigantor]

To understand these concepts you would have to do a Uni degree in engineering or work with someone that crunches calcs every day for a few years. That said the best thing to do first is to draw your design with all the members. Work out dimensions and then estimate what you believe to be all the loads that will be applied to the frame with their respective angles.

Ji

[dusse123]

To understand these concepts you would have to do a Uni degree in engineering or work with someone that crunches calcs every day for a few years. That said the best thing to do first is to draw your design with all the members. Work out dimensions and then estimate what you believe to be all the loads that will be applied to the frame with their respective angles.

Ji

Or I could just over build it to remove any risks? he says hopefully...

[Jigantor]

Yep that will work too.
Good luck.
Ji

[Jigantor]

If you are going to over build it why have it post heat treated?
From what I have read most high end mountain bike builders do not post heat treat their frames.
They say stuff like "6061 heat treated to T6 TIG welded frame"
That just means that the material they started with was heat treated.
The only reason for heat treating a frame would be that your design was running close to the wind and that is why I suggested the engineering input.
Some more advise make it out of round or oval.
Square section is stronger than round for the same depth member but square will hurt more during an accident.

Ji

[Jigantor]

Actually, just thinking about it, I would buy a cheap mountain bike from Wall Mart and convert it.
You get a mono shock, forks, handle bars, steering head, seat and post, aluminium frame........
The shock and forks would cost you more than the bike if you bought them seperately.
Still a great project and you still get to TIG weld aluminium.

Ji

[dusse123]

I would buy a bike and convert it if i could but this is my design here so that wouldnt work.


What would you consider over built for my purpose? 2-3mm?

[Jigantor]

Are you going to have a rear shock?
The rear ski post connections will be in shear (not the best for load carrying nor for accidents, looks kinda sharp).
The thickness of tube really in this case has more to do with weldability.
I would have to know the loads to be able to advise.
That is the problem with new designs.
Most manufacturers fabricating a new device over build then test it to death. Once something lets go or bends they see where the loads are high and reinforce the next generation.

Ji