No screw threads are protruding, on the contrary actually.
... and they still don't want to come out? I thought someone wrote, somewhere around here, that the corroded threads of the screw get inside the bracket and ruin the threads that way, but if they don't even stick out, how can they do that? If they get stripped a different way, then can they get so corroded that no penetrating oil will help, because it can't repair what's not there?
I'm not an expert on metals, so I don't know, but is corroded aluminium/steel (i.e. in this case, the bracket/steel threads) really all that strong? If not, then the bracket threads were hopefully designed not to corrode totally, as to not lose tensile strength of the assembly, and well, may be salvageable? Wishful thinking?
Hmm, corrosion probably expands the volume of whatever metal, creating a heck of a tight 'fit' in there.
Kind of going in circles here, trying to figure out how they get stripped...
Looking at it more closely, does the section of Al thread closest to screw corrode
to the screw, bond to it more strongly than its surrouding 'brethren' Al
, and get ripped apart from its 'brethren' on rotational movement of the screw? Again, don't know exactly what goes on in there, so hypothesising.
From what I remember in high school, oxidation?, and material 'lowest on the scale' gets sacrificed?
Just wondering if there really is a way to loosen the interface between the very corroded bracket/screw, or if its corroded, you're
screwed and there's nothing you can do.
Maybe that's a topic for some engineering/metallurgy forum though.