In the current investigation, the loss of magnesium (Mg) in Nd:YAG pulsed laser welding of a number of aluminum (Al) alloys was studied both experimentally and numerically. The experimental results showed that at a fixed average laser power, with the increasing pulse frequency, Mg concentration of the weld metals decreased. A numerical model was developed for the calculation of Mg evaporation from the weld pool. The model predicted a trend in the changes of Mg concentration of the weld pool, working best for alloys containing the higher levels of Mg. The calculations showed that with the increasing pulse frequency from 15 to 40 Hz, due to a decrease in the average temperature of the weld pool, Mg loss in terms of mass per unit area of the weld spot actually decreased from 230 × 10−5 to 120 × 10−5 kg/m2. However, due to a decrease in the weld penetration/volume, the effective Mg loss of the weld metal in terms of concentration increased from 110 × 10−1 to 260 × 10−1 kg/m3. It was shown that due to interactions between Mg and other main alloying elements, the activity coefficient of Mg had to be modified for the model to accurately predict Mg evaporation of the weld pool.
