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Effects of Drying Temperature on Chromate Conversion Coatings on Aluminium

2005

After curing @ 60 °C for 10 minutes, my customer than cures it again @ 80 °C for 10 minutes,white spots are detected on the surface, why is this so?

This is done before silkscreening process as they claim that if additional curing is not done done, then after the silkscreen process the area within the silkscreen will be a lighter than the other areas.

Victor Seet
PIE Electroplating Pte. Ltd. - Singapore

80 °C is way to hot for a chem-film. The white dots that you are seeing are most likely the result of the conversion coating being dehydrated and cracking - this basically destroys any corrosion resistance it provides and probably severely degrades adhesion as well.

You should advise your customer to find another method - possibly a time delay would help let the coating cure enough without using temperatures above 60 Celsius, or you may want to look into anodizing in place of chemical conversion coating.

Good luck,

Jim Gorsich
Compton, California, USA
2005

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