Lightweight contender

Automotive supplier Wagon is convinced that magnesium is the right choice for making lightweight components.

In the drive for fuel efficiency automotive supplier Wagon, with its work on magnesium alloy components, is convinced the metal is a strong competitor for making lightweight components

In the quest by automotive engineers to reduce vehicle weight, the material that has received most attention as a possible alternative to steel is aluminium. Now, another challenger is on the scene — magnesium, a metal that was being used for engine blocks before World War II.

In the effort to improve fuel economy, vehicle development is increasingly focusing on weight reduction. All-aluminium construction for a car produced in relatively high volumes finally become a reality with Audi’s A2 hatchback.

Tom Chatterley, head of the materials engineering department at the Motor Industry Research Association (MIRA), says: ‘Aluminium is a big growth area. What we are seeing in mass production is coming mainly from Germany, but most vehicle manufacturers are looking at using larger quantities of aluminium and possibly full aluminium structures within the next three years.’

But UK automotive supplier Wagon is pushing forward with magnesium alloy components because they are lighter than other metals, including aluminium. The company expects to have magnesium products in luxury cars within the next five to 10 years.

A competing alternative

Magnesium could become a competing alternative, not for the next generation of new models, but initially for luxury cars currently on the drawing board. Its application to automotive design is not new. The Volkswagen Beetle, when first produced Germanyin the 1930s, had a magnesium alloy engine.

Chatterley suspects magnesium fell out of favour because fuel efficiency was not then a priority.

He says: ‘We are at the limit of engine performance, so the only thing left is to reduce vehicle mass or improve aerodynamics.’

He says: ‘Companies are working on magnesium structural cross beams, for example, and we can expect to see various components in production by 2003.’ He foresees the metal becoming a preferred material in car fascias, cylinder heads, instrument panels and wheels.

Wagon has a history of working with lightweight metals, winning a quality award from Audi for its work on the A2 model. Wagon’s Frankfurt plant uses 10,000 tonnes of aluminium a year. Employing 1,000 people, the plant produces 2.2 million doors each year, and has been designated a technical centre of excellence for door structures.Over the past 30 years car door weight has halved and the number of parts in a door frame reduced. Wagon, which sees magnesium as the cutting edge technology for door frames, wants to be at the forefront of this trend.

Axel Schulmeyer, managing director of Wagon Europe, says: ‘Some people point to the fact that there is no experience of volume production in magnesium, to the expense of the material, and to the fact that it is not yet available in the same quantity as aluminium — but for us, these are not reasons to avoid it.’

Wagon’s current aluminium design is made from strips of metal press-formed into profiles, which are then stretch-bent into the necessary contour. Stretch bending involves taking a long profile and forcing it into the required shape by bending it round with hydraulically driven tools. These profiles are then joined together using metal inert gas welding.

Wagon wants to replicate this process with magnesium. Its choice of magnesium alloy is a combination of 96% magnesium, 1% zinc, and 3% aluminium. Pure magnesium is flammable and highly reactive with water but this alloy is as inert as steel or aluminium itself.

Development processes

While initially developing the press metal and welding approach, in the longer term Wagon expects some combination of die casting, pressing and welding to emerge as the best method for mass production. Wagon has produced a prototype door window frame in magnesium, using a mixture of die cast and pressed profiled parts.

In addition, the company’s engineers faced the issue of whether the new designs can achieve the performance expected of door structures in crash tests. However, magnesium has greater tensile strength than aluminium, and tests revealed that it was as good as aluminium in static load testing, and performed even better than a steel door frame. In developing its aluminium production processes to operate with magnesium, Wagon engineers found that stretch bending was 30% faster and the MIG welds were 40% stronger than in their aluminium counterparts. Overall, in comparison with aluminium, magnesium door structures will incur a a 20% increase in process costs and a 20% increase in material costs, but will achieve a 20–25% decrease in weight.

The company’s next step will be to develop engine supports and instrument panel cross sections, which it hopes to manufacture from spring 2001.

Ultimately, Schulmeyer believes that progress in the use of magnesium components will help to reduce the typical car’s petrol consumption from the 8–10 litres of petrol currently needed to cover 100km to a figure of four litres or less.

He says: ‘People have mainly been put off magnesium by the manufacturing difficulties. Now that those have been overcome, volume and cost will be addressed — in the same way as they were for aluminium some years ago.’