Accelerated Cyclic Corrosion Testing in the Automotive Sector

Accelerated Cyclic Corrosion Testing in the Automotive Sector Let us begin this article with the following questions: "Do you know how long your car will last before it starts to corrode or rust? Have you even heard that, thanks to special devices and methods, your car's durability can be tested in hours rather than observing it over years?" As an answer to these questions, in line with technological developments in recent years, a test type has emerged in response to the continuous search to test and increase automotive durability: Accelerated Cyclic Corrosion Testing. This article will briefly explain why this test type delivers more reliable results and provides better outcomes even in the harshest environmental conditions compared to other static tests (such as Salt Fog/Spray Corrosion Testing), and why it has been regarded as revolutionary by major companies and organizations on a global scale. Finally, future developments, trends, and challenges awaiting Accelerated Cyclic Corrosion Testing will be discussed.

What is Corrosion?

As we all know, all living and non-living matter in the world deteriorates and ages due to natural environmental factors or industrial conditions (such as sun, rain, dust, chemicals) surrounding them. This aging can take various forms; if we are talking about construction materials such as metal and concrete, and electrochemical processes are involved, the technical term for this is corrosion. Below you can find some definitions from reliable sources operating globally around corrosion: • The AMPP organization, the Materials Protection and Performance Association headquartered in Houston and Pittsburgh, USA, defines corrosion as a naturally occurring event generally defined as the deterioration of a material (usually a metal) as a result of a chemical or electrochemical reaction with its environment. • The ACA organization, the Australian Corrosion Association headquartered in Victoria, Australia, defines corrosion as follows: The destruction or deterioration of a material due to its reaction with its environment. The term "corrosion" can refer both to a process and the damage caused by such a process. • The International Organization for Standardization (ISO) defines corrosion as the physicochemical interaction between a metal and its environment that causes changes in the metal's properties and can lead to significant deterioration in the functioning of the metal, the environment, or the technical systems in which they are used. To express it differently; particularly for metals, corrosion can be compared to cancer. Like cancer, it gnaws at their structures and weakens their functions. By spreading from one area to another, it can cause more damage and problems. Prevention or treatment is only possible through early detection and appropriate intervention.

What Does Corrosion Mean for the Automotive Industry? Economic and Safety Consequences of Corrosion-Related Issues

The economic effects of corrosion in the automotive industry are significant. In the United States alone, corrosion is estimated to cost the sector USD 300 billion annually. This includes repairs, replacements, and loss of productivity. The safety effects of corrosion in the automotive industry are also important. Corrosion weakens metal components, which increases their likelihood of failure. This can lead to accidents, injuries, and even deaths. Below are some specific examples of the economic and safety-related consequences of corrosion in the automotive industry: • Body corrosion can lead to rust, which makes the vehicle look unsightly and reduces its resale value. • Exhaust system corrosion can cause leaks that could pollute the environment and pose a safety hazard. • Underbody corrosion can cause damage to the suspension and other components, which can result in poor handling and increased risk of accidents. The automotive industry has made significant efforts in recent years to reduce corrosion. These efforts include the use of corrosion-resistant materials such as galvanized steel, the application of protective coatings such as multi-layer paint systems and advanced sealant materials, and the use of cyclic corrosion testing.

Corrosion/Weather Resistance Test Types

Generally speaking, there are two main types of corrosion/weather resistance testing in general industry and the automotive industry: Static (e.g., Salt Spray/Salt Fog) and Cyclic. Static Tests: These are conducted under controlled environmental conditions such as temperature, humidity, and salt concentration. Some of these tests are typically used to evaluate the long-term corrosion resistance of materials. • Salt Spray Test: Initially introduced with the ASTM B177 standard and widely known, this test, including variants such as AASS and CASS, exposes a test specimen to a fine salt water fog for a predetermined period. • Humidity Test: This test exposes specimens to a high-humidity environment. • Immersion Test: This test exposes sample pieces to a corrosive liquid. Cyclic Tests: These are conducted under continuously changing conditions. These tests are typically used to evaluate the resistance of materials to fatigue corrosion, a type of corrosion that occurs when a material is repeatedly exposed to a corrosive environment. • Cyclic Salt Spray Test: This test exposes the test specimen to a fine salt water fog for a predetermined period, then allows it to dry for a period. • Cyclic Wet/Dry Test: This test exposes the test specimen to a wet/dry cycle, such as immersing it in water for 24 hours and then drying it for 24 hours. • Cyclic Thermal Shock Test: This test exposes the test specimen to a heating and cooling cycle.

What are Accelerated Corrosion Tests (ACT)?

Accelerated corrosion/weather resistance tests are like time machines for materials. They allow us to see how they will behave in the future without having to wait for years or decades. They can reveal their strengths and weaknesses and help us improve them.

ACT and Its Purpose in the Automotive Sector

Accelerated corrosion testing (ACT) is a laboratory test method that exposes materials to corrosive environments at a faster rate than they would experience in real-world conditions. The purpose of ACT is to assess the corrosion resistance of materials and coatings in a relatively short period of time. In the automotive sector, ACT is used to evaluate the corrosion resistance of a wide variety of materials, including metals, plastics, and composites. ACT is also used to evaluate the performance of protective coatings such as paint and galvanizing. Basic Principles of Accelerated Test Methods The basic principle of all ACT methods is that the rate of corrosion is proportional to the concentration of the corrosive agent. For example, increasing the concentration of salt spray will increase the rate of corrosion. ACT methods are also based on the principle that different stages of corrosion can be accelerated by different environmental conditions. For example, the initiation of corrosion can be accelerated by high humidity or temperature or high levels, while the propagation of corrosion can be accelerated by salt spray. Therefore, a complex set of parameters plays a role in determining the correct test scheme. For this reason, correlating the results of ACT tests with real-world corrosion data is of vital importance. • Cyclic Corrosion Testing: Alternating exposure to humidity, temperature, and salt conditions can be used in cyclic corrosion testing (CCT) to replicate real-world scenarios. A CCT is typically conducted in a laboratory (and is therefore considered a laboratory test) that exposes materials to a series of cycles involving salt spray, drying, and humidity. CCT is more complex and expensive than salt spray testing (SST) but is also more realistic in terms of the corrosive environments to which vehicles are exposed in the real world. Some of the different accelerated corrosion tests commonly used in the automotive industry are as follows: • Salt Spray Test (SST): SST exposes materials to a continuous salt spray for a predetermined period. SST is a relatively simple and inexpensive test but can be overly corrosive to some materials. • Cyclic Corrosion Testing (CCT): CCT exposes materials to a series of cycles involving salt spray, drying, and humidity. CCT is more complex and expensive than SST but is also more realistic in terms of the corrosive environments to which vehicles are exposed in the real world. • Prohesion Test: The Prohesion test is a specialized CCT designed to evaluate the paint adhesion and corrosion resistance of automotive coatings. • Humidity Exposure Test: Humidity exposure testing exposes materials to a high-humidity environment for a predetermined period. Humidity exposure testing is less corrosive than SST or CCT but can still be used to evaluate the corrosion resistance of materials, especially those used in humid environments. Some real-world examples of how accelerated corrosion tests have led to improvements in automotive design and materials are as follows: • Use of Galvanized Steel: Galvanized steel is steel coated with a zinc layer. The zinc coating protects steel from corrosion. Accelerated corrosion tests have been used to develop and evaluate more corrosion-resistant galvanized steel coatings. This has led to increased use of galvanized steel in automotive design, particularly in areas exposed to corrosive environments such as vehicle underbodies. • Development of New Paint/Coating Systems: Accelerated corrosion tests have been used to develop new paint systems that are more resistant to corrosion. For example, accelerated corrosion tests have been used to develop paint systems that are more resistant to stone chipping and UV radiation. This has led to the development of paint systems that last longer and maintain their appearance for longer. • Use of Aluminum: Aluminum is a lightweight metal that is resistant to corrosion. Accelerated corrosion tests have been used to develop and evaluate aluminum alloys that are even more resistant to corrosion. This has led to increased use of aluminum in automotive design, particularly in areas where weight reduction is important.

Benefits of Accelerated Corrosion Testing

Accelerated corrosion/weather resistance testing (ACT) offers numerous advantages over static accelerated corrosion/weather resistance tests. Here are some key benefits: • Better Simulation of Real-World Conditions: ACT tests can be customized to replicate a wide range of real-world environmental conditions, including temperature, humidity, UV radiation, and salt spray. This provides more accurate and reliable results. • Faster Test Times: ACT tests are typically much faster than static tests due to the accelerated nature of the test. This can save time and money and allow manufacturers to bring their products to market faster. • Greater Flexibility: ACT tests can be used to test a wider range of materials and components than static tests. This is because ACT tests can be customized to meet the specific needs of the product or material being tested. • Reduces test time and cost. • Increases the accuracy of corrosion predictions. • Helps identify and select corrosion-resistant materials and coatings.

Case Studies and Real-World Applications

Today, nearly all global automotive companies, along with global professional organizations such as ASTM (American Society for Testing and Materials) and SAE (Society of Automotive Engineers), use accelerated corrosion/weather resistance tests for quality control and research and development purposes. Below are some examples from automotive companies that use these tests to improve design, extend component life, or prevent recalls. • Ford: Ford uses various test methods to evaluate the durability of its components. For example, Ford uses corrosion testing to evaluate the resistance of its components to rust and other types of corrosion. On one occasion, Ford discovered that the brake lines on the F-150 pickup truck were susceptible to corrosion. To solve this problem, Ford redesigned the brake lines, and the new design extended the life of the brake lines. • Toyota Prius: The Toyota Prius is a hybrid electric vehicle first introduced in 1997. Toyota used various test methods to evaluate the Prius, including accelerated corrosion testing and crash testing. This testing helped Toyota improve the design and reliability of the Prius, which contributed to its success as one of the world's most popular hybrid vehicles.

Industry Standards, Regulations, and Specifications

Industry standards and regulations play an important role in the adoption of accelerated corrosion testing (ACT), particularly cyclic corrosion testing (CCTs).

International and Industry Standards

Industry standards, such as those developed by the National Association of Corrosion Engineers (NACE) and the American Society for Testing and Materials (ASTM), provide guidance on the selection and performance of ACT tests. These standards help ensure that ACT tests are conducted in a consistent and reliable manner and that results can be compared across different laboratories. Some of the key industry standards and regulations that have enabled the adoption of ACT include: • ISO 9227: This standard provides a method for cyclic corrosion testing of metallic materials. • ASTM G85: This standard provides a method for cyclic corrosion testing of coated metallic materials. • SAE J2334: This standard provides a method for cyclic corrosion testing of automotive components. In addition to these standards, there are a number of other industry standards and regulations that reference ACT: • ISO 14563: This standard provides a method for testing the durability of automotive coatings. • ASTM D1005: This standard provides a method for testing the resistance of paints and related coatings to corrosion. • SAE J2277: This standard provides a test method for evaluating the corrosion resistance of automotive brake systems. Regulations Government regulations developed by entities such as the U.S. Environmental Protection Agency (EPA) and the European Union (EU) also play a role in the adoption of ACT. For example, the EPA requires new vehicles to meet certain corrosion resistance standards. ACT tests can be used to demonstrate that vehicles meet these standards. In general, industry standards, regulations, and specifications play an important role in the adoption of ACT, particularly cyclic ACT applications. Industry standards and regulations ensure that ACT is used in a consistent and reliable manner, helping to increase the durability and corrosion resistance of materials and components. This can lead to significant benefits such as reduced costs, increased performance, and enhanced safety.

Future Trends and Challenges: In Corrosion Test Methodologies and Technologies Emerging Trends

The automotive sector is continually evolving, with new materials and technologies being developed. This means there is an increasing need for new and innovative corrosion testing methodologies and technologies. Some of the emerging trends in this area include: • Use of More Complex and Realistic Test Environments: This includes the use of chambers that can simulate a wide variety of environmental conditions such as temperature, humidity, and pollution levels. It also includes the use of more realistic test specimens, such as those previously damaged or coated. • Development of New Non-Destructive Testing (NDT) Methods: NDT methods allow for the detection and measurement of corrosion without damaging the test specimen. This is important for testing expensive or critical components. • Increasing Use of Artificial Intelligence (AI) and Machine Learning (ML): AI and ML can be used to analyze large amounts of data obtained from corrosion tests to identify patterns and trends. This can help increase the accuracy and efficiency of the test. • The Role of Artificial Intelligence and Simulation in Improving Test Accuracy and Efficiency: Artificial intelligence and simulation can play an important role in improving the accuracy and efficiency of accelerated cyclic corrosion testing. AI can be used to analyze large amounts of data obtained from corrosion tests to identify patterns and trends. This can help develop more accurate and predictive corrosion models. Simulations can be used to create virtual test environments that can be used to test components under a wide variety of conditions. This can help reduce the need for physical testing and accelerate the development process.  

Potential Challenges

One of the greatest challenges in accelerated cyclic corrosion testing is striking a balance between the accelerated test and real-world performance. Accelerated tests are designed to achieve results quickly, but they may not always represent real-world conditions. This is because accelerated tests typically use more aggressive environments and shorter test periods than those experienced in the real world. Another challenge is the cost of corrosion testing. Advanced test chambers and equipment can be expensive, and the tests themselves can be time-consuming. This can make corrosion testing a barrier to entry for smaller companies.

Conclusion

This article began with brief corrosion definitions (including those from worldwide reliable and recognized sources such as AMPP, ACA, and ISO) and corrosion problems affecting automobiles and the automotive industry, then addressed accelerated corrosion tests (focusing on Accelerated Cyclic Corrosion and Weather Resistance Tests). Its importance in the automotive industry has been comprehensively addressed. Finally, the future of accelerated cyclic corrosion testing has been addressed with current trends and potential challenges that may be encountered. Research conducted over the past approximately 50 years shows that the oldest and most commonly used ASTM B117/ISO 9227 Salt Fog Spray Test is not trusted by industry experts due to its extremely poor correlation, and cyclic aging/corrosion tests incorporating different environmental and atmospheric parameters have been designed instead of this test. (You can find the most frequently encountered ones in international literature in the table.) However, beyond these, major players in the automotive industry in particular (such as BMW, Chrysler, General Motors, Honda, Volkswagen, Mercedes-Benz, and Volvo) also design their own cyclic tests and require materials to be tested accordingly.

The Future of Accelerated Cyclic Corrosion

The outlook for testing in the automotive sector truly appears bright. Emerging trends in corrosion testing methodologies and technologies, such as the use of more complex test environments, the development of new NDT methods, and the increasing use of artificial intelligence and machine learning, are helping to improve the accuracy and efficiency of tests. However, there are still some challenges that need to be addressed, such as striking a balance between accelerated testing and real-world performance and reducing test costs. Artificial intelligence, simulation, and computer programs can play an important role in overcoming these challenges. Overall, accelerated corrosion testing is extremely necessary to ensure the durability and reliability of automotive components. The automotive industry is making significant investments in new corrosion testing technologies and methodologies, and the future of accelerated cyclic corrosion testing appears quite promising.   References 1. Salt Spray vs. Cyclic Corrosion Tests - https://www.pfonline.com/articles/salt-spray-vs-cycle-corrosion-tests 2. "Cyclic Corrosion Testing in the Automotive Industry" from Q-Lab - https://www.q-lab.com/documents/public/6ed712e7-2980-4634-a529-38f0def75a7a.pdf?ReturnUrl=/resources/brochures.aspx 3. "Accelerated Cyclic Corrosion Tests: A Comparison of Real Performance to Cosmetic Corrosion", García-García and others - https://www.researchgate.net/publication/227783350_Accelerated_corrosion_tests_in_the_automotive_industry_A_comparison_of_the_performans_towards_cosmetic_corrosion 4. "Development and Validation of New Accelerated Cyclic Corrosion Testing for Automotive Applications", Stephens and others - https://www.sae.org/standards/content/j2334_201604/ 5. "Correlation of Accelerated Corrosion Tests to Field Performance of Automotive Paint Systems", Mansfeld and others - https://www.automotive-iq.com/car-body-and-materials/articles/corrosion-protection-car-parts-and-safety 6. "Accelerated Corrosion Testing of Automotive Materials: A Review", Garcia-Garcia and others - https://www.researchgate.net/publication/227783350_Accelerated_corrosion_tests_in_the_automotive_industry_A_comparison_of_the_performans_towards_cosmetic_corrosion 7. "The Importance of Accelerated Cyclic Corrosion Testing in the Automotive Sector" from ASTM - https://www.pfonline.com/articles/salt-spray-vs-cycle-corrosion-tests 8. "Accelerated Cyclic Corrosion Testing for Automotive Applications" with Salt Spray Testing - https://www.pfonline.com/articles/salt-spray-vs-cycle-corrosion-tests 9. "Cyclic Corrosion Testing: What You Need to Know" from Atlas Material Testing Solutions - https://www.atlas-mts.com/products/standard-instruments/corrosion-cabinets   PCS. Tolga Dıraz Chemical Engineer / Project Manager Specialist in Corrosion, Protective Paints and Coatings