don't know where your rule #1 came from, galling from movement of the same materials rubbing together is why you never see 2 brass gears together, always a brass and plastic, or steel and brass.
galling:
Galling is a type of wear that can cause a metal to unintentionally adhere to another metal that it is in contact with when friction is present.
www.metalsupermarkets.com
note the 2 most susceptible metals: aluminum (what you have), and stainless steel (what you proposed).
Both the worst choices.
Greg
Though the meaning is the same, I think this provides a fuller understanding:
Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of crystal structure beneath the surface. This will generally leave some material stuck or even friction welded to the adjacent surface, whereas the galled material may appear gouged with balled-up or torn lumps of material stuck to its surface.
Galling is most commonly found in metal surfaces that are in sliding contact with each other. It is especially common where there is inadequate lubrication between the surfaces. However, certain metals will generally be more prone to galling, due to the atomic structure of their crystals. For example, aluminium is a metal that will gall very easily, whereas annealed (softened) steel is slightly more resistant to galling. Steel that is fully hardened is very resistant to galling.
Galling is a common problem in most applications where metals slide while in contact with other metals. This can happen regardless of whether the metals are the same or of different kinds. Alloys such as brass and bronze are often chosen for bearings, bushings, and other sliding applications because of their resistance to galling, as well as other forms of mechanical abrasion.
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