When people started refining Aluminium in the 1880s, it was one of the most expensive metals in the world ($1200 per KG,) but the cost of the material quickly dropped in the early 1990s, going down as low as $1 per kilogram. Unfortunately, Aluminium was weak at that time, but in 1901, German scientist Alfred Wilm accidentally discovered age-hardening, which made the metal much more stronger.

[Real Engineering]