Research on Peeling Properties of Galvannealed Coatings

Galvannealed coatings are so quite hard and brittle that they are difficult to peel off from their substrates by conventional peeling tests. A special test to tear galvannealed coatings, based on asymmetry 90°peel test, is experimentally investigated. Rectangle shapes of specimens are asked in the test. Specimens have 100mm in length and 25mm in width. They were pulled apart in Zwick instron testing machine at 5mm/min. peeling stress of galvannealed coatings was measured in this test. Morphology of cross-section sample was observed by SEM. The difference of microstructure phases on sample’s surface before and after peel test was analyzed by XRD. Galvannealed coatings are consisted of δ-, Γ- and Γ₁ -phases. Gamma (Γ + Γ₁) phases are located in interface of coating and substrate. Delta phase is next to gamma phase. After the coatings are peeled off, there are only gamma phase on the fractured surfaces of substrate side. The results show the coatings’ fracture occurs along interface layer of coating and substrate.