The salt spray test chamber is an accelerated corrosion test equipment that simulates the marine or salty humid atmosphere environment, and evaluates the corrosion resistance of materials or coatings by atomizing and spraying sodium chloride solution evenly on the surface of the specimen. Its core principle is based on the electrochemical corrosion mechanism, which forms an electrolyte liquid film on the metal surface in a salt spray environment, accelerating the anodizing and cathodic reduction reactions. The test chamber is usually composed of a spray system, a temperature control unit, a saturation barrel and a specimen rack, etc., which can accurately control key parameters such as salt solution concentration, pH value, chamber temperature and spray sedimentation rate.
corrosion mechanism of auto parts
During the service process of automobiles, parts are often exposed to complex atmospheric environments containing salt, humidity and pollutants, which are prone to electrochemical corrosion, crevice corrosion or stress corrosion cracking. Corrosion not only affects the appearance and dimensional stability of parts, but can also lead to functional failure or potential safety hazards. Therefore, in the R&D and quality control stages, the salt spray test is used to accelerate the corrosion resistance of parts, which can effectively predict their long-term corrosion resistance and provide data support for material selection, process optimization and protective coating design.
Testing standards
The automotive industry generally adopts international and national standards to standardize salt spray testing processes, including ISO 9227, ASTM B117, and GB/T 10125. The test methods are mainly divided into neutral salt spray test (NSS), acetate spray test (AASS) and copper-accelerated acetate spray test (CASS), and the corresponding methods are selected according to the use environment and material characteristics of the parts. The test cycle typically ranges from 24 hours to thousands of hours, during which the specimen is regularly checked for corrosion status and data such as corrosion area, foaming level or weight changes are recorded.
Corrosion rate assessment is often based on the mass loss formula derived from Faraday's law:
ΔW = (I × t × M) / (n × F)
where ΔW is the mass loss, I is the current intensity, t is the time, M is the molar mass, n is the electron transfer number, and F is the Faraday constant.
Test parameter control
| Salt solution concentration | 50±5 g/L NaCl |
| pH (NSS) | 6.5-7.2 |
| Temperature inside the box | 35±2°C |
| Spray settling rate | 1.0-2.0 mL/80cm²·h |
| Relative humidity | ≥95% |
| Specimen tilt angle | 15°-30° |
Application in auto parts testing
Salt spray testing is widely used in the corrosion resistance evaluation of automotive metal parts and coatings, and typical applications include:
Body and structural parts:Evaluate the corrosion resistance of galvanized steel plates, aluminum alloy plates and welding parts, and check the adhesion and scratch expansion of the coating.
Chassis Components:The corrosion protection performance of brake calipers, suspension springs and fasteners in salt spray environment was tested, focusing on crevice corrosion and stress corrosion susceptibility.
Electrical and Electronic Components:Check the sealing performance of connectors and sensor housings and material compatibility to prevent circuit failure due to corrosion.
Exterior Parts:Verify the weather resistance of chrome trim strips, wheel hub coatings and plastic parts, and evaluate the appearance changes and substrate protection effects.
After testing, it is rated according to ISO 10289 or similar standards, including the percentage of corroded area, type and depth of corrosion. It should be noted that salt spray test, as an accelerated test, can quickly screen materials, but it cannot fully simulate the coupling effect of multiple factors such as dry-wet alternation, ultraviolet irradiation and mechanical wear in the real environment. Therefore, it is recommended to conduct a comprehensive evaluation in combination with cyclic corrosion test, outdoor exposure test, etc.
At present, salt spray testing technology is developing in the direction of multi-environmental factor coupling simulation, such as adding temperature and humidity cycle, ultraviolet light or sulfur dioxide gas modules to reproduce complex corrosion environments more realistically. At the same time, automatic image recognition technology is gradually applied to corrosion topography analysis to improve the efficiency and objectivity of ratings. In the future, with the popularization of lightweight materials and high-voltage electrical systems for new energy vehicles, higher requirements will be put forward for the test scope and accuracy of salt spray tests.
Cited Literature
ISO 9227:2017, Corrosion tests in artificial atmospheres – Salt spray tests
ASTM B117-19, Standard Practice for Operating Salt Spray (Fog) Apparatus
GB/T 10125-2021, Corrosion tests in artificial atmospheres – Salt spray tests
SAE J2334, Laboratory Cyclic Corrosion Test