**4. Conclusions**


near the root side fusion boundary in the absence of appreciable reinforcement, which would also affect the regular fracture route. The wavy ripples produced with high heat input had no evident effect on the tensile properties. It is required that a combination of appropriate heat input level and travel speed be selected, leading to the absence of undercut defect, either appreciable root side reinforcement or a combination of post-weld surface treatment with the absence of appreciable root side reinforcement. It has been demonstrated that the welding parameters should be carefully controlled to avoid defect formation and maintain tensile properties in the K-TIG-welded joint.

**Author Contributions:** Conceptualization, Z.F., B.W. and D.D.; methodology, Z.F. and L.S.; software, D.D. and L.S.; validation, Z.P. and D.C.; formal analysis, Z.F., B.W. and D.C.; investigation, Z.F. and D.C.; resources, Z.P. and H.L.; data curation, D.D., H.L. and Z.F.; writing—original draft preparation, Z.F.; writing—review and editing, Z.P., H.L. and D.C.; supervision, D.C., Z.P. and H.L.; project administration, L.S. and H.L.; funding acquisition, Z.P and H.L.

**Funding:** This research has been conducted with the support of the Australian Government Research Training Program Scholarship. This paper includes research that was supported by DMTC Limited (Australia). The authors have prepared this paper in accordance with the intellectual property rights granted to partners from the original DMTC project. This work was partially supported by NSFC under grant No. 51805085.

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