Effect of pulse frequency on arc behavior and droplet transfer of 2198 Al-Li alloy by ultrahigh-frequency pulse AC CMT welding

In this study, 2198 Al-Li alloy, a low density and high-performance material for aerospace equipment, was welded using ultrahigh-frequency pulse alternating current cold metal transfer (UHF-ACCMT) welding technique. Influence of different ultrahigh-frequencies on arc behavior and droplet transfer were experimentally studied and theoretically analyzed. The results show that the UHF-ACCMT arc exhibited a good stability. During one cycle of arc burning, trends of arc length and diameter of UHF-ACCMT were similar to that of CMT arc. The average arc length of UHF-ACCMT decreased as the pulse current frequency increased from 20 to 60 kHz. An increase in the current frequency decreased the electrical conductivity, leading to a decrease in distance for sustaining arc from wire tip to base metal. The effect of average arc diameter with current frequency was inversely proportional to that of average arc length. Furthermore, the droplet diameter decreased whereas droplet length increased with an increase in the pulse current frequencies from 20 to 50 kHz. With regards to the pinch effect, an increase in the pulse current frequency enhanced the pinch force, which could be attributed to an increasing current density flowing through droplet per unit time. From 60 to 80 kHz, diameter of the arc and length of the droplet were maintained within an optimum range. (C) 2019 The Authors. Published by Elsevier B.V.