Microstructure and properties of galvannealed coatings at different galvannealed time

•The structure of the galvannealed coatings (10 μm) was successfully characterized.•The phase transition of the galvannealed coatings was found.•The pulverization mechanism of the galvannealed coatings was established.•The optimal production process of the galvannealed sheet was summarized. Microstructure and properties of galvannealed coatings at different galvannealed time was studied by electron probe micro-analyzer (EPMA), X-ray diffractometer (XRD) and V-bend test. The study showed that δ and Γ1 phase was formed at galvannealed 15 s, and δ, Γ1 and Γ phases were formed at galvannealed 20 s and 25 s. The cracking area of coatings was propagated along Γ1/steel or Γ/steel interface and intersected with the serious cracks, which caused the coatings to be dropped. With the extension of galvannealed time, the areas of cracks and fracture at Γ/steel interface were reached 50% at galvannealed 25 s, and interfacial adhesion of Γ/steel was decreased due to the increase in thickness of Γ phase.