DIN 50961 Fe Zn: A Comprehensive Guide to Electroplating and Coating of Iron and Steel
What You Need to Know About DIN 50961 Fe Zn Specifications for Zinc Coatings on Iron and Steel
Zinc coatings are one of the most common and effective ways to protect iron and steel parts from corrosion. Zinc is a sacrificial metal that forms a protective layer of zinc oxide or zinc carbonate on the surface of the base metal, preventing rusting. Zinc also provides a good base for applying paints and powder coatings, improving the adhesion and durability of the finish. However, not all zinc coatings are the same. Depending on the application and the service environment, different types of zinc coatings with different thicknesses and supplementary treatments may be required. That's why it is important to follow the DIN 50961 Fe Zn specifications, which define the requirements and recommendations for zinc coatings on iron and steel parts.
Din 50961 Fe Zn.pdf
What are DIN 50961 Fe Zn specifications?
DIN 50961 Fe Zn specifications are a set of German standards that define the terms, testing, and corrosion resistance of zinc coatings on iron or steel parts. They are based on the international standard ISO 2081, which specifies the general properties and testing methods of zinc coatings. DIN 50961 Fe Zn specifications supplement ISO 2081 by providing additional information on the minimum corrosion resistance requirements for different service conditions, as well as recommending minimum coating thicknesses for various expected lifetimes.
What are the types of zinc coatings according to DIN 50961 Fe Zn specifications?
DIN 50961 Fe Zn specifications classify zinc coatings into two main categories: untreated and treated. Untreated zinc coatings are those that have not been subjected to any supplementary treatment after electroplating. Treated zinc coatings are those that have been passivated or post-treated with chromate or other substances to enhance their corrosion resistance and appearance.
Untreated zinc coatings are designated by the symbol Fe/Zn followed by a number indicating the minimum coating thickness in micrometers (µm). For example, Fe/Zn 8 means an untreated zinc coating with a minimum thickness of 8 µm.
Treated zinc coatings are designated by the symbol Fe/Zn followed by a number indicating the minimum coating thickness in micrometers (µm), a letter indicating the type of passivation (A for transparent, B for iridescent, C for yellow, D for olive green, E for black), and another letter indicating the type of post-treatment (F for organic sealant, G for inorganic sealant, H for phosphate conversion coating). For example, Fe/Zn 12 C F means a treated zinc coating with a minimum thickness of 12 µm, yellow passivation, and organic sealant.
What are the corrosion resistance requirements for zinc coatings according to DIN 50961 Fe Zn specifications?
DIN 50961 Fe Zn specifications specify the minimum corrosion resistance requirements for zinc coatings when they are tested using two methods: DIN 50018 KFW 2.0 S test and DIN EN ISO 9227 neutral salt spray test (NSS). The DIN 50018 KFW 2.0 S test is a cyclic corrosion test that alternates between exposure to a saturated sodium chloride solution and drying at room temperature. The DIN EN ISO 9227 NSS test is a continuous corrosion test that exposes the coated parts to a salt spray at a constant temperature and humidity.
The corrosion resistance requirements are expressed in terms of hours until white rust or red rust appears on the coated surface. White rust is the formation of white zinc oxide or hydroxide on the coating surface due to oxidation. Red rust is the formation of red iron oxide on the base metal due to corrosion. The longer it takes for white rust or red rust to appear, the better the corrosion resistance of the coating.
The table below shows the minimum corrosion resistance requirements for untreated and treated zinc coatings according to DIN 50961 Fe Zn specifications:
Coating designation
Minimum hours until white rust (DIN 50018 KFW 2.0 S)
Minimum hours until red rust (DIN 50018 KFW 2.0 S)
Minimum hours until white rust (DIN EN ISO 9227 NSS)
Minimum hours until red rust (DIN EN ISO 9227 NSS)
Fe/Zn 5
24
72
24
72
Fe/Zn 8
48
144
48
144
Fe/Zn 12
72
216
72
216
Fe/Zn 25
120
360
120
360
What are the recommended coating thicknesses for zinc coatings according to DIN 50961 Fe Zn specifications?
DIN 50961 Fe Zn specifications provide some guidance on the recommended coating thicknesses for zinc coatings depending on the service conditions and the expected lifetime of the coated parts. The service conditions are classified into five categories: indoor exposure (SC1), outdoor exposure with low corrosivity (SC2), outdoor exposure with medium corrosivity (SC3), outdoor exposure with high corrosivity (SC4), and special applications (SC5). The expected lifetime is expressed in years.
The table below shows the recommended coating thicknesses for untreated and treated zinc coatings according to DIN 50961 Fe Zn specifications:
Lifetime/Service condition
SC1
SC2
SC3
SC4
SC5
<1 year
-
-
-
-
-
<3 years
<5 µm
<8 µm
<12 µm
<25 µm
<25 µm
<10 years
<8 µm
<12 µm
<25 µm
>25 µm
>25 µm<
How to apply zinc coatings according to DIN 50961 Fe Zn specifications?
The application of zinc coatings according to DIN 50961 Fe Zn specifications requires careful preparation of the iron or steel parts, as well as proper control of the electroplating process and the supplementary treatments. The following steps are recommended:
Clean the iron or steel parts from any dirt, grease, oil, rust, scale, or other contaminants that may affect the adhesion and quality of the zinc coating. This can be done by using mechanical or chemical methods, such as abrasive blasting, degreasing, pickling, or etching.
Activate the iron or steel surface by applying a thin layer of copper or nickel to improve the electrical conductivity and the bonding of the zinc coating. This can be done by using a strike bath or a flash bath.
Electroplate the zinc coating by immersing the iron or steel parts in a zinc plating bath that contains zinc salts, additives, and an electric current. The thickness and uniformity of the zinc coating depend on several factors, such as the composition and temperature of the plating bath, the current density and duration, and the shape and size of the parts.
Passivate the zinc coating by immersing the coated parts in a solution that contains chromate or other substances that form a thin film on the zinc surface. This film enhances the corrosion resistance and appearance of the zinc coating by slowing down the oxidation process. The color and thickness of the passivation film depend on the type and concentration of the passivating agent, as well as the immersion time and temperature.
Post-treat the zinc coating by applying a sealant or a conversion coating that further improves the corrosion resistance and appearance of the zinc coating by filling in any pores or cracks in the passivation film. The sealant can be organic or inorganic, while the conversion coating can be phosphate or other substances that form a complex with zinc.
What are the advantages and disadvantages of zinc coatings according to DIN 50961 Fe Zn specifications?
Zinc coatings according to DIN 50961 Fe Zn specifications offer several advantages and disadvantages for iron and steel parts. Some of them are:
Advantages:
Zinc coatings provide excellent corrosion protection for iron and steel parts, especially in atmospheric, aqueous, and soil environments.
Zinc coatings are compatible with various paints and powder coatings, enhancing their adhesion and durability.
Zinc coatings are relatively cheap and easy to apply compared to other metallic coatings.
Zinc coatings are recyclable and environmentally friendly.
Disadvantages:
Zinc coatings have poor resistance to high temperatures, abrasion, wear, and some chemicals.
Zinc coatings may suffer from hydrogen embrittlement, which is a phenomenon that causes cracking and failure of high-strength steels due to hydrogen absorption during electroplating.
Zinc coatings may cause galvanic corrosion when they are in contact with dissimilar metals that have higher nobility than zinc.
How to test zinc coatings according to DIN 50961 Fe Zn specifications?
The testing of zinc coatings according to DIN 50961 Fe Zn specifications involves checking the appearance, thickness, adhesion, and corrosion resistance of the coatings. The following methods are recommended:
Appearance: The appearance of the zinc coatings should be uniform, smooth, and free from defects such as blisters, cracks, pores, or stains. The color and brightness of the coatings may vary depending on the type of passivation and post-treatment. The appearance of the coatings can be assessed by visual inspection or by using instruments such as gloss meters or colorimeters.
Thickness: The thickness of the zinc coatings should meet the minimum requirements or recommendations according to DIN 50961 Fe Zn specifications. The thickness of the coatings can be measured by using non-destructive methods such as magnetic, eddy current, or X-ray fluorescence techniques, or by using destructive methods such as coulometric, gravimetric, or microscopic techniques.
Adhesion: The adhesion of the zinc coatings to the iron or steel parts should be sufficient to withstand normal handling and service conditions. The adhesion of the coatings can be tested by using methods such as bending, twisting, impact, or pull-off tests.
Corrosion resistance: The corrosion resistance of the zinc coatings should meet the minimum requirements according to DIN 50961 Fe Zn specifications when they are tested using DIN 50018 KFW 2.0 S test or DIN EN ISO 9227 NSS test. The corrosion resistance of the coatings can be evaluated by measuring the time until white rust or red rust appears on the coated surface.
What are the applications and examples of zinc coatings according to DIN 50961 Fe Zn specifications?
Zinc coatings according to DIN 50961 Fe Zn specifications are widely used for various applications and industries that require corrosion protection, appearance, and functionality of iron and steel parts. Some of them are:
Automotive industry: Zinc coatings are used for electroplating and coating of car parts such as chassis, body panels, wheels, bumpers, fasteners, brackets, hinges, etc.
Construction industry: Zinc coatings are used for electroplating and coating of structural steel components such as beams, columns, pipes, fittings, bolts, nuts, washers, etc.
Electrical industry: Zinc coatings are used for electroplating and coating of electrical equipment and components such as transformers, motors, generators, switches, relays, connectors, wires, cables, etc.
Mechanical industry: Zinc coatings are used for electroplating and coating of mechanical parts and devices such as gears, bearings, springs, valves, pumps, compressors, etc.
Household industry: Zinc coatings are used for electroplating and coating of household items and appliances such as furniture, hardware, utensils, tools, etc.
Conclusion
Zinc coatings are a popular and effective way to protect iron and steel parts from corrosion, as well as to improve their appearance and functionality. However, not all zinc coatings are the same. Depending on the application and the service environment, different types of zinc coatings with different thicknesses and supplementary treatments may be required. That's why it is important to follow the DIN 50961 Fe Zn specifications, which define the requirements and recommendations for zinc coatings on iron and steel parts. By following these specifications, you can ensure the quality and performance of your zinc coatings and extend the lifetime of your iron and steel parts. a27c54c0b2
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