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topic 7152

Coating/Finishing/Plating Options for Magnesium?


(2001)

Q. I am looking for a general guideline, or outline, of all the possible alternatives for coating and finishing magnesium alloys. Our goal is to use magnesium as a base metal for some of our products, which are designed to be both aesthetically pleasing and corrosion resistant.

The products will have potentially intricate design detail, and we will need to offer metallic finishes, dyed metallic finishes, and painted surfaces. There will potentially be dissimilar materials, so protection from galvanic reactions will be necessary.

A spread sheet of the possibilities would be nice, if anyone has one--or direction to a good resource on magnesium finishing would be very helpful. We would like to put together a test plan to evaluate all, or as much of it as possible, that is out there to help guide our decisions. At this time, cost is not an issue.

Davin S [last name deleted for privacy by Editor]
Oakley - Foothill Ranch, California


(2001)

A. I reviewed some early work in "Finishing of Magnesium"

tom pullizzi portrait
Tom Pullizzi
Falls Township, Pennsylvania


(2001)

A. Magnesium has been around a long time, Davin, but with the explosive growth in cell phones and portable electronic devices, interest has certainly been renewed.

Tom Pullizzi put together his excellent "Finishing of Magnesium"; Fred Pearlstein, in his usual fine style, covered anodic coatings for magnesium in "Selection and Application of Inorganic Finishes" in the March 1979 issue of Plating & Surface Finishing, discussing them as both final finishes and bases for paint. He found them to be "considerably more protective" than painted conversion coatings.
Another possibility is electroless nickel plating, mentioned earlier in the thread.
Finally, magnesium can be electroplated with any plateable metal you wish. Good luck.

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


(2001)

A. Try the ASM Surface Engineering Handbook, it has a complete chapter on Magnesium surface treatment.

Good Luck.

S. Y. Yuen
- Hong Kong, China


ASM Metals Handbook
Vol. 5
Surface Engineering





Magnesium Finishing

(2001)

A. Dow Chemical Co. did much of the early work on finishes for magnesium. Their handbook, "Magnesium Finishing", although old and out of print, is still a coveted bible to many finishers. It covers cleaning, etching, conversion coatings, anodizing, and plating. These Dow coatings are still widely used in industry today even though Dow has exited the business and the handbooks have not been available for many years. Recently, new anodic coatings have been developed for magnesium. These offer improved corrosion and wear resistance over those older coatings at competitive costs.

adv.
Magoxid-Coat®,produced in the United States, by Luke Engineering is one of these coatings.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.
supporting advertiser
Wadsworth, Ohio

luke engineering banner


(1995)

Q. Does anyone have any experience plating (EN, in this case) onto magnesium? If so, could you recommend a process?

Ken Rosenblum
finishing shop - Minneapolis, Minnesota


(1995)

A. Hi, Ken. I don't have personal experience in this, but Atotech's Magenta process for electroless nickel on magnesium has a name that is easy to remember, and may be a starting point to learn what is special about magnesium when it comes to EN plating. Other major vendors presumably also offer similar processes. Good luck.

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


(2007)

A. Mg alloys can be protected in salt spray environment with pure aluminum coatings. Scribed samples coated with Al have survived ASTM B117 [link by ed. to spec at TechStreet] tests of up to 196 hours. This contrasts to less than 20 hours for the standard conversion coating. Still the coating must be completely hermetic, as the galvanic potential between Al and Mg is considerable. Thus the complex shape of a product could be a problem.

Howard Gabel
- Santa Barbara, California, USA



(1999) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I would like some information on corrosion resistant coatings for magnesium parts. Our company used to use magnesium for some engine components in the past (covers and other lightly stressed components), but corrosion was a massive problem, especially when parts became 'dinged' or scratched. What we are after is ideally a hard-wearing (or tough) corrosion resistant coating so that we might use magnesium components again. It would come into contact with air, de-ionised water, maybe water-glycol (engine coolant), fuel, oil etc.

I have seen a transparent gold coating, similar in appearance to TiN on some Italian motorbike mag wheels which looks very hard wearing, but I don't know where to start looking for this. The wheels were painted over the top of this, and so I don't know if the coating on its own would be sufficient.

It would be nice if the coating were very thin so that it didn't make too much difference to the fits of machined components. I would really appreciate any help that could be offered.

Wayne Ward
- England


(1999)

A. Electroless nickel plating sounds like it meets most of your needs, Wayne.

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


(1999)

adv.
Luke Engineering offers a patented hard anodic coating for magnesium, Magoxid-Coat(R) which is significantly more wear and corrosion resistant than other widely commercialized anodic coatings for magnesium. A typical coating thickness is 25 um (1 mil) with one half penetration and one half build-up. It can stand alone or be used as a paint base. A number of manufacturers of superchargers for drag racing use this hardcoating on their magnesium housings and end plates.

Chris Jurey
Luke Engineering & Mfg. Co. Inc.
Wadsworth, Ohio

(1999)

The gold coating on the Italian wheel might have been ZrN, used extensively for decorative coatings. It is very corrosion resistant if deposited correctly, i.e., by unbalanced magnetron sputtering. ZrN is also very hard and wear resistant, used extensively on cutting tools.

jim treglio portrait
Jim Treglio
- Vista, California



(1998)

Q. I am learning about how unstable magnesium is just in the air of a shop environment. We currently use a special oil between processes prior to dichromate to provide protection from reactions with moisture. Can anyone tell me if VCI bags will provide the right protection in lieu of the messier oils?

Eric Schneider



(1998)

Eric,

My company does finishing of aluminum & magnesium, including dichromate, and mag anodize among others.

You are right about mag corroding very easy - sometimes parts will corrode in shipment from the mfgr. to us.

We always advise our customers when sending in Mag parts for processing that they should be packed with a light machine oil on the parts & desiccant packages should be used in the packaging to absorb moisture.

David A. Kraft
- Long Island City, New York



(1998)

What magnesium alloys are most used in automobiles?
What are some of the problems that occur with corrosion of magnesium alloys used in automobiles?
What are some of the solutions to these problems?

Davin Moorman
University of Arkansas, Engineering Research Center - Fayetteville, Arkansas


(1998)

Good corrosion and protective qualities are the responsibility of the casting maker. Packaging, preservation, and proper process control during melting all contribute to end quality.

Too often in the past, foundries have been their own worst enemy with regards to the prevention of corrosion.

New alloys of high purity corrode slower, since trace elements causing galvanic corrosion are reduced in these alloys. AZ91E is a good choice for prototyping auto parts that will have good corrosion resistance.

Mark A. Vecchiarelli
- Enfield, Connecticut



(1998)

Q. I'm having problems coming up with a process for plating over magnesium. I'm currently using a zincate (non current) for bonding. From there I am trying an alkaline copper strike then sulfamate nickel. The problem I am having is the copper is having bad adhesion on the zincate. Any help would be helpful.

mike crabtree
- Raleigh, North Carolina


(2003) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Can anyone help with a prepping process for electroless nickel on magnesium? I understand that magnesium does not react well with any acids. I currently am plating nickel on aluminum. Can magnesium be processed on this line?

Regards,

Casey Weizel
- Minneapolis, Minnesota, U.S.A.


 

Hi, Mike.
I can't guarantee it, but I think you'll have less problems with an alkaline electroless nickel strike between the zincate and the sulfamate nickel than you are having with the alkaline copper plating. Good luck.

Hi, Casey
If the line includes zincating and an alkaline nickel strike, I think there's a good chance. Best of luck.

Regards,

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



(2003) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

I hope know about plating methods on magnesium. Could you tell me to plating methods?
Looking for good answer....

SE DO JANG
- ANSAN, EE, KOREA


(2003)

Magnesium can be plated by either using the zincate route or by direct plating. The zincate path uses an alkaline cleaner, followed by a chromic acid dip and another dip in phosphoric acid and fluoride. This is followed by a fluoride loaded zincate bath and Rochelle copper to about 5µm. The magnesium is then plated in electroless nickel.

The direct plating path is an alkaline soak, followed by a dip in 150 g/l CrO3 with a proprietary additive. This is followed by another dip in 15% HF at 25 °C and direct electroless nickel. The direct electroless nickel is a mixture of NiCO3/HF/ citric acid/NH3HF/ sodium hypophosphite/ NH4OH at about 85 °C

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


(2003)

Q. Thank you for the answer but I don't want to use HF. HF and NH4HF are very dangerous chemicals.
I'm looking for another methods.

Have a good day!

SE DO JANG [returning]
- ANSAN, EE, KOREA


(2003)

Mr. Crichton is correct. Magnesium is a highly reactive metal and your ordinary cleaning and deoxidizing solutions cannot be used for magnesium. All the job-shop platers that I came in contact with use fluoride base predips, and use special electroless nickel containing fluoride to improve adhesion.

June Kim
fine chemicals - Incheon, Korea


May 26, 2011

A. Don't forget that magnesium is not aluminium and only in some physical properties (mechanics, melting point, etc.) are the two metals similar, but their chemistry is quite different. For this reason, performance finishing methods are different. On the market, there are some technologies able to offer 1000 hours, or more, of salt spray resistance (Tagnite, Keronite, Anomag ...) but SweetMag® is able to offer high corrosion resistance at low cost.

Aurel Crisan
- Montreal, Quebec


November 5, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Will zinc immersion and copper strike make the surface of magnesium non-reactive so that I can coat other metals on it? I have tried with copper pyrophosphate, but it formed immersion coatings with zinc. Can you suggest some better methods?

Siddarth Kumar
- Wichita, Kansas, US



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