Microstructure and Mechanical Properties of Aluminum Alloy Prepared by WAAM Assisted with Ultrasonic Stirring

In the arc additive manufacturing (WAAM) of aluminum alloy, different frequencies (30, 40, 50 kHz) of ultrasonic stirring were applied in the molten pool using a stirring needle moving synchronously with the arc. Results show that the grains of the additive layer are refined, the number of columnar crystals decreases, and the number of equiaxed crystals increases compared with that without ultrasonic stirring, and the grain refinement becomes more obvious as the ultrasonic frequency increases. The porosity of the additive layer decreases with increasing ultrasonic frequency, which is 0.73%, 0.64%, and 0.59%at 30, 40, 50 kHz, respectively, but no more than 0.2% of the specimen without ultrasonic stirring. When ultrasonic frequency is 0, 30, 40, 50 kHz, the tensile strength of the additive layer is 266.57, 278, 282, and 299 MPa, and the elongation is 30.67%, 31.54%, 35.53%, 41.86%, respectively. With the increase in ultrasonic stirring frequency, the strength and plasticity of the reinforced layer increase.