Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Green hue on black anodize
2007
What is causing a green hue to appear on some black anodize parts?.The area is not uniform as it has apeared on different areas of the same part.The parts have been racked up identical to previous runs.
Anodizing parameters:1.5 amps per decimeter squared.
Anodizing temp 20 deg C.
Sanodol black MLW dye at 4.5 ph temp 60 deg C.
alloy 6061 fine bead blast finish
Anodizing time 1 hour
Seal with DI water boil for 1 hour ph6 for water seal.
What am I doing wrong?
Thanks,
Engineer - Nelson, New Zealand
Bead Blasting? Has the media been used on any other metal, like iron, copper, brass, etc? Bead blasting imbeds iron particles into the soft (Kleenex-like) aluminum metal, then when you anodize you also oxidize the imbedded metal. Iron usually comes out as red, but iron does form some green salts which may be forming in the seal. Always use blasting media that is 100% designated for aluminum.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
2007
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