I’m with Jack on the leads being backwards. Been there just the other day. Scratched my head for about a hour.

50 or so amps It will melt the electrode like butter.

Aluminum can be a problem child in so many cases. I’ve had similar problems. Had better results using 5356 than 4043 in so many jobs. Clean with ss brush pushing in only one direction then go to a carbide burr and grind area down. (No abrasives of any kind.) Thick material not cracked go down deep a...