Damage micromechanisms in a hot dip galvanized steel

Hot-dip galvanizing is one of the most used methods to apply zinc-based coatings on steels in order to provide sacrificial protection against corrosion over all the steel surface. The aim of this work is the analysis of the hot dip zinc coated steel plates mechanical properties by means of a non-standardized bending test performed minimizing both the bending moment differences along the bending axis and the interactions between the clamping system and the specimen coating. Bending tests are performed both on non-coated and on hot dip zinc coated plates, correlating the measured variables (applied load and crosshead displacement) with the bending moment and the specimen bending angle. Tests are characterised by a good repeatability. Results show that the main damaging mechanisms depend on the different mechanical behaviour of the intermetallic phases and on their thickness. For all the investigated coating conditions, radial cracks are observed. They initiate corresponding to the Γ phase and propagate up to the ζ-η interface. The coating thickness increase implies both an increase of the importance of the cracks in δ and ζ phases and the presence of cracks at ζ-η interfaces.