Light touch - sustainable light alloys in transport

Materials World magazine
,
3 Nov 2010

Developing cleaner and more sustainable light alloy manufacture in the aerospace and automotive sectors is the focus of a centre of excellence at The University of Manchester, UK. Programme Project Manager Susan Davis outlines the LATEST2 programme.

Mouse over images for captions

By the year 2050, the UK has committed to reduce its CO2 emissions by 80% and also cut its unsustainable dependence on fossil fuels. In addition, as a consequence of European directives, automotive manufacturers will also have to comply with a 130CO2g/km average fleet limit, and this will fall to 80g/km.

To reach these targets, light alloy application within the transport sector is projected to double in the next decade. However, in many cases the properties and cost of the materials and manufacturing processes are inhibiting progress in weight reduction. And the introduction of new renewable technologies, such as hydrogen and biofuels, as well as hybrid and electric drive trains, are presenting further challenges for light alloys in demanding applications.

Competitive advantage

The development of sheet thickness during forming of a fine grained aluminium alloy. Sheet thickness is calculated at every step from the measurements of in-plane strain made using 3D digital image correlation. Although the deformation of this alloy<br />
is very homogenous right up until failure, the region of high strain localisation before<br />
actual failure can be detectedEuropean automotive manufacturers have shown that polymer composites are too expensive for structural applications in large volume vehicle production. Aluminium intensive body structures with cast magnesium cross car beams are already in production, although only for premium class cars. Such designs are less costly than composite-based structures and give weight savings of around 40% and a smaller lifecycle CO2 footprint based on reduced fuel consumption.

However, they can only be cost competitive with steel body shells if a high level of recycling is achieved. In future, more substantial weight savings will only become possible at an acceptable cost, through the introduction of stronger, higher performance alloys in more efficient designs that combine the best attributes of advanced light alloys with composites, laminates, and steel products in multi material structures.

Furthermore, advanced computer-based design tools enable component architectures to be optimised for increased mass efficiency. This alone can dramatically reduce component weight if the challenges of manufacturing more complex components is overcome. This future for the transport industry presents important fundamental research challenges to the materials community.

LATEST news

The aerospace and automotive manufacturing sectors are critical to the UK economy, with a turnover of £30bln and employing 600,000 people, both directly and within the supply chain. The Engineering and Physical Sciences Research Council (EPSRC) from the UK, has recently awarded The University of Manchester a Programme Grant of £5.7m over the next five and a half years, as core funding for an investment of £9m to establish a centre of excellence in light alloy research for transport applications.

Light Alloys Towards Environmentally Sustainable Transport (LATEST2) builds on an earlier five-year Portfolio Award, also from the EPSRC. The University is providing £1m with the balance of funding coming from industrial contributions.

The LATEST2 team, led by Professor George Thompson, is comprised of eight academic investigators within the School of Materials at Manchester who have extensive experience of processing, modelling, microstructure and texture control, surface engineering, corrosion control, joining and forming of light alloys, and related materials for transport applications.
Three main overlapping themes have been identified –
• Conquering Low Formability.
• Joining Advanced Alloys and Dissimilar Materials.
• Surface Engineering for Low Environmental Impact.

The first theme requires a step back to fully understand the deformation mechanics of hexagonal metals, including titanium and magnesium, before implementing crystal plasticity models that capture the influences of microstructural and texture heterogeneity, which cause strain localisation and limit formability.

Theme two, will concentrate on severe joining problems that include poor weldability of high strength alloys, interfacial reaction between dissimilar metals, thermal damage, distortion and residual stress.

The focus will be on low energy friction joining processes and surface engineering to facilitate composite-to-metal joining. Solid-state friction welding techniques are highly efficient and have the advantage of far greater weldability with a reduced risk of interfacial reaction when welding dissimilar materials.

For light alloys, microgalvanic effects are decisive in determining corrosion performance and structural durability in service. Consequently, the major inputs to theme three will be to understand the roles of intermetallic particles, local sub-surface microstructures, textures and surface roughening, corrosion susceptibility through forming and joining.

Fully equipped

The LATEST2 programme has access to an extensive suite of state-of-the-art facilities, which will expand through investments from the EPSRC and The University of Manchester. Current facilities include high resolution scanning and transmission electron microscopes and surface analysis instruments, as well as equipment for process simulation. Recent notable investments include, 3D microstructural characterisation methods, based on both X-ray tomography and nanoscale serial sectioning using dual ion-beam tomography, a sub-nanometre resolution (0.8nm SE) Scanning Electron Microscope (SEM), which will be the first in the UK, and surface and texture analysis facilities with in situ strain mapping.

Research has been targeted to maximise impact by providing the step advance in the science base required in the move towards more efficient, lower emission products, essential to maintaining global competitiveness. The project will also facilitate significant indirect benefits in terms of maintaining the knowledge base, increasing the throughput of trained engineers, improving the environment by combating global warming, and increasing public awareness of research to cultivate future generations of engineers.

The LATEST2 Team is developing effective strategic relationships with industrial and academic organisations, as well as with regional, national and international stakeholders.

High resolution focused ion beam microscopy of a mixed metal ultrasonic weld (AA6111 to uncoated steel DC04) showing the time dependant development of an intermetallic layer.

(a)-(c) Serial backscattered electron images of a corrosion site in an aerospace aluminium alloy, showing a initiation induced by intermetallic particles. (d) Tomographic reconstruction showing the 3D propagation path, with selective transparency applied to the aluminium matrix, and blue, red and yellow applied to the intermetallic phase, the intermetallic particle remnant after dealloying and aluminium hydroxide respectively

Further information

Susan C Davis, LATEST2 Programme Project Manager, The University of Manchester, School of Materials E1, The Mill, Sackville Street, Manchester, M13 9PL, UK. Tel: +44 (0)161 306 5959. Website: www.manchester.ac.uk/latest2