Automotive body sheet – bright outlook for aluminium?

Expanded ABS capacity will be required

The automotive sector remains the dominant global market for aluminium components, especially in North America.

While aluminium has been able to largely conquer the drive train and heat exchanger areas of vehicle build, the chassis, body and general equipment and fittings must be regarded as areas for further potential development in lightweight construction using aluminium. The key issues have revolved around optimising the design to exploit the advantages of aluminium and, at the same time, be cost-effective. The body-in-white (BIW) accounts for about 27% of the weight of the entire average car. So it is in this area that development, innovation and further large-scale penetration of aluminium must continue.

Body-in-white – BIW – refers to the stage in automotive design and manufacturing at which a car body’s sheet metal components have been welded together. BIW is defined as the stage prior to painting and before moving parts (doors, bonnets, tailgates and hatch back doors, as well as bumpers), the engine, chassis sub-assemblies, or trim (glass, seats, upholstery and electronics) have been assembled in the frame structure.

Part-by-part substitution of aluminium for steel in body components and other parts, although realizing benefits of weight reduction, better corrosion resistance and other beneficial characteristics, is not the optimal solution. Since the majority of cars produced around the world still essentially comprise a higher steel content, a complete redesign of the automobile is necessary to make optimal use of aluminium.

Some aluminium and auto companies have promoted the aluminium space-frame design using stampings, castings, and extrusions of aluminium. Others have been developing the conventional unibody design, which is essentially a stamped aluminium body.

Pessimism dismissed

Despite the potential and proven benefits of deploying more aluminium, according to London-based CRU, independent multi-commodity market analysis and consultancy authority, addresses some of the doubts recently expressed in some corners of the North American market about forecasts of large increases in aluminium auto body sheet (ABS). The main argument is that there have been no major announcements following Ford’s aluminium-intensive redesign of its F-150 pickup truck, and without this momentum, no more are likely. There have even been statements suggesting that Ford will revert to steel for the F-150 when it reconsiders the position.

growth of abs

Resilient growth of aluminium ABS (Data courtesy: CRU)

Lloyd O’Carroll, CRU’s Senior Aluminium Analyst for North America and formerly Corporate Economist at Reynolds Metals Company, believes such pessimism to be unfounded, for three key reasons. First, the new ABS capacity coming on line over the next few years is already substantially committed and indeed contracted. Second, announcements of redesign by auto OEMs are not made in advance for competitive and marketing reasons.  For example, Ford admonished its suppliers when there were early leaks of details about the F-150. Ford’s recent announcement of the redesign of its Superduty F-250 and F-350 trucks was made less than a year before planned implementation.
Ford F-150

Ford’s aluminium-intensive F 150  truck, setting a material re-design trend? (Courtesy: Ford Motor Co.)

So, the lack of announcements on the redesign of the 2017 to 2020 models does not necessarily mean that they will not actually be implemented. Third, vehicle redesign incurs quite expensive engineering costs. Consequently, a vehicle model, once designed, typically has a market life of seven to nine years with only annual cosmetic changes: In some cases, there is a mid-cycle “refresh” – a partial redesign for slow-selling models. So CRU maintains, it is unrealistic to expect the success of the F-150 to trigger redesigns of other models in just a few years. Such redesigns can only be expected to be implemented over a longer period to coincide with the normal model redesign cycle. Hence CRU expects most major aluminium-intensive redesigns only in the 2020-2025 period, when the pressure from increasingly stringent CAFE standards will have greatest impact.

CRU believes that the rapid growth of ABS over the next five years will be driven more by the conversion to aluminium of closures – bonnets, boot lids, roofs and doors – commonly known as “hang on parts”. While adding aluminium closures to existing designs does not maximise the benefits of aluminium, it does still achieve substantial weight savings at a low engineering cost. It is understood that OEMs are aggressively seeking to convert closures to aluminium over the next five years, and this would add significant volume as a result.

Demand and required capacity

The extent of the growth of ABS over the next several years will be governed by prevailing capacity. The vast bulk of ABS is used in exterior skin applications that require wide coil with both outstanding surface quality and strength. The latter is achieved with heat-treatable alloys and both properties require a rolling mill with those characteristics, usually a can sheet mill with a complementary continuous heat-treatment line. This production combination is only achieved with dedicated capacity since conversion of a can stock mill to an ABS facility and adding a heat-treat line involves considerable time and plant expenditure. Furthermore, rolling mills are not committing investment required to convert capacity without guarantees of minimum volumes and prices for a major portion of this capacity – and this is why much of the growth expected up to 2020 is already committed.

CRU’s forecasts show that ABS demand in North America, for both closures and structures, will grow from 330,000 tonnes in 2015 to just over 1 million tonnes by 2020. The robust growth in demand over the past two years reflects the conversion trend to aluminium such as in the Ford F-150, but much of the growth in the next few years will be generated by the increased use of aluminium in closures.

Over the long-term, an anticipated increase in demand will be met in part by new technologies used in the production of automotive sheet. The Alcoa Arconic Micromill, for example, promises penetration for non-skin applications where the formability limitations of current alloys make it difficult to use aluminium. Specifically, the Micromill offers a low-cost process for continuous casting of new higher-strength alloys, which are 200% more formable than current aluminium generations and 25-35% lighter than high-strength steel (HSS). Alcoa’s mill is specifically aimed at interior BIW applications competing with HSS.

Capacity beyond Alcoa’s current mill in San Antonio will be needed in order to supply larger volumes for wider applications. However, capacity can be added much more quickly and at lower cost than in conventional mills. While not included in its base forecast, CRU says capacity expansion announcements could be made in the next one or two years.

The prime driver for aluminium ABS demand growth in the long term is the requirement of increasingly stringent CAFE standards for combined cars and light trucks – from only 27.5 mpg in 2010 up to 54.5 by 2025

The strategies that will be implemented to achieve these standards include:

  • Improved engines and transmissions, which could achieve 50-60% of targets, but at a cost.
  • Hybrids that can make savings but are expensive.
  • Electric vehicles, which will grow in numbers over the very long term.
  • More diesel cars: However, the image and reputation of diesels were damaged following VW’s recent situation, and consumer acceptance has likely been affected. With limited availability and higher price for diesel fuel compared with gasoline in North America, unlike Europe, market acceptance could be a problem.

CRU believes that an increasing move to lighter vehicles while retaining the size and features that consumers demand, will likely be critical in meeting the CAFE requirements.

We believe that:

  • Reduced vehicle mass directly reduces fuel consumption and CO2
  • Further mass reductions and lower fuel consumption are generated in a multiplier effect by enabling, for example, smaller engines, wheels and brakes.
  • A lower vehicle center of gravity improves handling and safety.
  • But, most important, lightweighting allows production of larger vehicles that Americans want to buy.

Overall, reducing weight is complementary to all other strategies.
The main goals for the auto industry moving forward are to increasingly incorporate increasing amounts of lighter materials while accepting the substantial re-engineering required.

Among lightweight materials contenders, CRU identifies: carbon fibre and magnesium as the lightest alternatives but only in niche applications due to property limitations and very high cost. The major winners are aluminium and – High Strength Steel (HSS), while the main loser is mild steel.

In the ongoing aluminium vs steel debate, CRU highlights the advantages of aluminium as: lighter weight, greater stiffness – due to metallurgy and joining processes including application of adhesives, which deliver improved ride and handling; safer – absorbs more energy in event of a crash; better corrosion resistance; outstanding surface quality, and lower total production of CO2.

Challenges for increased application of aluminium center on the formability of certain alloys and issues associated with bonding, forming, assembly, and recycling, particularly involved with segregation, and realizing required strength in various alloy combinations.

CRU says that it expects, by 2025, to see many vehicles being redesigned as multi-material incorporating aluminium ABS and HSS, with mild steel content dramatically reduced. The proportions are likely to vary significantly from vehicle to vehicle and from OEM to OEM. Light trucks and SUVs will contain the highest aluminium content. Larger and more expensive vehicles could have higher than average content of aluminium, while smaller, lower-end vehicles will retain more mild steel. The one certain thing, CRU concludes, is that the CAFE standard in North America and emissions standards in the rest of the world will substantially impact vehicle design and fuel further moves away from the status quo.


Ken Stanford gained a B.Met. in Metallurgy and Materials Science from the University of Sheffield and an M.Sc. In Science & Technology Policy from the University of Manchester, UK.

Formerly Group Managing Editor and Technical Director at DMG World Media in the UK, responsible for editorial in publications including Aluminium International Today, and also the ALUMINIUM series of events, including in Germany and the USA. Particular industry interests centre on sustainability and environmental issues, new technologies, innovations and applications.

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