Zinc and galvanized steel
What types of galvanization are there?? What is the usual thickness of the zinc coating?
Most often, types of galvanization and standard thickness of the zinc coating layer are as follows:
| A type of galvanization | Coating thickness |
| Hot dip galvanizing | on single items 50-80 μm; on steel sheets (in the case of strip galvanizing) usually after approx. 20 μm on each side;
on a steel belt (width below 60 mm) – from every side 20-70 μm |
| Electro galvanizing | on building elements approx. 2,5 μm; on small parts (screws and fittings) 5 – 25 μm |
| Spray galvanizing | ok. 100 μm |
How can you recognize the different types of galvanization?
Hot dip galvanized parts are usually identified by floral patterned streaks on the surface. These patterned streaks indicate the presence of purely zinc, thin coating. They can be more or less pronounced. Homogeneous is formed during electro-galvanizing, silvery shiny surface. Spray galvanizing is recognizable by its rough surface.
How does the zinc coating protect the steel sheet?
Zinc is less inert than the steel sheet coated with it (in a galvanic voltage series). In the presence of corrosive factors, e.g. acid rain, the zinc dissolves. The electrochemical process taking place here protects the steel sheet against corrosion, while the zinc coating slowly dissolves.
4.Please list the zinc corrosion products and explain their formation
Zinc corrosion products and their formation are as follows:
| Zinc corrosion products | Formation |
| Zinc oxide (ZnO) | forms in the air quite quickly; a thin layer of zinc oxide protects the underlying material |
| Basic zinc carbonate [ZnC03 • Zn(OH)] | forms in clean air on the zinc oxide layer; a layer of this compound increases the effectiveness of corrosion protection |
| White rust | forms with increased humidity, as a result of electrochemical corrosion; it is a compound with a complex composition |
| Soluble zinc salts (e.g. ZnSO4) | chlorides and sulphates are formed under the influence of industrial pollution; the protective zinc layer is dissolved by them |
What defects of the substrate made of galvanized steel sheets should be taken into account when testing it?
When testing the substrate made of galvanized steel sheets, attention should be paid to dirt, the presence of corrosion products, fats, oils, inks for inscriptions and stamps, mortar contamination, mechanical damage, the presence of loose particles and the correct treatment of welds and welds.