Welding of titanium alloy by different types of lasers

Purpose: of this paper was focused on comparing the welding modes during laser welding of butt joints of titanium alloy Ti6Al4V sheets 1.5 and 2.0 mm thick with direct diode laser and Disk solid state laser. Design/methodology/approach: Bead-on-plate welds were produced at different parameters of laser welding, different welding speed, different output laser power resulted in different heat input of laser welding process. The test welds were investigated by visual test, metallographic observations including macro and microstructure analysis. Additionally mechanical test were carried out such as tensile tests and technological bending test of the joints. The influence of basic laser welding parameters on the penetration depth, shape of fusion zone, width of welds and width of heat affected zones were studied. Additionally the phenomena of laser heating and melting of the welded sheets were analyzed. Findings: It was found that the mechanism of HPDL laser welding of titanium alloy differs distinctly from the mechanism of Disk laser welding. The test welds produced by HPDL laser were high quality. Welds produced by the Disk laser are characterized by a columnar shape of fusion zones, very narrow with narrow and fine structure heat affected zone. Research limitations/implications: In further investigations of laser welding of titanium alloys applying the key-hole welding mode a special care must be taken to the shielding of the weld zone and protection the weld pool and weld metal against the harmful gases from air atmosphere. Practical implications: Results of investigations presented in this paper may be applied directly for welding high quality butt joints of titanium alloy with the HPDL laser. In a case of laser welding with the Disk laser practical application requires further study, especially concentrated on the effectiveness of gas protection of the welding area including the key-hole, weld pool and surrounding regions of metal. Originality/value: This paper describes results of investigation concerning laser welding of the most common used titanium alloy Ti6Al4V by two unique and modern lasers. The investigations were carried out using the high power diode laser with a rectangular laser beam spot and also using a new generation of Disk laser characterised very high power density of the laser beam spot.