Aluminum started as one of the world’s most expensive materials because it was difficult to refine—even though it made up 8 percent of the world’s crust. But eventually aluminum became one of the cheapest materials after methods of mass producing it were invented in the 1880s. It went from $1200 per kilogram down to a dollar in 50 years.
The aluminum used back then was still weak and malleable, though. It wasn’t until Alfred Wilm accidentally discovered age-hardening which transformed aluminum to duralumin, an alloy with a much stronger crystalline structure, that things began to change. Duralumin was used to create the first all-metal airplane, and its strength eventually led to new plane structures being built that changed air travel forever.
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