Comparative study on characteristics of laser welded-brazed AZ31/Ti-6Al-4V lap joints with and without coatings

Abstract

AZ31B and Ti-6Al-4V were lap welded using laser welding-brazing technique with and without Ni, Cu, and Cu-Ni coatings under similar welding conditions. The effect of the coatings on the appearance, microstructural evolution, and mechanical properties of the joint was studied. For the uncoated joint, only Ti3Al phase formed along the entire brazed interface. In comparison, Ti3Al phase was observed at direct irradiation and middle regions, whereas, Ti2Cu phase was produced at the weld toe region of Cu-added joint. For Ni- and Cu-Ni-coated joints, Ti2Ni mingled with Ti3Al interfacial reaction products evolved from the direct irradiation region to the weld toe region. Interestingly, the thickness of Cu-Ni joint mixed reaction layer was less than the critical thickness of 10 μm. The Cu-Ni-coated joint sustained the highest tensile shear fracture load of 2014 N (which was about 100% higher than that of the uncoated joint), followed by the Ni- and Cu-added joints with 1795 N and 1680 N, respectively. The fracture mode of the uncoated and Cu-added joints was interfacial failure, whereas, FZ fracture with typical dimple feature was observed for both Ni and Cu-Ni joints.