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Salt spray testing is a widely used accelerated corrosion test method that simulates the corrosion process of metallic materials and their protective coatings in a salt-laden environment by continuously spraying a 5% sodium chloride (NaCl) solution at a constant temperature. While this method does not exactly replicate real-world road or climatic conditions, it is favored in the automotive industry for its efficiency and high repeatability, making it ideal for quality control and materials development.
Common Salt Spray Test Standards and Test Conditions
The automotive industry commonly refers to the following salt spray test standards:
- ASTM B117: The most widely used neutral salt spray (NSS) standard globally, applicable to the automotive, aerospace, and electronics industries.
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ISO 9227: An international standard that defines three test types:
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NSS (Neutral Salt Spray): Suitable for most metals and organic coatings.
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AASS (Acetic Acid Salt Spray): Designed for decorative coatings.
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CASS (Copper-Accelerated Acetic Acid Salt Spray): Used for highly corrosion-resistant materials.
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GB/T 10125-2021: The Chinese national standard, technically equivalent to ISO 9227.
Test durations and conditions vary depending on the standard and the requirements of the part being tested. In the automotive sector, test durations typically range from several dozen to several hundred hours, based on material type and component design. To ensure valid and comparable results, companies should select appropriate test types and parameters based on product characteristics and the standards of their target markets.
Test Design and Best Operational Practices
To ensure accurate and reliable results, salt spray tests must be carefully designed and conducted in strict accordance with the standards. Key considerations include:
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Sample Preparation: All test samples must be thoroughly cleaned before testing to remove oil, fingerprints, and other contaminants. Surfaces should be dry and of consistent size for comparability. Careful clamping is essential to avoid scratches or damage to coatings or substrates, as these can become initiation points for corrosion.
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Salt Solution Preparation and Maintenance: A typical solution consists of 5% NaCl by mass. Deionized or distilled water must be used to avoid introducing impurities. Regular checks should be conducted to monitor salt concentration and pH (maintained between 6.5 and 7.2 for neutral tests). Adjustments should be made promptly if deviations are detected. Filtration systems are recommended to prevent nozzle clogging and ensure uniform spraying.
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Sample Placement: Samples should be positioned at an angle (typically 15°–30°) inside the salt fog chamber to allow the salt spray to run off the surface without pooling. Adequate spacing between samples is required to prevent mutual obstruction. Use inert materials such as plastic, stainless steel, or glass for mounting to avoid contamination from corroded supports.
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Chamber Settings and Calibration: Test chamber sensors (temperature, humidity, spray systems) must be regularly calibrated to ensure accuracy. For NSS testing, the chamber temperature is typically set at 35 °C. A stable ambient laboratory temperature (around 25 °C) further improves repeatability. Monitor fog density and collection volume throughout the test to maintain a consistent environment and avoid excessive droplet formation.
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Test Documentation and Evaluation: Test durations must follow the specified standards (e.g., 24h, 48h, 96h, or several hundred hours based on user requirements), with all test parameters recorded in detail. After the test, samples should be rinsed and inspected for corrosion spots, rust spread, and coating performance. Multiple test runs may be necessary to ensure data reliability.
Common Pitfalls and Prevention Strategies
Improper procedures or overlooking critical details can lead to deviations or invalid results. Key issues to avoid include:
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Incorrect Water Quality: Using tap water introduces impurities (e.g., calcium, magnesium ions) that can interfere with corrosion processes. Always use deionized water.
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Contaminated Reagents: Long-stored salt solutions may be contaminated by airborne impurities or microbial growth. Replace or filter regularly to maintain solution purity.
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Neglected Calibration: Uncalibrated sensors or spray systems can result in inaccurate temperatures or inadequate spray volumes. Establish a routine calibration plan per manufacturer recommendations.
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Overloaded Samples: Excessive sample loading reduces exposure uniformity and may distort results. Follow chamber capacity guidelines and conduct batch testing if needed.
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Non-Standard Test Durations: Modifying test durations to save time or cost can result in non-comparable outcomes. Always adhere to the specified exposure time and ensure repeatability by testing at least two samples of the same type and condition for comparison.
Additionally, it is important to note that salt spray test results provide relative corrosion resistance assessments and should not be directly interpreted as real-world service life. Testing should be designed with consideration of the component’s application environment (e.g., coastal exposure, humid or cold climates), and combined with other tests (e.g., cyclic corrosion testing) when necessary.
Advantages of DHT® Salt Spray Test Chambers
To meet the stringent requirements of the automotive industry, DHT® Salt fog chamber offer the following features:
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Contrôle précis de la température et de l'humidité: Temperature fluctuation within ±0.3°C and uniform atomization.
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Corrosion-Resistant Construction: Inner chambers made of FRP or high-performance polymers, suitable for long-term testing.
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Intelligent Operating System: PLC control with touchscreen interface, supporting test programming, data logging, and remote monitoring.
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Flexible Customization: Available in a range of models, suitable for testing everything from small fasteners to large body panels.
DHT® chambers are widely adopted by both domestic and international automotive manufacturers for corrosion testing of body parts, plated components, bolts, and more. Customers consistently report high accuracy in temperature and humidity control, excellent spray uniformity, and enhanced efficiency thanks to intelligent control and data recording features—providing strong support for the validation of automotive corrosion resistance.
Conclusion
Salt spray testing remains a vital method for evaluating the corrosion resistance of automotive components. Compliance with standards and best practices is essential to obtaining meaningful and repeatable results. Selecting a well-equipped and reliable chamber—such as those in the DHT® series—and conducting tests in accordance with established protocols is the key to successful performance validation. For more information about DHT® salt spray chambers or to discuss custom solutions, please contact our technical team.