Environmental Impact of AHSS vs. Aluminum in Vehicles

WorldAutoSteel (Detroit, MI), the automotive group of the World Steel Association, recently released findings of two new case studies that examine the effect various automotive materials can have on total life cycle greenhouse gas (GHG) emissions for light-duty truck and sport utility vehicle (SUV) classes. By conducting a life cycle assessment (LCA) of each vehicle class, the studies showed that advanced high strength steels (AHSS) lowered total life cycle emissions and decreased fuel consumption.

The case studies used the Automotive Materials Energy and GHG Comparison model (UCSB Model), developed by Dr. Roland Geyer of the University of California Santa Barbara Bren School of Environmental Sciences. They investigated whether or not an AHSS-intensive design would result in fewer emissions than an aluminum-intensive design, compared to a conventional steel baseline, when looking at the entire vehicle life.

“Numerous iterations of the model were conducted to simulate the many possible conditions a vehicle might see,” said Russell Balzer, the technical director of WorldAutoSteel. “In each vehicle’s best performance (lowest emissions) case, the steel design showed decreased total life cycle emissions over the aluminum vehicle by three percent for the light-duty truck and five percent for the SUV.”

For a fleet (annual production of 700,000 trucks; 200,000 SUVs), if both vehicles were manufactured in AHSS, it equates to approximately 1.7 million metric tons of total emissions savings over the aluminum-intensive vehicles.

The UCSB model also projects fuel savings by considering driving cycles, engines, fuel types, effects of lightweighting and other factors impacting fuel usage. Results showed that fuel consumption was not substantially decreased when substituting aluminum for steel. The AHSS and aluminum designs reduced structural* weight by 25 percent and 35 percent, respectively. For both the truck and SUV cases, the AHSS designs were within 70 kg of the aluminum weight savings.

The data showed that owners of an aluminum-intensive light-duty truck can expect to visit the fuel station four less times over the entire life of the vehicle (assuming a 26 gal tank and 12-year lifetime) than the AHSS-intensive truck owner, or a savings of one-third of one fuel fill up per year.

The aluminum SUV driver can expect to save about three visits to fill up over the entire vehicle life, or one-quarter of one fuel fill up per year less than steel. At recent U.S. average fuel prices of up to $4.00 per gal, that is a consumer cost savings of about $25 to $35 per year.

From a lightweighting perspective, the efforts to lower weight with aluminum to reduce fuel consumption resulted in an increased environmental footprint overall at a potential cost of three times that of steel.

“On a life cycle basis, the AHSS-intensive vehicles produce fewer emissions than the aluminum-intensive one,” said Balzer. “Steel performs better in these vehicle cases because the primary production of steel, including AHSS, produces seven to 20 times fewer emissions than other materials such as aluminum, magnesium and carbon fibre reinforced plastics.”

WorldAutoSteel believes a life cycle approach to vehicle emissions regulations will foster the approaches needed to truly reduce automotive industry emissions.

“Without a lifecycle approach to auto emissions, automotive designers can be forced into solutions that end up merely shifting the environmental impact, not reducing it,” said Balzer. “Regulations need to support a holistic big picture approach, from start to finish; otherwise, they will continue to lead automakers into approaches that may result in some fuel consumption savings but that can, in the end, lead to the unintended consequence of increased total vehicle emissions.”

LCA is a methodology that considers a vehicle’s entire life cycle, from the point where raw material is taken from the ground and the vehicle is built (manufacturing), to the time while the car is driving down the road and burning fuel (use or driving), to the point where it is hauled to the scrap yard and all of its recyclable content is removed and the rest disposed (end-of-life recycling and disposal).

The UCSB model is designed to quantify the energy and GHG impacts of automotive material substitution on a total vehicle life cycle basis, under a broad range of conditions and in a completely transparent fashion.  The model methodology has been peer-reviewed by members of the LCA community and the aluminum industry.

www.worldautosteel.org