Super Stretchy Metal Reduces Vehicle Weight

New understanding of how to form metals leads to improved materials and manufacturing advances for lightweight aluminum car parts.

A transmission electron micrograph of a grain boundary junction and associated defects following superplastic forming. — Image courtesy of Pacific Northwest National Laboratory

The Science

New, fundamental understanding of how the regions of metals with different orientations (grains) slide past one another during deformation leads to improved manufacturing processes.

The Impact

Auto makers seeking enhanced fuel efficiency by replacing heavier steel with lighter aluminum have been challenged by aluminum’s low formability. By understanding the basic mechanisms underpinning superplastic deformation, an approach that leads to high formability, new aluminum alloys and advanced forming processes were developed and commercialized to allow the manufacture of complex shapes.

Summary

In order to make vehicles more light weight – and therefore more fuel efficient – not only are new, lighter-weight materials needed but also efficient, cheap methods for manufacturing vehicle components. Research at Pacific Northwest National Laboratory (PNNL) made breakthroughs in basic science and applied technology research that improved superplastic forming (SPF) manufacturing methods for aluminum alloys. In SPF, a metal is heated and clamped against a hot die of the desired shape, such as a trunk lid. When the SPF metal is heated, it stretches easily and much further than a regular alloy, simplifying the manufacturing process. Metals are composed of individual crystals, regions with different atomic orientations, called grains. To create a material capable of SPF, the material needs to have very small grains that can then easily slide past each other when the metal is stretched. Fundamental research at PNNL was focused on the interfacial processes that control how grains move inside metals during deformation. This understanding aided the design of processing routes to optimize the structure of the metal. A unique partnership between PNNL, General Motors, Kaiser Aluminum, code developer MARC, and a number of universities moved this fundamental understanding to practical applications. The partnership allowed researchers to test materials under a few simple conditions and then accurately model the behavior in a computer over a wide range of complex conditions, an iterative approach that sped up the design process. Following additional development work, General Motors developed a process with an order-of-magnitude reduction in manufacturing time. The process was used to produce intricate components, including the hatchback on the Chevy Malibu Maxx, reducing the weight from 39 pounds to 20 pounds.

Contact

Brucer Harrer, PNNL (overall)

Stephen Bruemmer, PNNL (Basic Research)

Mark T. Smith, PNNL (Applied R&D)

Funding

Basic Research: DOE Office of Science, Office of Basic Energy Sciences.

Applied R&D: DOE Laboratory Technology Research CRADA with industrial partners; Office of Energy Efficiency and Renewable Energy; National Aeronautics and Space Administration

Publications

Vetrano JS, CA Lavender, CH Hamilton, MT Smith, and SM Bruemmer. 1994. “Superplastic Behavior in a Commercial 5083 aluminum alloy.” Scripta Materialia 30, 565-570.

Khaleel MA, KI Johnson, CA Lavendar, MT Smith, and CH Hamilton. 1996. “Specimen geometry effect on the accuracy of constitutive relations in a superplastic 5083 aluminum alloy.” Scripta Materialia 34, 1417-1423.

Vetrano JS, SM Bruemmer, LM Pawlowski, and IM Robertson. 1997. “Influence of the Particle Size on Recrystallization and Grain Growth in Al-Mg-X Alloys.” Materials Science and Engineering A238, 101.

Khaleel MA, HM Zbib, and EA Nyberg. 2001. “Constitutive modeling of deformation and damage in superplastic materials.” International Journal of Plasticity 17, 277-296.