Aluminium etching and desmutting

A. You can etch the aluminum for your needs with caustic solution But you must make it a little rough with the emery paper and then use the caustic solution. Then you can use mild nitric acid for the desmutting of the etched parts. Good luck.

A. Hi Firmin. This may not be the best way to get emergency help because knowledgeable readers wander in on their own schedule and it might be a week or a month or longer before they even see your inquiry; but in the meanwhile, here is what I believe ...

Keat-Seng was referring to etching as a pretreatment step in the electroplating of aluminum, and I have heard little of using nitric acid and hydrochloric acid for that purpose (although Wernick, Pinner & Sheasby mention it briefly, seemingly seeing it as impractical).

So I suspect that "etchant" holds a different meaning for you? I have heard of using these acids individually with electricity for electrograining of lithographic plates; and I've heard of using nitric plus hydroFLUoric acid to deeply etch aluminum. What do you mean by etchant -- are you attempting to plate onto aluminum, electrograin it, accentuate the grain for metallographic examination, dissolve it completely through in areas? What alloy are you working with. Thanks!

Regards,

A. Hi Frank. Acid etching in ammonium bifluoride and alkaline etching in caustic are commonly applied. Depending on the alloy, a desmutting step usually must follow to deal with the non-aluminum alloying materials. The previously mentioned book by Wernick, Pinner & Sheasby omits nothing about the finishing of aluminum and includes a 17-page chapter on acid etching, and a 13-page one on alkaline etching, plus many additional pages scattered under specialized topics. Good luck.

Regards,

A. Hi Peeter. Cleaning mixed metals is difficult for many reasons including the galvanic corrosion forces, and finding chemicals that will clean one metal well without damaging the other. "Non-toxic" is more of a buzzword than a clear description of what is permitted and proscribed, but solvent vapor degreasing is probably the best initial step if it is permitted because it is non-ionic (so no galvanic corrosion) and is effective on both steel and aluminum. If the cleaning must be aqueous based, a spray washer or ultrasonic system with a mild detergent is probably the best choice. Good luck.

Regards,

A. Hi, Baruvanath. You might want to look into "electrograining" of the aluminum in hydrochloric acid if you feel that etching is the best approach. Other durable methods of putting text on aluminum sheet include silk screening the text onto anodized aluminum before sealing it. The ink is absorbed and locked into the anodized pores and it's extremely durable (very hard to remove even with sandpaper). Best of luck.

Regards,

A. Hi Pegie. In my experience electrocleaning is not applicable to aluminum parts and the terms etching & desmutting are applicable to aluminum parts but not most other materials, so I don't have a clear understanding of what you are asking. But if the copper plating is not adhering, yes, inadequate cleaning and preparation is the most likely cause. Please give us some details.

Regards,

Q. Sir Ted, we do brush plating of rotor shaft which is SAE 4140 or SAE 4340 only and also we do brush plating of bearing housing which is a cast iron material. Can you help us what would be the best solution for the electro cleaning, etching and desmutting of this kind of material? Thanks in advance

A. Hi again Pegie. We are having a slight language difficulty because "etching" and "desmutting" are not terms that are used in the general preparation of steel and cast iron for plating; and you added your inquiry to a thread about etching and desmutting of aluminum.

I do not have experience with your situation, but Rubinstein's "Electrochemical Metallizing" .
seems to suggest that a good process may be electrocleaning, acid activation with current, no rinse, nickel strike, and alkaline copper plate. Things may be different in the Philippines than in the U.S., but here no applicator that I know of ever attempts to formulate a process solution for brush plating, they buy it from companies like Brooktronics, Gold Touch [a finishing.com supporting advertiser] or Sifco ... so I wouldn't know how to formulate such solutions. Sorry. Good luck.

Regards,

Thank you very much for your time to answer my questions sir Ted.