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Losing weight

The rising cost of fuel is driving a need to reduce aircraft weight. Currently in the spotlight is magnesium, but there are concerns about its safety, writes Ian Goold

In the eternal search to ‘add lightness’, aircraft manufacturers and suppliers are now looking to exploit new metallic alloys, despite the ascendancy of light but expensive composites. One metal with a distinguished aeronautical history is magnesium. German manufacturers developed an alloy from it during the First World War called elektron that has continued to be used in aerospace and race cars to this day.


There can be little doubt about magnesium’s basic durability – castings remain in service aboard US military aircraft after nearly 50 years – but there have always been reservations about its vulnerability to corrosion and fire.


While magnesium alloys have been developed with low corrosion rates, and coatings can also offer protection, only in recent years have aircraft manufacturers, materials suppliers and airworthiness authorities begun to work together to exploit magnesium’s inherent low weight and explore its flammability properties. Potential cabin applications for the material include passenger seats, galley carts, other furniture, and – below the floor – cargo containers.


“Magnesium is the lightest of the structural metals available, offering significant weight-saving opportunities with a density range of 1.77-1.95 g/cm3,” says Magnesium Elektron, a supplier that is working to lift prohibitions on the material’s use in passenger cabins. “Elektron alloys can be sand cast, investment cast, rolled, extruded, forged and machined.”


The alloys of choice are the company’s wrought Elektron 43 (WE43) and its Elektron 21 cast alloy, which have both given “good” performance in US Federal Aviation Administration (FAA) flammability tests, says Magnesium Elektron Market and Materials Development Manager, Paul Lyon.


But the company remains frustrated by regulations. “In 2010, we completed the installation of [a 2,750-tonne extrusion] press at our UK facility,” says Magnesium Elektron parent company Luxfer Holdings. “The press is capable of producing complex-profile extrusions, which may be significant if, at some date in the future, the FAA decides to change its current ban on use of magnesium components in the interior of commercial aircraft.”


According to the supplier, the low-weight advantages offered by magnesium alloys have not been adequately exploited due to restrictions against their use in aircraft interiors and, in particular, the passenger cabin. “The concern in [such] applications largely involves a perceived risk of fire,” claims Magnesium Elektron, which sees increased use as a way to offset fuel prices and environmental controls.


Apart from the FAA, another specific restriction comes from the US Society of Automotive Engineers (SAE) International. “It [has] a simple prohibition of magnesium and offers no supporting statement, test data, anecdotal argument or rationale,” according to Magnesium Elektron.


Aerospace proponents have successfully lobbied for FAA and SAE standards to be revised, and both agencies now have studies under way that could lead to change.


SAE has been reconsidering its position. Among ‘works in progress’, its Aircraft Seat Committee Project AIR 6160 (initiated in 2010) addresses support for “the use of magnesium alloys in aircraft-seat applications by removal of the restrictive paragraph in SAE Standard AS8049B (Para 3.3.3): ‘Magnesium alloys shall not be used’.” Magnesium Elektron is optimistic that AS8049B is “up for its five-year revision [and when] AS8049C [is] issued the restriction will be removed”. >>

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