Mechanical behaviour of overlap joints of titanium

Increasing demand for lightweight vehicles as well as for laser welding for automotive technologies in high rate production have pushed the automotive industry to consider the use of expensive lightweight materials with high specific mechanical properties and, as for example titanium, high corrosion resistance. Butt welds have too stringent requirements in relation to laser positioning and clamping methods, so the move to overlap joints is justified. The changes in welding design have to be requalified, in order to determine the geometries that allow the optimum exploitation of the bearing properties of a material. In this paper, the mechanical properties of overlap joints of thin sheets of titanium Grade 2 and of an alpha/beta alloy Ti-6Al-4V are investigated. The results presented allow a very precise classification of the two materials and should help engineers by indicating the optimum material for any given purpose. Ti-6Al-4V offers, for example, the highest strength when statically loaded, while, in contrast, the high notch sensibility results in a very poor fatigue limit when it is used for overlap joints, which is comparable to the low strength titanium Grade 2 in the same configuration.