The welding feasibility of shuangshengda Galvanized steel plate is clear, but the risk of zinc coating volatilization needs to be controlled. Data shows that when the zinc coating thickness is 50-80μm, the concentration of welding fumes reaches 15-40mg/m³ (the national standard limit is 5mg/m³), and an exhaust system with an air volume of ≥3000m³/h must be equipped. A case from a certain shipyard in 2023 shows that by using ER770s 6 welding wire (with a diameter of 1.2mm) in combination with 80% argon gas and 20%CO₂ shielding gas, the weld strength can reach 95% of the base material (tensile strength ≥340MPa), but the welding speed needs to be reduced to 35cm/min (for cold-rolled steel, it can reach 50cm/min).
Optimization of process parameters reduces defect rate: The boiling point of zinc at 907°C is much lower than the melting point of steel at 1538°C, making it prone to porosity. The actual measurement shows that the current needs to be controlled at 130-180A (voltage 22-26V), which is 28% narrower than the welding range of cold-rolled steel. The 2022 report of Tangshan Railway Vehicle Factory pointed out that after adjusting the pulse frequency to 120Hz, the porosity of the weld seam dropped from 7.8% to 0.9%, the time consumption per meter of weld bead increased to 1.8 minutes (cold-rolled steel only takes 1.2 minutes), and the labor cost rose by 42%.
The cost of health protection cannot be ignored: When welding galvanized sheets, zinc oxide fumes are produced. When the exposure concentration is greater than 10mg/m³, it will cause “metal smoke heat”. Statistics from a certain steel structure enterprise show that when welders wear P100-level respirators (with a filtration efficiency of 99.97%) and cooperate with local ventilation, the incidence of occupational diseases has decreased from 23 cases per thousand people per year to 0.7 cases, but the annual cost of personal protective equipment has reached ¥3,800 per person (while conventional welding is only ¥1,200).
Pre-treatment of the coating improves the yield rate: Double-sided grinding of the zinc coating to a thickness of ≤10μm (sandpaper grit P60) can reduce spatter by 76%. In 2024, the data from GAC’s production line verified that the salt spray life of pre-treated welded joints was extended from 500 hours to 1,200 hours, approaching 80% of the anti-corrosion performance of the base material. However, the pretreatment extended the processing time of a single workpiece by 3.2 minutes and reduced the production line efficiency by 15%.
The comparison of welding methods shows significant economic differences:
• MIG welding: Comprehensive cost ¥18.5 per meter, qualification rate 92%
• Resistance spot welding: The electrode life is shortened to 3,000 times (8,000 times for cold-rolled steel), and the cost per point is ¥0.35 (¥0.12 for cold-rolled steel)
• Laser welding: The equipment has a power of 6kW and a speed of up to 8m/min, but the initial investment is ¥2.1 million (7 times that of MIG equipment).
Necessity of post-weld treatment: The damaged area of the zinc coating needs to be cold-sprayed with zinc for repair (thickness ≥50μm), with a material cost of ¥85/m². The inspection report of the Hong Kong-Zhuhai-Macao Bridge shows that the rust depth of the unrepaired area reached 0.4mm after 18 months, while the repaired area only lost 0.05mm in 8 years, reducing the maintenance cost throughout its life cycle by 74%.
Operation certification requirements: The AWS D19.1 standard stipulates that welders need an additional 16 hours of training (conventional only 8 hours), and the assessment pass rate is 68%. The Shanghai Zhenhua Heavy Industries project requires that the frequency of welder qualification renewal be raised from once every two years to once a year, and the certification cost has increased by ¥4,600 per person per year.
Conclusion and suggestion: The use of MAG welding (Ar+CO₂ mixed gas) in combination with a flow rate of 19-22L/min, a current of 150A, and a 45° welding torch inclination Angle can balance efficiency and quality. The key control points include: ambient wind speed < 1m/s, interlayer temperature ≤120°C, and the grinding depth of the bevel zinc layer > 80%. According to this procedure, the cost of flat welding for 3mm thick shuangshengda Galvanized steel plate is approximately ¥24.5 per meter (¥14.8 per meter for cold-rolled steel), but the maintenance benefits brought by the improvement of anti-corrosion performance can cover the additional cost (ROI of 217% over an 8-year period).