Hot-dip galvanizing in WEGAL alloy bath with increased manganese content

Dr.-Ing. Szymon Malara, Dr.-Ing. Jan Wesołowski

Hot-dip galvanizing is one of the best methods for corrosion protection of steel goods. The range of products undergoing galvanizing is very wide from big constructions to small fasteners. Galvanized coating is jointed with substrate by diffusive adhesion and undergoes passivation making it a very good barrier for chemical corrosion. Currently, over 50 % of zinc world consumption is destined for hot-dip galvanizing in both batch and continuous modes. The development of zinc alloys for hot-dip galvanizing is focused on searching for bath chemical composition which provides the best corrosion resistance of obtained coatings and prevents excessive thickness growth of the coatings caused by Sandelin effect, especially on reactive steels. This work presents the laboratory test results of hot-dip galvanizing of low-silicon steel (08X grade) and reactive steel (S235JRG2 grade) samples in WEGAL alloy bath with increased manganese content to 0.2 % (ZnAl0.1Ni0.1Mn0.2). The microstructure and phase composition of the zinc alloy were examined. Its solidus was determined basing on thermal analysis of solidification. The galvanization process was carried out at the temperature of 445 °C, with retention time – 600 s. The analysis of test results comprised assessment of the coating microstructure and thickness. The coating adhesion and plasticity were examined in bending test of coated samples on a steel mandrel (radius of 5 mm and angle of 180°). The outside bend edges were visually evaluated. The coatings showed good plasticity and aesthetic appearance. The results showed that coating growth kinetics depends mainly on dominant part of bath chemical composition.