Effect of interlayer ultrasonic impact on the microstructure, mechanical and corrosion properties of wire arc additive manufacturing AZ31 Mg alloy thin wall

AZ31 Mg alloy thin walls are prepared using wire arc additive manufacturing (WAAM) and interlayer ultrasonic impact (UI) techniques with cold metal transition (CMT) serving as the heat source. The microstructure, mechanical and corrosion properties of thin walls prepared by WAAM and WAAM + UI are studied. Results showed that the recrystallization area fraction along traveling direction (TD) increased by 68.6% after UI treatment, and many fine equiaxed crystals were formed, resulting in grain refinement, anisotropy reduction, mechanical and corrosion properties improvement. The average grain size along TD decreased from 66.6 +/- 3.5 mu m to 32.7 +/- 1.6 mu m. Through UI treatment, the ultimate tensile strength (UTS) and elongation (EL) along TD increased from 205 MPa to 230 MPa and 13.5%-17%, respectively. The anisotropic percentage of UTS and EL were decreased from 10.8% to 4.5%, and 42.1%-9.7%, respectively. Electrochemical experimental results showed that the average corrosion rate along TD decreased from 1.93 mm year(-1) to 1.53 mm year(-1). Grain refinement, dislocation density variation and texture strength reduction were the main reasons for these results.