1.How to optimize the galvanizing process?
Control the thickness and structure of the alloy layer
Lower the temperature of the zinc pot: avoid excessively high temperature resulting in an overly thick alloy layer, and control the target temperature at 440-455°C.
Shorten the zinc immersion time: reduce the reaction time and limit the growth of the brittle δ phase.
Optimize cooling rate
Step cooling: After plating, first cool slowly (250-300°C insulation) and then cool quickly to reduce thermal stress cracks. Avoid water quenching: Direct water cooling is prone to aggravate cracks due to thermal shock, so air cooling or natural cooling is recommended.
2.How can materials and design be improved?
Choose a high-ductility substrate: give priority to low-carbon steel and low-Si content steel to avoid the risk of cold bending cracking of high-strength steel.
Increase the bending radius: The minimum bending radius (R) ≥ 3 times the plate thickness (t). The larger the R/t ratio, the lower the risk of zinc layer cracking.
Avoid sharp-angle design: Use arc transition instead of right angle (such as R angle ≥ 2t) to disperse stress concentration.
Slotting/pre-cut optimization: pre-cut stress relief grooves at the bend to reduce local deformation.
3.How to accurately control the cold bending process?
Forming speed and deformation rate
Low-speed forming: speed ≤5m/min, to avoid brittle fracture caused by high-speed impact.
Multi-pass progressive forming: complete large-angle bending in steps (such as 90° bending in 3 steps), single deformation ≤30°.
Mold adaptation and lubrication
Mold gap control: upper and lower mold gap = (1.03-1.08) t, too tight will squeeze the zinc layer.
Polish the mold surface: Ra≤0.4μm, reduce friction damage.
Use special lubricants: high viscosity polymer lubricants (such as PTFE coating) to reduce the friction coefficient between the zinc layer and the mold.
Temperature management
Winter preheating: When the ambient temperature is <10℃, preheat the plate to 20-40℃ (such as infrared heating) to improve the toughness of the zinc layer.
Mold constant temperature: Maintain the mold temperature at 30-50℃ to prevent low-temperature embrittlement.
4.What are the alternative coating options?
Zinc-aluminum-magnesium coating: Mg addition improves self-healing ability and its crack resistance is 3-5 times higher than that of pure zinc.
Electroplating zinc: The pure zinc layer has no brittle alloy phase and has excellent ductility.
Post-passivation treatment: Chromate passivation film fills microcracks and delays the onset of corrosion.
5.How to repair cracks?
Minor cracks (no exposed steel): Spray zinc-aluminum coating (such as ZRC cold galvanizing) to seal the cracks.
Exposed steel substrate:
Repair process: Sandblasting (Sa2.5) → Apply epoxy zinc-rich primer (80μm) → Apply compatible topcoat ◦ Cracks in key load-bearing parts: Scrap directly to avoid structural hazards.