A novel ultrasonic rolling assisted direct energy deposition method with semi-solid thixo-forming characteristics for AA6061

Abstract

In order to overcome the defects during the process of additive manufacturing for AA6061, a novel ultrasonic rolling assisted direct energy deposition method with semi-solid thixo-forming characteristics was proposed in this study, which used cold deformed AA6061 wire as raw material, and a corresponding process platform was established. The results showed that under the conditions of laser heating temperature of 750 ℃ and heating plate temperature of 200 ℃, the sample could achieve continuous multi-pass deposition while retaining some of the cold-drawn plastic deformation energy. When the vertical deformation rate was 0.153 and the ultrasonic amplitude was 20 μm, the microstructure of deposition sample after semi-solid heat-treat exhibited typical equiaxed grain characteristics, corresponding to average grain diameter of 95.6 μm and shape coefficient of 1.263. Thin-walled samples with different shapes were formed to verify the capability of process platform. The inference of the formation mechanism of semi-solid microstructure was revealed at last: the introduction of ultrasonic rolling supplemented the plastic deformation energy, and semi-solid heat-treat provided temperature and time for the incubation of equiaxed grains, both of which were crucial for the formation of the semi-solid microstructure.