Microstructure and property enhancement of 7075 aluminium alloy via laser metal deposition augmented by in-situ ultrasonic vibration

This study employed laser directed energy deposition (DED) with in-situ ultrasonic vibration to obtain AA7075 deposits. The results showed that with ultrasonic treatment, the grain morphology of DED produced AA7075 was changed from columnar grains with an average area of 1751 µm2 to equiaxed grains of 118.2 µm2, representing a reduction of about 93%. Also, the application of ultrasonic treatment led to the increase of average hardness from 93.1 HV to 110.2 HV, and the increase of average ultimate tensile strength from 226.8 MPa to 314.7 MPa, representing relative increases of 18.36% and 38%, respectively. However, it did not result in a significant reduction of ductility. It is believed that ultrasonic vibration promotes the formation of additional nucleation sites due to cavitation and acoustic streaming, as well as the formation of secondary phase particles at grain boundaries. Both mechanisms effectively augment the mechanical properties of DED produced AA7075.