The range of alloys made use of is sensational: weathering steel for patina, marine-grade light weight aluminum for weight cost savings
https://www.mediafire.com/file/oppjs4t9uw3lgb3/pdf-7210-90490.pdf/file
The variety of alloys utilized is stunning: weathering steel for aging, marine-grade aluminum for weight savings, and duplex stainless for corrosion resistance in extreme climates.