Hydrodynamics of laser welding of metal alloys plates and electronic broadening

Abstract

Abstract

We are interested on properties of the plasma medium near the weld surface during laser welding of magnesium metal alloys plates. For a given surface temperature depending in time Ts. we calculate spatial and temporal distributions of the electronic temperature T,. of the gas temperature T,, of the electron density N, and of the neutral densities of Nz and O» and of the ion densities of N>* and Oo" using one dimensional (1D) fluid model. The model contains a set of gas dynamics equations, to describe the heat transfer by convection. The coupled equations for temperatures and species densities were solved simultaneously, using Exponential Scheme (SG Scheme) or Finite Differences Method (FDM) and iterative methods.

The spectroscopic diagnosis by spectral lines can be very useful tools for understanding phenomena in plasmas. These spectral lines can be broadened by Stark broadening (electronic and ionic) or by other causes. We propose a simple method for calculation the contribution of electrons to the broadening using impact theory. The model 1s based on two limits case of the reduced velocity: for (v. < 1) and for (v, > 1). We calculate electronic Stark widths for isolated lines of the non hydrogenic heavy element Be I, Mg I, Ca I. Our results are in good agreement with previous works. For the considered welding conditions. electron density is about 9 x 10° cm? and electron temperature is about 3000 K. The Stark broadening is negligible comparing with Doppler broadening; and the profiles of isolated lines of Mg I will be a good tool to evaluate gas temperature.