Characteristics of zinc behavior during laser welding of zinc “sandwich” sample

To address the problem of the zinc being easily gasified in laser welding of galvanized steel, laser welding of a zinc “sandwich” sample was performed to experimentally investigate the behavior and characteristics of the zinc inside and outside the keyhole, including the observation of the keyhole, the zinc vapor and zinc plasma, and the calculation of the electron temperature of the zinc plasma. Based on the principle of imaging amplification, the detected multi-points can be located precisely in order to study the distribution of the electron temperature of the zinc plasma. The results show that the zinc behavior played an important role in the formation of the weld-joint and the zinc plasma altered the energy distribution at the top of the keyhole whose diameter has been enlarged in the welding process. For both continuous-wave laser and pulsed laser welding of zinc “sandwich” sample, the average electron temperature of the zinc keyhole plasma was higher than that of the zinc plasma plume outside the keyhole. In the welding process, the continuous wave laser with higher input energy results in higher position of the zinc plasma with higher electron temperature above the sample surface. More zinc vapor resulted in a higher average electron temperature of the plasma.

► A special device to observe zinc behavior and to detect multipoint optical signal was developed.
► The behaviors of keyhole, vapor and plasma have been observed and their effects were analyzed.
► The temperatures of keyhole plasma and plasma plume and their distribution were investigated.
► The effects of the CW and pulsed laser and the amount of vapor to plasma temperature were studied.