It look like Electrolysis, if it where galvanic action it would be next to a dissimilar metal I believe, you know the antifreeze is suppose to have some chemicals in it to prevent this. When I worked at the hospital I asked our water chemist what the best thing to prevent this in a motor would be, besides a sacrificial anode he said changing the antifreeze according to recommendations would be the best. I just sold my supercharger off my roadster and figured the aluminum intake would have looked like this as it had been on the car for 20 years and 5 years before was on for another 5 but when pulled off it looked great, I guess the 5 year antifreeze changes helped?? Or was it the grounding of the motor? I don't know but I don't believe yours is fixable, sorry to say