Galvanic Corrosion? Threaded parts made of dissimilar metals often display the type of severe corrosion you describe. Few ways to prevent it. Avoidance of this problem should frankly be part of every design process.
Aluminum in contact with steel can form a galvanic cell with accelerated corrosion.
Ant-seize helps I suppose, but any small regions that are in contact would see a greatly accelerated attack concentrated at that region.
99 Tropic Green SVT, Tan Leather, 20K miles, "Nice Twin" (factory stock).
99 Tropic Green SVT, Tan Leather, 28K miles, "Evil Twin" (Turbo AER 3L and more in progress)
96 Red LX, Opal Grey Leather 2.5L, ATX, 22K miles
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