Bead formation characteristics in laser welding of high-strength steel under subatmospheric pressures

Abstract

A series of laser welding experiments were carried out on low-alloy high-strength steel specimens under subatmospheric pressure. The welding penetration and weld bead formation characteristics were evaluated by performing metallographic examination on weld bead cross sections. The effects of technological parameters such as ambient pressure, laser power, and welding speed on weld bead formation were investigated. A multi-factor regression prediction model of welding penetration was established on the basis of the above experimental investigation to evaluate the welding penetration in accordance with the adopted welding parameters under certain ambient pressures. To have more insights into the effect of dynamic behavior of molten pool on the bead formation, the laser welding on “glass-metal” composite samples was performed under varied ambient pressures, and a high-speed digital camera was employed to observe the keyhole profile and the molten pool surface during welding process. A correlation between the welding penetration and the ambient pressure for laser welding of high-strength steel was found that in the range of 101–3 kPa, the decrease of ambient pressure leads to the raise of welding penetration and a smoother weld bead appearance.