Hot Dip Galvanizing (HDG) vs Electroplating : Which is better and why?
Steel is a highly corrosive material. Bare steel can rust within a few days in favorable environment. In high humid weather or in the presence of water and oxygen steel can rust within 4-5 days. This tells us why protective coating is a must for steel wire products. As most of the low carbon wire products like barbed wire, chain link fence etc. remain exposed to weather. Whereas they have to provide service for a long time. Zinc is being used for a long time as a protective element over iron. According to ‘Galvanic Series’ Zinc is more anodic than iron. Therefore when both iron and zinc will be connected zinc will corrode ‘sacrificially’ and protect iron from rust.
There are many methods of applying Zinc coating on steel. Electroplating, Hot Dip Galvanizing, Zinc painting, Zinc plating etc. are some of the methods. In Bangladesh Electroplating and HDG are the most common methods. Although these are the most applied methods HDG has some great advantages than electroplating.
Why HDG is better than Electroplating?
In HDG process steel is completely immersed in a bath of molten Zinc. In the bath, Zinc is metallurgically bonded with iron in the steel to form the coating. In case of HDG a series of Zinc-Iron alloy layer is formed. These layers are namely Eta, Zeta, Delta & Gamma.
These layers are strongly bonded. The surface layer (i.e. Eta) is 100% Zinc and other layers are alloys of Zinc & Iron. These layers offer a hard resistance against abrasion and rust. In HDG process Zinc coating gives full coverage – edges, corners and threads have equal or more amount of Zinc than flat surface. Electroplating process consists of Zinc coating over steel by electrolytic deposition method. In local markets electroplating process is most commonly used for wire products. But electroplating has some disadvantages than Hot Dip Galvanizing. The thickness of Zinc in electroplating is much lesser than in HDG. Coating thickness is almost 2-3 times higher in HDG than electroplating. Moreover, electroplated wire is less resistant to abrasion due to non-continuous metallurgic bond. Whereas Hot Dip Galvanized wire has strong Zn-Fe alloy layers which are hard and resistant to abrasion. Due to high coating thickness and strong Zn-Fe layers Galvanized wire is more abrasion and corrosion resistant than electroplated wire. Moreover, in HDG Zinc protects the steel sacrificially by ‘cathodic protection’ method even if the intermetallic layers are damaged.
Due to these advantages Galvanized wire lasts way longer than electroplated wire.