As bobw indicates, one needs to consider the relative thermal expansion rates of the two dissimilar materials here. Aluminum expands about twice as much as steel at the same temperature. Heating the aluminum and cooling the steel screw will maximize any potential gap between the two pieces allowing for the possible entry of a penetrant.
Note the words “potential” and “possible” …. a bit of old fashioned luck may come into play as well
Joe b
“luck” is the most important ingredient for sure. But, in this case, I’m thinking a little heat is all it needs. Even if the screw head gets destroyed, you can still get small vice grips on it and work it gently while heating.
