NEWS&CASES
Time：2025-04-17
Class：News
An article to understand galvanized steel: categories, materials, advantages, disadvantages and applications
I. Categories of Galvanized Steel
Galvanized steel can be classified into various types according to its production and processing methods.
- Hot-dip Galvanized Steel: The steel is immersed in a molten zinc bath, allowing zinc to adhere to the surface of the steel. Factories mostly use the continuous galvanizing method, continuously immersing coiled steel into a zinc plating bath for production. The hot-dip galvanized layer is relatively thick and adheres closely to the steel substrate, providing strong corrosion resistance. It is widely used in construction structural components, power transmission towers, highway guardrails and other facilities that are exposed outdoors for a long time and have high requirements for corrosion resistance.
- Alloy Galvanized Steel: The manufacturing process is also the hot-dip method. Immediately after the steel comes out of the bath, it is heated to about 500°C to promote the formation of an alloy film between zinc and iron. This type of steel has good adhesion and weldability and is often used in industries with strict requirements for welding and painting effects, such as the automotive manufacturing and mechanical processing industries. For example, some auto parts will choose alloy galvanized steel.
- Electroplated Galvanized Steel: Through the electroplating method, a zinc layer is deposited on the surface of the steel using the principle of electrolysis. This type of steel has good processing performance and can be easily bent, stamped and other processing operations. However, its galvanized layer is relatively thin, and its corrosion resistance is inferior to that of hot-dip galvanized steel. It is often used in electronic device casings, small hardware products and other products that do not have very high requirements for corrosion resistance but pay more attention to processing accuracy and surface flatness.
- Single-sided and Double-sided Differential Galvanized Steel: Single-sided galvanized steel is only galvanized on one side and has better adaptability in welding, painting, anti-rust treatment, etc. than double-sided galvanized steel, making it suitable for specific scenarios with single-sided protection requirements. Double-sided differential galvanized steel is to overcome the shortcoming of no galvanizing on one side and apply a thin layer of zinc on the other side. For example, it is used in some packaging industries and simple building structural components where cost is sensitive and the corrosion risk on one side is relatively low.
- Alloy and Composite Galvanized Steel: Made of alloys of zinc with other metals such as aluminum and lead or composite plated, it has both excellent rust resistance and good painting performance and is often used in fields with high requirements for the comprehensive performance of materials, such as aerospace and high-end building decoration.
II. Material Composition of Galvanized Steel
Galvanized steel is mainly composed of a steel substrate and a galvanized layer.
- Steel Substrate: Carbon steel is commonly used. According to the different carbon content, it can be divided into low-carbon steel, medium-carbon steel and high-carbon steel. Low-carbon steel has good plasticity and weldability and is suitable for cold processing. In galvanized steel, it is used to manufacture parts that do not require high strength but need complex forming. Medium-carbon steel has moderate strength and toughness and can be used for structural components that bear certain loads. High-carbon steel has high strength and hardness and is often used to manufacture parts that need to be wear-resistant. In addition to carbon steel, alloy steel can also be used as the substrate. By adding alloying elements such as chromium, nickel and molybdenum, the comprehensive performance of the steel can be improved, such as improving corrosion resistance, strength and heat resistance, to meet the use requirements in special environments.
- Galvanized Layer: Zinc, as the main plating metal, can react with oxygen in the atmosphere to form a dense zinc oxide film, which is like putting a "protective suit" on the steel, effectively blocking oxygen and moisture from eroding the steel substrate and greatly extending the service life of the steel. In some special application scenarios, other elements will be added to the zinc plating layer to form an alloy plating layer. For example, adding aluminum can improve the high-temperature resistance and marine atmospheric corrosion resistance of the plating layer; adding magnesium can enhance the corrosion resistance and self-healing ability of the plating layer. These alloy plating layers further optimize the protective performance of galvanized steel in specific environments.
III. Advantages of Galvanized Steel
- Excellent Corrosion Resistance: This is the most prominent advantage of galvanized steel. The zinc layer builds a solid barrier on the surface of the steel, effectively blocking oxygen and moisture from contacting the steel substrate and slowing down the corrosion process. Taking hot-dip galvanized steel as an example, in a common suburban environment, a standard thickness anti-rust layer can last for more than 50 years without repair; even in urban areas or offshore areas with a harsh corrosion environment, it can ensure a protection period of about 20 years.
- High Cost-effectiveness: From the perspective of long-term maintenance costs, galvanized steel is cost-effective. The cost of hot-dip galvanizing anti-rust treatment is lower than that of most paint coatings, and it reduces the frequency of frequent replacement or maintenance of steel parts, reducing the overall cost. For example, when highway guardrails choose hot-dip galvanized steel, although the initial procurement cost is slightly higher, after many years of use, the maintenance cost is much lower than that of ordinary steel guardrails without galvanizing.
- Good Adhesion and Reliability: The galvanized layer and the steel substrate are metallurgically combined to become part of the steel surface, with strong adhesion and not easy to fall off. During transportation, installation and long-term use, the plating layer can adhere stably, ensuring the long-term reliability of the protective performance.
- Comprehensive Protection: Regardless of how complex the shape of the steel is, the galvanizing process can evenly cover the zinc layer on all parts of the plated part, including recesses, sharp corners and hidden parts, achieving all-round protection.
- Good Processing Performance: Galvanized steel basically retains the processing performance of the steel substrate and can be processed by bending, stamping, welding and other operations to meet diverse manufacturing needs. For example, electroplated galvanized steel has high processing accuracy and is suitable for making complex-shaped electronic device casings; alloy galvanized steel can meet the requirements for the comprehensive performance of materials such as auto parts while ensuring weldability.
IV. Disadvantages of Galvanized Steel
- Relatively High Initial Cost: Compared with ordinary steel, the production of galvanized steel requires an additional galvanizing process, which increases the costs of raw materials, equipment and labor, resulting in generally higher prices. For example, hot-dip galvanized steel has a higher price than ordinary steel of the same specification due to its thick plating layer and complex process.
- Increased Weight: The existence of the galvanized layer increases the weight of the steel. In weight-sensitive application scenarios, such as some parts in the aerospace field, it may bring problems such as increased transportation costs and energy consumption.
- Difficult Surface Treatment: The galvanized layer will affect the adhesion of subsequent coatings. In the case of further painting, special processes and pretreatment methods need to be adopted to ensure a good combination between the coating and the galvanized layer. Otherwise, problems such as coating peeling are likely to occur.
- Challenges in Welding: When welding galvanized steel, the zinc layer is prone to defects such as pores and cracks, affecting the welding quality. To ensure the welding effect, it is necessary to adjust welding parameters, select appropriate welding materials and methods, increasing the complexity of the welding process.
- Zinc Layer Prone to Damage: During handling and installation, if the zinc layer on the surface of galvanized steel is scratched or collided, its protective performance will be greatly reduced, reducing the overall service life. Special attention needs to be paid to protection during construction and use.
V. Application Scenarios of Different Categories and Materials
- Construction Field: Hot-dip galvanized steel is used for building structural frames to ensure the long-term stability of buildings in various climatic conditions; galvanized steel pipes are used as water supply and drainage pipes, which are corrosion-resistant, ensuring that the water quality is not polluted and has a long service life; alloy galvanized steel is used for building decoration parts due to its good weldability and painting performance, such as the galvanizing treatment of aluminum alloy door and window frames, which is both beautiful and durable.
- Industrial Field: In the chemical industry, hot-dip galvanized and alloy and composite galvanized steel are used to make reaction kettles, pipelines and other equipment to resist the erosion of corrosive chemicals; in the electronic and electrical industry, electroplated galvanized steel is used to manufacture electronic device casings, meeting the requirements for processing accuracy and surface quality while providing certain corrosion protection; in the automotive industry, alloy galvanized steel is used for automotive chassis, body structural parts, etc., improving the overall corrosion resistance and safety of automobiles.
- Transportation Field: Hot-dip galvanized steel is an ideal material for highway guardrails and railway bridge structural parts, which can withstand harsh outdoor environmental tests; traffic signs are often made of single-sided or double-sided differential galvanized steel to meet the requirements of single-sided visibility and cost control; in shipbuilding, alloy and composite galvanized steel are used to manufacture some parts on ships to adapt to the high-salinity and high-humidity corrosion environment of the ocean.