a trick i've used in the past... stick an Arc welding rod to a stuck screw... then use the arc rod to back the screw out... and the heat cycling from the arc process loosened the corrosion bond too... there is an actual Dedicated product for this procedure... any welding supply house would know if they're still available... it's worth a call, eh?

i've seen an Auto Body shop dude use something similar.. the guy used a bolt of a slightly larger size, and then used a Spot Welder to stick the bolt to the busted bolt, in a threaded blind hole situation... and, once again, the rapid heating aided in corrosion destruction .
it was a small fender mount bolt... and the AB man was a veteran of the trade. A 6x1 metric bolt in a toyota

i've welded a nut to a protruding broken bolt several times... Ag. tractors and golf mowers, mostly.
yep, they came out, except one on a long-retired path sweeper... i then cut/drilled/retapped that one.