The problem with heating up broken steel bolts in aluminum frames is that it takes some practice. Many years ago I was heating up a pedal spindle that was frozen in an Alu crankarm. Just when I thought I was getting to the point where I could put a wrench on it, the end of the crankarm VERY SUDDENLY shimmered slightly and then turned into a puddle. The pedal was saved, unfortunately, it had been my intent to reuse the crankarm. Thank heavens it was the left side, and a cheap 170 at that. A potentially expensive lesson learned on the cheap.