Refining microstructure of medium-thick AA2219 aluminium alloy welded joint by ultrasonic frequency double-pulsed arc

The increasing demand for achieving high-efficiency and high-quality medium-thick aluminium alloy welded structures, especially large scale aerospace components, presents an urgent challenge to the conventional TIG arc welding process. This work proposed a novel double-pulsed variable polarity tungsten inert gas (DP-VPTIG) arc, in which square wave current was simultaneously modulated into ultrasonic frequency (20–80 kHz) low (0.5–10 Hz) pulses. Full penetration welds of 6 mm thick AA2219 aluminum were successfully obtained by using this microstructure mechanical properties weld produced DP-VPTIG investigated, taking VPTIG as comparative study. Results show that zone showed alternating distribution fine equiaxed grain band slightly coarse band. Compared structure effectively refined with showing significant reduction average size 51.2% along transverse section 61.3% longitudinal section. morphology α-Al+θ-CuAl2 eutectics transformed from continuously distributed netlike shape separately granular shape, segregation Cu solute element obviously improved. microhardness increased about 8.7% 5.6% tensile ultimate strength, yield strength elongation 6.6%, 10.6% 20.5%, respectively. results provide valuable basis improving efficiency joint quality through hybrid pulsed arc.