World's strongest aluminum alloy

April 26, 2007
A new patent-pending aluminum alloy from Kobe Steel is made using a spray forming process and is said to be the strongest aluminum alloy available.

It has a tensile strength of 780 MPa. That's reportedly 10% 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.

The ductility of Kobe Steel's alloy is also high. In general, as strength increases, material workability goes down. However, with a breaking elongation of 14%, the new material has nearly three times the ductility of Weldalite's 5%. Ductility is 1.4 times that of titanium alloy. Additionally, it reportedly 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.

"The aluminum alloy is a candidate where high performance is required," says 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."

Spray Forming Process

In spray forming, molten metal is "sprayed" into droplets and quickly quenched, and transforms from liquid to solid state. Molten metal in an induction furnace flows from a small hole in the bottom of the furnace. Nitrogen gas blows over the molten metal as it exits the furnace, atomizing the material into a fine mist of droplets. The droplets accumulate and solidify on a table into a preform. Spray forming prevents 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.

The result is an alloy with a uniform and fine microstructure. Zinc, magnesium and copper are added to strengthen the material. In conventional melting and casting processes, the amount of the alloy elements is increased, and segregation during solidification and coarsening of the material structure result. This limits the amount of the alloy elements. Kobe Steel's spray forming process eliminates these problems.

Kobe Steel originally began using a spray-forming process developed by Sandvik Osprey Ltd. 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 can be produced to make large parts.

Sample bars are currently 10-mm in diameter and 100-mm long. Kobe Steel is working to establish the technology to mass-produce bars, wire rods, shapes and plates made of the alloy.

To see how the new aluminum alloy stacks up to other aluminum alloys, click here

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