Steel sheets that have been zinc-coated are referred to as galvanized iron (GI) sheets. These sheets are available in both hot dip and electro galvanized metal sheet forms and different sizes. The continuous barrier created by the zinc coating prevents oxygen and moisture from reaching the steel. To safeguard the base steel, it responds with the environment. Galvanizing considerably improves the protection of steel sheets against corrosion resistance. Because zinc is anodic to iron and works as a sacrificial metal in watery or humid environments, zinc-based coatings provide corrosion protection through the galvanic effect. However, putting a top coat to the galvanized surface can boost surface degradation resistance even further. 
Galvanized steel sheets have an acceptable peel-off resistance and a coating that completely clings to the steel surface, in addition to a good shining surface and high formability. Because zinc weathers slowly, the coating might last for a long time. Because zinc has a higher electro-negativity than iron, it provides cathodic (or sacrificial) protection to steel. In addition to providing galvanic protection, this causes the zinc to corrode rather than the steel if the coating is chipped or damaged, exposing the base metal. The term "galvanizing" comes from the Italian scientist Luigi Galvani. Steel sheets are increasingly being used in everyday life. Galvanized steel sheets and other coated steel products have grown especially quickly in businesses that value corrosion resistance and process cost savings. The lower cost of galvanized steel sheets benefits electric appliances, electronic equipment, construction, and automotive applications. Galvanizing is the process of applying a protective zinc coating on steel. Galvanized steel sheet is one of the most commonly used roofing materials in homes, businesses, and industries. The roof is made of zinc-coated mild steel. Galvanized steel roofing sheets are frequently available in a range of long run roofing types, such as corrugated, trapezoidal, and trough section / concealed fix. It is also available as flat sheets on occasion. Lead-headed nails are commonly used to hold galvanized steel sheets to the surface to prevent rusting. The zinc layer on galvanized steel sheets also serves the following functions: I it keeps the steel intact and at full initial strength; (ii) it improves the surface's aesthetic appeal; (iii) it extends the life of any suitable organic finishing system applied over it; and (iv) it protects the steel from corrosive attack in the majority of environments, acting as an ongoing and durable barrier between the steel and the environment. The thickness or gauge of galvanized steel sheet is the most essential component in determining how well it resists "pulling" forces like suction in high winds. 
The gauge and kind of corrugation are also crucial for stability and resistance to increased stresses. Coating mass and coating thickness have a linear relationship. However, the length and breadth can be determined based on the purpose and the necessary parameters. The galvanized coating on steel sheets is composed of a steel core, an external layer of an intermetallic alloy, and zinc on both surfaces. Figure 1 shows a cross-section of the zinc coating. In addition to the zinc layer on the outside, it has gamma, delta, and zeta layers (eta layer). As assessed by the DPN, the zinc coating's Gamma, Delta, and Zeta layers are harder than the underlying steel (diamond pyramid number). Because of their increased hardness, these layers provide excellent protection against coating abrasion damage. The thickness of hot-dip galvanized coatings is determined by the thickness of the zinc-iron alloy layers that occur when steel reacts with zinc. The alloy layer is typically 95% iron and 5% alloy. Thicker galvanized coatings provide more durability. The tensile strength of the zinc coated layer increases with thickness. The eta layer of the coating provides some impact protection due to its low hardness and great ductility. Galvanized steel's exceptional resistance to abrasion and mechanical damage is owing to the fact that the zeta, delta, and gamma zinc-iron alloy layers are really harder than the underlying steel. Under abrasive or strong loading circumstances in service, the comparatively brittle eta layer of zinc can be removed from a galvanized surface, while the exceptionally hard zeta alloy layer remains exposed to survive further abrasion and heavy stress. 
The alloy layer is critical for achieving a strong bond between steel and zinc. Galvanized steel sheets have the following key properties: corrosion resistance, good surface appearance, good formability for meeting deep drawing requirements, good paintability if appropriate pre-treatment is performed, and good weldability. The combination of hardness, ductility, and adhesion provides the galvanized coating with excellent abrasion resistance during harsh handling. Coating mass and coating thickness have a linear relationship. The thickness of hot-dip galvanized coatings is determined by the thickness of the zinc-iron alloy layers that occur when steel reacts with zinc. Galvanized steel with a thicker coating is more corrosion resistant and lasts longer. It can, however, make the steel less formable. The tensile strength of the zinc coated layer increases with thickness. Furthermore, unlike most organic coatings, which thin down in these critical areas, galvanized coatings are slightly thicker at the corners and edges. 
hot dip galvanized sheet
The technology for galvanized steel sheet was developed concurrently in France and England in 1837. To apply zinc to steel sheet, both of these procedures required a "hot dip" procedure. Hot dip and electro-galvanizing are the two major types of galvanizing procedures. The hot dip process is more suitable for larger coating weights, such as electro-galvanizing. Because it is more efficient, galvanizing cold rolled strips rather than cold rolled sheets is more common. Galvanized steel sheets are manufactured under both annealed and completely hardened conditions. Steel strips are immersed in molten zinc as part of the "hot dip galvanizing" process principle. Galvanizing uses high grade zinc with a minimum zinc content of 99.95%. During the manufacturing process, molten zinc is continually poured to the surface of the steel substrate, as shown in Fig. 3. The steel is coated by passing it in a continuous strip at roughly 180 meters per minute through a bath of molten zinc. Prior to the continuous hot dip coating process, the steel is typically washed with alkaline solutions, followed by rinsing and drying. The steel is then transported into an annealing or heating furnace to soften it and give it the appropriate formability and strength. Steel is heated in a furnace in a low gas atmosphere of nitrogen and hydrogen to remove any oxide traces that may be present on the steel's surface. A vacuum chamber known as the "snout" is connected to the exit end of the furnace and the molten zinc coating bath to prevent the heated steel product from being re-oxidized by air. Before being retrieved vertically, the steel product is wrapped around a submerging roll in the zinc coating bath, where it reacts with the molten zinc metal to form a sticky coating. After the coated steel has been taken from the bath, any excess molten zinc is evaporated using high-pressure air to achieve a perfectly regulated coating thickness. 
Finally, the steel is allowed to cool so that the zinc coating may cling to the surface. The molten metal must solidify before coming into contact with another roll to avoid damaging or deforming the zinc coating. In order to produce galvanized steel sheets, there are six primary procedures that must be completed. They are as follows: I a welding process to join the ends of the sheared steel sheet to the previous sheets to create one continuous sheet, (ii) a straightening process to achieve good flatness on the steel sheet using a high-performance tension leveler, and (iii) a cleaning process in which the steel sheet is first cleaned in an alkali bath and brushed for initial degreasing to remove surface oxides and achieve complete adhesion of the coating. Each of these processes must be completed before the (iv) Continuous annealing, which involves continuously putting the steel sheet through a reduction furnace to reduce the oxidized film on the surface; (v) Galvanizing, which involves leaving the steel sheet in a reduction atmosphere before submerging it directly into a bath of molten zinc; and (vi) Removing additional molten zinc from the bath by pulling vertically. The treatment consists of a phosphate treatment, which makes the surface exceptionally paintable, and a chromate-free special treatment, which makes the surface more corrosion resistant. In order to activate the surface with a reducing gas and apply the necessary heat cycle in order to obtain the requisite mechanical qualities, the annealing furnace is utilized. The surface of the strip can then be zinc-plated easily as a result. A purge gas jet is blown from a nozzle above the pot onto both surfaces of the strip in order to adjust the coating weight and remove extra molten zinc. This is done in order to remove the surplus zinc. This method results in a thick covering of zinc, which, when allowed to crystallize, takes on the pattern of the spangles surface. A multilayered structure of iron-zinc alloys is created during the process between the inner surface of the zinc coating and the steel strip. This structure is sandwiched between the two materials. 
Coating thicknesses for hot-dip galvanization can range anywhere from 12 micrometers all the way up to more than 160 micrometers (for both sides together). Galvannealing was developed to improve these qualities since the surface of the zinc layer isn't always optimal for weldability and paint adhesion. In the basic procedure for galvannealed strip, the zinc-coated strip is heated in a galvannealing furnace after emerging from the pot, resulting in the formation of an iron-zinc alloy layer by the inter-diffusion of iron and zinc coating layer, so that the surface of the zinc layer also contains some iron. Following the galvannealing furnace, the galvannealing line normally includes a skin pass mill, a tension leveller, and chromating chemical treatment equipment. Galvanizing by the use of electricity Electro-galvanizing makes it possible to create very thin zinc coatings that are formable, and these coatings are excellent for creating detailed sketches or paintings on coated steel strips. During this step of the process, zinc is deposited onto the steel sheet in an electrolytic manner. The coating is very uniform in appearance, despite its thinness, and it adheres well. The sheet that was hot-dip galvanized does not have any zinc crystals on it. The coating is composed entirely of zinc, and its structure is consistent throughout. There is also the possibility of using an electro-galvanized zinc-nickel or zinc-iron coating. In most cases, the coating that is produced through the electrogalvanizing process is thinner than the coating that is produced through the hot-dip galvanizing method. The fact that electro-galvanizing can be performed in a cold environment without compromising the steel's mechanical qualities is one of the process' many benefits. 
The procedure is carried out by immersing steel sheets in an electrolyte, which could be a solution of zinc sulfate or cyanide, respectively. The pure zinc that covers the surface of the steel sheet is the result of electrolytic activity. The ability to precisely regulate the coating thickness is one of the advantages provided by this technique. On the other hand, it is frequently unable to produce coatings that are as thick as those produced by the hot-dip galvanizing method. During the electro-galvanizing process, electroplating cells are utilized in order to deposit zinc onto the steel substrate. The procedure is ongoing, and it consists of cleaning the surface, plating it, and lubricating it. Surface preparation, which may involve brushing, electrolytic alkaline cleaning, spray alkaline cleaning, and surface activation with sulfuric acid, is essential for ensuring that a coating will adhere well. In the plating section, zinc ions are present in an aqueous solution, and an electrical current is passed through a strip that is submerged in the solution. Because of this, the coating of zinc that covers the steel substrate is consistent throughout its thickness. An in-line x-ray coating weight gauge is utilized all during the process in order to continuously measure the thickness of the deposit. The strip is then electrostatically coated with a homogeneous layer of rust-preventive oil or pre-lube after the plating process has been completed. 