2025 aluminum propeller alloy (mid-1920s)

The toughest aluminum alloy — ten times tougher than any other aluminum alloy — is one that was developed in the mid-twenties. They use it for propellers, aluminum propellers. It will bend 180 degrees before it'll break. But we don't use that for aluminum structures because we need more strength. It's actually 2025 alloy. If you look in here for 2025, there's all kinds of data in the old Mil Handbook. Its toughness is five to ten times greater than 2024, but its strength is probably about two-thirds as much. It can bend like steel. But it's the only aluminum alloy that comes anywhere close to that. Because we're usually trying to push the aluminums — just like baseball bats — to higher and higher strength, which means more and more corrosion problems, stress corrosion cracking and other things. We're using aluminum because we need the performance of the lightweight for whatever structural reason.