Comparative study on microstructure and mechanical properties of CMT wire-arc directed energy deposited magnesium alloy assisted by water bath cooling and ultrasonic vibration

• Water bath cooling has minimal impact on microstructure and mechanical properties. • Interlayer ultrasonic vibration significantly refined grain size by 36.8%. • Interlayer ultrasonic vibration enhanced both strength and ductility of AZ31. This study investigates the effects of water bath cooling and interlayer ultrasonic vibration on magnesium alloy (AZ31) components produced through cold metal transfer-based wire arc additive manufacturing (CMT-WAAM). The results showed that water bath cooling had little impact on refining grain size or improving mechanical properties compared to air cooling. In contrast, interlayer ultrasonic vibration treatment significantly refined grain size by 36.8 %, due to cavitation and acoustic streaming effects caused by ultrasonic vibrations. Ultrasonic vibration-treated specimens exhibited enhanced mechanical properties, with yield strength of ∼73 MPa, ultimate tensile strength of ∼220 MPa, and elongation of ∼20 %. The improved strength-ductility synergy was attributed to refinement of grain size and uniform distribution of fine precipitates induced by ultrasonic vibration treatment. These finding suggests that interlayer ultrasonic vibration treatment is an effective method for enhancing the mechanical properties of CMT WAAM-prepared magnesium alloys.