Worth Even A Stack of Dimes? 1

Last year, I had a brief love affair with aluminum. I bought a spool gun for my old Lincoln 180, a canister of argon, and went about learning how to weld and work with aluminum. It went so well in the beginning, that I imagined making everything out of aluminum. Nevermind intercooler piping and catch tanks, I was thinking struts, suspension arms, engine mounts… I wanted to make a whole car out of the stuff.

Aluminum was cheap, so easy to cut and shape that giving it the stink eye practically put it into shape, and it welded together with nice clean dimes that made me feel like a hero.

And then one day, something broke.

Yes aluminum needs to be heat treated. I had been buying 6061 T6 stock from a local supplier (T6 indicated the level of heat treating/artificial aging), and realized that the act of welding essentially voided that designation, but it was no big deal.  Heat treating, treat eating… Most of what I was doing at the time wasn’t really structural, and if it was I just built it extra big and strong. This simple welded bracket that broke though, was extra big and strong.

It was a wake up call, with very small consequences, but I must say it totally annihilated my confidence in aluminum.  Now I’m trying to realize a little better than value of heat treating.

I must admit, I’m no engineer, but as I look into this further one thing is crystal clear.  If you weld aluminium, heat treating is absolutely critical.  I threw 4130 Chromoly on the chart above for another point of reference.  4130 is a whole other thing to understand, so lets compare instead to plain old, commonly available 1020 steel.  6061 T6 is roughly 33% as stiff as 1020, 75% as strong, and 33% the weight.  So again, not being an engineer, if you wanted to built something out of 6061 T6 that was as strong as the same part made from 1020, it would be only 44% as stiff, but also only 44% the weight.  If stiffness is critical, the part would be essentially the same weight, but more than twice the strength.

Of course I’m over simplifying things as there is more to it than that, and aluminum parts can be designed differently than steel ones because of material properties… but I’ll save that for the engineers.

The real point is, 6061 that needs heat treating (i.e. 6061 T6 that has been welded) possesses the same stiffness and density, but only 20% of the strength of 6061 T6 (approximately 15% of the strength of 1020 steel).  In other words, give your sister some popsicle sticks and glue and see who can build the better part.

Now, I have a shop in my contact list that can heat treat the welded parts I make, but that severely impacts both the affordability and simplicity of working with aluminum.  The better alternative is to get things CNC cut from solid chunks of material and avoid welding all together, but that introduces other costs… although it does also allow for the use of some better aluminums that aren’t as easily weldable.

For now though, the summary is: even run of the mill plain ass steel > aluminum.