技术文章

SAE J2334 International surface vehicle standard（盐雾试验标准三）

5 Test Procedure
5.1 Test Cycle－The test cycle is outlined in Figure 1（5 day/week-manual operation） and Figure 2（7 day/week-automatic operation）. It consists of three basic stages;

1. Humid Stage－50℃ and 100% Humidity, 6 h in duration,
2. Salt Application Stage— 15 min duration conducted at ambient conditions
3. Dry Stage— 60℃ and 50% RH, 17 h and 45 min in duration.

The test cycle is repeated daily. Fully automatic cabinets have the option of running during the weekends or porgramming 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 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. If two or more laboratories will be conduting tests on similar parts, it is recommended that a constant/common weekend condition be defined before testing beings.

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 1654）. Scribe length should be a minimum of 2 in. Scribe creepback measurements are to be taken at predetermined intervals depending on the level of corrosion resistance desired. Scribe orientation, on the 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 theat the scribe line be made in a diagonal across the panel face）.

5.2 Test Duration—Typically, SAE J2334 is conducted for a minimum of 60 cycles when evaluationg coated products. 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.

Cosmetic Corrosion LabTest Cycles SAE J2334-5Day/Week - Manual Operation

                       Humidity 50C and 100% RH（6 hours）

                       Salt Application（Dip, Fog or Spray） at ambient conditions（15 minutes）

                       Dry Off 60C and 50% RH（17 hours, 45 minutes）

                             Weekends Only
                                  Dry Off 60C and 50%RH

Cosmetic Corrosion LabTest Cycles SAE J2334-7 Day/Week- Automatic Operation

                     Humidity 50C and 100% RH（6 hours）

                     Salt Appliation （Dip, Fog or Spray） at ambient conditions （15 minutes）

                     Dry Off 60C and 50% RH（17 hours, 45 minutes）

5.3 Coupon Monitoring-The testing process will be monitored with bare steel corrosion coupons.

    a. Corrosion coupons generally consist of 25.4 mm by 50.8 mm pieces of bare sheet metal which serve to monitor the corrosivity of the test environment during the test. The sheet metal coupon will always include low-carbon cold rolled steel sheet （AISI 1006-1010）, and may also include other bare metals, such as zinc.
    b. Each coupon shall be permanently identified by stamping a number onto the surface.
    c. Corrosion coupons shall be thoroughly cleaned to remove all forming and storage oils/lubes with a commercially available degreaser followed by a methanol rinse. Then the mass in milligrams shall be recorded and retained for future reference.
    d. 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.
    e. 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.
    f. The coupon rack shall be placed in the general vicinity of the samples being tested, such that the coupons receive the same environmental exposure.
    g. Coupons shall be removed and analyzed after a predetermined number of cycles throughout the test to monitor corrosion. To analyze coupons, remove 1 coupon form each end of the rack and prepare for weighing and mass loss determination. Insure enough coupons are exposed in te 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.
    h. Before weighing, clean the coupons using a mild "sand blast" （preferably glass beads） to remove all corrosion by-products from the coupon surface. An alternative/equivalent cleaning method, using a chemical process, is described in ASTM G 1. Once clean, wipe the coupons with methanol and weigh to determine the coupon mass loss using Equation 1:
              Mass Loss= （Initial Mass） - （End-of-Exposure Mass）
       Corrosion losses may also be expressed in term of average corrosion rates from the mass loss, coupon area, test duration, and metal density by use of the calculation described in ASTM G 1.