Since the surface of the galvanized sheet is covered with a zinc layer, the electrode potential of zinc is higher than that of the steel, and the zinc sheet and the atmosphere form a thicker passivation film in a corrosive environment. This passivation film will be effective to a certain extent. It can prevent the steel plate from being corroded, and further prolong the service life of the steel plate by preventing the steel plate from being corroded. If the zinc layer falls off, the steel plate will be exposed, which is not conducive to prolonging the service life.
1 Analysis of the reasons for the peeling off of the zinc layer of the hot-dip galvanized steel sheet
1.1 Analysis of production process
The main process flow of a steel galvanizing production line in a steel plant is a series of production processes such as acceptance, annealing, galvanizing, cooling, finishing, winding, and packaging. After investigation and analysis by relevant professionals, it is concluded that the raw materials, cleaning and other links of this process need to be controlled to a certain extent to prevent the zinc layer from falling off. In addition, another main reason for the shedding of the zinc layer is the improper control of the actual temperature of the furnace temperature.
However, no matter whether the temperature is high or low, it is not conducive to the original adhesion of the zinc layer. If the atmosphere in the furnace is unreasonable, it will also affect the quality of galvanizing to a certain extent. Therefore, only by accurately understanding the main reasons for the shedding of the zinc layer of the hot-dip galvanized steel sheet can we carry out targeted production and avoid the occurrence of the shedding of the zinc layer.
1.2 Analysis of specific reasons for the peeling off of zinc layer of galvanized steel sheet
First, the excessive residue on the surface of the substrate will cause the zinc layer of the galvanized steel sheet to fall off. In the production process of galvanized steel sheet, there are certain requirements for the total amount of residue on the substrate, so a cleaning section is provided.
Secondly, if the steel strip stays in the annealing furnace for too long and has a high temperature after entering the zinc pot, it will also cause the zinc layer to fall off to a certain extent. If the operation of the unit fails during production, it will It happens that the annealing furnace cannot work better.
Under this circumstance, the steel strip will bring a lot of heat into the zinc pot and cause the zinc liquid to heat up. When the zinc liquid heats up, the diffusivity of zinc will increase sharply.
2 The specific experiment of the stamping and peeling of the zinc layer of the hot-dip galvanized steel sheet
2.1 Test method
In order to better understand the actual situation of the zinc layer of the hot-dip galvanized steel sheet, the relevant staff took samples from the defective products with the zinc layer falling off, and used professional instruments to analyze their components.
After the conclusion is drawn, the coating is observed by electron microscope, so as to better discover the components in it. In order to better highlight the effect of the experiment, nitric acid alcohol with a concentration of 4% to 6% should be selected, and a certain amount of nitric acid alcohol should be added to the nitric acid alcohol. After a series of chemical reactions, professional observation instruments and equipment are used to observe the surface of the newly formed chemical substances, and the products with certain defects will be put into the corrosive agent prepared in advance. The better part is cut, the approximate size is about 15mm × 30mm, and it is also polished and polished, and the indenter with a radius of 0.6mm is used to bend it through a folding machine. Observe the actual situation after bending and draw relevant conclusions.
After determining the relevant experimental methods, a series of tests should be carried out to check the actual bending of the hot-dip galvanized steel sheet and the falling off of the zinc layer. The relevant professional staff selected normal products and polished the surface. And bending, after bending, through actual observation, it is known that the zinc layer at the bend has broken and other phenomena, and the degree of breakage is proportional to the degree of bending, which is mainly reflected when the bending is 90 At around 100 degrees, more cracks appeared in the coating in the bending area.
The outer coating of the bent steel plate is subjected to a certain degree of tension to form an open crack. After the inner coating of the bent steel plate is subjected to a certain pressure, an extrusion crack is formed. There isn’t much nudity either.
After the above-mentioned experimental analysis, the relevant staff learned that the structure and state of the substrate material did not show major abnormalities during the experiment, but the formation of transitional zinc can, to a certain extent, affect the actual adhesion of the zinc layer. It will have a certain influence on the adhesion, and even hinder the formation of the adhesion of the zinc layer to a certain extent.
At the same time, the aluminum-rich transition layer also helps to improve the adhesion and deformation resistance of the coating.
However, for the coating with poor adhesion and the substrate interface, a relatively flat aluminum-poor transition layer is formed. The relevant research conducted by the staff shows that the aluminum in the zinc liquid preferentially reacts with iron to form an aluminum-rich transition layer. In this process, the diffusion of iron to the aluminum layer is reduced to a certain extent, which is also of great help to the actual toughness and adhesion of the coating.
Through the above experiments, it is known that the higher the actual temperature of the strip into the pot, the lower the aluminum content in the zinc pot. This phenomenon has a relative relationship with the products with stamping dezincification defects.
Therefore, in order to further improve the actual efficiency of zinc production in iron and steel plants and maximize the service life of the zinc pot, it is necessary to optimize the composition of the zinc liquid, and to control the temperature of the strip into the zinc pot reasonably.
Sheet fabrication services for mild steel, high strength low alloy (HSLA) steel, cold/hot rolled steel, galvanized steel, stainless steel, aluminum, copper and brass. Capable of fabricating parts up to 12 ft. length and +/-0.001 in. tolerance. Various capabilities include contract manufacturing,custom stamping,edge rolling, forming,top laser cutting, roll bending and welding. Finishing and secondary services such as hardware installation, tapping, deburring, cleaning, heat treating, plating, anodizing and painting available. Sheet Metal Prototype and low to high volume production runs offered. Suitable for commercial/residential architectural, aluminum brake shape parts, wall panel systems, brackets, general flashings, rails, call button plates and ship building component parts.