Fun fact: the success of the Wright brothers in achieving powered flight was due in part to having an engine with an aluminum block, giving a better power-to-weight ratio than one with a cast iron block. The block was actually made from an alloy containing 8% copper, which gave it much better strength than pure aluminum. Because Al/Cu alloys harden through tiny particles of copper precipitating out of solution over time, the Wrights’ 1903 engine block is now actually stronger than it was when first built.

John

Wouldn't that engine be weaker today?

Have you heard of over aging?

To harden the alloy you are basically heating and artificially aging it to its optimum point.

I would think that after a 100 years or so after the optimum point, those copper particles are gone or doing more harm than good.

 

FMM, no, the reverse is (surprisingly and counterintuitively) true. I got this particular nugget from a video of a lecture by a professor of metallurgy at MIT. Apparently, the copper particles disrupt the continuity of the aluminum’s crystalline lattice, making the material more resistant to deformation in much the same way that crystalline dislocations function in work-hardening. Because the precipitation takes time, an aging step is actually incorporated in the manufacturing process. 

1 hour ago, Mike BR said:

But I keep seeing the description on consumer products that don’t need any particular strength.

Yeah, that’s what happens after an actual term starts getting used as a commercial buzzword. 

That is all true when being manufactured.

So according to you a hundred plus years of oxidation and hardening makes an engine stronger.

If it is getting harder every day through the processes you described.

So how hard is to brittle. 

To me the laymen I can't fathom it being stronger today, than the day it was manufactured.

 

The oxidation is irrelevant; that’s only going to affect the surface. The precipitation isn’t a linear process, continuing at the same rate indefinitely. Most of it happens fairly quickly, and the alloy reaches its optimal strength without having to age for years and years (unlike, say, seasoning lumber or aging wine). However, even though precipitation slows waaaaaaaaay down, it doesn’t actually stop until all the copper has precipitated out. 

(This can be compared to the half-life of radioactive materials. Consider a sample of uranium-235, which has a half-life of 704 million years. After 704 million years, half of the sample will have decayed into thorium-231. After another 704 million years, half of the remaining uranium will have decayed, leaving 1/4 of the original amount as uranium and 3/4 as various decay products (isotopes of thorium, actinium, protactinium, etc). After another 704 million years, we’re down to 1/8 of the original amount of uranium, with 7/8 as decay products, and so on.)

Thus, while the Wright engine is indeed stronger than when it was built, it’s not a *lot* stronger, and its strength isn’t going to increase to the point that it becomes brittle, because it will run out of unprecipitated copper first. 

52 minutes ago, Florida Man Metals said:

To me the laymen I can't fathom it being stronger today, than the day it was manufactured.

Yeah, that blew my mind, too. 

If you say so. I know parallels.

I work with silver. Which is to soft so you have to alloy it for strength.

Funny enough 7.5% of copper to be exact.

Do all of those same principles apply?

I think precipitation hardening is only a thing in aluminum alloys, so it wouldn’t apply to silver. 

Plug this into your preferred search engine:

17-4 ph stainless steel

Interesting. Not just aluminum, then.

The AI answer indicated that copper is a key alloying element.  There are also other grades like 15-5.

Here's a real rabbit hole for you:

what alloys are precipitation hardening

And now we get confusion between "AI" as the abbreviation for Artificial Intelligence and "Al" as the chemical symbol for aluminum! Using serifs would clear things up, but unfortunately, the forum software doesn't appear to support different fonts.

Didn't the Bible have something about Serif Serpents? 

Numbers 21:9 does not give the metallurgical composition of the נחש נחשת, alas.

Well John you were right. I think.

I needed a parallel to grasp. 

To soften sterling silver you anneal it. Heat to dull red and quench.

To harden, I have only ever work hardened a piece. 

Apparently you can harden it another way. 

Basically you temper it at 550f for an hour which causes the fine copper particles to dissipate and strength the alloy somehow. Magic.

Thought I'd share since you made me learn. Something I probably should have already known. Thank you.

 

Copper is definitely a key alloying material.

My other parallel is American pewter. (I know I never shut up about it). 

90% tin 10% copper.

Tin is such a crazy metal I didn't even want to bring it up.

All bets are off when tin is involved. I wouldn't even want to guess at what is taking place there.

I think I figured out why it all seems so wrong. Its in the words.

Super saturated solution. Precipate out. We are talking about a solid metal.

I would swear we were having a conversation about wet refining methods.

Beakers full of colorful liquids and metal in solution.

Frosty has mentioned fallen friends many times to me and I would like to bring up an old thread I read sometime back, from Thomas. Parallels again.

It was about depletion gilding gold and tumbaga.

Not exactly the same but it remindeds me of it, but a wet method.

In this case they made an alloy high in copper and low in gold. Put the object in an acid (some plant sap) and it dissolved the copper on the surface and left the gold. 

The Conquistadors thought they were stealing solid gold objects.

This (quasi) parallel has always grabbed me.  Quench steel, and the carbon is trapped within the grains, distorting them and locking them together.  Reheat to a few hundred degrees (temper) and some of the carbon precipitates out, ending up between the grains and doing, basically, nothing.

Quench aluminum, and the copper (or other alloying metal) is trapped within the grains, doing, basically, nothing.  Reheat to a few hundred degrees (age) and it precipitates out, ending up between the grains and locking them together.

Thanks Mike, that helps put some things together for me. Simple enough for me to understand.

I was willing to go with magic. I don't always need to know why. But it is sure nice to know.

 

You guys sure are making me think tonight.

The one constant is that they are both technically impurities?

As to the why aluminum copper alloy acts the opposite way to steel and carbon. Not sure but maybe has to do with those two metals being to similar.

Eutectic point is the word. Here's another monkey wrench.

13 hours ago, Florida Man Metals said:

To soften sterling silver you anneal it. Heat to dull red and quench.

Is annealing not heating it up and letting it cool slowly to relieve internal stress? I've never worked with silver so I can belive that quenching it might somehow soften it but is it still called annealing when working with silver? (Or maybe jewellery -gold&silver- its called annealing) im not sure if the terminology with silver is different or not.

Also how can an alloy age at room temperature? How are the particles able to move and disperse at room temperature, are they not locked solid in place?  Mind blowing stuff

Yes, it's still annealing. As Mike BR notes above, silver, copper, brass, aluminum, etc don't harden when quenched, simply because they don't behave the same way as steel. In many ways, the hardenability of steel is the exception to the properties of most metals rather than the rule.

Materials behave in interesting ways at the atomic level, and we have to be careful about how we think about our reference points. From our point of view, room temperature is "normal", but not only are there still things going on within a crystalline structure, but different things can happen at even lower temperatures. This is why cryotreatment is a thing for the heat treatment of some steel alloys.

If we're calling room temp 70f then it's actually 295.2611K where the atoms play.

Frosty The Lucky.