Probing laser induced metal vaporization by gas dynamics and liquid pool transport phenomena

Abstract

During laser beam welding of many important engineering alloys, an appreciable amount of alloying element vaporization takes place from the weld pool surface. As a consequence, the composition of the solidified weld pool is often significantly different from that of the alloy being welded. Currently there is no comprehensive theoretical model to predict, from first principles, laser induced metal vaporization rates and the resulting weld pool composition changes. The weld pool heat transfer and fluid flow phenomena have been coupled with the velocity distribution functions of the gas molecules at various locations above the weld pool to determine the rates of the laser induced element vaporization for pure metals. The procedure allows for calculations of the condensation flux based on the equations of conservation of mass, momentum and energy in both the vapor and the liquid phases. Computed values of the rates of vaporization of pure metals were found to be in good agreement with the corresponding experimentally determined values. The synthesis of the principles of gas dynamics and weld pool transport phenomena can serve as a basis for weld metal composition control.