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Stainless or zinc plated a better galvanic couple with aluminum?

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I have a question regarding the appropriate choice between zinc plated steel and stainless steel part when in contact with aluminum.

We are designing an electronic enclosure which has Aluminum Extruded Side walls. The aluminum sidewall has grooves running the length of the part. The lid is currently a stainless steel plate which runs through the groove and in contact with the sidewall. The aluminum side wall is anodized on the outside surfaces but the grooves are left natural. The reason for this is to ensure there is an electrical connection between the side wall and the lid (this is essential for EMC Shielding). We are now considering changing the plate from stainless steel to zinc plated steel to reduce galvanic corrosion. Both these materials will serve our mechanical requirements, we are only concerned about the galvanic corrosion issue.

Is zinc plated steel a better choice than our current stainless steel part?

Sarva Thurairatnam
- Kensington, Victoria, Australia


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Due to their relative closeness in the nobility of metals chart, zinc plating would be the better choice to mate with aluminum. Stainless steel will actually cause the aluminum panel to corrode in an attempt to protect the stainless steel fastener (because it is more noble). If you wanted to take it a step further, I recommend using a zinc lamella dispersion coating instead of standard zinc plating. Zinc dispersions usually offer superior corrosion protection (around 500-1000 hours ASTM B117 [link is to spec at TechStreet] ), and many times offer an aluminum rich topcoat to further diffuse bi-metallic corrosion.

King Drummond
- Cleveland, Tennessee, USA


First of two simultaneous responses -- ++++++

Using zinc plated coach screws to fix aluminium frames,is there a problem? I am fixing an aluminium framed building to a concrete base.I intend using zinc plated coach screws.Question:- Will there be any chemical reaction or corrosion possible.

John keenan
- Belfast Northern, Ireland


Second of two simultaneous responses -- ++++++

There can only be galvanic corrosion if there is moisture (or some electrically-conducting aqueous solution) present.

In the absence of an electrolyte, it doesn't really matter what two metals are in contact, they won't react.

Bill Reynolds
   consultant metallurgist
Ballarat, Victoria, Australia

It is this website's profoundly sad
duty to relate the news that Bill
passed away on Jan. 29, 2010.



May 6, 2011

I had a lot of problems finding suitable screws for aluminum screens doors in the area where bottom seals made of some type of aluminum and rubber are been added, the area around the screws goes to a fluffy white corrosion almost bonded to the frame and difficult to unscrew, and far worse close to sea areas. Any suggestion would be welcome. Many Thanks.

Lucio Rizzo
- Sydney NSW Australia



October 2, 2012appended

Q. I am currently working on a project where a contractor has fixed a powdercoated aluminium louvre to an aluminium bracket using 2 different types of fixings, one being a stainless steel bolt connection and the other a galvanised tech screw. What is the likelihood of this corroding?

Simon Kelly
Commercial Builder - Melbourne, Victoria, Australia


December 16, 2012

A. It all depends on which is the larger surface area that will ultimately start the galvanic corrosive action. In all likelihood the Galvanized screw may be the first chap to go, assuming that the Aluminum in contact with it is larger in area, If its powder coated from both sides with no exposure of the Aluminum to the weather of any kind, they may both live happily ever after till death do them part.

khozema Khozema Vahanwala
Saify Ind
 
Bangalore, Karnataka, India
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