Galvalume, galvanized, and aluminum are all characterized by hot-dip coating processes. The coating metal does not directly contact the steel base. Unlike electroplating, the bonding force between the coating and the steel base is the attraction between atoms. It is formed into a compound and held together. The compound is characterized by high hardness and poor plasticity. Therefore, the presence of this layer of compound greatly affects the corrosion resistance of the coated product after processing and bending.
Galvanized sheet: Among the three coatings, the compound layer of hot-dip galvanizing is the thinnest and the thickness is the easiest to control. It can be thinner after adding a small amount of aluminum, so its processing performance is better Of course, the corrosion resistance of coated products mainly depends on the coating. When the coating is intact, the anti-corrosion performance of the zinc coating is not very good, because the product after corrosion is very loose, and a dense oxide film protective layer cannot be formed to prevent further corrosion of the internal structure. But it can basically meet the needs of various uses. The anti-corrosion ability of the galvanized layer has its unique advantages after the coating is scratched and the steel base is exposed. After the galvanized layer is scratched, the physical protection of the coating on the steel base disappears, and the electrochemical protection must be used at this time. Because the electrode potential of the zinc-plated layer is different from that of the steel base, a galvanic cell will be formed in a humid environment. The zinc-plated layer generally loses electrons and is oxidized as an anode, while the steel base gets electrons as a cathode to be protected. Because zinc oxide is not very dense, this sacrificial anticorrosion effect is strong, and it can protect the steel base until the zinc coating is completely corroded.
Aluminized plate: Similar to the hot-dip galvanized layer, the aluminized plate also has two layers, the outer layer is a pure aluminum crystalline layer, and the inner layer is an iron-aluminum compound layer. Because aluminum is more active, the diffusion and chemical interaction between liquid aluminum and solid iron is very strong, so its compound layer is also the thickest and the most difficult to control. This affects its processing performance, and it is easy to cause the coating to crack or even fall off during drawing and deep drawing. The anti-corrosion performance of the aluminized layer can be fully reflected when the coating is not scratched. On the one hand, because the aluminum surface can form a dense protective film, it will not be further corroded under very harsh conditions, so its anti-corrosion effect is very strong. On the other hand, the high temperature and oxidation resistance of the aluminum-plated layer is also very strong, and there is no problem when it is used below 450 degrees Celsius, and its heat resistance is equivalent to that of stainless steel. However, once the coating is scratched and the steel base is exposed to the environmental medium, the protective effect of the aluminum coating will be greatly weakened. Although the aluminum-plated layer has the same cathodic protection effect as the zinc-plated layer, the dense oxide formed on the aluminum surface weakens the sacrificial protection of the coating, and the steel base is corroded before the coating.
3. Galvalume: Galvalume steel combines the advantages of aluminized steel and galvanized steel while overcoming the shortcomings of both because of its special structure. The weight ratio and volume ratio of aluminum are larger than zinc, so its mechanism is closer to that of aluminum-plated plates, but it is more complicated than both galvanized and aluminum-plated layers. In addition to the aluminum-iron compound layer, the intermediate compound has the same aluminum-iron compound layer as the aluminum-plated layer. In addition, due to the addition of a certain amount of silicon, silicon preferentially forms an iron-silicon compound layer on the surface of the steel base, making the aluminum-iron compound layer very thin, thereby improving its processing performance. Such a surface coating is very complicated and just right. A large amount of aluminum first formed extremely fine aluminum-rich dendrites, which accounted for 80% of the volume, and formed a fine network framework in the entire coating, and the remaining about 20% of the gap was zinc-rich eutectic organization. The combination of these two characteristics of organic organization, which makes the coating have a good comprehensive performance. The aluminum-rich dendritic network establishes that the coating has the corrosion resistance and thermal oxidation resistance of aluminum plating, and the intergranular zinc-rich structure makes the coating have the same anodic protection effect as the galvanized sheet in the environmental medium after scratching, and The product film produced by corrosion is retained by the aluminum-rich dendritic network and fills the gaps between the dendrites. A protective film is formed on the surface of the coating to slow down the corrosion rate and make it resistant The corrosion performance is much higher than that of the galvanized layer of the same thickness. At present, galvanized sheets are beginning to be used in ovens, dryers and coolers in household appliances, automobile tail pipes, mufflers, heat dissipation panels, etc. In addition, galvanized sheets of the same thickness, width, and weight are longer than galvanized sheets About 5%.