Zinc in general
The use of zinc as corrosion protection in using zinc-coated panels for vehicle construction is problematic due to the availability of zinc.
Estimates from experts assume that the availability of this metal worldwide will meet requirements for a maximum of 20 - 25 years.
At Mercedes-Benz we therefore only use zinc-coated panels (and then only in combination with organic protective layers) where extreme corrosion can be expected, i.e. due to exposure to salts.
By accurately checking and weighing economic and ecological aspects, Mercedes-Benz has proven a mixed construction for all products (a combination of different materials) depending on the list of requirements.
Various plastics and aluminum are increasingly being used as the basic material in areas at risk of corrosion, these materials also contribute to a lighter construction.
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Corrosion protection by zinc
Steel (sheet metal) can be zinc-coated by various processes. A distinction is made between electrolytically zinc-coated (galvanically), sendzimir zinc-coated and hot galvanized zinc-coated.
Corrosion protection by zinc coating occurs due to the electrochemical behavior of the protective metal (zinc) towards the basic material (steel). If the protective zinc layer is penetrated at a point, a local, galvanic element arises under the effect of the electrolytes (diluted, electrically conductive solution).
In doing this the zinc forms the anode and the basic metal steel forms the cathode. Zinc as the more base metal goes into solution and the steel surface is not attacked.
The cataphoretic protective effect of the zinc can be understood from the position of zinc and steel in the electrochemical series of metals. This is known as zinc acting as the sacrificial anode. Optimum corrosion protection is thus achieved in conjunction with organic protective layers.
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Corrosion protection with Bona zinc
The Bona zinc treatment introduced represents a new item in the area of corrosion protection on Mercedes-Benz vehicles.
Bona zinc is the trade name of the PPG company and designates an organic zinc compound suitable for requirements in automotive construction.
The Bona zinc coating adheres exceptionally well to the base material beneath. As a rule, electrolytically galvanized sheet metal is coated with Bona zinc. However, it is possible to protect "bare" sheet metal surfaces with Bona zinc.
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At the end of the production process at the steel producers, the sheet metal runs through a station at which the liquid Bona zinc coating is applied.
The coating thickness is approx. 3 - 4 μm. The sheet metal is coated on one or both sides depending on the application.
A primary advantage of using Bona zinc is that it is possible to completely eliminate hollow cavity preservation and reduce PVC seam sealing to a minimum.
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