An interesting article in engineering.com explains why a movement away from aluminum makes sense. One of the facts is that because steel is so much stronger than aluminum, it can be thinner. The thicker aluminum used to replace it is not that much lighter, and the extra thickness is often a design problem.
In spite of all of the design challenges, we are convinced that aluminum makes sense for some automotive components. Jeep is using lightweight, high-strength aluminum for closures, which includes parts of the doors, fenders, swing gate and windshield surround. As a result, the all-new Wrangler is 200 pounds lighter than the previous steel version, and gas mileage is expected to rise by 3 MPG.