Galvanization is the process by which zinc is coated over corrosive (easily rusted) metals. Galvanizing involves coating corrosive metals, such as steel and iron, with a non-corrosive metal. The process of galvanizing, not only protects from corrosion of various ‘soft metals’ but also adds strength of the original, uncoated metal. Apparently, galvanized metal is thicker than the uncoated metal and so fittings and fastenings are generally measured with the additional galvanizing layer height specs in mind. American Society for Testing and Materials (ASTM) specifications provide guidelines for the thickness of galvanized metals based on the underlying metal and the type of application. Galvanization refers to any of several electrochemical (branch of chemistry that studies chemical reaction which take place in a solution) processes named after the Italian scientist Luigi Galvani. Now the term generally refers to an electro deposition (electroplating) process used to add a thin layer of another metal to a ferrous substrate, in order to prevent rusting.
The process of galvanization was patented by Stanislas Sorel, a French engineer of Paris, France in December 1837. Sorel filed a patent for a “galvanic” method of protecting iron from rust by either coating it in a bath of molten zinc or by covering it with so-called “galvanic-paint”. This was the precursor to the modern day hot-dip galvanizing.
Galvanizing is the practice of immersing clean, oxide-free steel into molten zinc to from a protective coating over the metal. The coating is bonded metallurgically to the steel and this coating helps to protect the surface against corrosion. In recent use, the term refers to the coating of steel or iron with zinc. This is done to prevent corrosion (specifically rusting) of the ferrous item. The zinc is consumed as a sacrificial anode (metallic anode or sacrificial rod used in cathodic protection), so that it protects the exposed steel. Cathodic protection is a technique of preventing metal from corroding. So, in case of scratches through the zinc coating, the exposed steel will be cathodically (or sacrificially) protected by the surrounding zinc coating, unlike an item which is painted with no prior galvanizing where the scratched surface would rust. Additionally, galvanizing to protect the surface of iron and steel is favored due to its low cost, ease of application, and the extended maintenance-free service that it provides. The zinc coating protects the steel in 2 ways