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I wonder if those bands have different grain sizes?

I wonder if those bands have different grain sizes?

Jeff:
I believe with this defect you will not see any difference in mechanical properties.  Also, bulk chemical analysis will not provide any insight as to the source and cause of the defect.  The reason is that this is a surface phenomenon.  I worked for an electrogalvanizing facility more than 20 years ago and we had to contend with it.  Unfortunately I don't remember for sure what was determined to be the root cause of the defect, so my suggestion to you is to look at factors that can cause staining of the surface.  Check the condition of your squeegee rolls and anywhere else where acid may be left in contact with the strip.  I know this comment may create more questions for you and I am not sure I will be able to answer them, but anyway, this is what I can think of at this time.  Good luck with your investigation.