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topic 27533

Equipment and parameters for hard anodizing

A discussion started in 2004 but continuing through 2017


Is it preferable to use aluminium or lead anode for sulphuric acid hard anodizing on 2xxx and 7xxx light alloys? (Thickness 50-100 microns according to Mil-A-8625 [link is to free spec at Defense Logistics Agency,] type III) How about process parameters?

Thank you,

Massimiliano Luraschi
industrial engineer - Saronno, Varese, ITALY

Surface Treatment & Finishing of Aluminium and Its Alloys
Wernick, Pinner & Sheasby
from Abe Books



A. Hi Massimiliano. If we compare the number of shops switching from lead to aluminum, to the number of shops switching from aluminum back to lead, the trend is quite convincing that aluminum is preferable to more people. Still, whether a Ford truck is better than a Chevy will always be personal opinion :-)

Type III process parameters are shown in the anodizing books. A lot of readers don't want to say exactly what they do that differs from that, in the interest of preserving some of their own trade secrets and expensively acquired know-how. But if you tell us what you are doing, people will generally be kind enough to tell you if they think something you are doing is wrong :-)

For example, expecting a thickness over 50 microns seems to be a lot, especially on those alloys. Good luck.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. Assuming you mean cathodes, if you use aluminum instead of lead you will save a smidgen on energy cost for cooling and another smidgen to keep trace amounts trace amounts of lead out of the effluent.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como


Q. Thank you for your prompt reply. I'm responsible for technologies and equipment in my company. We're going to introduce and qualify in our shop the hard anodizing process. That's the reason why we're interested in finding quickly the right process parameters. The equipment is under installation, with aluminium cathodes. We'll start to hard anodize sliding areas of airplane structural parts machined from solid (7075). approx. dimensions 1500 * 200 * 200 mm. Parameters intended to be used for testing and qualification: T = around -2 °C, Max Al in solution: less than 8 g/l, Sulphuric acid: around 200 g/l, Current: 2 to 4 amps/dm2, Oxide thickness: 50 - 100 microns.

In addition, I would get your suggestion regarding the way to "regulate" the rectifiers (current density or voltage?).

Thank you for your comments, sincerely,

Massimiliano Luraschi
aerospace industry - Saronno, Varese, Italy

A. Hi. I think the high end of your amperage will prove too much; maybe 2-1/2 to 3 amps/dm2? Again, I think over 50 microns is a problem. Anodizing should be done by current, although some operators prefer various programmed cycles rather than a fixed amperage for the entire process time. And some people advise pulse anodizing -- which I don't argue against, but merely note as yet another variable to tame in a process with already a lot of variables to tame. Best of luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Q. Cracks on the anodized layer

Hello ... my name is Levente from Romania, I'm the surface engineering department at my company.
I would like you to help me ... if you can ... about anodizing.
The problem came when we built a bigger tank for hard anodizing: the inside of the tank (in contact with the electrolyte) is manufactured from stainless steel and the parameters is I+ =5A/dm2; I- =190-200mA/dm2, and the anode is Pb. The oxide layer is cracked after the process. What can be the answer?
Excuse my English.

Sincerely yours,

Szalo Barna Levente
- Romania

Hi Szalo. We appended your inquiry to an existing thread where I expressed my opinion that over 3 A/dm2 sounded like a problem to me for 2xxx and 7xxx alloys. Maybe a little higher for 1xxx and 6xxx. I think you should put a drop-in liner in that stainless steel tank. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

March 18, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We're installing a automatic hard anodize line and planning to set-up the recipe.

Panels are 10 X 3 inches with a quantity of 10.

What are the best set-up parameters without burning the panel?

The make-up is 165 mg/l of sufuric acid.

Alex Guzman
Support - Torrance, California, USA

August 27, 2017

Q. I want to start a hard anodizing bath, size: 6 feet length, 4 feet height, 4feet width. For that, which capacity rectifier & chiller do I want to purchase. Please help me

nageshwararao rao
vigneshprocess - chennai tamilnadu india

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