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The salt spray test is a corrosion test conducted in simulated environments in accordance with DIN EN ISO 9227.
We primarily test metals and alloys, as well as metallic, inorganic, or organic coatings by exposing them to a fine salt spray mist. Hence the name salt spray test. The most common and frequently requested salt spray test is the neutral salt spray test. As the name suggests, this is carried out under pH-neutral conditions.
The spray solution with 5% sodium chloride is pumped from the reservoir tank and atomized in the spray nozzle using compressed air. The droplets are so fine that they do not fall directly downward but form a very fine mist. The heating of the test chamber is carried out either via the base tray or through wall heating. In the heated test chamber, the water in the base tray evaporates, and the resulting water vapor keeps the sprayed droplets suspended, ensuring that the test samples are surrounded by the mist.
What may sound like a wellness treatment or a day at the seaside is actually real stress for the test samples. The aggressor is the chloride in the spray solution. Iron-based materials in particular can be severely attacked and show corrosion in the form of red rust. However, all other metallic substrates or coatings also react to the salt spray test by forming corrosion products. The color and shape of these corrosion products provide indications of weaknesses in the component.
The progression of corrosion reveals a lot about the lifecycle of a component.
Here, you can see a steel part with a galvanic zinc coating that has been passivated afterward to increase corrosion protection. In the neutral salt spray test, the cobalt-containing passivation layer is initially attacked by the chloride. The dark spots indicate that the passivation layer – or the cobalt within it – is actively working to protect the underlying zinc layer.
At some point, the protective barrier of the passivation layer is breached, and the zinc is attacked. White rust forms, a voluminous corrosion product consisting of zinc hydroxide, zinc oxide, and zinc carbonate.
The zinc layer continues to be converted into white rust until it is penetrated and the base metal is attacked. In the samples shown here, this would appear as red rust.
The images also clearly show the weak points of the components – namely where the corrosion attack first becomes visible. Edges are often particularly susceptible to impact damage. If the coating is damaged through impact, its protective function is reduced or lost.
In salt spray testing, we not only assess the general suitability of materials but also evaluate the functionality of coating systems and the behavior of components under real conditions. In addition, the salt spray test is suitable for comparing different systems with one another.
The salt spray test can therefore either simulate the operating conditions of a component or, through the targeted combination of aggressive factors, reveal and highlight weaknesses.
Corrosion is an important issue across many industries. In plant engineering, mechanical engineering, and automotive manufacturing, corrosion damage represents a significant economic factor. Materials are often pushed to their limits for cost reasons or used in corrosion-prone combinations. In such cases, the salt spray test, as a classic short-term test, provides valuable guidance.
It is important to note that the salt spray test is not intended to establish a direct correlation to real-life conditions, but rather to assess the fundamental suitability of materials or coatings.
