Measurement of the composition change in Al5754 alloy during long pulsed Nd : YAG laser welding based on LIBS

Weld metal composition change in aluminium alloy 5754 in keyhole mode welding, using a long pulsed Nd : YAG laser, was investigated theoretically and supported with experimental measurements. A comprehensive model for the calculation of vaporization rates was developed based on the kinetic theory of gases and the thermodynamic laws. During the laser welding process, the significant variables were pulse duration and power density. It was predicted in the model and concurred experimentally that the concentration of magnesium in the weld metal decreases with an increase in the laser pulse duration, while the aluminium concentration increases. Moreover, the concentrations of aluminium and magnesium elements in the weld metal were determined by laser induced breakdown spectroscopy for different welding conditions.