1、 WORLDWIDE ENGINEERING STANDARDS Test Procedure GMW17026 Accelerated Corrosion Laboratory Test for Galvanic Corrosion Mechanisms Copyright 2013 General Motors Company All Rights Reserved September 2013 Page 1 of 13 1 Scope Note: Nothing in this standard supercedes applicable laws and regulations. No
2、te: In the event of conflict between the English and domestic language, the English language shall take precedence. 1.1 Purpose. This standard describes an accelerated corrosion test. This test is designed for corrosion replication where galvanic corrosion mechanisms are present. 1.2 Foreword. This
3、is a cyclic environmental test which exposes test items to periodic wetting with a salt/mud solution followed by drying all at an elevated temperature. 1.3 Applicability. This procedure is applicable to passenger car and truck components or assemblies. This test has shown good test-to-field correlat
4、ion of accelerated galvanic corrosion. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. ASTM D1193 SAE J2329 ISO 8407 2.2 GM Standards/Specifications. GMW14700 GMW15282 GMW15264 2.3 Additional References. Componen
5、t Technical Specifications Material Specifications Part Drawings SAE 1008-1010 Carbon Steel Subsystem Technical Specifications 3 Resources 3.1 Facilities. Floor space adequate for appropriate corrosion chamber, fixturing, controls, and pneumatic capability. 3.1.1 Calibration. The test facilities and
6、 equipment shall be in good working order and shall have a valid calibration 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.
7、3.2 Equipment. 3.2.1 Test Chamber. A test chamber is required that is of sufficient size to contain the test items, with adequate space for air and solution circulation around them. It is recommended that the size be approximately 1 m x 1 m x 2 m. The chamber must be constructed of materials which a
8、re resistant to corrosion such as stainless steel or plastic. Likewise all fittings, hardware and attachments must be corrosion resistant. It is extremely beneficial if the test chamber has windows for observing testing while in progress. The test chamber must have available pass-throughs for sampli
9、ng and/or instrumentation connections. The test chamber must be designed so that the test solution/slurry will drain back to the reservoir. 3.2.1.1 Solution System. The chamber must have a solution circulating pump and a spray capable of spraying the salt/mud mixture in a consistent and reliable man
10、ner. The mixture holding tank must have agitation to maintain the proper solution concentration and solids dispersion. 3.2.1.2 Spray System. Spray systems should spray from a direction corresponding to vehicle tire patch(s) or other locations where spray would originate on a vehicle. Spray pumps are
11、 usually pneumatic powered for use in the corrosive environment. The initial spray volume at each nozzle should be between 1.5 L/minute and 3.0 L/minute. 3.2.1.3 Heating System. The test chamber must have a heating and control system capable of maintaining a constant uniform temperature (3 C) at 66
12、C where measured, the only exception being the first 60 minutes after spray events. The temperature is measured at the closest available location to the test parts. The test chamber must have provisions to circulate heated Copyright General Motors Company Provided by IHS under license with General M
13、otors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW17026 Copyright 2013 General Motors Company All Rights Reserved September 2013 Page 2 of 13 air within the chamber. A vehicle fan turning at 900 rpm to 1800 rpm is su
14、fficient. 3.2.1.4 Vent System. The test chamber must have provisions for passive venting or purging the atmosphere in the chamber. Pneumatic actuators controlling the vents are the best for use in the corrosive environment. 3.2.2 Chamber Control. 3.2.2.1 Chamber Temperature Controller. The controlle
15、r must be able to vary the temperature with time in order to create temperature cycles from a given external command. The controller timing functions must be controlled to 1 s. The test chamber must have a heating and control system capable of maintaining a constant uniform temperature (3 C) at 66 C
16、. 3.2.2.2 Chamber Vent Controller. The controller must be able to signal solenoids to open and close the vent(s) on the top of the booth. 3.2.2.3 Chamber Spray Controller. The controller must be able to start and stop the pneumatic spray system pump solenoids. 3.2.3 Test Solution Reservoir. The rese
17、rvoir must be sized to hold sufficient solution to support the spray system in the chamber. Generally a 100 L to 200 L tank will support a 1 m x 1 m x 2 m chamber with up to 20 spray nozzles. The reservoir must have agitation to maintain the solids in suspension for uniform spray application to the
18、test samples. The reservoir and its associated plumbing and pumps must be able to handle the water-salt-mud slurry that is the test solution. Adequate screen and filter are required to prevent large stones and debris from damaging pumps and/or plugging the system. 3.2.4 Air Supply. The compressed ai
19、r supply used to operate the spray pumps that spray the corrosive solution in the chamber must be free of oil and dirt and controllable between 70 kPa and 500 kPa. 3.2.5 Corrosion Coupons and Mounting Hardware. Coupons serve to monitor the average general bare steel corrosion produced by the test en
20、vironment. Coupons consist of 25.4 mm wide x 50.8 mm long x 3.18 mm thick pieces of bare SAE 1008-1010 carbon steel, cold rolled steel per SAE J2329 CR1E, uncoated, no post coating treatment, which are stamped with an alphanumeric identification number (reference Appendix A, Figure A1). The coupons
21、shall be secured to an aluminum or non-metallic coupon rack with fasteners as shown in Appendix A, Figure A2. The bolt, nut and washers shall be made from a non-black plastic material, preferably nylon. Appendix A, Figure A3 shows a completed coupon rack configuration. The number of coupons recommen
22、ded is at least 12 per test. 3.3 Test Vehicle/Test Piece. The test specimens can be anything from test panels to complete components and/or subassemblies. Expose the test specimen in the vehicle position in the test chamber to achieve the most realistic exposure. The number of samples required to te
23、st should be enough to provide adequate statistical data at the required confidence level. Note: It is sometimes desirable to pre-damage the specimens before testing to simulate field exposure. Scribes through the paint coating, as specified in GMW15282, or chipping from GMW14700 exposure are two of
24、 the more common techniques. 3.4 Test Time. This is a coupon correlated test. Test times are approximate. Calendar time: 50 days Test hours: 1200 hours Phase hours: 120 hours Cycle hours: 12 hours Block hours: 3 hours A cycle is defined as 1% of test. An option to run to 15 years (150%) of test is a
25、vailable. Calendar and test hours listed would simply be multiplied by 1.5. 3.5 Test Required Information. Not applicable. 3.6 Personnel/Skills. Not applicable. 4 Procedure 4.1 Preparation. 4.1.1 Test Solution. The solution is prepared by volume. Instructions for this follow. 4.1.1.1 Test Solution b
26、y Volume. Fill a cleaned and rinsed tank with 200 L tank (within 1 in of the top of the tank lid extension) with reverse osmosis (RO) water conforming to ASTM D1193, Type IV. Turn on the agitator pump. Add 5.7 kg of sodium chloride. Sodium chloride must be reagent grade or Morton Culinox 999 food gr
27、ade. Fill the container marked “GMW15264 Solution Prep Container” to the fill line with food grade sodium chloride twice and empty into the 200 L tank. Add 5.7 kg of Fireclay. Fill the container marked “GMW15264 Solution Prep Container” to the fill line once with Fireclay and empty into the 200 L ta
28、nk. 4.1.1.2 Test Solution by Weight Alternative. Alternately, the solution can be prepared in a two-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 ST
29、ANDARDS GMW17026 Copyright 2013 General Motors Company All Rights Reserved September 2013 Page 3 of 13 step procedure. First a 3% salt solution is prepared by dissolving three parts by weight of sodium chloride in 97 parts of reverse osmosis water to achieve a 3% by weight sodium chloride solution p
30、er specification ASTM D1193, Type IV. Sodium chloride must be reagent grade or Morton Culinox 999 food grade. Second, add 38 g of Fireclay to each liter of salt solution from the first step. Instructions and some example batch mixture formulae are shown in Appendix B, Table B1. Sources of Fireclay a
31、re listed in Appendix C. The salt concentration in the solution shall be checked at 20% intervals and maintained at 3% 1.0%. These measurements shall be made either electrochemically or gravimetrically. The pH of the solution as sprayed in the chamber shall be maintained between 6.0 and 8.0. 4.1.2 C
32、oupon Preparation. Corrosion coupons should be cleaned with ethanol or acetone solution and accurately weighed prior to use. A two-step process using first ethanol then acetone is acceptable. The weight, in grams (g), shall be recorded and retained for future reference. If coupons are not used immed
33、iately, they should 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 or white
34、 spirits prior to ethanol or acetone clean. 4.1.3 Coupon Rack Preparation. Prior to start of test; prepare a coupon rack with sufficient coupons to monitor the environmental exposure. Sufficient coupons should be enough to allow at least two coupons to be removed at least five times during the expos
35、ure as listed in Appendix A, Figure A6. The exact location of each coupon on the rack shall be identified and recorded using the pre-stamped numbers for reference. Allow a minimum 5 mm spacing between the coupons and the rack surface. All coupons shall be secured vertically with no more than 15 degr
36、ees angle rearward deviation from vertical (as shown in Appendix A, Figure A3) and must not contact each other. The coupon rack shall be placed in the general vicinity of the test samples being tested, such that the coupons receive the same environmental exposure as the test samples. Sources of coup
37、ons and coupon racks are listed in Appendix C. 4.2 Conditions. 4.2.1 Environmental Conditions. Not applicable. 4.2.2 Test Conditions. Deviations from the requirements of this standard shall have been agreed upon. Such requirements shall be specified on component drawings, test certificates, reports,
38、 etc. 4.3 Instructions. The test chamber is operated 24 h/day on the following wet/dry cycle: 4.3.1 First the test chamber temperature is set to 66 C and vent is closed. Then a minimum 90 s corrosion solution spray is performed (maximum not to exceed 5 minutes). After the minimum 90 s spray, the ven
39、t is opened for balance of 90 minutes to dry parts. After 90 minutes, the vent is closed. 4.3.2 The time histories of the vent, spray, and temperature are shown in Appendix A, Figure A4. A Flow Diagram for the steps that comprise one cycle of the test method is shown in Appendix A, Figure A5. 4.3.3
40、This is a cyclic corrosion test which consists of wet and dry periods at elevated temperature. Any variation from the basic test schedule must be agreed upon between the test requestor and the tester and be reported in detail in the final report. 4.3.4 Test samples must be placed in the chamber in a
41、 manner that insures they all receive an equal and representative quantity of test solution during the spray portion of the cycle. They must also be oriented to avoid shielding other samples or trapping unrealistic quantities of test solution. Any test component actuation must be done in such a way
42、that it accurately reproduced operation in the hands of the customer. 4.4 Test Environment Monitoring. Corrosion coupons shall be removed and analyzed throughout the test to monitor the corrosion. Recommended intervals of 25% would suffice to monitor test progress. The recommended number of coupons
43、is listed in Appendix A, Table A1. To analyze coupons, remove one coupon from each end of the rack, clean per paragraph 4.4.1 to prepare for weighing, and an average mass loss determination. Note: Although not preferred, corrosion by-product removal by chemical cleaning per ISO 8407 may be used. 4.4
44、.1 Coupon Preparation. Before weighing, clean the coupons using a mild sand/bead blast process to remove all corrosion by-products from the coupon surface. Wipe the coupons free of grit and weigh to determine the coupon mass loss using the formula: Mass Loss = (Initial Mass) (End-of-Exposure Mass) C
45、opyright 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 GMW17026 Copyright 2013 General Motors Company All Rights Reserved September 2013 Page 4 of 1
46、3 4.4.2 Coupon Mass Loss. The targeted mass loss at the end of test is 9.5 g 2.38 g. The test is designed to achieve required mass loss in 100 cycles 24 cycles, or 50 days 12 days. When the option to run the test to 150% is employed, the coupon mass loss should be 17.25 g 4.31 g, and achieve the req
47、uired mass loss in 150 cycles 36 cycles, or 75 days 18 days. Note: Desired incremental test durations corresponding to coupon mass loss are plotted on the chart in Appendix A, Figure A6. To check test progress, compare the actual mass loss to the desired total mass loss. When the actual mass loss ha
48、s achieved the desired 9.5 g 2.38 g of mass loss for 100% of test, the test is completed. If the 150% option is desired, when the actual mass loss has achieved the desired 17.25 g 4.31 g of mass loss, the test is 150% of test. 4.5 Inspection. The test sample(s) shall be inspected for corrosion, and
49、photographed (as necessary) at the end of predetermined number of cycles. If test samples containing plastic materials are being tested, any discoloration or degradation and/or adhesive bond failure (delamination) shall be noted and recorded. If scribing is required, on either test samples, follow the methods described in GMW15282. This method also includes measurement of corrosion creepback from a scribe line, and describes how to evaluate corrosion formation
