Scope—The SAE J lab test procedure should be used when determining SAE J—Guidelines for Laboratory Cyclic Corrosion Test Procedures for. The SAE J lab test procedure should be used when determining corrosion performance for a particular coating system, substrate, process, or design. sae j Laboratory Cyclic Corrosion Test - SURFACE VEHICLE do not have fully automatic capabilities is desired (for manual operations.
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temperature, a Cyclic corrosion test (SAE J) having prescribed cycles of . Much work has been conducted on this test by the SAE J Committee over. aracer.mobi Current Practice. Despite the method, a commonly accepted test is SAE J A cyclic test developed. SAE J Summary of Testing and Results. Selected panels per coating group were subjected to gravel impact and scribed prior to.
This method was used as the basis when comparing other methods of humidity generation as well as other variables. Air circulation must be sufficient to prevent temperature stratification and allow drying of test parts during the dry-off portion of the test cycle. Air circulation can be obtained through the use of a fan or forced air. Immersion Method—Test specimens are to be immersed in the salt solution for a minute interval of each test cycle.
Spray Method—A periodic or continuous direct impingement spray of the salt solution over the minute interval that ensures the test specimens are kept wet for the entire minute interval.
Avoid a high intensity pressure spray that may affect test results. Note 5 Both direct solution displacement and atomized spray are suitable for this method.
If a precipitate forms and a spray application is used to apply the solution, it may be necessary to remove the precipitate to avoid clogging of nozzles i. Any filter media used must be inert to the solution being used. A 20 to micron cotton or nylon mesh filter would be suitable. Do not attempt to dissolve the precipitate by adding acid. Do not attempt to adjust the pH with any form of buffers. NOTE 3—The majority of the development of this specification was performed using the immersion method of salt solution application.
This method was used as the basis when comparing other methods of salt solution applications as well as other variables. NOTE 5—Careful attention should be paid to the spray method to avoid a high intensity spray that may affect test results by removal of the corrosion product, removal of the coating or driving solution into the corrosion products. It consists of three basic stages: 1. Salt Application Stage—15 min duration conducted at ambient conditions 3.
Fully automatic cabinets have the option of running during the weekends or programming in a dry stage soak for the weekends typically it would be desired to run on weekends and holidays to complete the test sooner. An exception to this rule would be if comparisons to other laboratories who do not have fully automatic capabilities is desired for manual operations, the weekend exposure is typically maintained at dry stage conditions unless 7 day operations are available.
Total test duration and weekend conditions must be documented in the test results.
Ramp time between the salt application stage 2 and dry stage 3 are part of the dry stage time. Similarly, ramp time between the dry stage 3 and humid stage 1 are part of the humid stage. Ramp times should be documented for each test set-up. For cosmetic corrosion evaluations of coatings susceptible to damage, test samples will be scribed prior to exposure Reference ASTM D Scribe length should be a minimum of 50 mm. Scribe creepback measurements are to be taken at predetermined intervals depending on the level of corrosion resistance desired.
Scribe orientation, on the specimen, must be specified and documented for typical flat panel specimens, it is recommended that panels be oriented 15 degrees from the vertical such that no one panel shadows another and that the scribe line be made in a diagonal across the panel face. Longer durations may be required to observe performance differences in the heavier weight metallic precoats.
Different test durations may be appropriate based on other materials, corrosion mechanisms of interest, or past history. Corrosion coupons generally consist of The sheet metal coupon will always include low-carbon cold rolled steel sheet SAE to SAE , and may also include other bare metals, such as zinc.
Each coupon shall be permanently identified by stamping a number onto the surface. Then the mass in milligrams shall be recorded and retained for future reference. The coupons shall be secured to an aluminum or nonmetallic coupon rack.
The coupons shall be electrically isolated from the rack by using fasteners and washers made from a non-black plastic material, preferably nylon. Allow a minimum 5 mm spacing between the coupons and the rack surface.
All coupons shall be secured at a maximum 15 degrees from vertical and must not contact each other. The coupon rack shall be placed in the general vicinity of the samples being tested, such that the coupons receive the same environmental exposure.
Coupons shall be removed and analyzed after a predetermined number of cycles throughout the test to monitor corrosion. To analyze coupons, remove 1 coupon from each end of the rack and prepare for weighing and mass loss determination. Insure enough coupons are exposed in the test so monitoring frequency can be accomplished.
Additional unexposed coupons can be added throughout the test to obtain interval data in addition to cumulative data. This will be a cumulative value.
Additional unexposed coupons can be installed and removed after the next set of cycles to obtain interval coupon data if desired. Test Samples—The test samples will have scribe creepback values or corrosion rate measurements recorded at predetermined intervals typically, 20 cycles — in a rinsed only condition. At end-of-test two sets of creepback values will be recorded if coated samples are to be evaluated one set in a rinsed only condition and one set after the scrape and tape process Reference SAE Automotive Corrosion and Prevention Conference P, pages , see 2.
As a guideline, scribe creepback measurements of average, maximum, and minimum total width will be recorded. Total Width Creepback—A measurement of the distance between the unaffected paint film areas, in millimeters, on each side of the scribed line measured across and perpendicular to the scribe line. Loss of adhesion between paint film and substrate. Average—The mean of a set of measurements of Total Width Creepback, at points spaced equidistant apart centered on the scribed line.
Maximum—A measurement of the Total Width Creepback at the point with the most extensive adhesion loss, discounting the areas at the ends of the scribed line.
Minimum—A measurement of the Total Width Creepback at the point with the least extensive adhesion loss, discounting the areas at the ends of the scribed line. Frequency of Salt Solution Changes recommend weekly or sooner if contamination is a suspected concern b. Method of Salt Application c. In most cases, the specimens have an intentional bare metal area in the crevice and a wide crevice gap, since it is believed that these controlled conditions lead to less variation of the test results.
However, they do not necessarily reflect the structures of actual automotive parts.
If the crevice at the lapped portion is wide, the inside will be covered by electrodeposition, and a bare metal area will not be formed in the crevice. Therefore, the influence of the specimen configuration on perforation corrosion was investigated. The corrosion resistance of zinc and zinc alloy coated steels was evaluated by using two types of test coupons with different configurations. One was prepared by overlapping two plates directly without an intentional gap configuration A.
The bare metal area was the surface of the zinc or zinc alloy coating without phosphating and electrodeposition. Figure 8 shows a comparison of the corrosion appearances with configuration A and B after 60 cycles of the SAE J test.
With this test coupon confirmation, the alloy composition of the existing coatings did not have a significant impact on corrosion prevention. The tendency observed in this evaluation is similar to the corrosion experienced in actual automotive parts. On the contrary, in the evaluation with configuration B, the occurrence of red rust on the ZnNi coated steel was much smaller compared to the other coatings.
Thus, the alloy composition of the coatings is considered to be more significant than the coating thickness when the specimens have the wide crevice and bare metal area. Comparison of corrosion appearances of lapped portion for specimens with different crevice structures. With both configurations, an increase in the coating thickness improves corrosion resistance. However, the corrosion depth of the pure zinc coatings was deeper with configuration B than with configuration A.
The larger crevice and bare surface in the crevice tended to significantly accelerate corrosion of EG and GI. As shown in Fig. Contrary to this, with configuration A, the corrosion depths of ZnNi and GA fall on the regression line obtained from EG and GI, which implies that the coating thickness is the dominant factor determining perforation corrosion resistance.
In order to evaluate corrosion resistance in actual automotive parts, specimens that reproduce the effect of the coating thickness, including existing alloy coatings, must be used for CCT evaluations.
Therefore, the intended wide crevice and bare metal area in the specimen should be avoided in order to obtain an appropriate evaluation.