Investigation Of The Application Of Surface Self-nanocrystallization In Galvanizing And Sherardizing

Recently, nano-technology gets more and more attention. Nano-material has manyunique properties such as higher specific surface energy, activation and diffusion rate.Due to the special properties, nano-technology becomes an effective way to improvetraditional processes.The corrosion phenomena of steel material cause heavy loss and security risks tothe national economy. As anti-corrosion methods, hot dip galvanizing and sherardizingare widely used, and many researches have been done to keep the processes advancing.This article studied the application of surface self-nanocrystallization (SSNC) ingalvanizing and sherardizing. The nanocrystallization samples were made by highenergy shot peening (HESP) and formed experiment couples with original coarse grain(CG) samples. After galvanizing or sherardizing, the coating performances were testedand analyzed by several experimental methods. It was found thatsurface self-nanocrystallization made an improvement both in galvanizing andsherardizing.Galvanizing experiments showed that of the HESP-sample, the coating wascombined with the matrix more closely, and the Г1, δ, ζ and η phases in the alloy layercould be clearly distinguished, while the ζ phase was significantly thinner than in theCG-sample and nano-scaled compound layer was found close to the matrix, which wasgood for ductility. The hardness of surface after galvanizing was75~80HV, and reachedabout240HV across the alloy layer, finally back to the matrix hardness (85HV) indifferent forms. The variation of hardness was associated with the grain structure of thesample. In corrosion test, the HESP-sample showed a better corrosion resistance.Sherardizing experiments found that, FeZn7phase was formed in the surface ofsamples after sherardizing. The thickness of Fe-Zn compounds layers increased with theincreasing sherardizing temperature and duration, and the compound layer in theHESP-sample was always thicker than that in the CG-sample. During reaction, theactivation energy of the compound layer in HESP-sample was114.0±12.7kJ/mol, whileit was to157±20.1kJ/mol in the CG-sample. After sherardizing, the surface hardness ofthe CG-sample was improved to250~260HV, then decreased sharply to about85HV.And it was up to270~280HV of the HESP-sample, then reduced gradually with theincreasing depth to the matrix hardness. In corrosion test, the HESP-sample also showed a better corrosion resistance, and its corrosion rate was always lower than theCG-sample.The interface combination, ductility and corrosion resistance of the coating aftergalvanizing were improved by the application of SSNC. And the application of SSNC insherardizing enhanced Fe-Zn reactive diffusion, leading to lower sherardizingtemperature and shorter duration. In general, the application of SSNC could improve thetraditional galvanizing and sherardizing processes.