There are many processes that use zinc to prevent corrosion of steel, such as: electro-galvanizing process, the thickness of the zinc layer is generally controlled at 5 ~ 15μm; the blown hot-dip galvanizing process (this book refers to "blow plating", the same below), the galvanized layer is more Thickness, generally less than 35μm; the thickness of the galvanized layer of the hanging plating process is more than 65μm, and some products require the thickness of the galvanized layer to be as high as 100μm or more. For large steel structures and box sections (this book is unified as "cavity workpieces" ", the same below) For steel structures, the thickness of the galvanized layer is larger.
The hot-dip galvanizing process has good coverage, the galvanized layer is dense, without organic inclusions, and its corrosion protection or corrosion resistance is much higher than that of electro-galvanized; however, for the hanging plating process, the thickness of the galvanized layer has a higher value. The lower limit of thickness, that is to say, the galvanized layer is too thin, but it is not easy to achieve; for the blow plating process, according to the technical index requirements of profiles, pipes, etc., the control of the thickness of the galvanized layer is relatively more flexible .
The protective effect of the galvanized layer on steel is twofold. First, the galvanized layer with good penetration resistance completely isolates the protected steel from the corrosive environment, thereby completely eliminating one of the main conditions for steel corrosion, that is, "electrolyte" . Secondly, because zinc is more chemically active than steel, it is more likely to be corroded and dissolved (the principle of sacrificial anode). Once the galvanized layer is locally damaged and the surface of the steel is exposed, zinc becomes an anode, which corrodes before steel, so as to achieve In order to protect the steel.
In the electrochemical protection, compactness, durability, maintenance-free of the galvanized layer, the bonding force of the galvanized layer and the steel matrix, the economics of the galvanized layer, and the adaptability of the hot-dip galvanizing process to the shape and size of the workpiece, the production Compared with all aspects such as high efficiency, the hot-dip galvanizing process has the unparalleled and unique advantages of other metal corrosion protection processes.