Comparative Study of Laser Weldability of Titanium Alloys

Abstract

The weldability of titanium alloys depends on their chemical composition and microstructure. Thus, pure titanium, α alloys and α + β alloys are claimed to have excellent weldability, although metastable β alloys have bad weldability. These general weldability considerations are applied regardless of the joining technology, but specific novel welding techniques, as laser beam welding, can improve this property. The main objective of this paper is to determine experimentally and precisely the range of laser weldability of the most common three families of titanium alloys. To carry out this study, butt welds were prepared using LBW under conduction regime, in specimens of different titanium alloys (α, α + β, and β) with the same thickness and size. The analyses of required input laser energy to generate full penetration welds, metallographic examinations of welds and mechanical evaluation of the joints were performed on welded samples. Results showed that much higher input laser energy density was required to achieve full penetration welds in the β alloy than in the α and α + β alloys. In addition, in both α and α + β samples, microhardness values of the fusion zone of welds were similar to the base metal. However, the microhardness values at fusion zone of β alloy were slightly lower than those measured at base metal. Tensile strength tests of these welds generated good results for both α and α + β samples (the specimens did not break at the welded area, presenting UTS and YS values similar to the base metal). Tensile specimens of β welds, however, presented worse results, as they broke at the weld, the load values being lower than those obtained for its base metal. Nevertheless, LBW induced some improvements in welds of β alloy, in comparison with other welding techniques. All these results have allowed us to state an order of laser weldability in conduction mode, according to which, β alloy would have a worse laser weldability than α and α + β alloys.