DIFFUSION ZINC COATINGS FOR CORROSION PROTECTION OF BUILDING STRUCTURE ELEMENTS IN ACCORDANCE WITH INTERNATIONAL STANDARD ISO/FDIS 17668:2015

Abstract. Purpose. Study of protective properties of diffusion zinc coatings (DZC) on fasteners for structural elements under mechanical loads applied to threaded tube joints in weak corrosive media. Proceeding. As the test material, specimens with M10 thread and actual bolts M24 of high-strength 40X grade steel with no coating, with diffusion zinc coating and with 22-24 µm thick electroplated zinc coating were taken for this study. Effect of surface preparation and methods of application of zinc coatings on physical-mechanical properties of threaded specimens made of 40X steel was studied. Results. Based on the obtained data, it was shown that long-term tests during 18 months under loads equal to 0.7 of ultimate strength of M10 specimens with diffusion zinc coating did not lead to considerable changes in strength and plasticity and in residual hydrogen content in steel. Chemical etching and electroplating operations result in a decrease of plasticity and in an increase of the content of residual hydrogen in steel. Diffusion zincing at temperature of 450 оС restores steel plasticity due to removal of diffusion-mobile hydrogen. Scientific novelty. Regularities of corrosion behavior of diffusion zinc coatings of a new generation applied on metal products working in stress conditions were established. Practical significance. Appreciation of the mechanism and acquisition of qualitative regularities of the corrosion process in protective diffusion zinc coatings with the objective of improvement of service life and reliability of fasteners for structural elements.