Type 1100 Aluminum Burns During Anodizing

Q. DEAR COLLEAGUES,
I'M HAVING PROBLEMS WITH PARTS WITH BURNED APPEARANCE. THEY ARE DECORATIVE PARTS OF ALLOY ALUMINUM 1100. THESE PARTS GO THROUGH TREATMENT OF ETCHING WITH caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] . THEY NEXT ARE NEUTRALIZED IN A SOLUTION WITH NITRIC ACID (30%) AND THEN THROUGH THE ELECTROLYTIC PROCESS OF ANODIZATION, WITH AMPERAGE OF 1.0 DURING 20 MINUTES.

WHEN THE PIECES ARE BURNED, I CHANGE THE NEUTRALIZATION SOLUTION AND THE PROBLEM IS OVER, BUT THE PROBLEM RESUMES VERY FAST. IT IS IMPORTANT TO INFORM THAT I HAVE NEVER HAD THIS PROBLEM. BEGAN A FEW MONTHS AGO. KNOWING YOUR EXPERIENCES, I WOULD LIKE TO KNOW WHAT MAY BE CAUSING THIS DEFECT.
I AM WAITING FOR SOME INFORMATION.
THANK YOU VERY MUCH. HUG !

A. Come on back with more info: (1) Tell us the anodizing concentration, dissolved aluminum, temperature, and current density ("1.0 does not make sense"), Be aware that the 1100's are very conductive and take less voltage to get 12 ASF. (2) Are you neutralizing the Nitric deox by dragging in too much caustic from the etch? Improve the rinsing in between.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

October 27, 2020

Nadcap Chemical Processing Auditor - PRI, traveling
Process Engineer / Chemist - Denver Metal Finishing, Colorado