Characterizing forming lubricant on Magnesium alloy 3

[OSUMaterials]

I have warm-formed AZ31 sheet material. The lubricant used during the warm-forming process remains on the surface and is hard to remove. What method(s) would be best to characterize and study the oil layer? We think the oil may have underwent a chemical reaction with the surface of the Mg, and we need to determine whether this is the case or not.

The oil is preventing a subsequent conversion coating from maintaining its integrity through the remainder of the production process.

We have several options for characterization available including XRD, SEM, TEM, STEM, FTIR, FIR, optical, etc...

Thanks for any help you can give!

 

[TVP]

Do you know the actual composition of the lubricant? You say oil, but none of the commercially used lubricants for warm forming Mg are oil-based. Typical lubricants are water-based with either gaphite + polymer or organic carboxylates as the active component. Fuchs Forge Ease is a boron nitride based lubricant that also has been tried with Mg. All of these can be cleaned using water-based alkaline cleaners.

To answer your direct question, SEM and EDS would be the first technique I would use for characterizing the surface. Any reaction should be limited to the magnesium hydroxide surface layer, and not directly to the primary Mg. Elemental mapping within the SEM together with the contrast provided by backscatter electron mode should prove useful. If you have access to Auger Electron Spectroscopy, then this would be ideal for characterizing the change in elemental composition through the reaction layer.

 

[CoryPad]

If you have material that is in the as-received condition, then take a swab and conduct infrared spectrometry (FTIR) to determine the type of lubricant.

 

[OSUMaterials]

Thanks for the tips; I will look into both. Unfortunately I don't have access to the rolling lube composition (supplier proprietary). The as-received sheet was warm-formed without removing the rolling lubricant - thus baking it into the surface layer. Subsequent application of MagPASS failed because the rolling lubricant polymerizes with the MagPASS.

The main issue is there is no more of this batch of base material without the rolling lubricant, and there is no material with the lubricant prior to warm-forming - so we have to reverse engineer the process. I will try EDS, but I was warned that due to baking there will probably be a great number of irrelevant carbon compounds. I will also try the FTIR swab.

Thank you, again for the help. I'm new to the forum - I'm very happy to have stumbled upon this resource.

 

[TVP]

Thanks for the additional information. The rolling lubricant could be an animal fat-based product or some type of hydrocarbon (oil). Either way, the decomposition product formed on the surface during warm forming is going to be difficult to remove with conventional cleaning techniques. Have you investigated acid cleaning or light acid pickling rather than alkaline cleaning?