Audi A8: steel makes a comeback

New Audi A8 follows recent trend of automakers to increase the use of advanced steels

 

Audi’s A8 switches back to steel after experimenting with aluminium in its luxury models. Scheduled for release in 2018, the body structure of the new A8 will be made up of over 40 percent steel, following the trend to use more advanced steels. That’s a marked turnaround on the all-aluminium body-in-white which Audi developed for the A8 in 1994.

 

Audi A8: steel makes a comeback

  Aluminium-blech
Aluminum sheet
  Ultrahochfester Stahl (warmumgeformt)
Ultra-high strength(hot-formed)
  Magnesium
  Aluminium-Profil
 Aluminum section
  Konventioneller Stahl
 Conventional steel
   
  Aluminium-Guss
 Aluminum castings
  Kohlenstofffaserverstarkter Kunststoff (CFK)
 Carbon fiber-reinforced plastic(CFK)
   

–source:www.audi.co.uk

 

Press hardenable steels lead in safety

 

Steel has moved on dramatically since the 1990s. Around 17 percent of the new A8 body structure will be comprised of press hardenable steel (PHS), some of which will be supplied by ArcelorMittal. These steels have yield strengths up to 1500 MPa after press hardening. The strength-to-weight ratio of these grades outperforms even the most advanced (and costly) aluminium.

 

“There will be no cars made of aluminium alone in the future. Press hardened steels (PHS) will play a special role in this development. PHS grades are at the core of a car’s occupant cell, which protects the driver and passengers in case of a collision. If you compare the stiffness-weight ratio, PHS is currently ahead of aluminium."

—— Dr. Bernd Mlekusch, head of the Audi’s Leichtbauzentrum

 

Change in composition of the A8 body structure

 

  Old A8 D4 (2009) New A8 D5 Change
Steel 8% 40.5% (17% PHS) +32.5%
Aluminium 92% 58% -34.0%
Other materials 1.5% +1.5%

 

One area that benefits is safety. Dr. Bernd Mlekusch, head of the Audi’s ‘Leichtbauzentrum’ (Lightweight Construction Center) was recently quoted as saying that the use of more steel in the new Audi A8 should help to improve the way cars are made lighter: “There will be no cars made of aluminium alone in the future. Press hardened steels (PHS) will play a special role in this development. PHS grades are at the core of a car’s occupant cell, which protects the driver and passengers in case of a collision. If you compare the stiffness-weight ratio, PHS is currently ahead of aluminium.”

(source: Frankfurter Allgemeine Zeitung, ‘Audi: more steel in cars in the future’, published 11 April 2017)

 

Growing trend to use advanced steels

 

The use of AHSS in today’s vehicles is outpacing the steel industry’s own forecasts:

 

Year Forecast (kg) Actual (kg) Change (kg) Increase of AHSS (%)
2012 88.0 93.0 5.0 +5.7%
2013 96.6 106.6 10.0 +10.3%
2014 105.2 115.2 10.0 +9.5%
2015 113.9 124.7 10.9 +9.6%

Increase in the use of AHSS grades in automotive 2006-2015 (source: Steel Market Development Institute – SMDI):

 

Audi A8: steel makes a comeback

  2014 Additional AHSS Pounds per Vehlcle AHSS continues its growth trajectory with 254 pounds per vehlcle in 2014, surpassing our estimates in 2010 for 2014 by over 20 pounds per vehlcle (prior 2014 estimate was 232 pounds)
  2010 Release

 

New joining technologies

 

With the advent of new joining technologies, it has never been easier for automakers to incorporate advanced high strength steels into their vehicles. As these technologies mature and are adopted by carmakers, the use of PHS in the multi-material vehicles of the future is set to grow strongly.

 

Life Cycle Analysis benefits

 

ArcelorMittal and the steel industry as a whole have been working collaboratively to educate automakers and stakeholders on the importance of life cycle analysis, or LCA. LCA looks at total emissions generated during the three stages of a vehicle’s life – production, drive phase and disposal.

 

“Right now, regulations only consider tailpipe emissions generated during the drive phase,” said Brad Davey, chief marketing officer, NAFTA and global automotive for ArcelorMittal. “However, each material used in vehicle production contributes to lightweighting and improves fuel economy, but each does so at a different cost to the manufacturer – and to the environment.”

 

Studies show that aluminum emits four to five times more GHGs than steel. “If we want to know how “green” a vehicle really is, we have to measure emissions over its entire life cycle. Otherwise, choosing an alternative material over advanced steel will result in a huge and irreversible environmental mistake,” said Davey.