Wright brothers' aircraft engine

Aluminum-copper precipitation-hardened engine block at Kitty Hawk. Used to make the point that "nanotechnology" is older than the term — and that the engine is still in the Smithsonian.

There are other alloy systems that can be hardened. We're going to talk about aluminum, but aluminum is precipitation-hardened. You heat it up, solutionize everything, quench it, and then you bring it up to an intermediate temperature — we call it tempering. You get little precipitates, and some people will tell you that's nanotechnology. Well, the Wright brothers used nanotechnology in their engine at Kitty Hawk. It was an aluminum-copper alloy that had been precipitation-hardened — aluminum for lightweight because it's an aircraft, precipitation-hardening so it'd have decent wear resistance. And it's still sitting in the Smithsonian today.

Origin reference for aluminum-copper precipitation hardening alloys — "the original Wright brothers aluminum copper alloys, developed back 100 years ago."

When you get to the heat-treated alloys: 4043 is high silicon weld filler wire; copper — that's the original Wright brothers aluminum-copper alloys, developed about a hundred years ago. We learned with copper in aluminum — or magnesium, a couple of others — over the years that they are serious problems for pitting corrosion. Because of the precipitation hardening, you've got little specks of copper alloy. Copper's more noble than aluminum, so now you have little cathodes surrounding your anode. Pitting corrosion occurs at the anode. So you have little galvanic cells just eating away at it.

First aerospace use of aluminum-copper alloy (engine housing, 1903). Used to anchor the historical depth of the 2000-series aerospace alloys.

The non-heat-treatable aluminum alloys, which are the 1000, 3000, 4000, 5000 series, have lower strengths. The heat-treatable ones — 2000, 6000, 7000 — the aluminum-copper alloys were the first aerospace alloys. I think I mentioned that the housing for the engine of the Wright brothers aircraft, the first one to fly, was an aluminum-copper alloy, and that was sort of new back in 1903 or so. The 6000 series are common high-strength aluminum alloys — general-purpose, structural, architectural alloys. The 7000 and 8000 series are most of the aviation, aircraft, Boeing, Airbus type alloys nowadays, and we'll talk about some of that.

Used twice. First in §3 as the date-marker for 2014 aluminum alloy ("over a hundred years"). Second in §5 as the cracking-on-welding example — GTAW the Wright brothers' crankcase and you'd get equation-melting cracks in the HAZ, same problem as Monel.

This is percent copper, increasing. This is a hundred percent aluminum, and this is five percent. 660 centigrade is the melting point here, 540 or so here — about a 120 degree centigrade temperature differential. Since aluminum melts at 660, it doesn't have really good high-temperature properties. In fact some of these alloys are not very good at all at temperatures above even 200 degrees Fahrenheit. Boil water and you wipe them out. So these are heat-treatable alloys, and 2219 is a modern alloy. That's what they used to build the Space Shuttle main tank. These are lightweight. 2219 was a four-and-a-half percent copper alloy that was more weldable than some of the others. If you tried to weld the Wright brothers' crankcase or the cylinder housing for their engine with gas tungsten arc, you'd crack it. You'd melt it and you'd have nice cracks — pull that rope, melted metal right out. Same type of problem as you have on Monel — you get cracking, equation melting in the heat-affected zone in the copper interiors.

Used to push back on the framing of aluminum as a "new" structural material.

You don't think of aluminum as a new material in aircraft — we've been making aluminum aircraft since the 1940s. Actually the engine in the Wright Brothers' aircraft was an aluminum-copper alloy casting. They were using aluminum on the first flight. And certainly by the 1940s many of the military aircraft were mostly made out of aluminum. It was a big deal in the 1990s, only 20 years ago, when Audi came out with all-aluminum vehicles. Was that really a big deal? I could show you pictures of Andrew Mellon, of Carnegie Mellon Bank fame, in the 1930s with his all-aluminum Pierce-Arrow. He could have Pierce-Arrow build him an aluminum Pierce-Arrow because he was the investor for Alcoa. He made a lot of money off the aluminum business.

Engine block was aluminum-copper heat-treated alloy — used as early structural-aluminum example.

At one time there were three companies that were merged together: Alcoa, Boeing, and Pratt & Whitney were all one company. The trust-busters in the early 1900s broke them up. Can you imagine what those people would be doing in the aerospace industry if they kept that monopoly? Tremendous decrease in price, and everyone thought this was a wonderful industry. It was the darling of Wall Street because there was no aluminum industry before, and all of a sudden you had another metal to compete with steel for certain structural applications. The engine block of the Wright Brothers' aircraft was aluminum-copper alloy. Heat-treated aluminum-copper alloy. We'll talk about aluminum next week when I'm lecturing some more about why you heat-treat it.

Cited twice as the earliest precipitation-hardened aluminum-copper aircraft engine, now in the Smithsonian. Used to establish the hundred-year lineage of 2000-series aluminum alloys.

Then here's the aluminum alloy 7075, used to be the workhorse alloy for the skins of Boeing aircraft. 2024, which isn't on here but it would be down like 2014. 3003 is beer can stock, okay. 2024, 2014 are similar in strength, in the heat-treated condition, to the aluminum-copper alloys that we've been using for a hundred years. The Wright Brothers' aircraft engine case was a cast 2000-series aluminum like this, and it's in the Smithsonian.

First successful precipitation-hardened aluminum-copper alloy. A *Science* paper twenty years prior measured the precipitate coarsening in the Smithsonian sample (eighty-to-ninety year aging) and confirmed it matched diffusion-of-copper-in-aluminum kinetics extrapolated from short-term aging studies.

Okay so I've got this iron. That actually started out as why is cast iron over here and why is steel over here. It's historical. But also cast iron melts at a lower temperature because of the eutectic. What you really like to have historically is something you can harden. I've got aluminum — I didn't have a piece of hardenable aluminum in my office, this is a piece of 5454 aluminum plate, it's non-hardenable. But many aluminum alloys — the aircraft alloys, the aluminum-copper that the Wright brothers used for their engine — was an aluminum-copper alloy. You heat it up, it has a phase diagram that looks something like this. You heat it up into a region over here, put the copper into solution, quench it, then after it's cooled to room temperature you heat it back up to an intermediate temperature and you form these copper precipitates.

Brief teaching aside on natural aging. SEM study of the engine block in the Smithsonian showed aluminum-copper precipitates still coarsening after a hundred years at room temperature; data fell on a straight line on a log-time scale.

They once did a study of the Wright brothers' engine, the one in the Smithsonian. Someone took a little sample off, ran it under the scanning electron microscope, and looked at how the aluminum-copper precipitates had grown over a hundred years. They put it on a log-scale graph, and those things are still precipitating at room temperature sitting in the Smithsonian. Everything falls on a straight line. They're getting coarser over time.

Flyer One's aluminum-copper engine block, now in the Smithsonian, sampled and examined by TEM to measure century-long coarsening of Al-Cu precipitates. Used as the founding example of heat-treatable aluminum alloys and as a demonstration of long-term softening in service.

Copper — the 2000 series — was the original heat-treatable aluminum alloys. The Wright Brothers' engine block on Flyer One, the one they flew at Kitty Hawk, was an aluminum-copper alloy. That engine block is in the Smithsonian. A few years ago they took a little piece out of it and looked at it in the transmission electron microscope, to see how big the aluminum-copper precipitates had grown after a hundred years since they'd been heat-treated. They're coarsening over time. One of the problems with aluminum alloys: they melt at low temperatures, but they will also soften. You can heat-treat them and get 10 to 12 times the strength of pure aluminum, but they can degrade over time at relatively low temperatures.