Investigation on laser welding of selective laser melted Ti-6Al-4V parts: Weldability, microstructure and mechanical properties

In this study, laser welding was successfully used to join selective laser melted (SLMed) to SLMed and SLMed to wrought Ti-6Al-4V specimens. The microstructures, microhardnesses, tensile performances, fatigue lives and fatigue crack growth rates (FCGRs) of the welded specimens as well as SLMed specimens were investigated. It is found that the stress-relieved SLMed Ti-6Al-4V has a good laser weldability. The SLMed to SLMed and SLMed to wrought joints have similar microstructures (columnar prior β grain boundaries with inside acicular α′), microhardnesses (410 HV-450 HV), ultimate tensile strengths (UTSs) (~ 1200 MPa), yield strengths (YSs) (~ 1080 MPa) and FCGRs in the welding zones, which are also similar to those of SLMed specimens. But the fatigue lives of SLMed to SLMed and SLMed to wrought joints are lower than those of SLMed Ti-6Al-4V, and much lower than those of traditionally wrought annealed Ti-6Al-4V. Heat treatment on SLMed to SLMed joints decreases the microhardnesses (390 HV-410 HV), UTSs (1106 MPa), YSs (1008 MPa) and FCGRs in the welding zones, but shows no improvements on the fatigue lives. It can be concluded that microstructures significantly influence the microhardnesses, UTSs, YSs and FCGRs of the welded and SLMed specimens, but have very limited influences on the fatigue lives due to the existences of pores. Pores play a more decisive role in the fatigue lives, but have very limited influences on the UTSs, YSs and FCGRs.