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What is the difference between pre-galvanized and galvanized steel?
What is the difference between pre-galvanized and galvanized steel?
The main difference between pre-galvanized steel and galvanized steel lies in the timing of the galvanizing process, application scenarios, and performance characteristics. The following is a detailed comparison of the two.
1. Definition and Process
Galvanized Steel
Definition: A zinc coating is applied to the surface of steel using hot-dip galvanizing or electro-galvanizing processes to enhance corrosion resistance.
Process:
Hot-dip galvanizing: The steel is immersed in molten zinc, forming a zinc-iron alloy layer and a pure zinc layer.
Electro-galvanizing: A thin, uniform zinc layer is deposited on the steel surface through electrolysis.
Typical Applications: Building structures, pipes, guardrails, etc.
Pre-Galvanized Steel
Definition: Steel that has been galvanized before forming (e.g., during rolling), typically using a continuous galvanizing line (e.g., a CAGL line).
Process:
Continuous hot-dip galvanizing: The steel is galvanized directly on a continuous production line, resulting in a strong bond between the zinc layer and the substrate.
Pretreatment: The steel undergoes pickling and cleaning before galvanizing to ensure a clean surface. Typical applications: parts that require complex processing (such as stamping, bending), or products with high surface quality requirements (such as home appliances, automotive parts)
2. Performance comparison
| Galvanized Steel | Pre-Galvanized Steel |
| Usually thicker (hot-dip galvanizing can reach 60–100 μm) | Thinner (electrogalvanizing, approximately 5–20 μm) |
| Excellent (the zinc layer sacrifices the steel substrate) | Good, but durability is slightly reduced when the zinc layer is thinner |
| Post-molding galvanizing is suitable for simple structures. | Pre-molding galvanizing is suitable for complex processes (such as stamping). |
May have zinc bumps or unevenness (hot-dip galvanizing) | Smooth and uniform surface (electrogalvanizing or continuous galvanizing) |
Hot-dip galvanizing is more expensive; electrogalvanizing is less expensive. | Usually higher (due to process complexity and equipment requirements) |
3. Applications
Galvanized Steel
Hot-dip galvanized steel: Suitable for outdoor use or in highly corrosive environments (such as bridges, water pipelines, and agricultural machinery).
Electrogalvanized steel: Suitable for indoor use or in mildly corrosive environments (such as appliance housings and automotive interiors).
Pre-Galvanized Steel
Continuously galvanized steel strip: Widely used in applications requiring high strength and complex forming, such as automotive manufacturing (doors and roofs), construction (color-coated steel sheets), and appliance manufacturing (refrigerator housings).
Advantages: Prevents zinc layer loss or damage during processing, reducing subsequent processing steps.
4. Process Differences
Galvanized Steel (Taking Hot-Dip Galvanizing as an Example)
Pickling removes surface scale.
Immersed in molten zinc (approximately 450°C) to form a zinc layer.
The surface cools and solidifies, and may develop zinc nodules or a rough texture.
Pre-Galvanized Steel (Taking Continuous Galvanizing Line as an Example)
After rolling, the steel enters the galvanizing line directly.
After pickling and cleaning, it is continuously galvanized in a zinc bath.
Annealing, cooling, and oiling or passivation ensure uniform and strong zinc layer adhesion.
5. Advantages and Disadvantages
Galvanized Steel
Advantages:
High corrosion resistance (especially hot-dip galvanizing).
Relatively low cost (electrogalvanizing).
Suitable for large-scale outdoor applications.
Disadvantages:
Hot-dip galvanizing may result in surface unevenness.
The electrogalvanized zinc layer is thin and has limited durability.
Pre-Galvanized Steel
Advantages:
Smooth surface, suitable for precision machining.
Evenly distributed zinc layer reduces post-processing.
Suitable for complex forming (such as stamping).
Disadvantages:
High cost (due to the high investment required for continuous production lines).
Corrosion protection design is required when the zinc layer is thin.
Galvanized Steel: Water pipelines, solar panels, and agricultural machinery frames.
Pre-Galvanized Steel: Automotive body panels, appliance casings, and architectural color-coated steel sheets.