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Pretreatment for high mag aluminum

none is made possible by ...
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Q. High Mg Al alloy etch?
Trying to mild etch High Mg Al alloy.
Caustic is not possible (due to Mg), Phosphoric is not possible (due to Mg).
Ferric sulphate is expensive for the application.

Thought about:
15:5:5 (H2SO4:HNO3:ACETIC)

Any thoughts?

Dvir Cohen
- Haifa, Israel
October 2, 2023

? Hi Dvir,
Can you give us a little more detail, like what you mean by 'etch'? If this for metallographic examination, pretreatment for chromating or anodizing, etching for artistic purposes?
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

(to help newbies follow along)
It is not usually possible to electroplate directly on aluminum because electroplating must be done on metal, not on metal oxides, and aluminum oxidizes almost instantly. The most common answer is to do an immersion/displacement step in a zincate solution, and then to electroplate onto the zincated surface.

Q. Hi Ted,
It's an EP Nickel over Al 5083 via Zincate.
Functional coating, not decorative, good adhesion required.

Dvir Cohen [returning]
- Haifa Israel
October 3, 2023

A. Hi again, Dvir. I don't have a good answer but topic 32156 at least talks about possibilities.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

⇩ Closely related postings, oldest first ⇩

Q. I am plating an aluminum (Suzuki engine casings) which is going white in the zincate.
It is fizzing a little in the acid nickel, but plating well.
I'm just not happy with the fizzing and fear poor adhesion, though I have no visible signs.
Aluminum is patchy (varying color and grain,) during polishing and slow buffing speeds (2300 sfpm) are still making pores appear.
Hand sanding doesn't.
I suspect a high magnesium content.
Something anyway, I have found this before in custom built bars and a few castings.
I'm sure it's not zinc.

Steve Clark
- Maine, U.S.A.

A. Apparently you have one of those (almost) impossible alloys where the magnesium is not uniformly alloyed and appears in patches.

Try a dilute zincate, then a 4 oz/gal Sodium Bicarbonate at room temp, then alkaline electroless nickel for 10 minutes, then your final acid nickel.

If that does not work tell your client to get a better alloy.

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

A. The covers on Suzukis & Kawasakis are magnesium alloy AZ-91, not aluminum.

Stephen Rohrbacher
- Lowell, Massachusetts

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