Are you also accounting for the corrosion that will occur at EVERY place in the aircraft where there are dissimilar metals?
Check this chart out:
Note that the closer the metals are to one another on the list, the less corrosion potential exists. Looking at Aluminum, we find that mild steel is on one side and cadmium is on the other. This means that although there IS a corrosion potential between these dissimilar metals, it is comparatively very small. The potential is typically dependent upon an electrolyte (water) as well. So if you were to use a mild steel or Cadmium plated steel ring, there won't be much of an issue. Further, if you were to apply a thin coat of grease or anti seize to the threads, you in effect prevent the incursion of water which reduces the potential for corrosion even further.