Black oxide is a common heat treatment method for metal. The principle is to produce an oxide film on the metal surface to isolate air and prevent rust.
High machinability and ductility, good strength-to-weight ratio. Aluminum alloys have good strength-to-weight ratio, high thermal and electrical conductivity, low density and natural corrosion resistance.
Stainless steel alloys have high strength, ductility, wear and corrosion resistance. They can be easily welded, machined and polished. The hardness and the cost of stainless steel is higher than that of aluminum alloy.