Context
Introduction - from the Management Team
With a turnover of £30 billion and employing 600,000 people directly and within the supply chain, it is difficult to overstate the importance of aerospace and automotive manufacturing to the UK economy. Our over-dependence on fossil fuels is clearly unsustainable, both in terms of the demand on supply and the effect of the pollution it creates. The world produced approximately 35 billion tonnes of carbon dioxide in 2011, which is double that seen only twenty five years ago. This upward trend can be attributed to the rapid industrialisation of Brazil, Russia, India and China (BRIC) nations and continued world population growth (Figure. 1). Transport is currently responsible for 14% of global emissions of which road traffic accounts for by far the greatest share. Airbus predicts a more than doubling of the world passenger airline fleet by 2030 and, while this presents an unprecedented business opportunity with an estimated value of $4 trillion in aircraft orders, this growth rate is unsustainable without a step change in fuel efficient airfcraft designs. Fortunately this impending crisis is now being taken seriously by governments and industry. In the EC the automotive sector is on track to reach the 130 CO2 g/km average fleet limit by 2015. However, the next target of 95 g/km by 2020 is far more demanding and there is already talk of a 65 g/km limit by 2050. Other important aspects of sustainability include the impact of the entire product life cycle, and thus the avoidance of the use of energy intensive materials and manufacturing processes, as well as issues such as resource scarcity. Energy use in transport is closely linked to vehicle mass and, due to the low energy storage density of batteries, electric vehicles also need to be as light as possible to extend their range to the level where they become a credible alternative.
Annual global CO2 emissions, by sector [Center for Climate and Energy Solutions]
Materials and manufacturing technology is now advancing at a frenetic pace to meet this challenge, with demand out-stripping the supply of new scientists and researchers across the sector. LATEST2 is thus proud to be involved in the Sheffield-Manchester EPSRC Centre of Doctoral Training (CDT) in Metallic Systems, which is aimed at providing high quality, industrially focused, PhD graduates to become the next generation of metallurgical specialists.
In order to reach these ambitious emission reduction targets, applications for light alloys within the transport sector are projected to more than double in the next decade and the trend is accelerating. However, in many cases the properties and cost of the materials and manufacturing processes are inhibiting progress in weight reduction. In the automotive industry the material mix depends on the intended market position. At one end of the market the high volume sector is currently still dependent on steel intensive vehicles. At the top end, carbon fibre reinforced composites are increasingly making their presence felt, but until the cost falls below $10 /kg CFRP will not enter the mass car market. In between these two extremes, in order of volume, companies are introducing hybrid steel-light alloy designs, fully light alloy car bodies and light alloy CFRP composite multi-material products. With reducing costs and increasing pressure it is predicted that the higher cost options solutions will move to higher volume production and fully steel vehicle bodies will soon be replaced with a light alloy intensive multi-material approach. Indeed, the slogan ‘right material, right place’ has become the mantra of many automotive designs teams. Examples include the ultra-high strength boron steel safety cell with aluminium crash members and closure panels used by Daimler in the 2013 S-class, the new aluminium intensive Jaguar Land Rover (JLR) product range that involves widespread use of magnesium die castings and the CFRP composite- aluminium BMW3i, which incorporates an aluminium intensive chassis, or ‘drive module’, with a carbon fibre body, ‘life module’.
To be able to introduce more lighter materials in vehicle designs there is an increasing focus on offsetting their higher cost by reducing the part count through the use of larger integral components and nearnet- shape technologies. A further issue with the use of carbon fibre composites is that they currently require 286 MJ/kg to produce compared to 23 MJ/Kg for recycled aluminium, and this energy is not recoverable as CFRPs cannot be recycled into the same product form (Figure 2).
Comparison of the energy required to produce 1 kg of aluminium, steel and carbon fibre reinforced plastic.
In the aerospace sector metals use is also rapidly changing. The first generation of composite dominated multi-material aircraft that are now entering service still contain over 40% metallic structure but have a much higher reliance on titanium alloys owing to incompatibility problems between CFRP and aluminium. The greater use of expensive materials like titanium has increased the focus on near-net-shape manufacturing processes to improve the traditionally high buy-to-fly ratio, and similar issues have been highlighted in automotive manufacturing where reducing costs through greater use of integrated structures and new joining technologies is a high priority. New higher performance titanium and aluminium alloys will also be substituted into existing legacy airframe designs to achieve incremental weight savings for many years to come and essential research is required to industrialise potential solutions for hexavalent chromate replacement, to comply with Registration, Evaluation, Authorisation and restriction of Chemicals (REACH) legislation. In the UK Airbus are investing £1 billion in the ‘wing of the future’ to develop new ultra-efficient wing concepts, an ambitious project in which LATEST2 has recently been invited to participate.
In this rapidly changing landscape it is essential to develop the knowledge base that supports advanced metals manufacturing. LATEST2 endeavours to continue to serve this role by providing a fundamental view on strategically important materials issues. Examples within the three themed areas of forming, joining and surface engineering include: developing crystal plasticity models of important materials like magnesium and titanium so that we can use sound scientific principles to improve formability of higher specific strength materials than are currently used in industry; developing models of interface reaction between dissimilar metals so that we can design alloy compositions, or coating systems, that prevent intermetallic compound formation during welding dissimilar metals like aluminium to magnesium, or titanium; studying the fundamentals of electrochemical oxide growth on metals so that we can tailor surfaces to have better performance in both corrosive environments and for adhesive bonding and paint finishing, with lower energy input processes.
LATEST2 benefits from the ‘joined-up’ style of the multidisciplinary team, which allows an integrated approach to tackling challenging problems. For example, 7xxx aluminium alloys have the potential to deliver yields stresses in excess of 600 MPa and could be used in automotive applications with a substantial weight saving if we can better understand how to form them with a cost-effective process. However, at the same time, we also need to tackle the poor stress corrosion behaviour of 7xxx service alloys, particularly when welded, or around self-piercing rivets or fasteners. Other important topics that benefit from this multidisciplinary approach include: the effect of surface deformation in situations such as forming or rectification on corrosion; protection of heterogeneous microstructures associated with welded joints; development of surface treatments to improve adhesion on titanium - composite hyper-joints; the transfer of microstructure models developed for welding processes to predict product variability in additive manufacturing; and the prediction of the influence tramp elements accumulating in closed loop recycling on forming and corrosion behaviour.