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topic 1665

Protecting magnesium parts from corrosion -- anodizing, chromating, VCI


(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)

A. I wouldn't be confident of that, Eric; that's a very tough application. Is it not possible to chromate the magnesium right away?

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


(1998)

A. 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 mfg 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)

Q. 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, AR


(1998)

A. 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 a 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



A. Hi Mike.

There are now electroless nickel plating processes available from the major suppliers that are tailored specifically for magnesium -- they might be worth considering. Good luck.

Regards,

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



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