Any metallurgists in the house?

[RizzoTheRat]

Anyone know much about galvanic corrosion?

Someone on another forum is on about replacing various bolts on his motorbike that are renown for corroding with stainless ones. My understanding of galvanic corrosion is that putting a stainless bolt in to an aluminium alloy component is going to result in about 0.5V potential, and increase the rate of corrosion of the aluminium. Brass would be even worse at 0.6V, where as a normal steel, such as fitted by the manufacturer, has a very small potential difference so won't get much galvanic corrosion. On the other hand the steel itself will corrode a lot more easily than the brass or stainless, but is more easily replaced than the alloy component it's screwed in to.

Is it a bit enough problem to worry about?

[Simpo Two]

RizzoTheRat said:

My understanding of galvanic corrosion is that putting a stainless bolt in to an aluminium alloy component is going to result in about 0.5V potential, and increase the rate of corrosion of the aluminium.

If he diverted the 0.5V to charge the battery, would it stop the corrosion...?

That's my crazy idea for Friday



NB It is certainly an issue in boats, but that's where the metals are connected by water.

[Shaolin]

I remember seeing some programme about skyscrapers, attaching big copper sheets to the top of a large building, so copper to steel. The answer involved a fairly complicated system of insulating washers and spacers to prevent currents flowing - could you do something like this?

[ianrb]

In part it depends or the relative mass of the two components. If you're talking about a stainless bolt into an aluminium engine there the amount of galvanic corrosion which would take place would be small.
As mentioned above this can be reduced by insulating the two different metals. In the case of an engine bolt Loctite on the thread and some Duralac under the head of the bolt should do the trick. I have done this with stainless spring and bolts holding the brake-pads into the calipers of my bike, and it seems to have halted the corrosion.