Weight watchers

One of the UK’s oldest established car makers is to collaborate in a pioneering R&D project to make a lightweight car chassis from extruded magnesium sections.

One of the UK’s oldest established car makers is to collaborate in a pioneering R&D project to make a lightweight car chassis from extruded magnesium sections.

AC Cars and Alubin of Israel have won e3.1m (£2m) of funding from Eureka, the European network for market-oriented research and development, for the three-year project.

Magnesium is strong and has only a quarter of the density of steel, and two-thirds that of aluminium. Car makers are desperate to save weight in their vehicles because of the benefits to perform-ance, handling and especially fuel economy. Magnesium also has good energy-absorbing characteristics which promise good crash performance.

The metal is used to a small extent by the car industry – Volkswagen, for example, has used it for components such as gearbox casings – but only in the form of castings. Use of extruded magnesium is almost unexplored and alloys suitable for extrusion are not widely produced.

The project will also include an economic assessment of other potential applications for the new technology.

Alubin has comprehensive facilities for producing, extruding and finishing aluminium and for the last four years has been a pioneer in magnesium extrusion.

AC Cars chairman and chief executive Alan Lubinsky approached Alubin around two years ago to propose collaboration. ‘Alubin was comfortable with the idea of taking a proven chassis, with known hard points and forces, as a simple way to move forward,’ he said.

The project will take AC’s existing ladder-frame chassis, a well-proven design in tubular steel, and replicate it in magnesium with essentially the same geometry – though Lubinsky added that there could be changes as the project progressed. ‘We have people already looking at the figures to see what magnesium sections we would need to have similar properties.’ So far, he added, no problems had been encountered.

Alubin participated in the Israeli Consortium for the Development of Magnesium, which ran until 2002, to develop alloys with better plastic deformation characteristics needed for extrusion. It now manufactures small extruded sections. Alubin chief executive Gal Segal said: ‘For the AC project we will develop the possibility of extruding bigger profiles.’

The company is continuing to work on improved alloys in another Eureka project involving six partners from Israel and the Netherlands, and is also looking into ways of modifying the crystal structure of the material used in the extrusion process. ‘Magnesium is harder to extrude than aluminium. The matrix of the metal is hexagonal, whereas aluminium is cubic,’ said Segal.

Another problem, said Segal, is that magnesium billets, the starting point of the process, are not widely produced with the right shape or physical properties for extrusion, and are expensive.

Alubin plans to cast its own billets using the direct-chill method, well-established for aluminium. In the process the molten metal is drawn into the mould at a controlled rate while the outside is cooled. The finished casting has a good crystallographic structure with a small grain size, which improves strength.

At the end of the project AC expects to have a chassis it can put into production. It also plans to license the technology to other car makers, expected initially to be other low-volume specialist car builders. He added: ‘Once we’ve got the chassis, the next stage would be to look at other parts, such as suspension components.’

AC is generally known more for being traditional than for innovation, but it was an early user of glass fibre for footwells in the 1950s. In 1999 it became the first manufacturer to introduce a one-piece carbon fibre body, in its CRS model.

Currently, it hand-builds the steel chassis and aluminium body for its Cobra marque in Frimley, Surrey. This is then exported to Shelby Automobiles in the US for completion. It is currently commissioning a plant in Malta for the composite-bodied car.

On the web