Galvanized steel sheet: the "all-round guard" of steel corrosion protection

Galvanized steel sheet is the "anti-corrosion armor" of steel materials. By coating the surface of the steel sheet with zinc, the corrosion resistance of ordinary carbon steel is extended from 2-3 years to more than 20 years, and an anti-corrosion barrier is built in the fields of construction, automobiles, and home appliances. From precision electronic components with a thickness of 0.1mm to building curtain wall panels with a width of 2.5m, galvanized steel sheets have achieved a material revolution of "steel as the skeleton and zinc as the shield" through process innovations such as hot-dip and electroplating, and have become one of the most widely used anti-corrosion steel materials in the world.
1. Definition and classification system of galvanized steel sheet
Definition: Galvanized steel sheet refers to steel with a layer of zinc coating on the surface of the steel sheet through hot-dip plating, electroplating or spraying. The thickness of the zinc layer is usually 5-275μm. The sacrificial anode protection principle of zinc (potential - 0.76V vs iron - 0.44V) is used to protect the steel sheet from corrosion in the atmosphere, water and other environments. According to GB/T 2518-2019 standard, the substrate of galvanized steel sheet can be low carbon steel, high strength steel or stainless steel, and the coating types include pure zinc, zinc-iron alloy, zinc-aluminum-magnesium, etc.
Classification by substrate strength
Ordinary strength galvanized sheet: substrate yield strength ≤260MPa, such as DX51D, used for non-stressed components;
High strength galvanized sheet: substrate yield strength 260-550MPa, such as S350GD+Z, used for automotive structural parts;
Ultra-high strength galvanized sheet: substrate yield strength ≥550MPa, such as HC700/980DP+Z, used for automotive anti-collision beams;
Stainless steel galvanized sheet: substrate is 304 stainless steel, coating is zinc-nickel alloy, used in extreme corrosive environments.
2. Production process and key technological breakthroughs
Full process analysis
Substrate pretreatment:
Pickling and rust removal: Use hydrochloric acid or sulfuric acid to remove the oxide scale on the surface of the substrate, the acid concentration is 10-15%, and the temperature is 60-80℃;
Electrolytic cleaning: Electrolytic degreasing in sodium hydroxide solution (concentration 5-10%), voltage 5-15V, to remove oil residue.
Hot-dip galvanizing process:
Annealing treatment: The substrate is heated to 850-950℃ in a continuous annealing furnace to form a uniform ferrite structure and improve the adhesion of the coating;
Hot-dip plating: Immerse in a 450-480℃ zinc pot, the immersion time is 3-10 seconds, and 0.1-0.3% aluminum is added to the zinc liquid to improve the uniformity of the coating;
Alloying: After plating, heat to 500-550℃ to form a Fe-Zn alloy layer with the substrate to improve weldability.
Electrogalvanizing process:
Electroplating tank: chloride zinc plating tank (Zn2 + concentration 40-60g/L, pH 1.0-2.0), current density 10-30A/dm²;
Passivation treatment: Chromium-free passivation uses silane or titanium salt treatment, film thickness 0.1-0.5μm, replacing traditional hexavalent chromium passivation;
Post-treatment: Apply fingerprint-resistant coating, the friction coefficient is controlled at 0.2-0.4, used for home appliance panels.
Cutting-edge technology cases
Zinc-aluminum-magnesium coating technology: The Zn-5% Al-3% Mg coated steel plate developed by Hesteel Group has a corrosion rate of only 1/3 of hot-dip galvanizing in the marine environment and has been used in the ancillary facilities of the Hong Kong-Zhuhai-Macao Bridge;
Digital galvanizing line: The intelligent hot-dip galvanizing line deployed by Baowu Group uses AI algorithms to adjust the zinc pot temperature and immersion time in real time, and controls the coating thickness tolerance to ±3μm;
Galvanized sheet for 3D printing: The galvanized steel sheet powder developed by Ansteel is 3D printed into automotive parts using SLM technology, and the uniformity of the zinc layer distribution reaches 98%.
3. Performance advantages and engineering applications
Construction and infrastructure fields
Steel structure anti-corrosion:
DX51D+Z275 hot-dip galvanized sheet (thickness 1.2mm) is used for the roof of Xiongan New Area high-speed railway station, with a zinc layer thickness of 275μm and an estimated corrosion resistance life of more than 50 years;
Zinc-aluminum-magnesium steel sheet (thickness 2.0mm) is used for the Qinghai-Tibet Railway bridge guardrail. In the strong ultraviolet environment of the plateau, there is no obvious rust for 10 years.
Building enclosure:
SECC electrogalvanized sheet (thickness 0.8mm) is used for the ceiling of the terminal building of Beijing Daxing International Airport. It is treated with fingerprint resistance and can resist oil and dirt wiping for ≥1000 times;
Galvalume AZ55 sheet (thickness 0.5mm) is used for the greenhouse of Singapore Marina Bay Gardens. The reflectivity of the aluminum-zinc alloy coating is ≥75%, which reduces the indoor temperature.
Automobile and transportation field
Lightweight body:
The Tesla Model Y body uses HC550/690DP+ZF80 zinc-iron alloy plate (thickness 0.7mm), with a yield strength of 550MPa, reducing weight by 15% while improving collision performance;
The BYD blade battery shell uses 5052 aluminum alloy-galvanized steel composite plate, which combines the lightweight of aluminum with the corrosion resistance of zinc.
Rail transportation:
The CRRC Sifang subway car uses S350GD+Z hot-dip galvanized plate (thickness 1.5mm), which has no rust after salt spray resistance test (1000 hours) and is suitable for underground humid environments;
The high-speed rail contact network bracket uses zinc-aluminum-magnesium steel plate (thickness 3.0mm), which has a service life of 20 years in acid rain areas (pH≤4.5).
Home appliances and electronics
White appliances:
The SECC-N5 electrogalvanized sheet (thickness 0.5mm) is used for the shell of Haier refrigerators. The surface is sprayed with anti-fingerprint coating and has no rust after salt spray test (500 hours);
DX53D+Z100 hot-dip galvanized sheet (thickness 0.6mm) is used for the outdoor unit of Midea air conditioner. The zinc layer is 100μm, which can resist acid rain erosion.
Electronic equipment:
Huawei server cabinet uses electrogalvanized sheet (thickness 1.0mm), with electromagnetic shielding efficiency ≥60dB, meeting EMC standards;
Galvanized steel sheet-plastic composite sheet is used for the shell of Apple mobile phone charger, which has both strength and insulation.
Energy and marine fields
New energy:
Zinc-aluminum-magnesium steel plates (thickness 2.5mm) for CATL battery storage containers, salt spray resistance test (3000 hours) without red rust, suitable for coastal power stations;
Goldwind Technology's wind turbine tower uses Galvalume AZ55 plates (thickness 2.0mm), which have a lifespan of 25 years in offshore wind power (humidity ≥ 95% RH) environment.
Marine engineering:
China's "Deep Sea No. 1" energy station uses zinc-aluminum-magnesium steel plates (thickness 8.0mm) to make seawater pipelines, which are resistant to Cl- corrosion (Cl-≤50000ppm);
Dalian Shipyard uses hot-dip galvanized plates (thickness 3.0mm) for ship cabins, with a zinc layer of 275μm, and a paint coating that is resistant to seawater vapor corrosion.
IV. Market dynamics and technological trends
Global industry status
Capacity distribution: In 2024, the global output of galvanized steel sheets will be about 120 million tons, of which China will account for 58% (Hebei, Shandong and Jiangsu are the main production areas), followed by Europe (15%), North America (12%) and Japan (8%);
Price dynamics: The average price of DX51D+Z80 hot-dip galvanized sheet (1.0mm×1250×2500mm) in 2024 is about US$850/ton, which is 10% higher than that in 2023 due to the zinc price (US$2500-3000/ton);
Import and export pattern: China exports about 15 million tons of galvanized steel sheets annually, mainly to Southeast Asia (accounting for 40%), and imports about 2 million tons, mainly high-end zinc-aluminum-magnesium sheets (such as KMC510P imported from South Korea, which is 30% higher than domestically produced).
Technology development direction
Green and low-carbon production:
Low-temperature galvanizing process: Develop 430℃ low-temperature hot-dip galvanizing technology, reduce energy consumption by 12%, and reduce zinc liquid volatilization by 50%;
Recycled zinc utilization: Use zinc slag direct electrolytic recovery technology, the purity of recycled zinc is ≥99.99%, which is used for electrogalvanizing production;
Popularization of chromium-free passivation: Promote silane-titanium zirconium composite passivation, and the domestic chromium-free passivation rate will reach 75% in 2024, which complies with the EU RoHS directive.
High-performance innovation:
Ultra-high-strength galvanized sheet: HC980/1180DP+Zn100 dual-phase galvanized sheet, tensile strength ≥1180MPa, used for automobile A-pillars and anti-collision beams;
Self-repairing galvanized sheet: Add microcapsule repair agent to the zinc layer, release corrosion inhibitor when the coating is damaged, and automatically repair microcracks;
Functional composite galvanized sheet: Galvanized sheet with integrated photocatalytic TiO₂ coating on the surface, formaldehyde degradation efficiency ≥90%, used for interior decoration.
Intelligent manufacturing:
AI detection of galvanized sheet surface defects: using deep learning algorithms to identify zinc particles and scratches larger than 0.1mm with an accuracy rate of 99.5%;
Digital twin galvanizing line: establishing a digital twin model of the hot-dip galvanizing process to predict the coating thickness deviation of ≤1μm, reducing trial and error costs;
Blockchain traceability: applying blockchain technology to galvanized sheets for automobiles to record the entire process data from steelmaking to stamping, meeting IATF 16949 certification.
New coating development:
Zinc-aluminum-magnesium-calcium coating: Zn-5% Al-3% Mg coating with 0.5% calcium added has 20% higher corrosion resistance than traditional zinc-aluminum-magnesium coating, and is used for photovoltaic brackets;
Graphene-enhanced zinc coating: Adding 0.1% graphene to the zinc solution increases the coating hardness from HV120 to HV180, and increases the wear resistance by 3 times;
Gradient-coated galvanized sheet: The zinc content changes gradually from the substrate to the surface, taking into account both strength and corrosion resistance, and is used for complex stamping parts.
5. Selection Guide and Maintenance Points
Selection Decision Factors
Environmental Corrosion Level:
Rural Environment: Select Z60 (60g/m²) hot-dip galvanized sheet, corrosion resistance life of 15 years;
Urban/Industrial Environment: Select Z100-Z150 hot-dip galvanized sheet, or zinc-iron alloy sheet;
Marine/High-salt Environment: Select zinc-aluminum-magnesium sheet (AlMg1.5) or Z275 hot-dip galvanized sheet, with coating.
Mechanical Performance Requirements:
Non-stressed components: Select DX51D+Z, yield strength ≥220MPa;
Automobile structural parts: Select S350GD+Z, yield strength 350MPa;
Anti-collision components: Select HC700/980DP+Z, tensile strength ≥980MPa.
Processing requirements:
Deep drawing: select DX56D+ZF zinc-iron alloy plate, r value ≥1.8;
Welding connection: select zinc-iron alloy plate, zinc layer iron content 10-15%, reduce welding spatter;
Coating requirements: select electrogalvanized plate, surface roughness Ra≤1.6μm, improve paint adhesion.
Storage and maintenance technology
Rust-proof storage:
Indoor storage: overhead stacking, humidity ≤60% RH, temperature 15-30℃, avoid contact with acidic substances;
Open-air storage: cover with waterproof canvas, raise the bottom 300mm, and place moisture-proof paper between steel plates;
Sea transportation protection: the surface of the galvanized plate is coated with a water-based rust inhibitor, wrapped with a heat shrink film, and a silica gel desiccant is placed in the container (dosage 500g/ton).
Surface maintenance:
Daily cleaning: Wipe with a neutral detergent (pH7-8), avoid using steel wool to damage the zinc layer;
Minor rust treatment: Clean with 10% citric acid solution (temperature 50℃, time 5 minutes), then apply zinc powder paint;
Coating repair: When the zinc coating is damaged, use cold spray zinc repair (zinc content ≥95%), and the dry film thickness is consistent with the original coating.
Special environment maintenance:
Coastal buildings: Rinse the surface of the galvanized sheet with high-pressure water (pressure ≥8MPa) every year to remove salt spray deposits;
Industrial atmosphere: Neutralize surface acidic pollutants with 10% trisodium phosphate solution every quarter;
Automobile body: Use nano-ceramic coating (thickness 5-8μm) to increase the surface hardness of the galvanized sheet to 9H and resist scratches.