I haven’t cut an axle, but one time I was cutting stuck rusted brake rotors off my car cause I didn’t want to hammer the crap out of it and possibly damage the bearings. Perhaps I was overly cautious.Use the biggest Sawzall with the toughest blade you can find. That is a miserable, miserable job with the cheapest Harbor Freight Sawzall even with a quality blade.
Anyway, I had a cheap metal blade, wore out like nothing. Got a Dewalk metal cutting blade, got like 1/8” inch before it was worn out. Bought a Diablo carbide tooth metal cutting blade, and it cut through the brake rotors like butter. It was absolutely unbelievable how fast and easy it cut that 1/4” thick steel.
I had Harbor Frieght’s midrange sawzall, which I bought about 12 years ago. It’s all about the blade. If cutting more than nails, get a quality carbide tooth blade.