Does anyone know of new methods for testing Magnesium in respects to corrosion. One test that comes to mind when inquiring about Magnesium corrosion test however outdated is the salt spray test. However results where not comparable with real life situations. I have also reviewed the ASTM G97, this deals moreso with underground pipes while I am interested in usage in the automotive field. Are there any new more accurate( than the salt spray) test that can be performed? Any new technological advances?
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Magnesium Test corrosion methods 1
- Thread starter Autim
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“There are corrosion tests that have been developed in efforts to improve upon salt spray. You will want to also review specifications for the Kesternich test that uses sulfur dioxide, CASS test (ASTM B368) that uses copper ions and acetic acid, cyclic tests such as GM9540P and SAE J2334. These are all different accelerated corrosion tests.”
Magnesium can be chromated or anodized and then painted for very good corrosion protection. See MIL-M-45202C for the chromating and anodizing processes. Newer, proprietary anodizing processes claim major improvements in wear and corrosion resistance. Also, Mg can be plated, but these are barrier type coatings (not sacrificial), as Mg is anodic to Ni, for example.
In automotive useage, magnesium can suffer severe galvanic damage in contact with steel. Galvanizing or aluminizing the steel will help, as will coating of the magnesium.
Magnesium can be chromated or anodized and then painted for very good corrosion protection. See MIL-M-45202C for the chromating and anodizing processes. Newer, proprietary anodizing processes claim major improvements in wear and corrosion resistance. Also, Mg can be plated, but these are barrier type coatings (not sacrificial), as Mg is anodic to Ni, for example.
In automotive useage, magnesium can suffer severe galvanic damage in contact with steel. Galvanizing or aluminizing the steel will help, as will coating of the magnesium.
Automotive criteria depends on the auto maker and where the component is located on the vehicle. If it is in a splash zone then salt spray may be applicable. If it is not, then high temp/high humidity is usually more appropriate. Accellerated environmental testing of Mg usually does not directly correlate with real use due to numerous variables including air quality, temperature, exposure time, humidity, condesation, etc. Corrosion is time dependent and the other variable often change quite frequenly relative to the overall time scale. Therefore these accellerated test are better for comparing materials, coatings, and designs than predicting end life.
A common and effective test (non-splash zone) would be 80 degrees C at 80% relative humidity for a given time (say 500 or 1000 hours). CASS and other spray tests yield very different results than high temp/high humidity for obvious reasons.
If you are evaluating coating, anodizing (alone or as a prep for painting) is very effective for non-conductive applications. Henkel also offers a non-chromate version. If you need electrical or thermal conductivity however, metallic coating might be the only option. Nickel being the best perhaps. As mentioned, metallic coating are "barrier coatings" and it may be impossible to get total coverage on Mg. Therefore, expect local galvanic corrosion sites where the coating is discontinous. Spray test will reveal these sites quickly. Temp/humidity tests will take longer to unfold, but you will surely find them.
DD
A common and effective test (non-splash zone) would be 80 degrees C at 80% relative humidity for a given time (say 500 or 1000 hours). CASS and other spray tests yield very different results than high temp/high humidity for obvious reasons.
If you are evaluating coating, anodizing (alone or as a prep for painting) is very effective for non-conductive applications. Henkel also offers a non-chromate version. If you need electrical or thermal conductivity however, metallic coating might be the only option. Nickel being the best perhaps. As mentioned, metallic coating are "barrier coatings" and it may be impossible to get total coverage on Mg. Therefore, expect local galvanic corrosion sites where the coating is discontinous. Spray test will reveal these sites quickly. Temp/humidity tests will take longer to unfold, but you will surely find them.
DD
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