Abstract
Hot-dip galvanised coatings used either alone or with an organic coating (duplex system) constitute an effective anticorrosion protection. Adhesion between the coating and the zinc substrate plays a vital role in the durability of the duplex system. Conditions of the galvanising process and alloying additives incorporated into the zinc bath influence mechanical and protective properties as well as thickness, structure, and surface morphology of the zinc coatings. The influence of the surface morphology of zinc coatings on the adhesion of organic coatings was studied. The tests were carried out on zinc coatings produced in baths with varying Pb content and by employing various cooling methods after the galvanising process. It was noted that a rapid cooling in water produces zinc coatings with a fine-grain structure, more suitable for paint application compared to the air-cooled ones, with a spangle.
Highlights
Zinc’s capabilities to effectively protect steel against corrosion have been known for over 200 years and make zinc coatings widely appreciated and used all over the world [1,2,3,4]
Macroscopic tests revealed that the presence of a well-developed spangle is specific for the surface of air-cooled zinc coatings produced in baths and is a manifestation of the solidification of zinc with Pb addition (Figure 1)
Results of the tests show that there is a strong correlation between the surface morphology of hot-dip galvanised coatings and the adhesion of an organic coating to zinc surface
Summary
Zinc’s capabilities to effectively protect steel against corrosion have been known for over 200 years and make zinc coatings widely appreciated and used all over the world [1,2,3,4]. Apart from zinc, zinc baths contain alloying additives that influence the properties of the produced coating. Depending on the bath type and temperature, duration of the galvanising process, postgalvanising cooling methods, the type of steel, and surface preparation prior to galvanising, zinc coatings differ in terms of thickness, chemical composition, phase composition, morphology, crystallographic structure of the surface, appearance, mechanical and corrosion properties, etc. An addition of alloying elements impacts the morphology of zinc coatings in many different ways. Anticorrosive properties of zinc coatings are influenced by the alloying additives, as there is a correlation between the alloying additives content and the texture of the zinc coating surface as well as the shape of its dendrites
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