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How might one more precisely characterize the coating system (consisting of substrate, pre-treatment, ecoat, primer, and top coats) on the hood and doors of a passenger vehicle, specifically to identify the layer from which a defect originates, beyond the current methodology of visual inspection?

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Vikram Tomar
material engineer 2
atotech
Meerut
07017475745
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Something to consider is eddy current testing. This method has been used to detect flaws in various multi-layer coatings for automotive and aircraft paint/coating systems. There are portable testers and also more sophisticated related methods such as multi-frequency testing and pulsed eddy current. There are limitations as in all techniques such as thickness of the coating, conductivity, etc. There is a paper funded by Saab AB, " Automatic Scanning with Multifrequency Eddy Current on Multilayers Structures," Barend van den Bos et al. Just one of many references describing this method for detecting flaws in multi-layer coatings. 

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Ronald Myers
President/Owner
Myers Consulting Services
Strongsville OH
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A big thank you to Ronald for the insightful answer to my question. Your expertise and willingness to share knowledge are greatly appreciated!

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Vikram Tomar
material engineer 2
atotech
Meerut
07017475745
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Original Message:
Sent: 04-15-2024 07:27
From: Ronald Myers
Subject: Characterization of rust-related defects in the coating systems of passenger vehicle hoods and doors.

Something to consider is eddy current testing. This method has been used to detect flaws in various multi-layer coatings for automotive and aircraft paint/coating systems. There are portable testers and also more sophisticated related methods such as multi-frequency testing and pulsed eddy current. There are limitations as in all techniques such as thickness of the coating, conductivity, etc. There is a paper funded by Saab AB, " Automatic Scanning with Multifrequency Eddy Current on Multilayers Structures," Barend van den Bos et al. Just one of many references describing this method for detecting flaws in multi-layer coatings. 

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Ronald Myers
President/Owner
Myers Consulting Services
Strongsville OH
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What tools do you have available?  If you have a metallography lab, specific defects can be marked (typically with scribe lines) mounted in clear epoxy and cross sectioned.  Depending on the skill of the metallographer, sub millimeter defects can be successfully cross sectioned.  Optical examination can distinguish some of the different layers, but SEM/EDS is really needed to identify the elements present in the defect.   There are methods to examine the different surfaces.  This typically involves stripping the paint with a heated phenol based solution or other paint stripping solution.  Unfortunately this will remove all paint layers and not specific ones.  The pretreatment could then be examined in a SEM/EDS system.   After examining the pretreatment, the pretreatment could then be stripped with the appropriate solution (depends on pretreatment) and then the substrate surface can be examined.

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Paul Janavicius
Lead Research Engineer
Cleveland-Cliffs Steel Corporation
Middletown OH
(513) 425-2670
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