Improving microstructure and mechanical properties of 7075 aluminum alloys prepared via wire-arc directed energy deposition using ultrasonic-frequency pulsed arc

The complex composition and inherent defects in 7075 aluminum alloys (AA7075) make them prone to grain coarsening and high porosity under wire-arc directed energy deposition using arc (DED-A), leading to inferior mechanical properties in the as-deposited AA7075. To address these issues, this study employs an ultrasonic-frequency pulsed (UFP) variable-polarity tungsten–inert-gas arc process, utilizing specific ultrasonic frequencies of 20, 30, and 40 kHz, for the DED-A of AA7075. A comprehensive comparative investigation is conducted on the microstructure, defects, and mechanical properties of as-deposited AA7075 to elucidate the effects of the UFP arc on DED-A–processed as-deposited AA7075. By utilizing UFP current to excite ultrasonic vibrations, the associated cavitation and acoustic-streaming effects are leveraged to fundamentally alter the solidification dynamics of the melt pool. This process effectively achieves grain refinement and porosity reduction, thereby significantly enhancing the mechanical properties. The results demonstrate that the 30 kHz UFP arc provides optimal microstructural control and performance enhancement for the as-built AA7075, by refining the grain size from 58.86 (non-pulsed) to 50.96 μm, reducing the secondary-phase volume fraction from 9.5 % to 3.63 %, and decreasing the porosity from 1.03 % to 0.38 %. Consequently, the mechanical properties are substantially enhanced. This work proposes a straightforward, yet effective, process for regulating the microstructure and properties of the as-deposited AA7075 prepared via wire-arc DED-A, namely, UFP arc application, which holds significant potential for advancing the DED-A of AA7075 toward aerospace-grade applications.