aluminum's number 1 anti corrosive agent is zinc. long term heating up and cooling down cycles can put moisture in the threads area = oxidation . if you are worried about it , use zinc chromates on the threads . i am pretty sure most [not all] come with a coating on them anyhow..
Oxidation of alum is almost unpreventable. Actually one of Alum best attributes is the hardness/toughness of the normal oxidised alum surface.
I believe what is the issue here is one of the combustion by products of every power stroke, among other things, is H2O, albeit its at very high temps, but nevertheless, it is still present. And I also suspect under the pressures the plug endures, some, even a minute amount, will find some H2O forced into the threads, where it will eventually condense. Electrolysis requires moisture, and a steel spark plug and an alum head are good candidates for electrolytic corrosion, and will overcome the alum oxide layer noted above. I also suspect the anti seize mainly fills the microscopic gaps in the thread interface, reducing the area electrolysis can occur easily and any space for any water to accumulate. Any OEM plug plated coating of the plug that reduces the electrical electrolysis potential between the two items has to be a plus.
Ok, maybe not a diamond, but its shiny.
