1.What are the core difficulties in galvanized steel welding?
Zinc layer evaporation and pore defects
Impact: Porosity reduces weld strength and sealing, and in severe cases leads to welding failure.
Interference of zinc layer on arc stability
Impact: Poor weld formation (such as weld bead, undercut), substandard surface quality.
Deterioration of heat affected zone (HAZ) performance
Impact: Plasticity and toughness of the HAZ are reduced, and cracks are prone to occur, especially in high-constraint welding.
Increased electrode/welding gun loss
Impact: Increased welding consumables costs and reduced production efficiency.
2.What are the causes of the core difficulties in galvanized steel welding?
Zinc layer evaporation and pore defects
Cause: The melting point of zinc is 419℃ and the boiling point is 907℃, which is much lower than the melting point of steel (about 1500℃). During welding, the zinc layer evaporates rapidly due to heat, producing a large amount of zinc vapor. If it fails to escape in time, hydrogen pores or carbon monoxide pores will form in the weld.
Interference of zinc layer on arc stability
Cause: Zinc vapor has a low ionization potential (about 9.39eV), which easily forms plasma in the arc zone during welding, causing arc drift and increased spatter, affecting molten pool control.
Deterioration of heat affected zone (HAZ) performance
Cause: The solid solubility of zinc in iron is extremely low. The high welding temperature causes zinc to diffuse into the substrate, forming a brittle phase (such as Fe-Zn alloy layer) in the heat affected zone. At the same time, the substrate is partially decarburized and the hardness decreases.
Increased electrode/welding gun wear
Cause: During resistance welding (such as spot welding), the zinc layer forms a low-melting-point alloy (such as Zn-Cu) on the contact surface between the electrode and the workpiece, causing electrode adhesion and burning; during metal arc welding (MIG), zinc vapor corrodes the welding gun nozzle, shortening its service life.
3.How to improve weld performance?
Post-weld heat treatment: stress relief annealing (temperature 150-200℃, insulation 1-2h) is performed on important structural parts (such as bridges and pressure vessels) to reduce the brittleness of the heat-affected zone and promote the escape of residual zinc vapor in the weld.
Surface protection: After welding, zinc is added to the weld and surrounding areas (such as thermal spraying zinc, zinc-rich paint) to restore corrosion resistance; for example, after welding galvanized steel plates, cold spray zinc with a zinc content of ≥95% is often used to repair welds, and the corrosion resistance of the salt spray test can reach more than 500 hours.
4.What are the solutions for special scenarios?
Thick plate galvanized steel welding: use multi-layer and multi-pass welding, and clean the zinc slag before each layer of welding; use submerged arc welding (SAW), and the flux coverage suppresses the escape of zinc vapor.
Welding of galvanized steel and stainless steel: Use nickel-based welding wire (such as ERNi-1) to isolate zinc from contact with stainless steel; apply an insulating coating (such as epoxy resin) after welding.
On-site high-altitude galvanized steel welding: Use self-shielded flux-cored wire (such as E71T-GS), no additional gas protection is required, and on-site preparation work is reduced; operators wear gas masks (inhalation of zinc vapor can cause "metal fume fever").
5.How to reduce the zinc layer during pretreatment before welding?
Mechanical grinding/sandblasting: Remove the zinc layer within 5-10mm around the weld to expose the metal substrate. Sandpaper (80-120 mesh) or sandblasting can be used.
Chemical degreasing/pickling: Use dilute hydrochloric acid (5-10% concentration) or a special zinc layer remover to dissolve the zinc layer, then rinse with clean water and dry.
Laser/arc pre-galvanizing layer evaporation: Use low-energy laser or arc to scan the weld area to evaporate the zinc layer in advance and reduce the release of zinc vapor during welding.