## 4 Conclusions  
In this study, microstructural analysis, an examination of thermal history, and an evaluation of the mechanical properties of the AZ31 GTA welds prepared with different welding speeds were carried out. The following conclusions were drawn:  
1. The GTA welding technique produced sound AZ31 Mg weldments, without any defects, such as solidification cracking or liquation cracking, except in a few scattered pores;
2. The microstructural examination of the fusion zone reveals that the average grain size of the equiaxed zone decreases with increasing welding speed;
3. The welds prepared with high welding speed (low heat input) exhibit improved strength and ductility compared with low welding speeds, due to finer equiaxed dendritic grains;
4. The welds prepared with low welding speed exhibit a reduction in strength and ductility compared with high welding speed. This is attributed to the coarse columnar dendrites present in the fusion zone. However, the AZ31 base metal exhibits good strength and ductility values compared with all welded joints, due to the work hardening effect of the wrought base metal;
5. Increased welding speed lowers the heat input and increases the cooling rates, thereby reducing the temperature gradient G, and increasing constitutional supercooling, to allow more nuclei to survive and grow into fine equiaxed dendritic grains in the fusion zone.  
Figure 12: The tensile fracture surfaces of the welded joints fabricated with high and low welding speeds. (**a**) 5 mm/s. (**b**) 3 mm/s.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Condition**} & \multirow{2}{*}{**Welding Speed (mm/s)**} & \multirow{2}{*}{**Yield Strength (YS), MPa**} & \multicolumn{2}{c}{**Ultimate Tensile Strength**} & \multirow{2}{*}{**Elongation (\%)**} \\  & & & **(UTS), MPa** & \\ \hline AZ31 base metal & - & 210 \(\pm\) 5 & 255 \(\pm\) 8 & 17 \(\pm\) 1 \\ AZ31 GTA weld & 3 & 120 \(\pm\) 5 & 165 \(\pm\) 7 & 5 \(\pm\) 1 \\ AZ31 GTA weld & 4 & 140 \(\pm\) 9 & 198 \(\pm\) 7 & 6.5 \(\pm\) 1 \\ AZ31 GTA weld & 5 & 160 \(\pm\) 6 & 215 \(\pm\) 4 & 8 \(\pm\) 0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Tensile properties of AZ31 base metal and GTA welded joints made at different welded speeds.  
**Author Contributions:** Conceptualization, N.K.B., M.K.T. and P.S.; methodology, N.K.B., M.K.T., P.S., A.U.R. and A.Y.A.; formal analysis, N.K.B., M.K.T., P.S., A.U.R. and A.Y.A.; investigation, N.K.B., M.K.T., P.S., A.U.R. and A.Y.A.; resources, N.K.B. and M.K.T.; data curation, N.K.B., M.K.T., P.S., A.U.R. and A.Y.A.; writing--original draft preparation, N.K.B., M.K.T. and A.U.R.; writing--review and editing, N.K.B., M.K.T., P.S., A.U.R. and A.Y.A.; visualization, N.K.B., M.K.T. and A.U.R.; supervision, N.K.B., M.K.T. and A.U.R.; project administration, N.K.B. and M.K.T.; funding acquisition, A.U.R. and A.Y.A. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by King Saud University through Researchers Supporting Project number (RSP-2021/256), King Saud University, Riyadh, Saudi Arabia.  
**Institutional Review Board Statement:** Not applicable.  
**Infrared Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors are thankful to King Saud University for funding this work through Researchers Supporting Project number (RSP-2021/256), King Saud University, Riyadh, Saudi Arabia.  
**Conflicts of Interest:** The authors declare no conflict of interest.