A corrosion test known as Salt Spray Test is conducted to test the coatings on the automobile parts, for testing salt or mist resistance, in particular. The Salt Spray Test can be used to extrapolate the corrosion resistance of materials such as electroplated chromium, phosphate surfaces, nickel, copper, zinc, and aluminum alloys.
The machinery for Salt Spray Test comprises of a closed testing chamber, where salt water solution will be sprayed by using the pressurized air. Abbreviated as SST, the test is popular among the Mexican die casters due to its benefits including affordability, flexibility, and repeatability.
The standard SST is atomizing the salt solution into the chamber, supported or suspended in between 15 to 30 Degree Celsius, from a vertical angle. The solution will comprise of 5 percent NaCl (Sodium Chloride), while the exposure zone remaining at 35 Degree Celsius. As the Salt Spray Test is a continuous process, the product being tested will be exposed to continuous salt fog for the duration.
The period of the test is subject to ranging up to more than 1000 hours. However, few products won’t require such exposure and they will be given a modified Salt Spray Test.
The test is done to predict which materials will stay corrosion free when exposed to real conditions and so are the modified versions of the extrapolation test. For instance, the standard SST has modified tests alluded to in ASTM G85 as annexes A1 to A5. Many of such modified tests are industry specific and will be done based on the corrosion effect of the environment.
The ASTM G85 Annex A1 is a non-cyclic test used to extrapolate the corrosion resistance of chromium plating for zinc die casting. The test samples will be placed into a chamber and be exposed to an indirect salt water spray solution. The test will suggest how well zinc will resist corrosion if exposed to an acetic acid salt spray at a higher temperature. The ASTM G85 Annex A2 is a cyclic acidified salt fog test done to test the corrosion resistance of the aluminum alloys.
Compared to other materials, zinc has better corrosion resistant properties, but testing the formation of a surface barrier is important to know the corrosion resistance of zinc in practice. Usually, when galvanized products get exposed in marine or salt environments, zinc will create a layer of zinc carbonate which will resist salt attacks and the product remains durable.