Bolts: differentiating between a Hot dip galvanized vs passivated 2

[sunshine419]

Hi please,
I would appreciate if some good people out there could help me with how i could distinguish between a hot dip galvanized bolt sample from a zinc passivated one. What test requirements could one likely carry out or inspection techniques.
many thanks

 

[TVP]

With some experience, you can distinguish between the appearance of hot-dip galvanize and electroplated zinc by just visual inspection with no magnification. Hot-dip galv has a matte, dark grey appearance, while electroplated zinc tends to be bright and may show some interference effects (irridescence, rainbow colors). A Google Images search using the different terms will show examples like these:

http://fastenertips.fastenfinder.com/wp-content/uploads/2010/11/hot_dip_galvanized.jpg

http://www.walkers-garage.co.uk/shop/contents/media/l_Bolts Zinc Plated 002.jpg

However, two simple techniques are (1) thickness measurement and (2) optical microscopy of a cross-section. The thickness of hot-dip galvanize is typically 50 micrometers or more, with minimum requirements of 36 micrometers in standards like ASTM A153. Electroplated coatings are rarely thickness than 18 micrometers, and usually in the range of 5-12 micrometers. Here is a site that has quite a bit of information on zinc coatings:

http://www.galvanizeit.org/about-ho...dip-galvanizing/the-hdg-coating/zinc-coating/