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Steel vs. Light Metals in Automotive Weight Reduction
(Released October 1999)

 
  by Scott Ryan  
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Overview

As the automotive industry addresses environmental concerns, the problem of fuel consumption and weight reduction has come to the fore.

Reducing the weight of automobiles is one of the primary means by which their fuel consumption is lowered. The two basic approaches are in automotive design and in materials selection, and they are closely related.

Regarding materials, there has been a trend toward the use of light metals and their alloys in automotive components, particularly automotive bodies. The most commonly used materials are aluminum, magnesium, and their alloys, though some research has also been done on the use of titanium, zinc, and nonmetallic materials.

On the other side there has been strong competition from the steel industry, which for obvious reasons would prefer that steel be retained as the primary automotive material.

Both sides face important design issues. On the steel side, one primary problem is to find new ways to design automotive components that permit the use of less material while not sacrificing strength and safety; such research efforts as the Ultra-Light Steel Auto Body (ULSAB) project exemplify the attempt to optimize the use of steel in automobile design. Also of importance are efforts to develop new high-strength steels as replacements for (usually) carbon steels. On the light metals side, the design issue is similarly twofold: not only do automotive components have to be designed in new ways in order to provide safe and reliable components, but -- since light metals in their pure form do not have the same desirable mechanical properties as even carbon steel -- the alloys themselves must also be designed for optimum strength.

As a result there are a host of new light alloys (and composites based on such alloys) intended for automotive use, together with new designs especially adapted for these alloys -- and also a host of new steel-based designs that make more efficient use of steel than was formerly typical.

Related issues include the design of production and fabrication processes (e.g. casting, forming, welding) suitable for use with such materials. Hydroforming, for example, shows promise in the fabrication of lighter-weight steel components, allowing the formation of a chassis component as a single part rather than as a piece spot-welded together from up to six different stampings. Hydroforming eliminates the flanges ordinarily required for welding, and maintains stiffness by eliminating the welds themselves. And for aluminum components, such techniques as the brazing of honeycomb panels, the production of lightweight squeeze castings, and the extrusion of large-scale shapes have shown promise.

The rivalries are not limited to automotive bodies but extend to other components as well. For engine and other components, magnesium is arguably the prime candidate as a lightweight alternative to cast iron and steel. Typical uses of magnesium and its alloys include seat frames, instrument panels, steering wheels, and engine and transmission components. The most common production process for such components is die casting, a process for which magnesium is well-suited. Some research efforts have focused on improving the die casting process (for example to fabricate large thin-walled parts), and others on the development of optimal welding processes for such castings. Also of importance is the corrosion protection of such components, as untreated magnesium has poor corrosion resistance.

In all of the foregoing there is also an economic tradeoff: aluminum and magnesium are significantly more expensive than steel. In some cases a combination of materials may therefore be desirable for reasons of cost, and so some research efforts have focused on the joining of dissimilar metals (e.g. aluminum alloys and stainless steels) in the fabrication of hybrid autobodies.

It seems likely that these developments, and with them the competition between steels and light metals in automotive applications, will continue into the foreseeable future.

Editor

Scott Ryan

  • CSA Editor, Materials Information

  • B.S. (Applied Mathematics and Computer Science), Kent State University, Kent, OH

  • M.A. (Mathematics), State University of New York at Stony Brook, Stony Brook, NY

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