[VAC] Re: Galvanic Action

["Frank M. 'Mitch' Hill" <fmhill@xxxxxxxxxx>]

Ted Byrd,

Based on what the marine industries have learned over the years, 316 stainless
screws (most stainless hardware is 316 stainless) are your best choice for use
in aluminum where a aluminum fastener is not strong enough.

Any metallic fastener will have some reaction with aluminum,  even a 
aluminum fastener of a slightly different alloy. In the case of zinc plated 
steel in aluminum, zinc is sacrificial. The zinc goes away quite quickly 
leaving raw steel behind to rust and stain. Stainless is preferred... I 
refer you to a commonly used design tool in the marine industry, the chart 
of nobility of metals...

In extremely critical applications such as marine instrument housings that 
are intended to be under water in the ocean for long periods of time, 
plastic washers and bushings are used to separate the metals. However in 
any application where continuos submersion is not an issue, stainless in 
aluminum is acceptable. I refer you to the construction of outboard motors. 
If you are concerned about corrosion and electrolyses, there are aluminum 
particle based anti-seize compounds readily available, "a little dab will 
do ya" ...

As a Airstream will not be submerged, (hopefully), the use of stainless screws
should have minimal opportunity for galvanic reaction compared to any other 
fastener outside of aluminum fasteners, such reaction should be very 
slight, I don't think its a issue. I am replacing any screws in my '64 with 
stainless as I remove rusty hardware. Keeping a Airstream on Cape Cod is 
the next worst thing
to having a submerged Airstream...


TNX, 73, Mitch - WA1YKN