Here's a
table of metal reactivity sorted from most reactive to least reactive. On this list, the further away from each other on the list 2 metals are, the more likely they will react with one another.
There are 92 metals listed.
The aluminum alloys are #s 6-9 and 12-22, meaning they are very reactive.
The likely iron alloys used in the motor shaft are #s 30 and 31, which tells me there is a slight reaction. Unless there is a stainless steel in use on the shaft, and the most likely to react to aluminum is #78, which indicates a nearly instantaneous reaction.
Another useful quote from the above page.
Quote:
Galvanic series relationships are useful as a guide for selecting metals to be joined, will help the selection of metals having minimal tendency to interact galvanically, or will indicate the need or degree of protection to be applied to lessen the expected potential interactions. Generally, the closer one metal is to another in the series, the more compatible they will be, i.e., the galvanic effects will be minimal. Conversely, the farther one metal is from another, the greater the corrosion will be.
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