Orientation Dependence of Cracking in Hot-Dip Zn-Al-Mg Alloy Coatings on a Sheet Steel

The present study was aimed at investigating a basic cause of cracking in hot-dip Zn-Al-Mg alloy coatings on an extra deep drawing quality sheet steel. The electron backscattering diffraction technique was employed to examine the crystallographic planes of the cracks generated before and after bending deformation of the coated steel sheets. It was clarified that the occurrence of cracking in the Zn-Al-Mg alloy coatings absolutely depends on the orientation of the primary Zn and eutectic Zn alloy phases. Finally, a cracking mechanism was proposed on the basis of the anisotropy of thermal expansion and the Young’s modulus in the phases constituting the coatings.