plasma arc. As nozzle diameter decreased, penetration depth increased but bead width did not change. Because nozzle diameter increased plasma arc temperature, length and droplet rate except plasma arc width. Based on regression analysis, penetration depth is mainly affected by wire feeding speed than plasma current. On the other hand, bead width is affected by wire feeding speed under 100 A and by plasma current over 150 A.
Asymmetric undercut is created near the left fusion line of PMH welds by the electromagnetic stirring force induced by high plasma current density. It can be controlled by lowering plasma current density such as lowering plasma current and using small nozzle diameters.
Smut on MIG welds is a Mg?Al?O amorphous layer that includes nano-sized MgO particles less than 100 nm in diameter and MgO particles 1?2 ?m in diameter. Smut on MIG welds is created by large amounts of metal vapor from the arc explosion generated between the welding wire and the weld pool after a short circuit transfer.
As the plasma current increased, three types of smut appear in the welding bead: Smut outside the welding Bead (SOB) on the MIG weld, Smut spots on the welding bead (SS) and Smut inside the welding Bead (SIB) on the PMH weld. Three types of smut formed changed from SOB, to SS, and finally to SIB. The smut formation area moved from the base metal onto the welding bead. The amount heating the wire and the base metal. But, PMHW is not applied in Al
alloy thick plates with thickness over 5mm because of the lack of penetration control from hybridization of PAW arc and MIG arc, surface defect of the weld bead and the high consumption rate of some internal parts of the welding torch. Since the temperature and electromagnetic force of the MIG arc and plasma arc in PMHW arc affect the weld pool flow and droplet explosion transfer, the penetration phenomena and surface defect are expected to depend
on PMHW variables. However, there have been few studies about the effect of the PMHW variables on penetration control method and surface defect such as the asymmetric undercut and smut phenomena.
For establishing PMHW condition of Al alloy thick plate with
thickness over 10 mm, control method of the arc, penetration and defects in the PMH welding were investigated through arc phenomena with high-speed imaging and metallurgical analysis as compared with MIG welding and PAW.
As wire feeding speed of MIG welding in PMHW increased,
penetration depth and bead width increased because of shorter arc length and higher MIG arc temperature from higher MIG welding current. As plasma current of plasma arc in PMHW increased, penetration depth and bead width also increased because of higher plasma arc temperature, wider plasma arc width, and accelerated droplet rate by stronger magnetic pinch effect and plasma stream of plasma arc. As nozzle diameter decreased, penetration depth increased but bead width did not change. Because nozzle diameter increased plasma arc temperature, length and droplet rate except plasma arc width. Based on regression analysis, penetration depth is mainly affected by wire feeding speed than plasma current. On the other hand, bead width is affected by wire feeding speed under 100 A and by plasma current over 150 A.
Asymmetric undercut is created near the left fusion line of PMH welds by the electromagnetic stirring force induced by high plasma current density. It can be controlled by lowering plasma current density such as lowering plasma current and using small nozzle diameters.
Smut on MIG welds is a Mg?Al?O amorphous layer that includes nano-sized MgO particles less than 100 nm in diameter and MgO particles 1?2 ?m in diameter. Smut on MIG welds is created by large amounts of metal vapor from the arc explosion generated between the welding wire and the weld pool after a short circuit transfer.
As the plasma current increased, three types of smut appear in the welding bead: Smut outside the welding Bead (SOB) on the MIG weld, Smut spots on the welding bead (SS) and Smut inside the welding Bead (SIB) on the PMH weld. Three types of smut formed changed from SOB, to SS, and finally to SIB. The smut formation area moved from the base metal onto the welding bead. The amount of smut formed on the PMH weld is less than that of MIG weld.
Smut on MIG and PMH weld have an identical chemical composition including aluminum, magnesium and oxygen from the base metal and the weld metal. SOB is generated by the arc generated between the wire and edge of the weld pool after short circuit transfer, as well as droplet explosion transfer depending on MIG current. SS is formed by the combination of oxide layers remained on the droplet and the weld pool. SIB is enerated by a combination of the MIG welding wire feeding point, the asymmetric undercut and metal vapor from a droplet explosion transfer under a strong plasma forces induced by a plasma arc with plasma currents over 200 A.
Consequently, the plasma current influences the weld pool flow and type of smut by changing the metal transfer mode and strong plasma arc forces.
1 pass full penetration welding condition of 10 and 13 mm Al alloy thick plate were established without surface defect. Mechanical properties of the welds were satisfied with ship class’s rules.