## 2 Materials and Methods
### Microstructural Analysis and Mechanical Tests  
The macroscopic microstructure of the sample was observed with a Nikon EPIPHOT 300 metallographic microscope. The sample was pre-ground and then polished. Finally, the polished samples were chemically etched. The etchant was a picric acid solution (5 g picric acid, 5 mL acetic acid, 10 mL deionized water, 100 mL ethanol), and the etching time was 30 s. The FEI Nvo Nano SEM 450 electron microscope was used to observe the microstructure and fracture morphology. In order to study the effect of milling on the microstructure of the magnesium alloy samples, the grain size was measured by the line intercept method [14]. The tensile test instrument was a Shimadzu AGS-X universal material testing machine, used according to the ISO 6892-1-2009 standard. During a tensile test with a tensile speed of 1.5 mm/min, three specimens were taken along the feeding and building directions of the HWMM-produced thin wall, whose dimensions were 12 mm in width, 2 mm in thickness and 60 mm in length, and the model and physical diagram of the tensile specimens are shown in Figure 1. The results reported for the ultimate tensile strength, yield strength and elongation represent the averages for the three specimens. The anisotropic percentages of ultimate tensile strength or elongation corresponds to the ratio of the difference in test values between the building and feeding directions to the value of the feeding direction.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Material** & **Al** & **Zn** & **Mn** & **Si** & **Fe** & **Cu** & **Ni** & **Mg** \\ \hline AZ31B & 2.8 & 0.99 & 0.25 & 0.019 & 0.0027 & 0.0076 & 0.00071 & Balance \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical compositions of AZ31B wire/wt-%.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{\
\begin{tabular}{c} **CMT** \\ **Process** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Deposition** \\ **Mode** \\ \end{tabular} } & \multicolumn{2}{c}{**Swing Welding**} & \multicolumn{2}{c}{**Wire Filling**} & \multicolumn{1}{c}{**Scanning**} & \multicolumn{1}{c}{**Arc**} & \multicolumn{1}{c}{**Arc**} \\ \cline{3-8}  & & & **Frequency** & **Amplitude** & **Speed** & **Speed** & **Current** & **Voltage** \\  & & & & **Hz** & **mm** & **m/min** & **mm/s** & **A** & **V** \\ \hline
1 & \begin{tabular}{c} AlMg\({}_{4,5}\)Mn \\ 2 \\ 3 \\ 4 \\ 5 \\ \end{tabular} & \begin{tabular}{c} CMT \\ 2 \\ 3 \\ 3 \\ 4 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} 6 \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \begin{tabular}{c} 8 \\ 3 \\ 5 \\ 5 \\ \end{tabular} & \
\begin{tabular}{c} 93 \\ 5 \\ 5 \\ \end{tabular} &
\begin{tabular}{c} 13.3 \\ 5 \\ 5 \\ \end{tabular} \\
5 & \begin{tabular}{c} Mg alloy \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ \end{tabular} & \begin{tabular}{c} — \\ 3 \\ 5 \\ \end{tabular} & \
\begin{tabular}{c} — \\ 3 \\ 5 \\ \end{tabular} &
\begin{tabular}{c} — \\ 3 \\ 5 \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main processing parameters in the HWMM experiment.