In recent years, aluminum alloys have become the dominant material for body-in-white (BiW) and battery enclosures (“BE”) in electric vehicles (“EV”) due to their low density. Aluminum BiW and BE, or other platform parts, typically provide weight savings of ~40% compared to equivalent commercially-used steels. The best-suited materials for BiW are 2000, 5000, and 6000-series aluminum alloys and for BE are 6000-series aluminum alloys.
Despite its light weight and recyclability benefits, the aluminum alloys have a crucial disadvantage if the heat generated by batteries raises the temperature of BE above 315°C. At the exposure of more than 300 sec at 315°C or higher, the yield strength, especially for parts that are in direct contact with the battery cells drastically drops by more than 70%, and in the critical situation of fire (~1200°C), BE fail within ~5 sec, creating a paramount safety concern for EV passengers. Applications of the aluminum alloys for BiW are limited by their moderate strength, poor welding, and high cost.
New high strength steel for cold stamping (“ColdStamp-Steel”) is an attractive alternative to aluminum alloys. ColdStamp-Steel developed by AMD Corp. (see http://amdoncorp.com/coldstamp-steel ) possesses high stiffness, high strength, and moderate ductility. A comparison of the specific stiffness and strength of ColdStamp-Steel and the high strength 6083 aluminum alloy shows that the proposed steel can substitute any aluminum alloys without increasing the weight of BiW and BE while rising their durability and life-time. ColdStamp-Steel can be coated by the commonly used electro-galvanizing, hot dip galvanizing, galvannealing, and aluminizing processes for corrosion and oxidation protection.
The coated ColdStamp-Steel is an attractive material for BE applications. ColdStamp-Steel can prevent failure of BE at temperatures of up to 500°C, and withstand fires of up to 1200°C, allowing for sufficient time to evacuate the EV passengers in the event of an emergency. In fact, battery enclosures made from any aluminum alloys cannot compete with the same weight BE made from the coated ColdStamp-Steel at ambient and elevated temperatures.
BiW made from high strength aluminum alloy can be substituted by the same weight BiW made from the coated ColdStamp-Steel while strength, stiffness, durability, and life-time of the steel BiW are higher.
Furthermore, the cost of production of the coated ColdStamp-Steel is 40-50% less than the cost of production of the high strength aluminum alloys.