Galvanizing is the electrochemical coating of a metal surface with a different metal. The main metal coating additives are SN (tin), CU (copper), NI (nickel), CR (chromium), but the most popular are: ZN (zinc) coated metal; and AlZn (aluminum zinc) coated metal. As a construction material, a sheet of metal can be coated in different metals:
The coating layer is classified according to weight groups (g/m2). Both sides of a sheet are coated. The sheet is coated using the three-step test according to SS-EN 10142. Galvanizing provides dual protection for a metal sheet: it is an effective means of protection against oxygen and moisture and provides cathodic protection of steel when cutting or otherwise damaging the tin surface. When fastening a galvanized sheet, galvanic elements are formed due to moisture. The steel works as a cathode and the zinc works as an anode. The anode is sacrificed in order to produce a corrosion product, which blocks the inevitable damage to come, thus preventing the corrosion process.
Aluminum zinc creates a more effective barrier than pure zinc because non-volatile aluminum oxides are formed. Zinc, which is also present in the coating layer, provides cathodic protection to the sheet. In a short time period, this cathodic protection in the aluminum zinc works much slower, which may result in the cut area appearing brown at first. However, due to this combination of protective measures, the aluminum zinc sheet becomes a perfect form of protection against corrosion in the long run. Aluminum zinc with AZ 185 additives serves as great anti-corrosive protection during processing (without any additional coating) and can therefore be used in the M3 environmental class according to the resolution of the Corrosion Institute. Aluminum zinc has been successfully used in roofing for 30 years in the USA, nearly 30 years in Australia and over 20 years in Europe.
