Galvanized steel sheet: innovation of anti-corrosion process and application in many fields

First, the definition and core value of galvanized steel sheets

          Galvanized steel sheets is a metal material that achieves anti-corrosion by forming a zinc layer on the steel surface, and its process principle is based on the sacrificial anode protection mechanism of zinc. When the zinc layer is in contact with the steel matrix, the zinc is prefertively oxidized to form a dense oxide film, effectively isolating oxygen and moisture, and extending the service life of the steel by 5-8 times. About 50% of the world's zinc production is used for galvanizing process, and the annual production capacity of galvanized steel plate in China in 2024 has exceeded 3 million tons, becoming the core basic material in construction, automobiles, home appliances and other fields.

    1.1 Breakthrough of anti-corrosion mechanism

          The electrode potential of zinc (-0.76V) is significantly lower than that of iron (-0.44V), which forms a potential difference in the electrolyte environment, and zinc preferential corrosion forms Zn(OH)₂, ZnO and other compounds to prevent the oxidation of the steel matrix. This "active protection" mechanism makes the corrosion resistance of galvanized steel plate in Marine climate more than 10 times that of ordinary steel plate.

Second, the production process system analysis

    2.1 Evolution of hot dip galvanizing process

    2.1.1 Traditional flux method

          Using ZnCl₂+NH₄Cl mixture flux. Dipped in zinc solution at 450-460 ° C for 3-8 min. Formed a 50-200μm zinc layer. This method is suitable for mass production, but there is a problem of zinc residue, and the zinc pan needs to be cleaned every 8 hours.

    2.1.2 Senjimir Method

          Modern continuous galvanizing unit adopts H₂+N₂ protective gas reduction process, eliminates stress through 700-850℃ annealing furnace, and controls zinc layer thickness accuracy up to ±3g/m² by gas knife system. The C618 production line of Baosteel has achieved the mass production of 0.18mm ultra-thin alloyed coating.

    Process parameters Traditional flux Fasenjimire process

          Zinc liquid temperature 460℃ 450℃

          Zinc thickness error ±10% ±3%

          Production speed 60m/min 180m/min

    2.2 Electrogalvanizing technology innovation

          Using ZnSO₄·7H₂O electrolyte, a 5-25μm zinc layer was deposited at a 30-50A/dm² current density. The new chromium-free passivation technology reduces the hexavalent chromium content from 120mg/m² to less than 0.1mg/m², and the salt spray resistance time exceeds 720 hours.

Third, product classification and performance characteristics

    3.1 Comparison of Major types

           Hot dip galvanizing (SGCC) : Zinc layer thickness 50-200g/m², the preferred material for building envelope system, shengyu steel can produce zinc-free products

           Electrogalvanizing (SECC) : zinc layer 5-25g/m², surface roughness Ra≤0.8μm, suitable for precision electronic components

          Alloyed galvanizing (GA) : The Zn-Fe alloy layer is formed by thermal diffusion treatment at 500℃, and the welding strength is increased by 40%

    3.2 Development of special coating

          Aluminized zinc plate (SGLD) : containing 55%Al+43.4%Zn+1.6%Si, heat resistance up to 315℃, photovoltaic bracket service life of 25 years

          Zinc magnesium alloy coating: when the Mg content is 3%, the corrosion resistance of the incision is increased by 10 times, and the occurrence time of red rust is extended to 15 years

Fourth. Analysis of key application areas

    4.1 Innovation in the field of construction

          275g/m² thick coating products are used in steel structure plants, saving 60% maintenance costs compared to traditional coating solutions. Wuhan Tianhe Terminal 3 adopts aluminum-plated zinc roofing system to achieve 15 years of maintenance-free.

    4.2 Breakthroughs in the automotive industry

          The proportion of galvanized steel in the body consumption increased from 35% in 2000 to 78% in 2024, of which:

          The battery pack shell uses a 1.2mm aluminum-plated magnesium plate, which increases the impact energy absorption rate by 30%

          The inner plate of the door is made of 340MPa grade alloyed galvanized plate, which is thinned by 0.15mm to achieve lightweight

    4.3 Appliance manufacturing upgrade

          Fingerprint resistant (AF) technology makes the surface resistance of the refrigerator panel ≤10⁶Ω, and the antibacterial rate reaches 99.9%. Midea's new refrigerator in 2024 uses double-sided differential thickness coating (20/10g/m²), reducing material costs by 12%.

Fivth. Quality control and development trend

    5.1 Defect prevention and control system

          Defect type cause solution

          The particle size of zinc residue is > 0.5mm and the electromagnetic purification device is installed

          White rust storage humidity > 70%RH chromate passivation treatment

          Uneven distribution of edge wave tension added four-roll precision straightener

    5.2 Environmental technology breakthrough

          The waste acid recycling system recovers 98%HCl, and the acid consumption per ton of steel is reduced from 35kg to 1.2kg

          Chromium-free passivation film thickness 0.3-0.5μm, C5 treatment agent through RoHS certification

    5.3 Intelligent Production

          Anshan Steel CGL production line deployed 1500 sensors to build a digital twin model to achieve:

          The temperature control accuracy of zinc pan is ±1℃

          The prediction accuracy of phase change in alloying furnace is 98%

          Defect recognition rate increased to 99.7%