Good corrosion resistance is the greatest advantage of hot galvanizing products, but people demand more and more high corrosion resistance of hot galvanizing products. At present, common methods to improve the corrosion resistance of hot galvanizing coating are as follows:
(1) increase the coating thickness.
(2) for alloying, the zinc alloy plating, the corrosion resistance of the coating obviously better than pure zinc coating, um thick alloying coating is equivalent to 10:7 m thick pure zinc coating 131 (3) improve the zinc liquid ingredients, in addition to the 70-80 - s of the 20th century, and has set up a commercial zinc - 5% A1 alloy plating (Galfan), people also developed a high corrosion resistance of zinc alloy galvanized layer of coating and special properties, such as 55% 55% zinc Al - 43.5% - Si alloy plating (Galvalume), 7 Mg Al n - 6% - 6%Alloy coating 132, zn-ni alloy coating 33 and zinc magnesium alloy.Coating, etc. By improving the formula of zinc liquid, a high corrosion resistant coating 18 times higher than the traditional coating has been developed and put into industrial production .
(4) the two-step thermal plating method, the first time pure zinc plating and the second time 7n-6a1-0.5 mg-0.1 Si alloy plating can further improve the corrosion resistance , in which alloying, also known as diffusion annealing treatment of the plating, has been developed earlier. The coating with alloying treatment not only increases the corrosion resistance, but also improves the welding and coating performance, so it is widely used in automobile and household appliances. In addition, Galvalume products have been developing rapidly in recent years, with higher corrosion resistance and beautiful surface, which are mainly used in architecture. In addition, the improvement of the composition of zinc liquid and the effect on the addition of trace elements such as rare earth are still an important direction of the research.
The surface quality of steel plate should include three parts: surface defect state, cleanliness and surface topography. In recent years, hot dip galvanized the requirement of increasing the car outside threatening the surface quality of steel, at the same time of coating and coating of bright mirror of coating are also put forward higher request, to thereby, hot dip the requirements of the product's surface roughness is becoming more and more strict, the coating surface quality are not only related with coating on the surface of various defects, and is closely related to the air knife and its injection of medium. In the aspect of gas knife technology, China mainly relies on the introduction of gas knife technology. At present, research should be carried out on the shape of the blade, the influence of the spraying medium on the surface quality, the solution of the thickening of the plating edge and the influence of the vibration of the eyelet strip steel.