FORD FLTM AB 110-01-2016 TESTING THE RESISTANCE OF 6000 SERIES ALUMINUM BOLTS TO INTERGRANULAR CORROSION.pdf

1、 FORD LABORATORY TEST METHOD FLTM AB 110-01 Date Action Revisions Rev. 0 2016 01 11 Released K. Lazarz, NA Controlled document at www.MATS Copyright 2016, Ford Global Technologies, LLC Page 1 of 5 TESTING THE RESISTANCE OF 6000 SERIES ALUMINUM BOLTS TO INTERGRANULAR CORROSION Application This proced

2、ure is designed to evaluate the susceptibility for corrosion initiation in areas near grain boundaries. Test bolt must be representative of the forming operation, heat treatment, installation torque, and degree of elastic or plastic deformation. The process is applicable to 6000 series aluminum as r

3、olled, forged, and extruded bolts. If the bolt is coated it must be threaded into a substrate to the proper torque and then uninstalled for testing. The production representative bolt (unassembled) is immersed in an acid salt bath for two hours. Parts are then cross-sectioned and intergranular corro

4、sion (IGC) is evaluated microscopically. Apparatus and Materials Required Reverse Osmosis or Deionized Water Salt (NaCl) Food Grade, Non-Iodized Concentrated Hydrochloric Acid (HCl, 37%) Volumetric Flasks 400 ml Beaker Band Saw or Cut-Off Wheel (Water Cooled) Metallographic Epoxy Resin Metallographi

5、c Polishing Supplies Kellers Reagent Optical Microscope Balance/Scale Chemicals, materials, parts, and equipment referenced in this document must be used and handled properly. Each party is responsible for determining proper use and handling in its facilities. FORD LABORATORY TEST METHOD FLTM AB 110

6、-01 Copyright 2016, Ford Global Technologies, LLC Page 2 of 5 Procedure Number of samples Non-coated bolts: a. Two bolts sectioned longitudinally after acid immersion (for determination of IGC). b. If grain size determination is required, sectioned one longitudinally and one transversely through the

7、 threads in the as-received condition. Coated bolts, including anodized: a. Two bolts sectioned longitudinally after acid immersion (for determination of IGC). b. Two bolts after installation/removal and acid immersion sectioned longitudinally (for determination of IGC). c. as-received longitudinal

8、(to evaluate coating for cracks) d. If grain size determination is required, sectioned one transversely through the threads in the as-received condition. 1. Prepare the 1000 ml test solution by adding 933 ml of water to a volumetric flask. Add 67 ml of HCl to the water. Gently swirl the flask or use

9、 a stir bar to mix the solution. Use an ice bath if necessary to handle the exothermic reaction. Mix solution thoroughly. 2. Add 25 g of NaCl to the solution and mix thoroughly. 3. If the bolt has a barrier type surface coating, tighten the bolt to the high end of the torque range in a production re

10、presentative joint to simulate installation. Remove and continue to step 4. 4. Place the bolts at the bottom of a beaker, so they do not touch each other. Multiple bolts can be immersed at the same time. 5. Pour test solution into the beaker fully covering the bolts. Use a glass stir bar to realign

11、the bolts if necessary. The test solution is used only once. 6. Expose the bolts for a minimum of 2 hours (+ 0.5 h) at room temperature. 7. Remove the bolts from the test solution and immediately rinse under cool running tap water. Mechanical aids such as brushes must not be used during rinsing. 8.

12、For the longitudinal samples, cut the bolt in half length-wise using a band saw or water cooled abrasive saw. Other methods can be used as long as they dont introduce heat into the samples. 9. For transverse samples, cut the bolt in half in the threaded region. 10. Prepare metallographic mounts for

13、each sample. For the longitudinal samples, use one mount to evaluate the full length of the bolt when possible. If the bolt is too long for a single mount, use multiple mounts to include the full length, noting the orientation of the threads with respect to the head of the bolt. 11. Polish per ASTM

14、E3. Use Kellers Reagent per ASTM E407 to reveal the grain structure. 12. Evaluate the metallographic mounts microscopically 13. Evaluate the four areas shown in Figure 1, including all of the threads. Include photomicrographs at 10x and 75x magnification in the report for the four areas. The orienta

15、tion of the sample relative to the head of the bolt and magnification scale bar must be clear in the images (pressure flank of the threads is toward the head of the bolt). FORD LABORATORY TEST METHOD FLTM AB 110-01 Copyright 2016, Ford Global Technologies, LLC Page 3 of 5 Figure 1 14. Report any evi

16、dence of IGC and the region it was observed. Refer to Appendix A. Figure A1 shows no evidence of IGC. Figure A2 depict various examples of IGC. 15. Report discovery of impermissible surface discontinuities as defined in ISO 6157-3. Figure A3 shows an example of an impermissible lap. Laps are not IGC

17、. 16. For coated bolts, provide photomicrographs of the surface coating along the length of the bolt in the as received and after installation/removal. Report any cracking of the coating. 17. If there is a requirement for grain size, evaluate the grain size in the longitudinal and transverse directi

18、on by the comparison method of ASTM E112 and report ratings. Figure 1 Longitudinal cross-section through a bolt. 1 Entire thread area 2 Transition from shank to thread 3 Radius between shank and under-head area 4 Under-head area FORD LABORATORY TEST METHOD FLTM AB 110-01 Copyright 2016, Ford Global

19、Technologies, LLC Page 4 of 5 Appendix A Figure A1: Example of no IGC. Figure A2: Examples of IGC. Aluminum bolts showing intergranular corrosion. Intergranular corrosion is observed in three locations: a) root of thread, b) mid-line of the thread, and c) crest of the thread. FORD LABORATORY TEST METHOD FLTM AB 110-01 Copyright 2016, Ford Global Technologies, LLC Page 5 of 5 Figure A3: Example of impermissible lap. Aluminum bolt shown in the as-received condition. Note that an impermissible lap is shown on the pressure flank side of the thread. This lap is not IGC.