Q:What does the coating on galvanized steel normally look like?
A:Pure zinc coating: uniform silver-white or silver-gray, slightly metallic, may have naturally formed zinc flowers (flaky crystals, depending on the cooling rate, does not affect the performance).
Aluminum coating: slightly lighter in color, bright silver, more delicate surface.
Gloss: The surface may be bright or matte, depending on the process (such as passivation treatment will affect the gloss), but the overall should not be locally dark or overly reflective.
Q:What does an abnormal coating look like on galvanized steel?
A:Dark black/burnt: The galvanizing temperature may be too high (zinc liquid is overheated) or the residence time is too long, which may cause the coating to oxidize and the anti-corrosion performance to decrease. Be vigilant.
Uneven color difference: The local color is too dark or too light, which may be due to uneven composition of the plating solution, incomplete pretreatment of the steel surface (such as oil residue), and uneven thickness of the coating.
Blue-white spots: If chromate passivation is used, a light blue passivation film may appear, which is normal; if the spots are dense and rough, it may be due to abnormal concentration of the passivation solution, and the salt spray resistance may be insufficient.
Q:What is the surface flatness acceptance standard for galvanized steel?
A:Touch by hand or visually inspect, the surface should be flat and smooth, without protrusions or depressions that affect use.
A slight "orange peel" texture is allowed (natural shrinkage marks when the coating solidifies), but there should be no sharp particles or roughness.
Q:What are the common types of defects on galvanized steel surfaces?
A:Bubbles or pinholes: There are tiny holes on the surface of the coating, small pits or black spots can be seen with the naked eye, which can easily become the starting point of corrosion.
Scratches and bumps: Mechanical damage caused by transportation or handling. If there is no zinc layer falling off at the scratch, the impact is small.
Cracks: Cracks appear on the coating or substrate, which may be due to the stress of the substrate not being released or the coating being too brittle.
Q:What are the common misunderstandings in judging the surface quality of galvanized steel?
A:"The brighter the surface, the better": Excessively high gloss may indicate electrogalvanizing or a post-treatment coating rather than pure hot-dip galvanizing.
"Completely flawless": Slight zinc spots or color differences are normal and do not affect the anti-corrosion performance.