Sealing Treatment of Aluminum Coating on S235 Steel with Thermal Diffusion of Zinc

摘要

The study introduced a thermal diffusion sealing treatment for arc-sprayed aluminum coating on S235 carbon steel. The sprayed aluminum-zinc duplex coating was heated to 420 A degrees C, so that the low-melting-point zinc could diffuse into the pores of the aluminum coating. Optical microscope, microhardness, electron probe microanalysis, and x-ray diffraction were used to evaluate the sealing treatment. The calculated diffusion coefficient for zinc in the arc-sprayed aluminum coating was approximately 7.735 x 10(-9) cm(2)/s. The diffused zinc could increase the compactness and microhardness of the aluminum coating. Nevertheless, adverse interface reactions could destroy the coating if the zinc made contact with the steel substrate. FeZn10 could form initially, and then the heat from the exothermic reactions between zinc and iron would initiate the reactions among iron, aluminum, and zinc. FeAl-Zn (x) , FeAl2-Zn (x) , and Fe2Al5-Zn (x) were generated following FeZn10. The defected structures were mainly composed of Fe2Al5-Zn (x) and FeZn10. All of these formed tough, brittle, intermetallics that have a negative effect on the coating performance. Thus, the contact between zinc and the steel substrate should be avoided, and the holding time should be restricted to 8.16 x 10(6) L (2) to prevent the generation of intermetallics.