Kobe Spray Forming Yields Strong Aluminum Alloy

Kobe Steel Ltd. says it has created the world's strongest aluminum alloy, with a tensile strength of 780 MPa, using a proprietary spray forming process.

Sample bars of 10 mm in diameter and 100 mm in length are now available for application testing, Initial tests are being conducted on thin film wiring used in liquid crystal display panels. But Kobe is seeking other applications that can make use of the new alloy's light weight, high strength and processing features. 

Mass production capabilities have not yet been established, but Kobe hopes to supply the metal alloy as bars, wire rods, shapes and plates. "This value-added aluminum is suitable in applications where high performance is required," said Senior Researcher Hideo Hata at Kobe Steel's Materials Research Lab.  "By 2008, we're aiming to commercialize the new material for use in special purpose vehicles – such as race cars – and aircraft and aerospace parts," he said. 

The tensile strength of the new aluminum alloy is said to be 10 percent higher than the 710 MPa of Weldalite, an aluminum-lithium alloy developed by Lockheed Martin Corp. and used in the external fuel tank of the Space Shuttle. Generally speaking, as strength increases, material workability goes down. However, with a breaking elongation of 14 percent, Kobe Steel says its new material has nearly three times the ductility of Weldalite's 5 percent. Ductility is 1.4 times that of titanium alloy and maraging steel. 

Key to the development is use of a process called spray forming. While still in a molten state, 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 a preform on a table. Spray forming prevents the segregation of high-density alloy elements and enables melting with a uniform, fine microstructure. This can not be achieved using conventional melting and casting processes. 

The result is an alloy with a uniform and fine microstructure. Zinc, magnesium and copper are added as alloys for strengthening. Kobe Steel developed its own proprietary after originally trying a spray-forming process developed by Sandvik Osprey Ltd. in the United Kingdom. Eventually, ingots of up to 240 kg will be produced to make large parts.