Effects of ultrasonic-frequency pulsed arc on wire-arc directed energy deposition 7075 aluminum alloy

Variable polarity TIG arc at non-pulsed current and ultrasonic-frequency pulsed (UFP) currents of 20 kHz, 30 kHz, and 40 kHz were applied to fabricate 7075 aluminum alloy (AA7075). A comprehensive comparative investigation was conducted on the microstructure, defects, and mechanical properties to elucidate the effects of UFP arc on wire-arc directed energy deposition AA7075. The results demonstrate that the 30 kHz UFP arc provides optimal microstructural control and performance enhancement for as-built AA7075. UFP arc significantly refined the microstructure, reducing the grain size from 58.86 μm (non-pulsed arc) to 50.96 μm (30 kHz), while effectively weakening crystallographic texture. Furthermore, defect density was dramatically reduced, with porosity decreasing from 2.02% (non-pulsed arc) to 0.16% under 30 kHz. The UFP arc of 30 kHz achieved the most substantial mechanical property enhancements: compared to the non-pulsed as-built AA7075, the horizontal direction exhibited a 20% increase in UTS (282 MPa) and a 217% improvement in elongation (5.4%), while the vertical direction showed 20% greater UTS (268 MPa) and 32% enhanced elongation (2.5%).