The porosity formation mechanism in the laser welded joint of TA15 titanium alloy

Abstract

The laser welding of 5 mm thick TA15 titanium alloy was realized by fiber laser of IPG YLS-6000. The microstructure and porosity formation mechanism of the welded joints were investigated under different welding conditions. The microstructure and porosity of welded joints were observed using optical microscope and energy dispersive spectrometer (EDS), respectively. Moreover, the influencing mechanisms of porosity formation and evolution induced by metallurgical and instability of keyhole were also discussed. The experimental results indicated that the outline of metallurgical porosity is regular, which is mainly caused by the absorption of water from the outside environment into the molten pool and the evaporation of Al element. Fast welding speed contributes to the keyhole fluctuating sharply or even collapsing, which causes the shielding gas to enter the molten pool and further form bubbles. The fundamental reason for the formation of porosity is that the laser welding speed is so fast that the molten pool cooling speed is high, which makes it difficult for dissolved gas to escape sufficiently and finally form porosities. It lays foundation for understanding the formation mechanism of porosity and optimizing the process for laser welding of TA15 titanium alloy.