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Kobe Steel achieves world's strongest aluminum alloy

Uses original spray forming process in manufacturing

March 29, 2007

Kobe Steel is seeking applications that can make use of the new alloy's light weight, high strength and excellent processing features. Kobe Steel is currently making sample bars of 10 mm in diameter and 100 mm in length. It is also working to establish the technology to mass-produce bars, wire rods, shapes and plates made of the alloy.

"This value-added aluminum is suitable in applications where high performance is required," said Senior Researcher Hideo Hata at Kobe Steel's Materials Research Laboratory. "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 new aluminum alloy, under patent application, has a tensile strength of 780MPa, 10% 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. Generally speaking, as strength increases, material workability goes down. However, with a breaking elongation of 14%, Kobe Steel's new material has nearly three times the ductility of Weldalite's 5%. Ductility is 1.4 times that of titanium alloy and maraging steel. In addition, the new alloy has one of the highest specific strengths (the tensile strength divided by the density of the new material). The higher the specific strength, the lighter and stronger the material is.

Spray forming Process
In spray forming, 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 a preform on a table. Spray forming prevents the segregation of high-density alloy elements and enables melting with a uniform, fine microstructure. This is impossible to achieve using conventional melting and casting processes.

Utilizing these characteristics of the process, Kobe Steel succeeded in creating an alloy with a uniform and fine microstructure. Zinc, magnesium and copper are added to strengthen the material. In conventional melting and casting processes, when the amount of the alloy elements is increased, segregation during solidification and a coarsening of the material structure occurs. This limits the amount of the alloy elements. However, Kobe Steel's spray forming process clears these problems.

Kobe Steel originally began using a spray-forming process developed by Sandvik Osprey Ltd. in the United Kingdom. It later developed its own spray-forming process for the manufacture of aluminum alloys. Kobe Steel's spray-forming technology is currently used by subsidiary Kobelco Research Institute, Inc. to produce aluminum alloy target material used in the thin-film wiring of liquid crystal display panels. As the sample pieces of the new aluminum alloy are made by the same spray-forming equipment used to produce target material, Kobe Steel will be able to achieve volume production of the new alloy in a relatively short time. Metal ingots of up to 240 kg in weight can be produced to make large parts.

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