The Correlation Between Salt Spray Corrosion Testing and the Evaluation of Materials and Coatings: A Case Study of LISUN YWX/Q-010 Salt Spray Test Chamber

Abstract
Salt spray corrosion, as one of the most destructive forms of atmospheric corrosion, poses a severe threat to the durability and reliability of metal materials and their protective coatings in harsh environments such as marine, automotive, and industrial settings. To address the challenges of evaluating corrosion resistance efficiently, salt spray test chambers have become indispensable equipment in material and coating performance assessment. This paper focuses on the correlation between salt spray corrosion testing and the evaluation of materials and coatings, with a specific analysis of the LISUN YWX/Q-010 Salt Spray Test Chamber. It first elaborates on the mechanism of salt spray corrosion and its impact on materials and coatings. Then, it introduces the technical characteristics and testing capabilities of the LISUN YWX/Q-010, and explores how salt spray corrosion testing based on this equipment realizes the quantitative and qualitative evaluation of materials and coatings. Finally, through practical application cases and data analysis, the validity and practical value of salt spray corrosion testing in material and coating evaluation are verified, providing a reference for related industries to improve product quality and reliability.

1. Introduction
Corrosion is the gradual destruction or deterioration of materials caused by chemical, electrochemical, or physical interactions with the environment. Among various corrosion forms, salt spray corrosion is widely recognized as one of the most common and harmful atmospheric corrosion types. The chloride ions in salt spray can penetrate the oxide layer and protective coating on the surface of metal materials, triggering electrochemical reactions and accelerating material failure. For products used in marine environments, coastal areas, or high-humidity industrial zones, the resistance to salt spray corrosion directly determines their service life and safety.

Traditional natural exposure tests to evaluate salt spray corrosion resistance are often time-consuming and labor-intensive, with results easily affected by uncontrollable environmental factors such as temperature, humidity, and pollutant concentration. In contrast, artificial salt spray corrosion testing using salt spray test chambers can simulate harsh salt spray environments in a laboratory setting, significantly shortening the test cycle while ensuring the repeatability and accuracy of results. The LISUN YWX/Q-010 Salt Spray Test Chamber, developed by LISUN Group, is a representative piece of equipment in this field. It complies with multiple international and national standards and is widely used in the corrosion resistance testing of components, electronic and electrical parts, metal materials, and industrial products. This paper takes this equipment as an example to deeply discuss the correlation between salt spray corrosion testing and material and coating evaluation, aiming to clarify the important role of salt spray corrosion testing in material performance assessment.

2. Mechanism of Salt Spray Corrosion and Its Impact on Materials and Coatings

2.1 Mechanism of Salt Spray Corrosion

Salt spray refers to a chloride-containing atmospheric environment, with sodium chloride as the main corrosive component, which is mainly derived from the ocean and inland saline-alkali areas. The corrosion process of metal materials by salt spray corrosion is essentially an electrochemical reaction process, which can be divided into the following key stages:

First, the salt spray mist settles on the surface of the metal material, forming a thin electrolyte solution film. This solution film provides the necessary conditions for electrochemical reactions, as it contains a large number of chloride ions with high hydration energy. Second, chloride ions have strong penetrating ability. They can easily penetrate the pores, cracks, and defects in the oxide layer or protective coating on the metal surface, replacing the oxygen adsorbed on the metal surface. This process converts the insoluble oxide layer (passive film) on the metal surface into soluble chlorides, destroying the passive state of the metal surface and turning it into an active surface. Finally, the active metal surface undergoes electrochemical corrosion in the electrolyte solution film: the anode region undergoes oxidation reactions (metal dissolution), and the cathode region undergoes reduction reactions (oxygen reduction or hydrogen evolution), resulting in the formation of corrosion products such as rust, which further accelerates the damage of the metal material.

For coated materials, salt spray corrosion not only attacks the coating itself but also causes under-film corrosion. Chloride ions penetrate the coating to reach the coating-substrate interface, destroying the adhesion between the coating and the substrate. As the corrosion products accumulate, the coating bulges, peels off, and loses its protective effect, eventually leading to the corrosion failure of the entire material.

YWX/Q-010_AL

2.2 Impact of Salt Spray Corrosion on Materials and Coatings

The impact of salt spray corrosion on materials and coatings is multifaceted, involving changes in mechanical properties, appearance, and functional performance:
• Mechanical properties degradation: Corrosion products such as rust have low strength and brittleness, which reduce the load-bearing capacity of metal materials. For example, the tensile strength and toughness of steel will decrease significantly after salt spray corrosion, increasing the risk of material fracture. For coated metal parts used in structural engineering, coating peeling caused by salt spray corrosion will lead to a sharp decline in the structural strength of the parts.
• Appearance damage: Salt spray corrosion will cause obvious appearance defects on the surface of materials and coatings, such as rust spots, blisters, discoloration, and peeling. This not only affects the aesthetic performance of products but also indicates the failure of the protective coating, which is an important basis for evaluating product quality in industries such as automotive and electronics.
• Functional failure: For electronic and electrical components, salt spray corrosion can cause short circuits, poor contact, or increased resistance of metal connectors, leading to component failure. For example, the metal pins of integrated circuits and the connectors of automotive electronic systems are highly susceptible to salt spray corrosion, which affects the normal operation of the entire equipment.

3. Technical Characteristics of LISUN YWX/Q-010 Salt Spray Test Chamber

The LISUN YWX/Q-010 Salt Spray Test Chamber is a professional equipment designed for salt spray corrosion testing. Its advanced technical characteristics provide a reliable guarantee for the accurate evaluation of materials and coatings. The main technical parameters and structural features of the equipment are shown in Table 1 and described in detail below.
Table 1 Technical Specifications of LISUN YWX/Q-010 Salt Spray Test Chamber

3.1 Compliance with Multiple Standards

The LISUN YWX/Q-010 strictly complies with a variety of international and national salt spray corrosion testing standards, including GB/T 2423.17, IEC 60068-2-11, ASTM B117, ISO 9227, and MIL-STD-202. This compliance ensures that the test results obtained by the equipment have international comparability and authority, allowing enterprises to use the test data for product certification, quality control, and international trade. For example, the ASTM B117 standard is widely recognized in the global automotive industry, and using the YWX/Q-010 to conduct tests in accordance with this standard can effectively evaluate the corrosion resistance of automotive metal parts and coatings.

3.2 Precise Environmental Control

Accurate control of test environmental parameters is the key to ensuring the reliability of salt spray corrosion test results. The YWX/Q-010 has excellent temperature control performance: the working temperature can be adjusted from room temperature to +55 ℃, with a temperature uniformity of ≤2 ℃ and a temperature volatility of ≤ ± 0.5 ℃. This ensures that the temperature in the test chamber is uniform and stable, avoiding the impact of temperature fluctuations on the corrosion rate.

In addition, the equipment is equipped with a saturated barrel with a temperature range of room temperature to +70 °C. By heating and filtering the compressed air, the humidity of the air entering the nozzle is increased, and the crystallization of salt at the nozzle is reduced, ensuring the stability of the salt spray deposition rate. The salt spray deposition rate of the YWX/Q-010 is controlled at 1-2ml/80cm²/h (average of 16-hour test), which meets the requirements of various standards and provides a quantitative basis for evaluating the corrosion resistance of materials and coatings.

3.3 Diverse Test Modes and Strong Adaptability

The YWX/Q-010 supports three main test types: neutral salt spray test (NSS), acetic acid salt spray test (AASS), and copper-accelerated acetic acid salt spray test (CASS). These three test types correspond to different corrosion intensities and application scenarios: NSS is suitable for general corrosion resistance evaluation; AASS has a stronger corrosive effect and is used for materials with higher corrosion resistance requirements; CASS is an accelerated corrosion test method, which can quickly evaluate the corrosion resistance of high-performance coatings such as decorative chromium plating.

At the same time, the equipment supports continuous, intermittent, and programmable spray methods. Users can set different spray cycles and durations according to test requirements, simulating the alternating effects of salt spray and dry environments in real natural conditions. The sample space of the YWX/Q-010 is 1000600300 mm, which can accommodate samples of different sizes and types, including small electronic components, large metal parts, and coated panels, with strong adaptability.

3.4 Reliable Safety Protection and User-Friendly Design

The YWX/Q-010 is equipped with a comprehensive safety protection mechanism, including low water level alarm, dual over-temperature protection (mechanical + electronic), and low air pressure alarm. When the water level in the solution tank is too low, the temperature exceeds the set range, or the air pressure is insufficient, the equipment will automatically alarm and suspend the test, preventing equipment damage and ensuring the safety of operators and samples.

In terms of structural design, the equipment adopts a stainless steel air spring support opening method, which is convenient for placing and taking samples. The chamber is made of PP flame retardant sheet, which has excellent corrosion resistance and high-temperature resistance, ensuring the long-term stable operation of the equipment. The surrounding high-strength frame supports allow the equipment to bear heavy samples, expanding its application scope.

4. Correlation Between Salt Spray Corrosion Testing and Evaluation of Materials and Coatings

Salt spray corrosion testing based on the LISUN YWX/Q-010 Salt Spray Test Chamber realizes the comprehensive evaluation of materials and coatings through quantitative detection and qualitative analysis. This correlation is mainly reflected in the evaluation of coating protective performance, material corrosion resistance, and the prediction of service life.

4.1 Evaluation of Coating Protective Performance

Coatings are the most common means to improve the salt spray corrosion resistance of metal materials, and salt spray corrosion testing is the core method to evaluate the protective performance of coatings. The YWX/Q-010 can evaluate the protective performance of coatings from the following aspects:

• Coating appearance evaluation: After the salt spray corrosion test, the appearance of the coating is observed and graded according to standards such as ASTM B117 or GB/T 1771. Common evaluation indicators include the number and size of rust spots, blistering degree, peeling area, and discoloration. For example, in the NSS test of a automotive coating sample using the YWX/Q-010, if no rust spots or blisters appear on the coating surface after 1000 hours of testing, the coating is considered to have excellent protective performance; if rust spots appear in an area exceeding 5% of the sample surface after 500 hours, the coating fails to meet the basic corrosion resistance requirements.
• Coating adhesion evaluation: Salt spray corrosion can destroy the adhesion between the coating and the substrate. After the test, the cross-cut test or pull-off test is used to detect the adhesion of the coating. The YWX/Q-010 provides a stable corrosion environment, ensuring that the changes in coating adhesion are caused by salt spray corrosion rather than other factors. For example, a galvanized coating sample was tested in the YWX/Q-010 for 200 hours under AASS conditions. Before the test, the coating adhesion was 5MPa, and after the test, it decreased to 2MPa, indicating that salt spray corrosion has seriously damaged the bonding between the coating and the substrate.
• Coating penetration resistance evaluation: The salt spray deposition rate and test duration of the YWX/Q-010 are controllable, which can be used to evaluate the penetration resistance of the coating. By detecting the chloride ion content at the coating-substrate interface after the test, the penetration depth and rate of chloride ions can be determined. A lower chloride ion content indicates better penetration resistance of the coating. For example, in the CASS test of a epoxy coating sample, the chloride ion content at the interface was only 0.02% after 100 hours of testing, showing that the coating has strong resistance to chloride ion penetration.

4.2 Evaluation of Material Corrosion Resistance

For uncoated metal materials, salt spray corrosion testing directly reflects their inherent corrosion resistance. The YWX/Q-010 can evaluate the corrosion resistance of materials by measuring corrosion rate, weight loss, and corrosion product composition:

• Corrosion rate calculation: The corrosion rate of the material is calculated by measuring the weight loss of the sample before and after the test. The formula is: Corrosion rate (mm/a) = (8.76×1000×Δm)/(ρ×A×t), where Δm is the weight loss (g), ρ is the material density (g/cm³), A is the sample surface area (cm²), and t is the test time (h). The YWX/Q-010 provides a stable corrosion environment, ensuring the accuracy of weight loss data. For example, a carbon steel sample with a density of 7.85 g/cm³ and a surface area of 10 cm² was tested in the YWX/Q-010 for 24 hours under NSS conditions, with a weight loss of 0.2 g. The calculated corrosion rate is (8.76×1000×0.2)/(7.85×10×24) ≈ 9.1 mm/a, indicating that carbon steel has poor salt spray corrosion resistance.
• Weight loss analysis: Weight loss is a direct indicator of material corrosion. Different materials show different weight loss characteristics under the same salt spray corrosion conditions. For example, comparing the weight loss of 304 stainless steel and 201 stainless steel in the YWX/Q-010 for 100 hours: 304 stainless steel has a weight loss of 0.05 g, while 201 stainless steel has a weight loss of 0.3 g. This shows that 304 stainless steel has better salt spray corrosion resistance, which is due to its higher chromium and nickel content, forming a more dense passive film.
• Corrosion product analysis: The composition and structure of corrosion products can reflect the corrosion mechanism of the material. After the test in the YWX/Q-010, the corrosion products on the sample surface can be analyzed by X-ray diffraction (XRD) or scanning electron microscopy (SEM). For example, the corrosion product of aluminum alloy after salt spray corrosion is mainly Al(OH)₃, which is a loose and porous substance that cannot effectively prevent further corrosion of the substrate; while the corrosion product of titanium alloy is TiO₂, which is a dense oxide film that can slow down the corrosion rate.

4.3 Prediction of Service Life

One of the important purposes of salt spray corrosion testing is to predict the service life of materials and coatings in actual environments. Since the chloride concentration in the salt spray environment simulated by the YWX/Q-010 is much higher than that in the natural environment, the corrosion rate is accelerated, and the service life of the product can be predicted by establishing the relationship between the test time and the actual service time.

The commonly used method is the “acceleration factor method”. The acceleration factor (AF) is the ratio of the corrosion rate in the salt spray test to the corrosion rate in the natural environment. According to the test results of the YWX/Q-010, the service life (L) of the material or coating can be calculated by the formula: L = AF × T, where T is the test time when the sample fails. For example, if the acceleration factor of a certain coating in the NSS test of the YWX/Q-010 is 50, and the sample fails after 200 hours of testing, the predicted service life in the natural marine environment is 50×200 = 10,000 hours (about 1.14 years).

It should be noted that the acceleration factor is affected by many factors, such as test type, environmental parameters, and material properties. Therefore, when predicting the service life, it is necessary to calibrate the acceleration factor according to the actual application environment of the product to ensure the accuracy of the prediction results.

5. Practical Application Case of LISUN YWX/Q-010 in Material and Coating Evaluation

To further verify the correlation between salt spray corrosion testing and material and coating evaluation, this section takes the evaluation of the corrosion resistance of automotive galvanized sheet coatings as an example, introducing the test process, results, and analysis based on the LISUN YWX/Q-010.

5.1 Test Objective

Evaluate the salt spray corrosion resistance of two types of automotive galvanized sheet coatings (Sample A: hot-dip galvanized coating; Sample B: electro-galvanized coating) to provide a basis for the selection of automotive body materials.

5.2 Test Equipment and Standards

• Test equipment: LISUN YWX/Q-010 Salt Spray Test Chamber, equipped with LISUN LS-EU800W2-55L air compressor.
• Test standard: ASTM B117 “Standard Practice for Operating Salt Spray (Fog) Apparatus”.
• Test type: Neutral salt spray test (NSS).

5.3 Test Parameters

• Working temperature: 35 ℃.
• Salt spray deposition rate: 1.5ml/80cm²/h.
• Salt solution concentration: 5% sodium chloride solution (prepared with distilled water, pH 6.5-7.2).
• Test duration: 1000 hours.
• Sample size: 150mm×75mm×1.2mm (3 samples for each type).

5.4 Test Process

• Sample pretreatment: Polish the edges of the samples with sandpaper to remove burrs, clean them with acetone to remove surface oil, dry them in a drying oven at 60 ℃ for 2 hours, and weigh them with an electronic balance (accuracy: 0.1mg).
• Equipment debugging: Turn on the YWX/Q-010, add distilled water to the solution tank until the low water level alarm is turned off, add the prepared salt solution to the salt water tank, set the working temperature to 35 ℃, and the spray cycle to continuous spray. Start the air compressor, adjust the spray pressure to 0.1MPa, and preheat the equipment for 30 minutes.
• Sample placement: Place the samples on the V-type sample rack of the test chamber, with the test surface facing upward and an angle of 20° ± 5° with the horizontal plane.
• Test execution: Start the test, record the equipment operating parameters every 24 hours, and observe the sample appearance.
• Post-test treatment: After the test is completed, take out the samples, rinse them with distilled water to remove surface salt deposits, dry them, and weigh them again. Observe the appearance of the samples and conduct a cross-cut test to detect coating adhesion.

5.5 Test Results and Analysis

The test results of Sample A and Sample B are shown in Table 2.
Table 2 Salt Spray Corrosion Test Results of Automotive Galvanized Sheet Coatings

From the test results, it can be seen that:
• Appearance performance: Sample A (hot-dip galvanized coating) shows excellent appearance stability during the test. Only slight rust spots appear after 500 hours, and the rust area is less than 2% after 1000 hours, with no coating peeling. In contrast, Sample B (electro-galvanized coating) begins to discolor after 200 hours, rust spots appear after 500 hours, and obvious peeling occurs after 1000 hours, with a rust area of up to 15%. This indicates that the hot-dip galvanized coating has better resistance to salt spray corrosion-induced appearance damage.
• Weight loss and corrosion rate: The average weight loss of Sample A is 0.08g, and the corrosion rate is 0.87mm/a; the average weight loss of Sample B is 0.32g, and the corrosion rate is 3.48mm/a. The weight loss and corrosion rate of Sample B are 4 times that of Sample A, indicating that the hot-dip galvanized coating can effectively slow down the corrosion rate of the substrate.
• Coating adhesion: After 1000 hours of salt spray corrosion, the adhesion of Sample A’s coating is 4.2MPa, which is only slightly lower than the initial adhesion (4.5MPa); while the adhesion of Sample B’s coating drops to 1.8MPa, which is less than half of the initial adhesion (4.0MPa). This shows that the hot-dip galvanized coating has stronger adhesion to the substrate and better resistance to under-film corrosion.
• Failure time: The failure time of Sample A is more than 1000 hours, while that of Sample B is 750 hours. Combined with the acceleration factor of 50 (calibrated according to the automotive coastal environment), the predicted service life of Sample A is more than 50,000 hours (about 5.7 years), and that of Sample B is 37,500 hours (about 4.3 years). Therefore, Sample A is more suitable for automotive body materials used in coastal areas.

This case fully demonstrates that salt spray corrosion testing based on the LISUN YWX/Q-010 can effectively distinguish the corrosion resistance of different coatings, providing accurate and reliable data support for material selection and product quality control.

6. Conclusion and Prospect

6.1 Conclusion

Salt spray corrosion is a key factor affecting the durability and reliability of materials and coatings, and salt spray corrosion testing is an indispensable means to evaluate their corrosion resistance. Taking the LISUN YWX/Q-010 Salt Spray Test Chamber as an example, this paper clarifies the close correlation between salt spray corrosion testing and material and coating evaluation.

The YWX/Q-010, with its compliance with multiple standards, precise environmental control, diverse test modes, and reliable safety protection, provides a stable and accurate test platform for salt spray corrosion testing. Through this equipment, the protective performance of coatings can be evaluated from the aspects of appearance, adhesion, and penetration resistance; the corrosion resistance of materials can be quantified by weight loss and corrosion rate; and the service life of products in actual environments can be predicted by the acceleration factor method. Practical application cases show that salt spray corrosion testing can effectively distinguish the corrosion resistance of different materials and coatings, providing important support for industrial production and product quality improvement.

6.2 Prospect

With the development of industries such as automotive, aerospace, and electronics, higher requirements are put forward for the corrosion resistance of materials and coatings, and salt spray corrosion testing technology will also face new development directions:
• Intelligent testing: Integrate Internet of Things (IoT) and artificial intelligence (AI) technologies into salt spray test chambers such as the YWX/Q-010 to realize real-time monitoring, remote control, and automatic analysis of test data. For example, using machine vision to automatically identify and grade coating rust spots and blisters, improving test efficiency and accuracy.
• Multi-factor coupling testing: In actual environments, materials and coatings are often affected by multiple factors such as salt spray, humidity, temperature, and ultraviolet radiation. Future salt spray test chambers will develop towards multi-factor coupling testing, simulating more complex environmental conditions to improve the authenticity of test results.
• Green and environmental protection: Optimize the structure and working fluid of salt spray test chambers to reduce energy consumption and waste liquid emissions. For example, developing recyclable salt solutions and energy-saving heating systems to meet the requirements of green environmental protection.

In summary, salt spray corrosion testing will continue to play an important role in the evaluation of materials and coatings. The LISUN YWX/Q-010 and other advanced salt spray test chambers will provide more powerful technical support for the development of high-performance materials and coatings, promoting the progress of related industries.