The aluminium industry and metal replacement

While many associate exotic materials with weight reduction, the aluminium industry is keen to remind engineers it is also part of the solution. Justin Cunningham reports.

The buzz word is metal replacement. Replacing those heavier older components with a plastic or composite is surely a logical exercise for anyone wanting to shed a few kg. Cars today, for example, are reportedly 50% by volume one type of plastic or another, but that represents only 10% of the overall weight.

So, with all this talk about metal replacement where does the aluminium industry fit in? While it is a lightweight option, is it in danger of being overlooked in favour of exotic, lighter, alternatives?

“It’s really tempting to assume that at some point everything is going to switch to plastics and composites,” says Ian Oliver, communications manager at the Aluminium Federation (ALFED). “But the reality is we are moving towards multi-material products, and every manufacturer is coming at the problem from a slightly different angle.

“And this is not a static situation, research into composites, aluminium and high strength steel is all happening, so it is very much a moving picture. But we do see metals as fundamental to manufacturing, despite what many people may say.”

Selecting materials to produce a car chassis is no longer a straightforward choice these days. BMW, for example, has put in place its own carbon fibre supply chain and is producing monocoque ‘tubs’ for both its i3 and i8 models (pictured below). The other extreme is the new VW Golf mk7 that has managed to reduce weight by 100kg despite the chassis being an all steel construction. And then, of course, there is JLR that has been resolute in its application of aluminium, firmly believing that it is the Goldilocks material of choice between the extremes of composites and steel.

“The Jaguar Land Rover range is generally aluminium intensive,” says Oliver. “And there are other examples around the world, the Ford F-150 pickup also having gone that route.”

A big enabler for aluminium is the joining methods available that include riveting and adhesives. JLR has had to adopt new machinery and tooling on its production lines, but while investment has been described as ‘intensive’, any switch to composite materials would likely be a different order of magnitude altogether.

Oliver explains: “There is a place for composites, but in mass production markets they’re still some way off being competitive when it comes to producing in volume.”

Aluminium at a glance

? JLR uses 50% recycled materials in their cars
? UK now produces 45,000 tonnes of aluminium a year. Worldwide production is 50 million tonnes
? It is estimated that three quarters of aluminium ever made is still in use

Despite the aircraft industry moving to composite materials in a major way, ALFED says that volumes of aluminium in aerospace are still growing. And, for these reasons, it’s confident about the continued growth of aluminium in the automotive sector as it can be a significant part of the lightweighting conundrum.

“We are seeing many adopt, what I would call, an aluminium-rich product,” says Oliver. “The body of the Mercedes C Class is 25% aluminium, for example, and that saves 40kg. And the new Mazda MX5, despite still being basically a steel car, uses a lot of aluminium. And we are seeing more of that.”

Compared to composites
Engineers on the whole are open to using exotic materials, but are put off because of the difficulties in building a viable business around a composite product. There are all sorts of complications and issues in the supply chain, in repair and recyclability, in the tooling and skills needed, and of course, the premium cost. Many have seen the initial advantageous headline weight savings quickly erode due to unforeseen complications.

This has led to a conservative approach by some. Individual components such as bonnets, roofs and tailgate are being increasingly made from composites, but only where it makes sense to do so. It’s a case of being selective. Making the roof from carbon fibre, for example, will lower centre of gravity and that then gives other advantages throughout the car.

The key phrase often muttered is: ‘the right material in the right place’. But this is only half the story. Design engineering should be about exploiting inherent properties, by making components that make the most of the materials used.

“It’s fine saying, yes, we’ll make this panel, which used to be in steel, in aluminium, and save 40% of the weight,” says Oliver. “But, the real benefit is when you ask, ‘does this material – and it may be aluminium, magnesium, or composites – enable us to amalgamate components or make new components because we’re using a different material?’ That’s when it becomes really exciting.”

There is no doubt aluminium is itself a part of the metal (and by metal we mean steel) replacement story. Engineers are certainly open to identifying components that might firstly be more suitable for aluminium, as opposed to a composite. Interestingly though, ALFED doesn’t see aluminium as a competitor of steel. Instead it firmly views itself - and aluminium - as part of the metals sector and is keen to remind engineers that all metals still very much have a key role to play.

The problem with aluminium
Despite the increased interest, the UK is home to just one aluminium smelting plant operated by Rio Tinto Alcan in Fort William, Scotland. Aluminium plants use a phenomenal amount of electricity, and so tend to be located very close to hydro-electric power plants, as the cost of electricity is prohibitive to a profitable operation.

However, while virgin aluminium from bauxite ore consumes enormous amounts of electricity, recycling the material requires just 5% of that by comparison. This has seen Jaguar Land Rover develop an aluminium alloy based on 50% recycled content. The new grade will save cost as well as lifecycle CO2, and will be used on new vehicle programmes.

JLR’s senior manager for body structures, Simon Black, says: “For the Range Rover, 63% of the carbon footprint comes from vehicle use, and 27% from material production.

“We call the new alloy RC5754, which can take up to 50% scrap from our in-house processes.”
The plan is to push the recycled content of 5000-series alloys up to 75%. This will require the implementation of the recycling process at suppliers, and will also mean using post-consumer waste such as aluminium beverage cans.

Justin Cunningham

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