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METAL TREATMENT TO PREVENT GALVANIC CORROSION

Our 70-meter antenna moves in azimuth on a hydrostatic bearing. We have had corrosion problems on our ground shims, which are made of C1018 [3/16" thick]. The ground shims are in contact with 316 stainless laminant shims above, and below it are sole plates made up of A36 steel. Obviously, some galvanic reaction due to the dissimilar metals is occurring. The simplest solution would be to apply some treatment to these metals to discourage the galvanic corrosion. I'd like to know what treatments are available out in industry.

Benjamin Saldua
- Pasadena, California, USA
2000

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Don't know anything about the galling in that application, but cadmium (very soft, sacrificial against steel) or electroless nickel ( specify hardness, barrier against corrosion) has been used on steel. Silver and other bearing materials can also be applied.

  
Tom Pullizzi
Falls Township, Pennsylvania
2000

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Galvanic corrosion is probably not a big problem here. The C1018 and A36 steels are nearly identical in composition and certainly will not be a galvanic corrosion couple. There is a potential difference between the two steels and the stainless steels, but the passive nature of the stainless will typically minimize galvanic corrosion in couples with stainless steel.

The corrosion that you are seeing is most likely general corrosion of the exposed steel, or possibly wear or fretting corrosion. Tom has made good suggestions. Zinc plating may be effective if the general corrosion is the problem. A better diagnosis of the corrosion root cause and service conditions are needed to make a reliable choice.

Larry Hanke
Minneapolis, Minnesota
2000