**7. Conclusions**

(1) The arc length plays a crucial role in the quality of weld bead formation. In this work, the partial projected transfer zone can be obtained in pulsed GMAW when the arc length was shorter than 3 mm, resulting in the increasement of instantaneous short circuits and inevitable spatters. However, when arc length became longer than 5 mm in the projected transfer zone, the asymmetry and offset of penetration can be enlarged a lot.

(2) For the purpose of obtaining high-quality weld bead formation and weld joints, a shorter arc in the projected transfer zone was recommended. However, the partial projected transfer zone should be avoided when the arc length was short, in order to reduce unnecessary spatters. For example, for the ER50-6 wire with diameter of 1.2 mm used in this work, the appropriate arc length was about 3–5 mm. The base current time should be adjusted according to the appropriate arc length range.

(3) Peak current and peak current time are not were parameters that determine ODPP transfer mode in pulsed GMAW, which was also affected by the arc length. More than 90% (but not 100%) ODPP transfer mode can be obtained when the pulse parameters were selected properly. The short arc trended to rise the proportion of MDPP, and the long arc trended to rise the proportion of ODMP.

(4) The droplet impact force with different arc lengths in the projected transfer zone was calculated. The droplet impact force declined with the growth of the arc length. The increase of arc heat dissipation, the fall of arc energy density, and droplet impact force contributed to the result in that the penetration tended to become shallower in the projected transfer zone.

**Author Contributions:** Methodology, P.Z.; software, P.Z. and J.W.; investigation, P.Z., W.C., T.C., and S.J.; writing—original draft preparation, P.Z.; writing—review and editing, S.X. and P.Z.; supervision, S.X.; project administration, S.X.; funding acquisition, S.X. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the National Natural Science Foundation of China, grant No. 51675269 and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

**Conflicts of Interest:** The authors declare no conflict of interest.
