Perspectives on coated advanced high strength steels for automotive applications

Advanced High Strength Steels (AHSS) is the fastest growing segment of sheet products in the automotive industry. Coated (galvanized or galvannealed) AHSS are the most important of this class of steels. AHSS includes various families of steels, major among them being dual-phase, multi-phase or complex-phase, TRIP and martensitic steels. Recently, Twin Induced Plasticity (TWIP) and Quenching and Partitioning (QP) steels are also becoming popular. Finally, press-hardened steels (PHS) are increasingly becoming a material of choice for many automotive manufacturers. In addition to tensile and yield strength properties, many of these steels are also required to possess other functionalities such as total and uniform elongation, sheared-edge stretch-flangeability, bendability and weldabilty. To achieve the combination of properties, most of these steels contain significant amounts of various alloying elements. Presence of both the alloying elements as well as the complex microstructures poses a challenge for coatability. These multi-faceted aspects of coated AHSS and their metallurgical challenges will be discussed in this paper: Mechanisms to explain coating behavior will be included as appropriate. Finally, new coatings for improved functionalities and future breakthrough products for automotive applications will also be briefly discussed.