Nope, no flux.After cleaning I do what I call pre tinning. Basically I heat the work 'til it will just melt the rod and coat the parts to be joined with a very thin coat of alumiweld. When this is complete I then go back over all the joint with a fillet, flows nicely. Again I repeat alumiweld is strong but doesn't like butt joints and vibration. Overlap joined parts if possible. Sometimes I also pop rivet the overlap. Good luck, red