Put two dissimilar metals in the same wet connection and one of them pays for the pairing: the more anodic metal corrodes at an accelerated rate while protecting the more noble one. The fastener-hardware version is instructive — stainless steel is strongly cathodic to zinc, so a stainless bolt through a galvanized hanger in damp service turns the galvanized part into a sacrificial anode and strips its coating far faster than weather alone would. The published rule that follows is to keep each connection all one metal class, matching fastener to connector, which is exactly how connector catalogs specify it.
The same electrochemistry, pointed in a useful direction, is how galvanizing works at all: a hot-dip galvanized bolt is ordinary steel wearing a sacrificial zinc layer that corrodes first, by design, and protects the steel galvanically even where the coating gets scratched — until the zinc is spent. Chemistry in contact with the metal matters too: modern copper-based lumber preservatives (ACQ, copper azole) are markedly more corrosive to steel and zinc than the old CCA formula, which is why treated-wood guidance draws hard lines — hot-dip galvanizing to ASTM A153 as the minimum in dry service, stepping up to 300-series stainless for high retentions, ground contact, and salt air.