Laser assisted joining of AA5754 aluminum alloy to T40 titanium with use of Al-Si filler wires was carried out. Continuous Yb:YAG laser beam was shaped into double spot tandem and defocalized to cover larger interaction zone in V shaped groove. Experimental design method was applied to study the influence of operational parameters on the tensile properties of the joints. Microstructure examination and fractography study were carried out to understand the relation between local phase content and fracture mode. Within defined window of operational parameters, statistically important factors that influenced the strength of T40 to AA5754 joints in V groove configuration were Si content in the filler metal and groove opening angle on T40 side. The best quality joint showed joint coefficient of 90% (or 200 MPa of apparent UTS). Tensile strength of the joints was found to be determined by the proportion between well-developed and underdeveloped reaction zones of T40/melted zone interface. The formation of 2-25 m thick Si-rich interlayers composed by Ti 5 Si 3 and 2 proved to enhance the strength of brazed interface. The creation of very thin (<0.5 m) Si-rich layers at the bottom of the groove was found not sufficient to establish mechanical continuity of the joint and thus should be avoided.

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