Tighten bolts and loosen them. Moods and bolts have died. Violence is always an option. But not always the best option.
There are dozens of solvents for rust removal on the market. Since the time we tinkered, we have used them with liters, so we sometimes lost a fortune while they hardly worked.
Now we use the expensive product 'Brunox', the nowadays often on offer WD 40 and the much cheaper Valvoline 1299 uninhibited. We almost enter the Valvoline at wagon loads. You can also use the stuff for cleaning.
This plea has never disappointed us. And the naming is ingenious. The product is good for one way of deployment, for two ways of use and is also good for 99 other things. 1299 So.
Where other products let us down at the most important moment, the more expensive 'Brunox' has proven its effectiveness in the final battle against rust. And it is not flammable.
It is of course important to work with the correct tools. To loosen a hex nut, use a suitable socket or pipe wrench with internal hexagon or a suitable piece of 'Metrinch' tool. Internal hexes have much better grip on bolt heads and nuts than the ones with internal hexes. The advantage of this is that it is possible to work with smaller strokes in more limited spaces. With a hex, you lock in the nut much better and the forces applied to it are evenly distributed over the whole of the six faces, making the effort effective.
A lot of force can also be applied with 'Metrinch' tools that are suitable for metric and inch sizes. The secret behind that tool is that the point of application of the forces on the flanks of the hexagon. The power transmission can thus be optimal without the risk of the socket, pipe or wrench shooting 'over the corners' of the nut. The disadvantage of 'Metrinch' ring and open-end wrenches is that it is difficult to work with in spaces where there is little 'striking space'.
With stuck bolts it is not a bad idea to give the culprit a shot of looser every day for a week. Or two shots. Patience pays off when working on tight screw connections.
It seems obvious and yet ...
Never use a lever that is too big, so don't put pieces of pipe on the taper to lengthen it. Because then there is a risk of breaking the screw underneath the nut. You will find that a vibration is ten times more effective than a big impact. You always unscrew by pulling the tool towards you: you pull towards yourself to control the applied force. Pushing is out of the question. And when the key comes loose, the pain is all the greater.
Again, no matter how hard it may be for you, you'll have to be patient if you want to keep your bolts, getting angry isn't an option. It is better to use solvent all day than to get the angle grinder to decapitate the screw bolt. This is only a choice if all other options have been exhaustively tried. Even if it took two weeks. Experience has shown that 90% of the original screws / nuts / bolt work can be saved without damaging them more than the test of time has already done.
Best of luck!