Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

finishing.com -- The Home Page of the Finishing Industry

  The authoritative public forum
  for Metal Finishing since 1989

-----

Electropolishing Aluminium Current Density

Q. Hello,

I have tried electropolishing aluminum. For the experiment, I used a solution of sulfuric acid and phosphoric acid (20/80) and a standard laboratory power supply. The test pieces were 3 cm2, and the polishing voltage was 15V, with the current fluctuating around 4-5 amps (the power supply lacks current regulation). During testing, I let the pieces polish for 10 minutes. After polishing, I rinsed the piece with distilled water, then with an alkaline solution, and finally with distilled water again. The results were good, so I also tried polishing larger pieces, but the results were not as good. I suspect that the power supply does not provide enough current and tends to drop the voltage when a higher current is required.

What would be the correct current per cm2 for aluminum if I want to polish larger pieces? What would be the correct voltage? Are there any other good ideas or changes that could improve the results?

Thanks!

Erkki
- Estonia
July 24, 2024

Ed. note: This forum enjoys the warm aloha of real names. People who offer their real name may be less likely to engage with those who don't.

ASM Metal Handbook
9th Edition, Vol. 5
"Surface Cleaning, Finishing & Coating"
asm_vol5old

on AbeBooks

or eBay or

Amazon

(affil links)

A. Hi Erkki,

If you recorded your variables correctly, you sort of answered your own question by successfully electropolishing at 4 to 5A / 3 cm2 = 1.33 to 1.67 A/cm2 [1235 to 1551 A/ft2]. However, I suspect that you measured something wrong because that is an awfully high current density. If you meant 3 dm2, then 1.33 to 1.55 A/dm2 sounds quite low but not quite unreasonable, whereas 133-155 A/dm2sounds quite high but not quite unreasonable, according to ASM's Surface Cleaning, Finishing, and Coating ⇨
and Wernick, Pinner, and Sheasby [on AbeBooks, Amazon & eBay affil links]

Voltage and amperage are not independent because V=IR; the voltage will be what it will be depending on anode-cathode ratio, spacing, solution conductivity, etc. 15V sounds high but possible. Luck & Regards,

ted_yosem
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories: