LAUSR

The wetting of a solid metal by a liquid metal takes place in a large number of industrial processes such as welding, brazing, tin plating and hot-dip galvanizing.1) The study presented here focuses on continuous hot-dip galvanizing. In this process, the steel strip is immersed in a bath of molten Zn–Al alloy for a very short time (about 3 s). In this way, the steel sheets are covered with a zinc coating that protects them against corrosion.2) Before immersion in the molten bath, the steel strip is annealed between 780 and 840°C, in a mixture of N2 and H2 (5 to 15 vol.%) containing a low H2O partial pressure (20 to 50 Pa). This annealing allows to recrystallize the steel structure after cold rolling. The conditions used favour the reduction of the native iron oxides present on the steel surface but also the segregation and oxidation of the most oxidizable steel elements (Si, Al and Mn for example). At the end of the annealing treatment, the steel surface is finally composed of metallic iron (wetted by liquid zinc) and oxide particles or films (not wetted by liquid zinc). In hot-dip galvanizing, the wetting of the steel substrate Improvement of Wettability between Steel and Liquid Zn–Al Alloy by Forced Wetting