Effect of pulse current on the micro-segregation and micro-electrochemical impedance distribution of aluminum alloy 7075 gas tungsten arc weld

In this study, aluminum alloy 7075-T651 plates were welded using conventional variable polarity gas tungsten arc welding (VP-GTAW) and variable polarity GTAW with a pulse-current wave-coupled mode (CPVP-GTAW). In CPVP-GTAW, pulse frequencies of 1–2 Hz and duty ratios of 33–67% were applied while maintaining comparable heat input to that of VP-GTAW. A combination of optical microscopy, EPMA, EBSD, fish-bone crack testing, and localized electrochemical impedance spectroscopy was employed to systematically characterize microstructural evolution, solidification cracking susceptibility, and micro-electrochemical behavior. The coupled pulse waveform generated a periodically reheated mushy zone at the trailing edge of the weld pool, where the temperature was estimated to reach 476–632 °C within the semi-solid range. As a result, the solidification cracking susceptibility index decreased from 91 in VP-GTAW welds to 27 in optimized CPVP-GTAW welds. In addition, localized electrochemical impedance spectroscopy revealed a significantly reduced micro-scale impedance inhomogeneity in CPVP-GTAW welds, indicating improved local electrochemical stability. These results demonstrate that CPVP-GTAW effectively suppresses micro-segregation, mitigates solidification cracking, and homogenizes micro-electrochemical properties in 7075 aluminum alloy welds.