Dynamics of keyhole and molten pool in laser welding

Abstract

In laser and electron-beam welding, a deep cavity called a keyhole or beam hole is formed in the weld pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. However, a hole drilled in a liquid is primarily unstable by its nature and the instability of the keyhole also causes the formation of porosity or cavities in the weld metal. In particular, the porosity formation is one of the serious problems in very high-power laser welding, but its mechanism has not been well understood. The authors have conducted systematic studies on observation of keyhole as well as weld pool dynamics and their related phenomena to reveal the mechanism of porosity formation and its suppression methods. The article will describe the real-time observation of keyhole and plume behaviors in the pulsed and continuous-wave laser welding by high-speed optical and x-ray transmission methods, the cavity formation process and its suppression measures.

Effects of Different Shielding Gases and Power Waveforms on Penetration Characteristics and Porosity Formation in Laser Welding of Inconel 690 Alloy

“…In high power CO 2 laser welding, laser-induced plume (plasma) is generated, composed of metallic plasma and gas plasma. 14,26) Metallic plasma, which is ejected from the keyhole and remains attached to it, is caused by the ionization of the vaporized metal by the laser beam. Meanwhile, gas plasma is formed by the ionization of the atoms or molecules of the shielding gas by the laser beam and appears to be attached both to the metallic plasma and the workpiece.…”

Effect of porosities on tensile properties of laser-welded Al-Li alloy: an experimental and modelling study

“…The formation of keyhole pores, including elongated and irregular root ones, is associated with the instability of the keyhole [26,27]. The laser-induced plasma can influence the keyhole stability, and thus, keyhole porosity is a more significant problem in CO 2 laser welding than in YAG and fibre laser welding [28].…”

Non-destructive Testing of Duralumin and Titanium Alloys

“…However, porosities and other defects will occur in the weld because of quick cooling velocity and bad protection [4]. Pores and other defects may cause a reduction of solidity of metal of construction, and thus lead to destruction of the material.…”