## 1 Introduction
At the same time, the WAAM of magnesium alloy can solve the problems of low forming efficiency and high costs, but magnesium alloy is prone to defects such as oxidation blackening, inclusions, cold shut and porosity in the process of WAAM [12], as well as low forming accuracy, poor surface quality and a small processing window. [PERSON] et al. conducted a study on the gas tungsten arc welding-wire arc additive manufacturing (GTAW-WAAM) of AZ31B magnesium alloy. It was found that the maximum tensile strength was 240 MPa, and the higher the welding speed, the smaller the grain size [13]. [PERSON] et al. carried out research on the pulsed GTAW-WAAM of AZ31 magnesium alloy and found that the change in pulse frequency brought about the oscillation of the molten pool and a change in the cooling rate. When the pulse frequency was 12 Hz, the grain size was reduced to 21 \(\upmu\)m, and the ultimate tensile strength (UTS) reached 263 MPa, but the geometric accuracy of the forming was poor [14]. [PERSON] et al. studied the tensile anisotropy of AZ31B magnesium alloy fabricated by cold metal transfer-wire arc additive manufacturing (CMT-WAAM) and found that epitaxial columnar dendrites were formed along the deposition direction [15]. [PERSON] et al. conducted a study on the swing welding process of AZ91 magnesium alloy by CMT-WAAM. It was found that the grain sizes above and below the fusion line were 13.9 \(\upmu\)m and 33.2 \(\upmu\)m, which were 69.7% and 25.2% lower than in the matrix, respectively [16]. [PERSON] et al. conducted research on the WAAM of AZ31B magnesium alloy and found that coarse grains and pores were the main causes of tensile fracture, and the heat-affected zone softening effect existed in the sample microstructure [17]. [PERSON] et al. studied the microstructure and mechanical properties of AZ61A magnesium alloy fabricated by WAAM. It was found that the anisotropy of tensile strength, yield strength and elongation was 3.0%, 5.2% and 0.7%, respectively. It was also found that the constitutional undercooling in the solidification front of the molten pool during deposition led to a fine grain structure [18]. [PERSON] et al. carried out a study on the scanning laser-arc hybrid additive manufacturing of AZ31 magnesium alloy thin-walled components and found that the average grain size was reduced by 37.5% compared to that without scanning, and the ultimate tensile strength and elongation were 205 MPa and 20.7%, respectively [19]. Therefore, the study of magnesium alloy fabricated by hybrid wire arc additive-milling subtractive manufacturing (HWMM) can improve the stability and quality of magnesium alloys by removing oxide inclusions on the arc surface. At present, research on hybrid additive and subtractive manufacturing focuses on the process planning of the forming process, mainly to improve the processing efficiency and processing accuracy and to reduce costs. [PERSON] et al. developed ER70S-6 low carbon steel semi-closed complex structural parts via cold metal transfer-hybrid wire arc additive-milling subtractive manufacturing (CMT-HWMM), and the side roughness Sa reached 18.7 \(\upmu\)m [20; 21]. [PERSON] et al. conducted a study on hybrid wire arc additive-milling subtractive manufactured (HWMMed) S235 JR structural steel blades and found that this process saves 60% and 34%, respectively, of material and energy compared with traditional milling [22]. [PERSON] et al. established an HWMM evaluation framework based on factors such as cost, manufacturing time, energy demand and carbon emissions, and carried out research on HWMM for ER70S-6 low-carbon steel complex frame structure parts, and they found that HWMM saves 50% and 57% of material and energy compared to traditional milling, respectively [23]. [PERSON] et al.