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In 2003 the American Iron and Steel Institute, in conjunction with a Committee of the SAE, conducted a study of existing cyclic corrosion tests in order to establish the best methods of predicting the performance of materials used in automotive applications. Twenty established corrosion test procedures were included within the study. The process itself comprised of undertaking tests on 10 different materials with each procedure, the results were compared to results gathered through real World exposure from 10 locations around the globe, undertaking the tests with identical materials.
The procedures were judged on:
The test established that the General Motors standard GM9540P, was one of the best methods of cosmetic corrosion prediction of cold rolled steel and resulted in the publication of it’s successor GMW14872.
The test method is composed of approximately 1% NaCL, CaCL2 and NaHCO3 salt mist applications combined with high temperature and humidity drying cycles, a single cycle of the test lasts for approximately 24 hours.
Specimens being tested are exposed to a multi-stage changing environment that is composed of three distinctive cycles, these stages can be varied depending on the nature of the specimen undertaking the test, for further information please refer to the full GMW14872 standard.
The individual cycles comprise of
The test length is variable dependant on the number of cycles within the total test duration.
Through analysis of historic data it has been determined that the GMW14872 test process very closely predicts the corrosion rates for steel and zinc materials exposed to periodic de-icing salts, for this reason the standard has become very popular within the automotive industry.
Additionally the US military regularly uses the standard to predict life of a variety of coatings and materials on tactical vehicles.