bebbetufs

...rapidly cooled down/ quenched from about 200c/392f?

Dave W.

I'm guessing that it'll warp? What shape is the object? cylinder head? or a bar, plate, tube?

67King

I dont believe that is hot enough for any recrystallization or anything that would otheewise cause any benefit or detrement. Need heat temperatures over half melt (660C) typically to have anything.

JohnKoaWood

Depending on how cold it was quenched, the original alloy, and any underlaying defects...

My bet is it cracked / shattered...

Scott H

Remember that scene from Terminator 2 with the T-1000 and the Liquid Nitrogen? I'm imagining something like that.

95ONE

LOL.. nothing happens. It cools off quickly.

944Phil

Nothing happens to the metal at those temps : see phase diagram here
http://chemsoc.velp.info/alloys/Al-Cu.jpg

However.... you can warp (yeild) it if it cools very unevenly. But i doubt it.
What part are you talking about?
What is "rapid"? (dunked in water?).

I am a materials engineer, not a metallurgist specifically, there are some metallurgists that i work with, i'll run it past them tomorrow. PM me if i forget to get back to you.

Phil

bebbetufs

I am talking about a control arm and by rapid I mean dunked in water, first one end, then the other. This was done by mistake to cool a powder coated and baked part.

Powder coating baking temperatures are hot enough to reduce spring rates in of springs, so I'm pretty sure something happens to the material at this temperature point.

67King

Disagree. Typical coil spring alloys are designed to operate at higher temperatures (http://optimumspring.com/technical_r...ring_wire.aspx). Furthermore, virtually all decent coil springs are powder coated by their manufacturers.

The temperatures being discussed here are aging temperatures, not what people are probably thinking of as precipitation hardening temperatures. That is done, again at well over half Tmelt, to get into the pure metal phase (e.g. Cu or Si). This moves the material close to the eutectic, and rapidly quenching it will result in a supersaturated mixture of solid alloying element plus eutectic, which gives it strength.

A control arm will probably be 319 (Al-6.3Si-3.5Cu). Very little Si is soluble in Al, and only a little more Cu is. And as Phil showed, at 200 degrees C, you aren't hot enough to get there.

So we are really talking about artificial aging. And that is done at elevated temperatures with durations extending days. And all it does is accelerate the natural aging process whereby stress concentrations are reduced and the metal becomes a little stronger. Furthermore, aging is more often done on wrought alloys, or alloys that are solution heat treated first (i.e. T6 heat treatment).

Again, you just aren't hot enough to do anything.

Side note, I do this kind of thing all the time when heating stuff. I don't "quench" stuff I powder coat, so that any rapid shrinking won't cause the powder coating to flake, but if I heat up stuff to remove loc-tite for example, I'll always "quench" it to make it easier to handle more quickly.

By the way, my undergraduate degree (97) was in materials engineering, with a specialty in metallurgy, though I never used it professionally. So I might have a few of the little details wrong, but by and large, I'm pretty confident in my opinion, and I'd like to feel my opinion is pretty educated.

95ONE

What he ^^^^^^^ said. To further ease your worry or pain. If your fears were real, an aluminum caliper would never be in production, or work. They do very well, and can handle the temps you speak of, even after being dunked in a puddle of water over and over.

bebbetufs

Thanks for your answers.

For the record #1. I just read a test wher a spring was, strippped for painted, and powder coated. The spring was tested in a calibrated spring gauge before and after curing. It lost 5% spring rate.

For the record #2. Spashing through a puddle would not really reduce the temp of the caliper. The water will just boil off it the caliper is this hot. Parking in a puddle covering the caliper would be different. But, as 76 KING says, it is likely nothing would happen, even then.

Van

Powder coating is typically done at 375-400 degrees F. However, some shops will do a "burn-off" phase that can be 800+ F.

Will Feather

Doing this exact stuff in my Material Science course in school now!

I was going to post a phase diagram photo but have been beat to it... as 67King said, just not hot enough to have any effect on your control arm.

Also as 67King said in his first post for certain metals you need to be at almost half of the melting temperature for any effects, what I believe we use in school for a value is 0.4*melting point

95ONE

Just trying a layman's explanation.

bebbetufs

It seems like everyone agrees that aluminium will not be affected by temps this low. Now all I need to do is to post some photos of my powder coated stuff. I'll have some by the end of the week.

Thanks to all posters for your answers.