Search our quarter-million Q&As

Home of the finishing HOTLINE since 1989

-----

Stubborn aluminum alloys to anodize

I have been pretty successful anodizing and black dying telescope parts I have made in my home shop from 6061 T6. Recently I machined some parts from an unknown alloy that I just can't get to take the black dye properly. I am using the same process as for the 6061 that being 6.25 amp-minutes per square inch current-time density, room temperature sulfuric acid solution, commercial black dye at manufacturer's recommended temp of 110 °F for 30 min.

The dye either washes out in the sealing bath or looks black but the surface remains conductive and exposure to sun turns it brown.

Can someone suggest either what I doing wrong or what alloys I should avoid. There were no obvious differences when I was machining the odd alloys. I have beautiful results with the 6061 but don't have the heart to re-machine the difficult pieces.

Thanks in Advance for you suggestions

Dave Sage
1998

---

The problems you describe are sometimes related to dyeing thin coatings; the dye will fill the pores and cover the surface. This is especially true if you are 2-step dyeing. Also the surface will not seal and will have a tendency to fade. Since the dye is metal based it will still be conductive. One parameter to check is the coating thickness. Different alloys have different conductivities and that will result in different coating thicknesses.

Lee C. Branch
- Albright & Wilson
1998

Sorry! Finishing.com is temporarily Read-Only.
Ted Mooney is retiring but I have several offers to take it over.
We're working hard to make sure we find it the best new home.

---

---