## 3 Results
### Mechanical Properties  
The distribution of hardness values along the height direction of the components is given for 0 Hz and 300 Hz in Figure 10. The average hardness values of the thin-walled components fluctuate in the range of 50-60 Hv without significant changes, which indicates that the beam oscillation does not affect the microhardness. [PERSON] et al. claimed that pores in laser-MIG welded AZ31 magnesium alloy would significantly reduce tensile properties [25]. To avoid the effect of pores, as shown in Figure 11, the mechanical properties of thin-walled component (300 Hz) and the base were compared. The mechanical properties of the lower specimen are slightly higher than those of the upper because the average grain size of the lower specimen is smaller. The ultimate tensile strength (UTS) of the additive component (210 MPa) is about 91.3% of that of the rolled plate (230 MPa), but the yield strength (YS) and elongation (EL) are significantly higher. In addition, compared to the reported CMT arc additive manufacturing of AZ31 magnesium alloy (UTS = 210 MPa, YS = 132 MPa, EL = 10.55%) [15], the UTS is similar, but the EL is significantly improved, and the thin-walled component in this study exhibits better ductility, which may be related to the effective suppression of porosity and grain refinement.  
Figure 8: Chemical composition of thin-walled components. (**a**) XRD phase spectral lines; (**b**) Test point location for EDS; (**c**) Composition spectral line at point A; (**d**) Composition spectral line at point B.  
Figure 9: Columnar statistics of precipitate content at various positions from 0 Hz to 300 Hz.  
SEM micrographs of the tensile fracture are exhibited in Figure 12. It can be found that there is a significant difference in the fracture characteristics of the additive component and the rolled base. As shown in Figure 12a, the tensile fractures have typical ductile fracture characteristics, with distinct dimples and some steep ductile tearing ridges visible, which are consistent with the excellent ductility they exhibit. However, as shown in Figure 12g-i, the fracture of the rolled plate is a dissociative fracture feature with obvious river patterns and dissociative steps. As shown in Figure 12b, a micro-pore is observed in the fracture, which may be the reason why the upper tensile strength is less than the lower. The tearing ridges present a feature of ductile-brittle hybrid fracture, including dimples and a quasi-cleavage layer (Figure 12c). Further, the pit was found in the tensile fracture of the lower specimen (Figure 11f), which may be related to the escape of the precipitated phase.  
The fracture morphology indicated that the AZ31 magnesium alloy component manufactured using the laser-arc hybrid process has relatively excellent mechanical properties after eliminating porosity defects. Laser oscillation improves the ductility of the component significantly; however, the small number of micropore defects and the escape behavior of the precipitated phase may inhibit the further improvement of mechanical properties.  
Figure 11: Comparative histogram of mechanical properties of the additive wall and the rolling plate.  
Figure 10: Distribution of hardness values along the height direction for the component. (a) 0 Hz; (b) 300 Hz.