Titanium is awesome, though. Has similar corrosion properties to aluminum (in that it only oxidizes on the surface), is similar in strength to iron/steel, but is only about 60% of the weight iron. So it’s lighter.
Plus if you mix in molybdenum and I think some nickel, you can have yourself a very long lasting spring that won’t sag like steel springs after several years.
Main downside is it’s so expensive compared to iron :(