Had this in the past, most owners with alloys have it at some point.

Simple fix is to visit your local tyre indy who will pop the tyre off the rim, clean up the rim to remove flaking paint and loose corrosion and refit the tyre using an orange coloured sealant instead of the usual tyre soap. The orange turns to a rubbery black within the day.

It lasts a couple of years, got me to the point of needing a new tyre and the fitter simply used some more of the same stuff.

Permanent fix is to get the wheels blasted and powder coated.

One simple fact is unless the damage has been caused by kerbing or other impact it will happen to the other 3 shortly.

Another fat is the posh diamond cut wheels suffer far more than simple painted or powder coated ones, My affected wheel was diamond cut, never again.