Aluminum baseball bat

Brief aside — the highest-strength aluminum alloys are in baseball bats, not aircraft. Used to land the precipitation-hardening point.

Twenty years ago someone published a paper in Science. They had gone to the Smithsonian, gotten the little sample from the Wright brothers' aluminum engine, put it in the transmission electron microscope, and measured the size of the precipitates which had been aging for eighty or ninety years at the time. They showed the size was consistent with an aging time of ninety years — the precipitates had been coarsening over ninety years. They compared that with a three-hour aging, a four-week aging, a one-year aging, plotted them on the same log plot and showed it was consistent with diffusion of copper in aluminum. So aluminum can be hardened. I could have brought my baseball bat — the highest strength aluminum alloys are actually baseball bats, they're not aircraft alloys. They're precipitation hardened.

Physical-object case. THT-100 scandium-bearing aluminum alloy, 100 ksi yield, ~28-thousandths wall, swaged from extruded tube. The world's largest single use for scandium (~2 tons/year global production). Sold through southern California aerospace-engineer-led firms. Used to land the "highest-strength aluminum is in consumer sports, not aerospace" homework answer.

[Tom produces an aluminum baseball bat.] So it's about the right time to tell you a story. I paid $130 on Amazon for this. Typically you might pay $300 for a bat. This has a THT-100 alloy, a scandium alloy. This is the world's largest use for scandium. We only make two tons of scandium a year. The Soviets discovered that scandium is a tremendous grain refiner. When they make these metal bats, they extrude them, and they have a relatively thin wall — this may have a 28-thousandths wall. It has 100 ksi strength, and when you hit it with the ball, it'll go farther than with a wooden bat. It's lighter than a wooden bat. It has to weigh a certain amount. This is a minus-10 bat — see the minus 10? That means it's 29 inches long and weighs 19 ounces. You take 19 ounces and subtract 29 inches, and you get minus 10. They were making minus-13 bats a few years ago, but they would almost crack the first time you hit a ball with them.