An asymmetric undercut and black-colored deposit (smut) are created on the surface of Plasma-MIGHybrid (PMH) weld in Al alloys. For the purpose of defect formation control, the effect of plasma currenton surface defects in the PMH weld was investigated through arc phenomena with high speed imagingand metallurgy analysis as compared with MIG weld. It was found that the asymmetric undercut iscreated near the left fusion line of PMH welds by the electromagnetic stirring force induced by highplasma currents over 200 A. As the plasma current increased, three types of smut appear in the weldingbead: Smut outside the welding Bead (SOB) on the MIG weld, Smut spots on the welding bead (SS) andSmut inside the welding Bead (SIB) on the PMH weld. Three types of smut formed changed from SOB, toSS, and finally to SIB. The smut formation area moved from the base metal onto the welding bead. Theamount of smut formed on the PMH weld is less than that of MIG weld. Smut on MIG and PMH weld havean identical chemical composition including aluminum, magnesium, oxygen and carbon from the basemetal and the weld metal. The carbon is from a graphite lubricant on the surface of Al 5183 wire. SOB isgenerated by the arc generated between the wire and edge of the weld pool after short circuit transfer, aswell as droplet explosion transfer depending on MIG current. SS is formed by the combination of graphitelayers remained on the droplet and the weld pool. SIB is generated by a combination of the MIG weldingwire feeding point, the asymmetric undercut and metal vapor from a droplet explosion transfer under astrong plasma forces induced by a plasma arc with plasma currents over 200 A. Consequently, the plasmacurrent influences the weld pool flow and type of smut by changing the metal transfer mode and strongplasma arc forces.