Magnesium partnership eyes low-volume production
A university has partnered with the world’s largest magnesium component producer in an attempt to dispel myths and make the light metal more practical for low-volume applications. Simon Frost reports.
It’s two-thirds the weight of aluminium, 100% recyclable and the eighth-most abundant element in the earth’s crust – so why don’t we use magnesium more? Hoping to answer this question and increase the material’s industrial reach, Birmingham City University (BCU), UK, has formed a strategic alliance with the world’s largest producer of magnesium components.
Meridian Lightweight Technologies UK, the Nottinghamshire-based arm of the international magnesium producer founded in Canada, signed an exclusive partnership with BCU in January to work together in R&D and education, with a focus on changing attitudes towards magnesium and improving its suitability for low-volume manufacture.
Speaking to Materials World, Makhan Singh, Development Manager at BCU’s Institute for Sustainable Futures, said, ‘In the UK, magnesium isn’t taught in schools or even universities as a prime material. When I think about my engineering degree, many years ago, I remember learning about plastics, thermoplastics, steels and aluminium, but magnesium never came into the curriculum.’
When engineers leave university and enter industry, he says, it is understandable that they design products to be made with the materials they know best. ‘Having worked for Land Rover for five years and held several senior appointments in the automotive industry over a period of 25 years, I have been surprised by the lack of knowledge of magnesium in the UK.’
Misguided fear of flames
BCU’s newly formed Magnesium Innovation Group pairs engineers from Meridian with ten of the university’s academics – eight in science and technology and two psychologists, who will interview engineers across the UK to better understand the roots of this apparent aversion to designing with magnesium.
‘People know magnesium as an ingredient in fireworks – they associate magnesium with fire,’ said Singh. This, he believes, led to a popular myth that magnesium’s flammability makes it unsafe. But it is not only the general public, as Steve Brown, Engineering Manager at Meridian UK, added, ‘Misconceptions of magnesium in the industry are still rife. A lot of people still believe it sets on fire easily. It doesn’t, but the myth still dictates most people’s present understanding, including engineers.’
Paul Lyon, Programmes Technology Manager at Manchester-based Magnesium Elektron, UK, told Materials World, ‘Usually, when we speak to designers and engineers, they have that image of magnesium ribbon being set on fire at school – that's the part that people remember, and if that's the only experience they have with magnesium then that stays in their mind.’
However, while magnesium is not the simplest material to extinguish when alight – it continues to burn in nitrogen, carbon dioxide and water – its thermal conductivity makes it difficult to ignite in the first place. ‘Magnesium is one of the best metals in terms of flammability, because it dissipates heat across its body so well, whereas steel, for example, localises the heat, so it can get very hot much more easily,’ said Singh.
The experiment popular in schools works only because of the magnesium ribbon’s high surface area compared with its low volume – proportions that wouldn’t be used in any application and which make it easy to surpass its melting point. ‘A similar experiment with iron wire ignited in oxygen was popular in schools, but people tend to forget that one because the magnesium experiment is more exciting to watch,’ Lyon said.
Turning down the volume
Attitudes towards magnesium aside, the partnership also aims to overcome technical challenges relating to high-pressure die casting (HPDC), particularly in making the process more applicable to low-volume components. ‘We’re trying to see what we can do to allow small volume companies like Aston Martin, Lotus, Bentley and Rolls-Royce access to magnesium. Aerospace, too, is a relatively low-volume industry,’ said Singh.
Difficulties in manufacturing relatively small product runs using HPDC stem from the up-front costs involved in equipment and tooling manufacture, complex tool and die setup involving multiple runners, and lengthy die changeovers.
‘Once the die is set up, you can be churning out a part every minute – so, you could produce enough of a particular part to last a small manufacturer a year in about three weeks,’ Singh explained. ‘A die changeover, however, can take a full day, so once the die is in place, you have to produce as many parts as you can. For low-volume companies, that is impractical, because the cost becomes so high, and the components then can’t be adapted at short notice.’
Brown added, ‘The up-front costs and unique equipment require a high volume to make a justifiable business case. However, if we can identify and develop some common platform parts to offer the industry, then the lower-volume vehicle manufacturers can also benefit from lower-cost parts that can be “tweaked” by secondary means to suit their needs, if necessary.’ Other methods, Brown said, are less repeatable, as the processes can involve either individual moulds or higher running costs per part.
Magnesium on the mind
The partnership is as much about adapting technical strategies as making engineering designers aware of the benefits of magnesium in components for which they would typically turn to aluminium.
‘Aluminium alloys cannot be manufactured in as thin a wall stock as magnesium, as it doesn't flow as well through the mould during the HPDC process. This also means the expensive dies and tooling deteriorate far more quickly with aluminium,’ said Brown. Rather than make changes to the process, he says, they must ensure that magnesium is in the designer’s arsenal.
The raw material, he admits, is twice as expensive as aluminium, but Brown does not see this as insurmountable. ‘With good design and engineering, a magnesium part can be produced to match the equivalent aluminium part in cost. The secret is to make sure the part is developed as a magnesium part and not as an aluminium part, which is a common mistake made in most industries. A well-designed magnesium part can match any aluminium part’s cost easily, as the magnesium part uses less volume and weight. If the part is half the weight, then the material is cost neutralised,’ he told Materials World.
Meridian and BCU’s hope is that demand for magnesium increases, reducing the price, as was the case for aluminium. ‘If the smelting industry invests in its production then magnesium prices will decrease in the same manner,’ Brown said. ‘It should be no more expensive to extract than aluminium, providing the same investment is made as usage increases. Aluminium is massively over-used in my opinion, and magnesium will play a big part in weight saving developments in the future.’
Reclaiming heat and removing dust
The partnership is also interested in recovering heat from production – Singh gave the example of the Abbey Stadium Leisure Centre in Gloucestershire, which heats its swimming pool using waste heat from an adjacent crematorium. ‘This is one of the areas in which BCU is going to prove invaluable to us, and our aim is to make Meridian a leader in this field,’ Brown said.
Finally, they will examine how to reduce the fire risk when linishing – filing sharp edges off a cast component, which creates magnesium dust particles that are more liable to ignite than the material in bulk.
‘As with flour, wood, aluminium and steel, it is dangerous in its dust form. These industries have to extract the dust and use fire suppressant technology, and we are no different,’ Brown said. ‘The best way to continually reduce the risks is by improving automation and containment so the suitable extraction equipment can be most effectively used […] working with BCU, we intend to continue on this path and develop further improvements to remain vigilant to the risks that exist in all industries where fine material is seen.’
The partnership has lofty ambitions for magnesium and, given the thrust towards light-weighting and recyclability throughout engineering, it is easy to see why. As Brown summarises, ‘With good design and knowledgeable engineering, magnesium can replace most commonly used materials in both structural and non-structural applications. Its strength-to-weight ratio is the best of any fully recyclable natural material.’
The Magnesium Innovation Group will present their initial findings at a conference planned for July 2017.
Until recently, the Society of Automotive Engineers’ (SAE) Performance Standard for Seats in Civil Rotorcraft, Transport Aircraft, and General Aviation Aircraft (AS8049) banned the use of magnesium alloys in aircraft seats.
‘It was quite surprising, bearing in mind that sand cast magnesium is used in aerospace applications such as engine and gearbox casings. Some helicopters actually hang from the structural magnesium alloy gearbox,’ Lyon said.
In August 2015, following the best part of a decade of development and testing by Magnesium Elektron and the Federal Aviation Administration, USA, SAE amended AS8049, allowing magnesium alloys to be used in aircraft seat construction provided they meet flammability requirements.
Magnesium Elektron’s alloys Elektron 43 (a light, high-strength wrought alloy containing yttrium, zirconium and rare earths) and Elektron 21 (a high-strength, heat-treatable casting alloy containing zinc, neodymium, gadolinium and zirconium) were found to be as safe as the wrought aluminium alloys currently used.