Traditionally automotive manufacturers have used two methods to increase a vehicles performance; increased engine size or overall weight reduction. As more countries introduce green initiatives and potential bans on internal combustion engines are being mooted, larger engines are no longer an option. The need to reduce a cars weight to increase its performance is even more important with the rise of electric vehicles; the overall weight of the car needs to be drastically reduced to counter the weight of the batteries.
Before bans on the sale of cars with internal combustion engines are put into place, which many countries governments are already suggesting could happen in the middle of this century, the United States is pushing ahead with increases to its CAFE (Corporate Average Fuel Economy) standards. The target set in 2012 for vehicles to reach by the 2025 model year is a fleet average of 54.5 mpg. The way most car makers are responding to this is to reduce vehicle weight.
Discounting the use of composite materials for mass production, which are expensive to use and have the further complication of being difficult to recycle, most automotive manufacturers are investing in either new types of advanced high-strength steel (AHSS) or turning to aluminium to replace the traditional use of steel, not only in body panel but increasingly in chassis components too. Total aluminium content is expected to grow from 397 lbs per vehicle in 2015 to 565 lbs per vehicle by 2028, representing 16% of total vehicle weight, according to the Aluminum Content in North American Light Vehicles 2016 to 2028 study by Ducker Worldwide.
One of the latest examples of a move away from steel in favor of aluminium is the latest version of the iconic London black cab. The latest model, the TX, utilizes aluminium in its construction in order to dramatically reduce the vehicles weight. The all-aluminium body structure used in the TX is bonded together with special adhesives and is 30% lighter than an equivalent steel body.
Norwegian aluminium producer Sapa reopened its facility in Wales, UK, in order to be able to supply LEVC, the manufacturer of the cabs, with the material it needs for the body structures.
In other markets, however, there are producers rebalancing their metal usage in favor of steel. When Audi launched the A8 in 1994, it featured an all-aluminium body-in-white and, more significantly, was the first mass-market car with an aluminium chassis. Now, steel producer and Audi supplier, ArcelorMittal has announced that the 2018 year model A8 will contain 40.5% steel, 58% aluminium and 1.5% other materials. This compares with 8% steel and 92% aluminium in the 2008 version.
Around 17% of the new A8 body structure will comprise press-hardened steel (PHS), some of which will be supplied by ArcelorMittal, the steelmaker said. The strength-to-weight ratio of these grades outperforms even the most advanced and costlier aluminium grades.
Advanced high-strength steels
One of the latest developments in steel for automotive use from ArcelorMittal is its third-generation cold stamping steel Fortiform. It is a range of advanced high-strength steel (AHSS) that the steelmaker says can offer weight savings of between 10 and 20% compared with conventional AHSS solutions. ArcelorMittal also notes that in automotive body designs Fortiform steels are able to absorb more crash energy with less steel, making them suitable for use in many of the structural parts of a vehicle such as front and rear members, B-pillars and windscreen pillars.
After melting and casting, the steel used for Fortiform is hot and cold rolled to achieve the desired dimensions. The rolling stage also controls some of the steels final properties. Fortiform is then continuously annealed to obtain the final microstructure and properties of the grade. If an anti-corrosion zinc coating is required, Fortiform can be electro-galvanized prior to delivery.
There are three variants in development: Fortiform 980, Fortiform 1050 and Fortiform 1180. The grade number indicates the tensile strength of each steel (in MPa) in the range.
ArcelorMittal has already made Fortiform 1050 available to carmakers following formability and weldability tests with leading global vehicle manufacturers. The other two variants are due to be released to auto companies for development testing.
For carmakers that require AHSS for hot stamping, ArcelorMittal has its second-generation Usibor 2000 and Ductibor 1000 press hardenable steels, which are suitable for use in areas such as chassis rails and outriggers.
An aluminium-silicon coated AHSS, Usibor 2000 is more than 30% stronger than its predecess or Usibor 1500. According to Jean-Luc Thirion, head of ArcelorMittal Global R&D for automotive: Usibor 2000 could typically bring 10 to 15% weight savings when compared to existing hot stamping solutions.
AK Steel is another steel producer that is expanding its product range to include AHSS dedicated to automotive manufacturing needs. In April 2017, it announced that demonstration samples of its new Nexmet 1000 and 1200 AHSS had been delivered to multiple automotive customers for evaluation.
First announced in August 2016, the Nexmet range began with the introduction of Nexmet 440EX, intended for use in surface-critical exposed auto body panels. The latest developments, Nexmet 1000 and 1200, have been designed specifically for use in automotive structural components. To allow engineers to design lightweight parts, Nexmet 1200 has better formability than conventional dual-phase 600 steel, at twice the strength level.
These new Nexmet 1000 and 1200 products are evidence of AK Steels work to drive innovation in the steel industry, and remain at the forefront of carbon, stainless and electrical steel technology to provide our customers with unsurpassed levels of value and support, said Roger Newport, chief executive officer of AK Steel.
Steels for use in body-in-white and other components are being developed by steel companies. Like ArcelorMittal and AK Steel, Nucor produces AHSS steel for bodywork, under the NuStrength brand, but it also has a range of specialty steels for use in other areas of automotive construction.
Nucors product range of automotive AHSS includes DualPhase for use in frame rails, reinforcements and structural components; press hardened steel for A-pillars, B-pillars, bumper beams, door impact beams, rocker panels; stretch flange grades for use in control arms, cradles, twist beams, truck frames, suspension components; and HSLA which is suitable for control arms, frames, seating, brackets, reinforcements, hinges, clutch and torque converters.
This is the greatest period of time for development in the US automobile industry, Doug Richman, technical chairman of the Aluminum Transportation Group and vice president of engineering and technology at Kaiser Aluminum Corp, said during a panel discussion at American Metal Markets Automotive Supply Chain Conference in September 2017. Indeed, the latter part of 2017 saw a number of developments in the aluminium industry directly relating to the materials use in automotive construction.
Among those developments was the announcement by Aleris of an expansion of its flat-rolled aluminium sheet program for automotive use. The company, which produces wide automotive body sheet at its facility in Duffel, Belgium, has invested $400 million in opening an aluminium automotive body sheet production unit at its facility in Lewisport, Kentucky, USA.
The opening of our new automotive facility in Kentucky marks the completion of a significant piece of our strategic realignment, which includes expanding our capacity and capabilities to serve the automotive industry and other high-value end uses, said Aleris chairman and ceo Sean Stack. As an experienced supplier to automotive manufacturers in Europe, we look forward to partnering with customers more closely now in North America to bring them the most advanced auto body sheet products in the industry.
Similarly, Novelis, a large supplier of aluminium sheet to the automotive industry, introduced new material technology to the North American market after launching it first in Europe. The company announced in November 2017 that its Advanz 6HF - e/s200, a heat-treatable, aluminium alloy, is now available to automakers in the US who require an alloy with superior formability, strength performance and weight savings for outer and inner applications.
Novelis Advanz 6HF - e/s200 is a highly-formable 6xxx-series alloy that gives automakers new opportunities to use aluminium for designs and applications that require bending without the risk of cracking. Novelis states that its new aluminium formulation creates a weight saving of nearly one-third over steel when used in inner door applications.
As a global leader in automotive alloy innovation, we are excited to offer solutions to meet the growing design and manufacturing needs of North American auto manufacturers, said Ganesh Panneer, vice-president and general manager of Automotive, Novelis. As automakers pursue more complex designs and increase the amount of in-vehicle content, the strength and advanced formability of Advanz 6HF - e/s200 unlocks new engineering potential while offering critical weight reduction compared to steel. The expansion of this alloy into the North American market demonstrates our ability to draw on our automotive expertise and provide proven solutions across the globe.