These mandates currently require an average of at least 27.5 mpg for passenger cars and 21.5 mpg for light trucks. These mileage regulations conflict with other government regulated mandates for safety features such as airbags, side-impact collision beams, and antilock braking systems. To accommodate these conflicting demands, automobile manufacturers have been looking for low density lighter materials to use in place of steel.
Aluminum alloys appear to be the most promising of the lighter materials available.
Table 1 shows the principal alloying element along with the corresponding designation. For about 10 years, the automotive industry has been using aluminum in parts like wheels and radiators. The use of these alloys is limited because they require a high temperature baking cycle to acquire the needed strength for body panel applications. This strength is normally achieved by age hardening during the paint baking process. With the increased use of plastics in automobile paint, the corresponding baking is being done at much lower temperatures.