1、 WORLDWIDE ENGINEERING STANDARDS Test Procedure GMW14872 Cyclic Corrosion Laboratory Test Copyright 2013 General Motors Company All Rights Reserved March 2013 Page 1 of 27 1 Scope Note: Nothing in this standard supercedes applicable laws and regulations. Note: In the event of conflict between the En
2、glish and domestic language, the English language shall take precedence. 1.1 Purpose. This procedure describes an accelerated laboratory corrosion test method to evaluate assemblies and components. The test procedure provides a combination of cyclic conditions (salt solution, various temperatures, h
3、umidity, and ambient environment) to accelerate metallic corrosion. The procedure is effective for evaluating a variety of corrosion mechanisms, such as general, galvanic, crevice, etc. The test exposure/conditions can be individually tailored to achieve any desired level of corrosion exposure. Also
4、, synergistic effects due to temperature, mechanical and electrical cycling, along with other stresses, can be comprehended by this test. See Deviations Section (pages 25 through 27) of this document for typical modifications. 1.2 Foreword. The test method is comprised of 1% (approximate) complex sa
5、lt mist applications coupled with high temperature and high humidity and high temperature dry off. One (1) test cycle is equal to 24 h. A cycle is made up of the daily events or test inputs illustrated in Figure A1. A cycle normally requires one (1) day to complete. The test exposure is dictated by
6、a targeted coupon mass loss. A target range for the number of cycles necessary to meet the required mass loss is provided in Table A1 for Method 1/2 and Table A2 for Method 3. The coupon mass loss values are used to verify that the correct amount of corrosion has been produced by the test. In additi
7、on to meeting mass loss requirements, the test must be conducted such that the number of cycles required to meet coupon mass loss requirements falls within the specified range. 1.3 Applicability. This is a cyclic corrosion test (refer to Figure A1) used for validation testing (cosmetic and/or functi
8、onal/general durability), development testing, and quality control testing, for all global environmental regions. The basic exposures for cosmetic corrosion are found below in exposures 0, A, B, and C. Exposures D and E are used for functional assessment (refer to Table A1 and Table A2). All corrosi
9、on mechanisms are accelerated at different rates on test. Completing the test may not ensure that a component passes the functional requirement. A comprehensive failure mode analysis must be conducted to ensure all failure modes are considered and life expectancy is met. Exposure 0: All Areas (0 Yea
10、r/Initial Delivery (ID). Exposure A: Underbody Components. Exposure B: Underhood Components. Exposure C: Exterior Components/Panels, Secondary Surfaces, and Interior Components. Exposure D/E: All Components (Functional). Note: For Exposure 0 (0 Year/ID) evaluate parts at two (2) cycles of the define
11、d exposure linked to the associated vehicle area and mounting location as defined in Table A1 for Method 1/2 and Table A2 for Method 3. Note: Reference the Deviations Section (pages 25 through 27) for optional modifications. 2 References Note: Only the latest approved standards are applicable unless
12、 otherwise specified. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW14872 Copyright 2013 General Motors Company All Rights Reserved Mar
13、ch 2013 Page 2 of 27 2.1 External Standards/Specifications. ASTM D610 ISO 6270-2 ISO 12103-1 SAE 2001-01-0640 ASTM D1193 ISO 8407 SAE 1008-1010 SAE J2329 2.2 GM Standards/Specifications. GMW14700 GMW15356 GMW15358 GMW16277 (I) GMW15282 GMW15357 GMW15359 (I) = This is a standard that is distributed o
14、nly internally within General Motors. This standard cannot be distributed outside of General Motors. Contact the GM lead engineer for any instructions. 2.3 Additional References. ACT Test Panels Auto Technology Company National Exposure Testing Powder Technology Incorporated Splash Shielding Best Pr
15、actices: The supplier shall work with the GM responsible engineer to comprehend this requirement. 3 Resources 3.1 Facilities. Laboratory (preferably with controlled ambient conditions). 3.1.1 Calibration. The test facilities and equipment shall be in good working order and shall have a valid calibra
16、tion label. 3.1.2 Alternatives. Alternative test facilities and equipment may also be used. However, all measuring variables as specified in this standard shall be determined correctly with respect to their physical definition. 3.2 Equipment. 3.2.1 Ambient Stage. The apparatus for the ambient stage
17、shall have the ability to maintain the following environmental conditions: Temperature: 25 C 3 C. Humidity: 45% 10% Relative Humidity (RH). Duration: Approximately 8 h per cycle. Note: For weekends and holidays, it is acceptable to open the chamber and allow chamber environment to mix with controlle
18、d ambient environment. 3.2.2 Humid Stage. The apparatus for the humid stage shall have the ability to ramp to (within 1 h) and maintain (for approximately 7 h) under the following environmental conditions: Temperature: 49 C 2 C. Humidity: Approximately 100% RH. Duration: Approximately 8 h per cycle.
19、 The apparatus shall consist of a fog/environmental chamber, suitable water supply conforming to ASTM D1193 Type IV, provisions for heating the chamber, and the necessary means of control. 3.2.2.1 Water Fog. The apparatus shall include provisions for a supply of suitably conditioned compressed air a
20、nd one or more nozzles for fog generation. The nozzle or nozzles used for the generation of the fog shall be directed or baffled to minimize any direct impingement on the test samples. At least two (2) clean fog collectors shall be placed within the exposure zone so that no drops of solution from th
21、e test specimens or any other runoff source shall be collected. The collectors shall be placed in the proximity of the test specimens, one nearest to any nozzle and the other farthest from all nozzles. Collection rates for each 80 cm2 of horizontal collection area should be in the range of 0.75 mL/h
22、 to 1.5 mL/h (on average) for water that is collected in the collectors within the Humid Stage. Fog collection rates may be adjusted within this range as necessary to meet mass loss target rates. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for Resale
23、No reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW14872 Copyright 2013 General Motors Company All Rights Reserved March 2013 Page 3 of 27 Suitable collecting devices include glass or plastic funnels with the stems inserted through stoppers int
24、o graduated cylinders. Funnels with a diameter of 10 cm have an area of about 80 cm2. Where samples cannot be read immediately upon completion of the humid stage, closed cell foam balls can be used in combination with the collections funnels (i.e., foam ball in mouth of funnel) to allow moisture to
25、collect while minimizing evaporation. 3.2.2.2 Wet-Bottom. The apparatus shall consist of the chamber design as defined in ISO 6270-2. During wet-bottom generated humidity cycles, the tester must ensure that visible water droplets are found on the samples to verify proper wetness. 3.2.2.3 Steam Gener
26、ated Humidity. Steam generated humidity may be used provided the source of water used in generating the steam is free of corrosion inhibitors. During steam generated humidity cycles, the tester must ensure that visible water droplets are found on the samples to verify proper wetness. 3.2.3 Dry Off S
27、tage. The apparatus for the dry off stage shall have the ability to ramp to (within 3 h) and maintain (for approximately 5 h) under the following environmental conditions: Temperature: 60 C 2 C. Humidity: 30% RH. Duration: Approximately 8 h per cycle. The apparatus shall also have sufficient air cir
28、culation to prevent temperature stratification, and also allow thorough drying of the test samples. 3.2.4 Salt Mist Application. The solution shall be sprayed as an atomized mist, and should be sufficient to rinse away any salt accumulation left from previous sprays. The test samples and coupons sha
29、ll be thoroughly wet/dripping. Suitable application techniques include using a plastic bottle, or a siphon spray powered by oil-free regulated air to spray the test samples and coupons. Note: The force/impingement from this salt application should not remove corrosion or damage coatings/paints syste
30、m of test samples. 3.2.5 Corrosion Coupons and Mounting Hardware. Coupons serve to monitor the average general bare steel corrosion produced by the test environment. Coupons consist of 25.4 wide 50.8 long 3.18 mm thick pieces of bare SAE 1008-1010 carbon steel, cold-rolled steel per SAE J2329 CR1E,
31、uncoated, no post-coating treatment, which are stamped with an alphanumeric identification number (reference Figure A2). The coupons shall be secured to an aluminum or nonmetallic coupon rack with fasteners as shown in Figure A3 and Figure A4. The bolt, nut, and washers shall be made from a non-blac
32、k plastic material, preferably nylon. Figure A4 shows a completed coupon rack configuration. The number of coupons recommended for different test durations are shown in Table A3. 3.3 Test Vehicle/Test Piece. The test sample (design, surface, and preparation) should be agreed to by the parties concer
33、ned (Design Engineer/Materials Engineer/Corrosion Engineer) and should simulate actual production materials and conditions when possible. The number of test samples selected should be sufficient to ensure that the test results are statistically significant at some predetermined confidence level, unl
34、ess otherwise specified. Any unusual observations made during sample preparation should be recorded and reported as part of the test results. Where appropriate, test samples and/or control panels of known performance, should be tested concurrently. These controls can allow the normalization of test
35、conditions during repeated running of the test (supplementing the required mass loss controls) and may also allow comparison of test results from different repeats of the test. Where actual/representative production samples are available and the in-service orientation is known, test samples should b
36、e oriented to simulate these conditions. When using test panels and/or the in-service orientation is not known, the sample shall, in principle, be oriented such that it is facing upward and at an angle of 20 degrees 5 degrees from vertical. 3.3.1. Preconditioning of Test Samples. The gravelometer an
37、d/or a scribing tool can be used to provide damage to coating layers prior to testing in order to better represent potential in-service damage when appropriate. The use of either of these preconditioning methods shall be agreed upon by the parties concerned and shall conform to the methods described
38、 in GMW14700 and/or GMW15282. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW14872 Copyright 2013 General Motors Company All Rights Rese
39、rved March 2013 Page 4 of 27 3.4 Test Time. See cycle times in Table A1 or Table A2. 3.5 Test Required Information. Not applicable. 3.6 Personnel/Skills. Not applicable. 4 Procedure 4.1 Preparation. 4.1.1 Salt Solution Preparation. The complex salt solution in percent (%) by mass shall be as specifi
40、ed below: Sodium Chloride (NaCl): 0.9%. Calcium Chloride (CaCl2): 0.1%. Sodium Bicarbonate (NaHCO3): 0.075%. Sodium Chloride must be reagent grade or Morton Culinox 999 Food grade. Calcium Chloride must be reagent grade. Sodium Bicarbonate must be reagent grade (e.g., Arm and Hammer Baking Soda or c
41、omparable product is acceptable). Water must meet ASTM D1193 Type IV requirements. Note: Either CaCl2 or NaHCO3 material must be dissolved separately in water and added to the solution of the other materials. If all solid materials are added dry, an insoluble precipitate may result. Salt solution ma
42、keup calculator for the appropriate amount of sodium chloride, calcium chloride, sodium bicarbonate, and water examples are shown in Appendix B, Figures B1 through B6. Additional contaminants (dust, grit, poultice, and exhaust condensate) called out in the Deviations Section (pages 25 through 27) ar
43、e defined in Appendices C through Appendix F. 4.1.2 Coupon Preparation. Corrosion coupons should be cleaned with methanol or acetone solution and accurately weighed prior to use. The weight, in grams, shall be recorded and retained for future reference. If coupons are not used immediately, they shou
44、ld be stored such that they are corrosion free at the start of test. It is critical that all forming or preservation oils/lubes be removed prior to exposure to allow for general/uniform corrosion of the coupon. This process can be aided by using a commercial grade degreaser prior to methanol or acet
45、one clean. 4.1.3 Coupon Rack Preparation. Prior to start of test; prepare the coupon rack with sufficient coupons to monitor the test. The number of coupons recommended for different test durations are shown in Table A3. The exact location of each coupon on the rack shall be identified and recorded
46、using the pre-stamped numbers for reference as illustrated in Figure A4. Allow a minimum 5 mm spacing between the coupons and the rack surface. All coupons shall be secured vertically with no more than 15 degree deviation from vertical and must not contact each other. The coupon rack shall be placed
47、 in the general vicinity of the test samples being tested, such that the coupons receive the same environmental exposure as the test samples. Note: Mass loss coupons are test monitoring devices and are not intended to be exposed to additional stresses which may be added to the base test (i.e., grave
48、lometer, dust, grit, exhaust condensate, thermal exposure, etc.) Additional coupons may be required to monitor special test conditions (refer to Deviations Section, pages 25 through 27). 4.2 Conditions. 4.2.1 Environmental Conditions. 4.2.2 Test Conditions. Deviations from the requirements of this s
49、tandard shall have been agreed upon. Such requirements shall be specified on component drawings, test certificates, reports, etc. 4.3 Instructions. 4.3.1 Test Execution. See Figure A1 (Flow Diagram) for the steps that comprise the test method. Repeat the cycle daily, as necessary, until the test exposure requirements are met. At the option of the test requestor, the test can be continued throughout weekends to decrease the overall
