Process Development and Mechanical Performance of 4mm Ti-6Al-4V Laser-GMAW Hybrid Welds

In this study, Laser-GMAW hybrid welding was developed in 4mm Ti-6Al-4V sheet. The purpose is to establish methods to eliminate the undercut issues inherent in autogenous laser welds, especially in thicknesses greater than 3 mm. Preliminary development focused on the effects that process parameters, such as laser power and speed, wire feed rate and wire amperage, have on weld quality. It was found that bead profile, including undercut, was most influenced by weld speed and wire feed rate while spatter was affected by wire amperage and the method of shielding used. Once parameters were identified that produced welds with an acceptable appearance and minimal porosity, tensile, fatigue, crack growth and fracture toughness tests were performed and compared to the mechanical properties of the base material. It was found that the properties of the joints were comparable to autogenous welds, with only slightly improved fatigue lives.  Even though undercut was eliminated, the stress concentration at the toe of the weld became the location of fatigue crack initiation.