A New Light-Weight Metal is Competition for Aero-Composites

Kobe Steel has created the world's strongest aluminum alloy, with a tensile strength of 780 MPa achieved by using a patented spray forming process. Metal ingots of up to 240 kg in weight can be produced for machining of large parts. Unlike conventional melting and casting processes, spray forming prevents the segregation of high-density alloy elements and enables melting with a uniform, fine microstructure. Molten metal is "sprayed" into droplets and is quickly quenched as it turns from a liquid to solid state. Molten metal in an induction furnace flows out of a small hole in the bottom of the furnace. Nitrogen gas is blown as the molten metal exits the hole, atomizing the material into a fine mist of droplets. The droplets accumulate and solidify into formwork on a table surface. Zinc, magnesium and copper are added during the process to strengthen the material. The new aluminum alloy's tensile strength is 10 percent higher than the 710 MPa of Weldalite(R), an aluminum-lithium alloy developed by Lockheed Martin Corporation and used in the External Fuel Tank of the Space Shuttle. The ductility of Kobe Steel's new alloy is also high. With a breaking elongation of 14 percent, Kobe Steel's alloy has nearly three times the ductility of Weldalite's 5 percent. Ductility is 1.4 times that of titanium alloy and maraging steel (a special class of low carbon ultra-high strength steels which derive their strength not from carbon but from precipitation of inter-metallic compounds). It is expected that its use in aerospace applications will eventually match that of light-weight composites for structural parts requiring exposure to fluids and the elements and high tensile strength.