INFLUENCE OF TEMPERATURE AND HOLDING TIME IN THE MELT ON THE MICROSTRUCTURE AND PHASE STRUCTURE Zn + 7 % Al COATINGS ON VARIOUS GRADES OF STEEL

Aluminum is one of the most common alloying elements for zinc melt. Alloys with a content of 1 ‒ 20 % Al exhibit high formability, ductility, and corrosion resistance. It is known that in the presence of aluminum, Fe ‒ Al intermetallides are formed at the interface between molten zinc and an iron substrate, which play the role of a diffusion barrier, controlling the reaction between iron and molten zinc, providing a lower coating thickness compared to traditional zinc coatings. The effect of temperature, exposure time, and chemical composition of steel on the structure and phase composition of zinc-aluminum coatings has not been sufficiently studied. A study of the microstructure and phase composition of coatings obtained in a Zn + 7 % Al melt at a temperature of                  420 – 520 °C with a holding time of up to 8 minutes on steels of various compositions was carried out. It was found that the exposure time in the melt does not affect the thickness of the coating. The latter does not depend on the steel grade, therefore, Zn + 7 % Al coatings are non-reactive with respect to silicon contained in steel. It is shown that the coating thickness is constant in the range of 420 – 460 °C and increases intensively at a melt temperature above 480 °C, which is associated with intensive dissolution of the steel substrate. The microstructure of the coating was studied by electron microscopy at temperatures of 420, 480, and 520 °C. X-ray phase analysis made it possible to establish a change in the phase composition of the coating with increasing melt temperature. The composition of the individual structural components of the coating was determined using energy-dispersive X-ray microanalysis. The microhardness of the coating phases was measured.

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