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Zinc flake coating: the solution to corrosion?
11/27/2024
Corrosion and control arms. An issue that owners of a VW Golf 7 in particular are often confronted with.
The reason for this is the special design of the rear lower wishbone, in which not only the spring sits in the rear axle suspension, but the entire wishbone is designed to be open at the top. This means that dirt and water can permanently reach the spring seat and water can penetrate through cracks underneath the paintwork.
The result: the drainage holes become blocked and the water can only drain away to a limited extent. If the paintwork is also damaged by stone chips, the material can rust so badly over time that the spring punctures the handlebars.
In such a case, the safety of the vehicle is no longer guaranteed and it is absolutely not advisable to continue driving!
Why are control arms so susceptible to corrosion?
The spring-loaded control arm is highly susceptible to corrosion as it is exposed to various external influences:
mechanical loads: Accumulation of sand and dirt on the spring support leads to greater wear of the protective layer and thus to premature wear.
Stone chips: Direct contact with the road surface damages the coating, allowing moisture to penetrate.
Moisture: Penetrating water under the paint layer causes infiltration and detachment, which in extreme cases can lead to spring breakage.
These problems are regularly criticized by testing institutions such as the TÜV, which often leads to the rejection of rusted control arms.
The basics of corrosion protection
Good corrosion protection is crucial for spare parts that are exposed to severe environmental stresses.
A distinction is made between passive and active corrosion protection.
Passive corrosion protection is achieved through a coating, for example in the form of conventional paint. This forms a barrier between the metal and the environment. But be careful: only as long as the coating remains undamaged!
Active corrosion protection, on the other hand, involves chemical processes that minimize corrosion. A well-known process is cathodic protection, in which the metal itself is protected against corrosion and no additional barrier, such as paint, is used.
It is important to note that not every material is suitable for active corrosion protection!
Not all coatings are the same
In addition to the conventional galvanic coating process, there are also so-called zinc flake coatings available today . In this process, zinc particles in the form of flakes are used, which adhere to the metal surface using special binding agents.
This means that it is an active protection!
The zinc flakes act as pigments or layers that not only passively protect the underlying steel by acting as a barrier, but also actively, as the zinc oxidizes preferentially and thus protects the steel from corrosion.
In addition, zinc flake coatings have a high temperature resistance, which creates a resistant and robust protective layer. This means that control arms with this coating can also withstand high mechanical loads.
Incidentally, the corrosion resistance is tested in so-called salt spray chambers.
In summary, it can be said that zinc flake coatings provide effective corrosion protection and significantly extend the service life of control arms.
