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"Corrosion? on gold dyed parts, Alloy 2024"

April 23, 2021

Q. We had a problem with anodizing and dying some parts in gold. There appears to be "corrosion" marks on the finished surface.

corrosion on gold anodized parts

Material: 2024T3 ALCLAD
Sulfuric Acid Type II anodizing

I wonder what variables may have caused this problem and how I should investigate / validate each of the variables.

Jason Chow
- Calgary, Alberta

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April 2021

A. Hi Jason. Unfortunately that photo is poorly focused so it's hard to say whether you have flaking, areas of pitting, or whatever. Based on the location of the discoloration it doesn't look like burning. From what I can see I'd probably call it "splotchy"; it's possible the part just wasn't clean enough. Maybe you can measure the anodizing thickness in the splotchy spots vs. the other areas?

One way to answer your question of what to investigate / validate would be to say "Why do you want to reject this part?". I am not saying the part is satisfactory by any means, I'm saying that very clearly and specifically annunciating exactly what you feel is wrong with it can be an essential step in fixing it.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

April 26, 2021

Q. Thank you Ted. This part was rejected first time by the customer when we first ran it. Then we reworked it and still got the same defect. Here is a better picture.:

corrosion in anodized 2024 aluminum

Jason Chow
- Calgary AB

April 27, 2021

A. Jason.
2024 is a problem alloy to anodize, I'm not saying it cannot be done but problems with burning and accepting dye are always a factor. My general rule for 2024 is stay away from etching as much as possible, if possible don't etch. Use a good deox and stay longer in it. One last thing, a slow ramp to the correct current 8-12 min is always a help.

drew nosti
Drew Nosti, CEF
Anodize USA
supporting advertiser
Ladson, South Carolina

April 27, 2021

A. Are you sure it is 2024. Did it turn black in the alkaline etch? Do you know if has been heat treated, hence disrupting the copper coming out of alloy? Do we have floating soil in the anodizing post rinsing that can enter the pores and limit dye adsorption?

robert probert

Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

April 29, 2021

Q. Thank you Robert. According to our customer, the material is 2024-T3 ALCLAD. It did look blackish after etching. We don't know if it was heat treated or not before the customer sent the part to us. The post anodizing rinse appears to be clean without floating soil if you are referring to floating soil to naked eyes. We anodized and dyed another part (of same material according to the customer) on the same load from the same customer and had no such a problem.

Jason Chow
- Calgary, AB

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