suck back in aliminium

I am getting suck back on the underside of my aluminium joint, has anyone got any answers please.

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if you are talking about a t joint, the answer can be tricky depending on thickness.

for thin aluminum or aluminium tee joints , suck back is usually caused by too much amperage, too little filler rod, too long an arc, too slow travel speed, or any combination of the above.

I use a forward and back step motion that lets me get back over the thicker part of the weld bead while I ad filler rod. That way i can use a really tight arc to move the puddle forward without using more amperage....then i back up over the bead and lengthen the arc while adding rod.