The Automotive Cyclic Corrosion Test

Introduction

By the 1980’s rapid growth of vehicle ownership and poor customer experience of corrosion resistance during the preceding 20 years, had given motor vehicle manufacturers and their component suppliers a significant issue to address. The industry required a more predictive method of testing which would allow component performance to be addressed before field trials and product releases. One method of testing which was shown to be particularly indicative of the performance of components in the conditions in which vehicles operate was the Cyclic Corrosion Test (CCT).

As a result of early experience, the automotive industry took a lead role in the development of cyclic corrosion tests with the objective of producing results that better correlate with field exposure. In 1984, The Automotive Corrosion and Prevention Committee, in collaboration with the Corrosion Task Force of the American Iron and Steel Institute and the Society of Automotive Engineers, began its work. This group strived to develop the knowledge of corrosion mechanisms and their replication in a controlled environment until, nearly 20 years later and after considering over 130 available laboratory, proving ground, and outdoor corrosion tests, the SAE Surface Vehicle Standard, J 2334 Cosmetic Corrosion Lab Test, was published in June 1998.

The development of SAE J2334 was time consuming, but thorough. Ten substrate materials were selected for use in the tests to reflect the materials most commonly used and/or   subject to the greatest corrosive damage in vehicle applications.. At least two substrates were chosen because the existence of proven corrosion testing results enabled them to be used to assure the consistency of the test. Canadian on-vehicle tests were conducted at Montreal, Quebec and St. John's Newfoundland for 5 years. The test panels were mounted on the vehicles in both horizontal and vertical orientations to better represent the various surface orientations typically found in vehicle applications. The corrosion mechanisms of on-vehicle and laboratory tests were studied by Lehigh University, and the resulting analysis showed that similar corrosion products and modes were found in these tests as were found after conducting SAE J2334 tests.

Test Conditions

Test specimens are placed in an enclosed chamber and exposed to a changing climate that comprises of the following 3 part repeating cycle.

1. 6 hours exposure to a water fog/condensing humidity climate of 100%RH at +50C.
2. 15 minutes immersion in (or a direct spray of) salt water at ambient.
3. 17 hours 45 minutes of air drying in a climate of 50%RH at +60C.

For the specimens a minimum of 6, each sized 25.4 x 50.8 mm and made of AISI 1006-1010 steel, are used.

The test cycle is repeated daily, fully automatic cabinets have the option of running during the weekends or programming in a dry stage soak.

The number of cycle repeats and therefore the test duration is variable.

The 100% relative humidity wet stage condition can be achieved by one of three methods shown as follows. Whichever method is employed, test samples and controls are required to be visibly moist/wet.

1. Wet-bottom method according to ASTM D2247 – except that the temperature shall be 50C +/-2^oC.
2. Water fog method according to ASTM D 1735, except that the collection rate is reduced from a range of 1.5 to 3ml/h to 0.75 to 1.5ml/l.
3. Steam (Vapour) method.

The samples must be subject to an application of salt solution consisting of the following formulas and by use of one of three methods shown as follows;

0.5% NaCl

0.1%CaCl₂

0.075% NaHCO₃

a. Immersion Method – test specimens immersed in the salt solution for a 15 minute interval of each test cycle.

b. Spray Method – periodic or continuous direct impingement spray of the salt solution over the 15 minute interval that ensures that the test specimens are kept wet for the entire 15 minute interval.

c. Air Atomised Fog Method –15 minute exposure to atomised fog provided the fog collection rate is 2ml/hr to 4ml/hr instead of 1ml/hr to 2ml/hr.

Note that either the CaCl₂  or the NaHCO₃  material must be dissolved separately in deionised water and then added to the solution of the other materials otherwise an insoluble precipitate may result.

Typical Applications

SAE J 2334 is used widely throughout the North American automotive industry - particularly by General Motors and their suppliers.

It is also used elsewhere in the world where these auto companies have satellite manufacturing facilities, or joint collaborative ventures with other auto manufacturers. 

If you would like further information please call our experienced team on 01827 318040 or email sales@ascott-analytical.com