Summary for titanium color anodizing Discussion
Titanium color anodizing in this thread centers on a part that came back blue instead of the expected matte gray, with threads and diameters apparently undersized by about 0.001 inch. Ali Motamedi asked what could have caused the loss, since AMS 2488 Type II was expected to produce little or no dimensional change. Jon Quirt said it sounded like a runaway etch tank, but noted he could not discuss process details. Another answerer was more specific: the parts looked like they had been acid anodized, not the caustic anodize called for by AMS 2488 Type II, and likely went through a conventional aluminum anodize pretreatment using nitric acid with bifluoride or hydrofluoric acid, which can pickle titanium. He advised auditing the supplier, requesting the purchase-order spec and the traveler or process map, and warned that titanium is too expensive to trust to a "garage shop."
Q. e recently sent parts to our supplier for Titanium Anodize (AMS 2488 Type II). The parts after the process were blue in color and seems like there was at least .001″ material removal since the threads, inside and outside diameters are undersized! What could have caused this? We expected a Greyish color finish and no material removal. Any input will help.
Ali Motamedi
– Canoga Park, California
2003
A. Sounds like someone had a run away etch tank. I cannot go into detail here as these processes are trade secrets. You should not have experienced 0.001″ removal however.
Jon Quirt
– Minneapolis, Minnesota
2003
A. Sounds like you got acid anodize as your titanium looks just like my titanium racks used to sulfuric acid anodize aluminum parts. This isn’t the CAUSTIC anodize clearly called for by AMS 2488, Type II.
Indeed you are correct, they should be matte gray in color. Lastly, they should have seen little, if any, dimensional change. Again, my guess would be they went through the firm’s conventional anodize pre-treatment cycle used for anodizing aluminum. This would typically include a nitric acid with bifluoride (or hydrofluoric acid ); this is a pickle (i.e. etch) for titanium. I suggest that you spot audit your supplier. Ask him for a copy of the spec called for in your PO. Ask for a copy of his traveler or process map for AMS 2488. My guess is that he has neither.
AMS2486, ISO 8080, ASTM B600 and ASTM F86. Titanium is too expensive to trust to some “garage shop.”
Milt Stevenson, Jr.
Plating shop technical manager – Syracuse, New York
2003