Aluminum, while it provides great benefits, does have a major drawback: cost. Compared to steel, manufacturers can expect to spend double on aluminum. For this reason, there are still good arguments for using steel, even in high end luxury cars like Audi's A8.
Heinrich Timm is the head of Audi's Aluminum and Lightweight Design Center and believes steel will play an important role in the future of automobile design. As they have already begun doing, their plan is to make use of aluminum, along with steel, carbon fiber, and plastic to balance weight reduction, strength, and cost.
Different types of steel can be used strategically to increase structural strength, or balance overall weight distribution on performance cars. For example, Timm explains that steel components are used at the rear of the new TT to balance weight, which would improve performance. It also helps keep the vehicle's cost down.
Look for Audi to continue making improvements like these through careful design and material selection. This strategy will be critical to maintain good fuel economy ratings, and customers usually don't argue about cost reduction efforts.
[Car and Driver]