Electrolysis and Galling
Electrolysis is the difference in chemical potential between two different materials. Iron and aluminum are both rather reactive metals. Aluminum does not rust because there usually a layer of aluminum oxide on the surface. If that surface is removed it will react.
Anybody that has ever worked in a shop where where aluminum is machined has seen this. You can watch the surface dull after the cuting tool passes.
Galling is the build up of aluminum oxide where the two metals meet. You will notice that it is white in color.
However something else has to be present for the reaction to occur, water. If there is no water there will be no reaction even though there is a difference in chemical potential.
Anybody that has ever worked in a shop where where aluminum is machined has seen this. You can watch the surface dull after the cuting tool passes.
Galling is the build up of aluminum oxide where the two metals meet. You will notice that it is white in color.
However something else has to be present for the reaction to occur, water. If there is no water there will be no reaction even though there is a difference in chemical potential.
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And where on earth do you find a workshop or other facility with 0% humidity? 0 -
It is usually done in a sealed inert gas filled chamber and done by CNC or similar remote process as we have a problem breathing in a pure Argon atmosphere. 0 -
Both are actually incorrect.
The first one is an approximate description of something known as galvanic corrosion. Electrolysis is a generic term that can be used for a wide range of things including hair removal.
Galling can be caused by aluminum oxide. but is mostly cause by using the same material on fasteners. IE a 316 SS bolt and nut. If possible use a 316 bolt and a 304 nut these two are dissimilar enough that it reduces but does not eliminate that possibility of galling. You must still use a good quality anti-seize compound. Galling is mostly caused by poor quality threads. There are microscopic tears in the threading process and these with certain types of materials will start to roll into a small ball this galls the threads and will make it impossible to disassemble. This can occur on a "press fit" sleeve or any other place where two materials come together. The presence of aluminum is just one of hundreds of materials that will gall.0 -
To possibly lock the subject.
I have always been told not to use anything on the threads unless a product was specified. Adding goop to torqued threads can change the torque.0 -
Galling refers to the adhesion and transfer of surface material between contacting metallic surfaces, not denoting what type of metals, similar or not. This generally results from friction due to insufficient or no lubrication. I am not a fan of unlubricated assembly of mechanical parts unless they have been specifically engineered as such. 0
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