Current waveform effects on AC-CMT arc welding of 7075 Al alloy with addition of ER7075 wire

7075 Al alloy was AC-CMT arc welded with addition of ER7075 wire using the synergic AC-CMT program for ER5083 wire. The electrical process parameters and metal transfer images were simultaneously sensed under the synergic and modified welding programs to investigate the effect of current waveform on the metal transfer process stability. When welding with the synergic AC-CMT welding program, the EN (electrode negative) half-cycle exhibits a stable cold metal transfer process with the droplets at the end of the wire taking a regular elliptical shape, while the EP (electrode positive) half-cycle presents an unstable transfer process in which the metal drop explosion occurs in the boost stage. The intense and ununiform Zn evaporation on the drop caused and enhanced by the anode spots inherently occurring on the Zn evaporating sites is responsible for the drop explosion. Reducing the EP-CMT boost current effectively suppresses the drop explosion, improving the metal transfer process stability. Reducing the EP-CMT boost duration could also enhance the process stability, but is not effective for suppressing the drop explosion. Furthermore, reducing the EP-CMT boost current or boost duration improves the weld appearance and does not obviously reduce the penetrating ability provided that the heat input remains constant.