Galvanised steel sheet is a type of metal material with corrosion-resistant properties. It is produced by coating the surface of ordinary steel with a layer of zinc metal to enhance the steel's corrosion resistance and extend its service life. It is widely used in industries such as construction, furniture, automobiles, and appliances, and has a broad range of applications and market demand.

1. Definition and Principle

Definition: Galvanised steel sheet refers to metal sheets with a layer of zinc coated on the surface of steel plates.

Principle: Zinc has relatively active chemical properties, forming a dense layer of zinc oxide on the surface of the steel plate. This layer prevents direct contact between the steel plate and oxygen and water in the air, thereby achieving corrosion protection.

2. Galvanised Steel Sheet Manufacturing Process

The manufacturing process for galvanised steel sheets primarily includes two methods: hot-dip galvanising and electrogalvanising.

Hot-dip galvanising is the most widely used galvanising method currently. Pre-treated steel plates are immersed in molten zinc solution, and after a certain period of time, a galvanised layer composed of a zinc-iron alloy layer and a pure zinc layer forms on the surface of the steel plate. Hot-dip galvanised steel sheets have a thicker galvanised layer, strong corrosion resistance, good adhesion, and excellent processing properties. They are suitable for applications requiring high corrosion resistance, such as steel structural components in construction and chassis components in automobiles.

Electrogalvanising, on the other hand, utilises electrochemistry. In an electrolyte solution containing zinc salts, the steel plate serves as the cathode and the zinc plate as the anode. An electric current causes zinc ions to deposit on the steel plate surface, forming a galvanised layer. Electrogalvanised steel sheets have a relatively thinner zinc coating but a smoother and more uniform surface, making them suitable for products with high aesthetic quality requirements and less severe corrosion environments, such as appliance housings and electronic device components. Both processes have their advantages and disadvantages, but either method effectively enhances the corrosion resistance of steel.

Secondly, galvanised steel sheets have excellent corrosion resistance. The zinc layer forms a protective film on the steel surface, effectively isolating air, water, and other corrosive media, thereby slowing down the corrosion rate of the steel. Galvanised steel sheets have a longer service life in humid and corrosive environments, reducing maintenance and replacement costs, and are widely used and favoured.

Additionally, galvanised steel sheets have good processing properties. They perform well in terms of processing, welding, and cutting. This makes galvanised steel sheets more convenient and efficient in the manufacture of various products, meeting the needs of different industries.

3. Analysis of the waterproof performance of galvanised steel sheets

(1) Corrosion resistance mechanism

The waterproof performance of galvanised steel sheets primarily relies on the protective effect of the zinc coating on the surface. Zinc reacts with oxygen in the air to form a dense zinc oxide film (ZnO), which further reacts with moisture and carbon dioxide to form basic zinc carbonate (Zn?(OH)?(CO?)?). This compound effectively blocks the penetration of water vapour and corrosive media. According to the American ASTM A123 standard, the average thickness of the galvanised layer must exceed 85 μm to ensure a corrosion resistance lifespan of over 10 years in ordinary atmospheric conditions.

(2) Galvanised layer thickness and waterproofing performance

Experimental data indicates that galvanised layer thickness is positively correlated with waterproofing performance:

- When the galvanised layer thickness is 20–40 μm, it is suitable for dry indoor environments (such as ceilings and partition walls), with a lifespan of approximately 5–8 years;

- At a thickness of 60–80 μm, it can withstand mildly humid environments (e.g., warehouses, carports), with a lifespan of approximately 10–15 years;

- At a thickness of ≥100 μm, it is suitable for high-humidity or industrially polluted areas (e.g., coastal buildings, chemical plants), with a lifespan of over 20 years (data source: International Zinc Association IZA).

(3) Environmental Adaptability Comparison

Simulating different environments through salt spray tests (ASTM B117):

- Neutral environment (pH 6-8): Corrosion rate of galvanised steel sheets <1 μm/year;

- Acidic environment (pH <5): Corrosion rate increases to 3-5 μm/year, requiring increased coating thickness or additional coating protection;

- Alkaline environment (pH > 9): The zinc layer is prone to dissolution, and direct use is not recommended.

 
4. Advantages of galvanised steel sheets  

(1) Durability. Galvanised steel sheets used for wall decoration will not dent or scratch easily during transportation or subsequent use due to external impacts.  

(2) Moisture-resistant and durable. The material of galvanised steel sheets will not be affected by environmental conditions or weather, preventing mould growth or moisture absorption, thereby maintaining product performance.

(3) Rust and Corrosion Resistance. The zinc coating on the surface of galvanised steel sheets forms an antioxidant layer on the steel surface, enhancing the corrosion and rust resistance of equipment, machinery, and other components, thereby effectively extending the product's service life.  

(4) Quick and Convenient Installation. Galvanised steel sheets are more time-efficient and labour-saving to install compared to other materials. Once installed, they can be put into use without on-site painting.

(5) High ductility. Galvanised steel sheets can be processed in various ways, including stamping, rolling, and bending, to meet different requirements.  

(6) Good heat resistance. Most materials can only withstand temperatures up to 230°C, otherwise they may deform or discolour. Galvanised steel sheets can withstand temperatures of around 310°C for 120 hours without discolouring or deforming.  

5. Application Areas  

Galvanised steel sheets are widely used across multiple industries due to their excellent corrosion resistance and aesthetically pleasing appearance:  

Construction Industry: Used in balconies, window sills, warehouses, and roll-up doors on rooftops, where welding, coating, and rust prevention requirements are high.  

Household Appliances: Used in refrigerators, microwave ovens, washing machines, and other household appliances, combining the properties of steel and zinc for durability and longevity.

Automotive Industry: Galvanised steel sheets are aesthetically pleasing, smooth, and highly corrosion-resistant, making them widely used for full-body coverage in automotive applications, such as car ceilings and body panels.

Transportation Industry: Used in various containers, ship compartment partitions, and road barriers where durable materials are required.

Furniture industry: The malleability of galvanised steel sheets is also highly suitable for the furniture industry, and they can be used in the manufacture of products such as lampshades, desks, counters, and bookshelves.

6. Limitations and precautions

(1) Welding area protection: Welding can damage the zinc layer, so it must be repaired with zinc-rich paint (zinc content ≥80%).

(2) Economic Considerations: Galvanised steel plates are 20%-30% more expensive than ordinary steel plates, but their lifecycle costs are reduced by over 40% (data source: China Society for Corrosion and Protection).

(3) Alternative Solutions for Special Environments: In strong acid (e.g., pH < 3) or high-temperature (＞200°C) environments, it is recommended to use stainless steel or fluorocarbon-coated steel plates instead.

In summary, galvanised steel sheets, as an important metal material, play an indispensable role in modern industrial production. Their excellent performance and broad application prospects ensure their stable market position, and they are expected to have even broader development prospects in the future. We hope the information provided in this article will be helpful and deepen your understanding of galvanised steel sheets.