As some of you might have seen, I am testing some Carbide3D ZrN single flute endmills and ran my 1/8” one too hard and got it gummed up with aluminum on the surface. With the naked eye, it just looked gray, almost like the coating wore off, but with closer inspection, it was aluminum coated onto the surface.
I decided to do some research on how to remove the aluminum and knowing that sodium hydroxide (NaOH) reacts with aluminum to form water soluble sodium aluminate (https://en.wikipedia.org/wiki/Sodium_aluminate) and hydrogen gas. Some people online were concerned about it reacting with the ZrN coating but a few different sources I found mentioned that this reaction won’t occur until 500C. (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660022570.pdf & https://chemiday.com/en/reaction/3-1-0-560)
As such, I went ahead and taped the endmill to the side of a beaker where the ZrN part was in a 1M NaOH solution. I left if for 30 min and returned to find it nearly entirely cleaned! The largest piece of aluminum was still stuck on, albeit much smaller. All the rest was nearly gone.
However, it was not without its costs. It looks like the aluminum that was stuck pitted the surface and left it slightly damaged, however still looking remarkably better than before. There also looked to be some small remnants on the surface that may react with more time. I have yet to test how well it cut again, I would imagine fairly well (certainly better than it did with aluminum coating the surface), but I did notice I broke the tip, which will impact performance.
(I also figured out how to make the entire image in focus so these pictures are better)
New 1/8" ZrN coated single flute endmill from Carbide3D
Pitting on the Surface
I recommend you give this a try to clean ZrN endmills covered in aluminum, it won’t return them perfectly to their former glory but you should be able to get a few more uses out of them.