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 automotiveindustry. Coated (galvanized or galvannealed) AHSS are the most important of this class of steels. AHSSincludes various families of steels, major among them being dual-phase, multi-phase or complex-phase, TRIPand martensitic steels. Recently, Twin Induced Plasticity (TWIP) and Quenching and Partitioning (QP) steelsare also becoming popular. Finally, press-hardened steels (PHS) are increasingly becoming a material ofchoice for many automotive manufacturers. In addition to tensile and yield strength properties, many of thesesteels are also required to possess other functionalities such as total and uniform elongation, sheared-edgestretch- flangeability, bendability and weldabilty. To achieve the combination of properties, most of these steelscontain significant amounts of various alloying elements. Presence of both the alloying elements as well as thecomplex microstructures poses a challenge for coatability. These multi-faceted aspects of coated AHSS andtheir metallurgical challenges will be discussed in this paper. Mechanisms to explain coating behavior will beincluded as appropriate. Finally, new coatings for improved functionalities and future breakthrough productsfor automotive applications will also be briefly discussed