Ford is fighting this process by electrocoating the aluminum panels to electrically and physically isolate the metals, and by using new coatings on all body bolts. To test the long-term durability of these kinds of joints, engineers normally bathe body panels in a saltwater spray during a hot/cold environmental cycle—this encourages the formation of iron oxide. But with aluminum that was just too slow. So they switched to a corrosive acid bath and found that tweaking the metallic coating on the bolts protected the metal admirably.