86. What impact does pre-treatment have on the adhesion of the galvanized layer?

When the pre-treatment employs the "solvent (melting) method", the steel pipe surface may develop various issues: residual iron oxide scale from insufficient acid washing, hydrogen ion accumulation from over-acidizing, incomplete removal of oil contaminants, iron salt adhesion, uncleaned carbon black and corrosion inhibitors, insufficient activation due to low solvent concentration, excessive iron content in the solvent, solvent impurities, solvent stagnation, solvent burn-off, partial solvent removal, and solvent drying deficiency. These factors collectively result in either missed plating or a pseudo-zinc coating with only pure zinc layer and no underlying iron-zinc alloy layer, ultimately compromising adhesion performance.
When pre-treatment employs the "protective gas reduction method," the steel pipe surface must undergo thorough reduction activation to achieve pure iron before zinc reaction formation of an iron-zinc alloy layer. Failure to properly control protective gas composition, dew point, furnace temperature, and sealing conditions may result in insufficient oxidation or reduction, leading to either missed coating or a zinc-only layer without the intended alloy layer. This can cause cracking or peeling during bending or cold working processes. Consequently, similar to the "flux method," poor adhesion becomes prevalent. In hot-dip galvanizing using the "flux method," ammonium chloride flux on the molten zinc surface tends to induce brittleness and coating detachment.