Steel seems to be making some headway in this ongoing battle. To keep aluminum from making further inroads, ArcelorMittal spends most of its $134 million annual product-development budget on auto research. The company says it can make steel car frames and panels that are 21% lighter than in 2010.

Electric vehicles could help steel. This may seem counterintuitive because Tesla had originally utilized aluminum over steel. In its newest mass-market car (Model 3), however, Tesla has moved away from aluminum. Similarly, the latest Audi A8 has moved from its heavy use of aluminum to a mix of steel, aluminum, magnesium and carbon fiber. For more.