Influence of steel substrate behavior on the deformation and cracking of Zn–Al–Mg coatings on galvanized steel sheets

The objective of this study is twofold: (i) to comprehensively describe the deformation modes of zinc coatings depending on their crystallographic texture and (ii) to investigate the effect of Lüders banding occurring in the steel substrate on the coating deformation and cracking modes. Microscopic characterization and mechanical tests were conducted on three types of galvanized steel: a mild steel substrate and a high-strength low-alloy (HSLA) steel substrate known to exhibit the Lüders banding phenomenon, and a dual-phase steel substrate. The results reveal a direct correlation between the coating texture, plastic deformation modes, and the mechanical behavior of the respective substrates. Digital Image Correlation (DIC) was employed to measure the strain fields and characterize strain localization phenomena resulting from Lüders banding. The strain field measured on the galvanized substrate specimens showed that Lüders band propagation leads to accelerated plastic deformation and cracking in the Zn–Al–Mg coating. Finite element simulations were performed by considering the real coating microstructure and incorporating the macroscopic behavior of the substrate. The simulation results demonstrate that slip and twinning activities of the coating grains are strongly influenced by the underlying substrate behavior.