WELDING RESEARCH A B C through the nozzle was 15 L/min. Experiments were performed at a welding speed of 0.4 m/min, wire feed speed of 11 m/min, and welding voltage of 25.5 V. RealTime Monitoring System A high-speed camera was positioned toward the welding arc and vertically to the welding direction to simultaneously acquire the shape of the arc and droplet. To characterize the arc temperature, a spectrograph was used to acquire the spectrum of the arc plasma. A computer was used to simultaneously control the highspeed WELDING JOURNAL / JULY 2016, VOL. 95 242-s camera and the spectrograph, and manage the information acquired. The schematic of the realtime monitoring system is shown in Fig. 2. In this experiment, the fiber head was accurately parallel with the workpiece and all the spectrum data were gained under the same acquiring condition. The electron temperature during the welding process was calculated based on the spectral emission of elemental aluminum detected within the arc. Under the welding conditions, the local thermodynamic equilibrium could be satisfied and the electron temperature was approximately equal to the excitation temperature (Ref. 26). Therefore, the same kinds of atoms or ions met the Boltzmann distribution on two levels (Em and En). For two close spectral lines of the same kind of atom or ion, the following relationship could be obtained: In Im = An gn��m Amgm��n �� exp – En –Em kTe ���� �� ���� (1) where I and are the emission line relative intensity and wavelength, respectively, A is the transition probability of electron from upper level m to lower level n, k is the Boltzmann constant, E is the emitted energy, and Te and g are the electron temperature and the statistical weight of the upper transition level, respectively. In order to improve the estimation accuracy, the spectral lines used for calculation should be carefully chosen. Weld Quality Analysis and Mechanical Property Testing To evaluate weld quality, the weld samples were sectioned, mounted, Fig. 7 — Distribution of the secondphase particles for different welding processes: A — GMAW; B — UGMAW; C — PUGMAW. Fig. 9 — EDS results of the weld joint obtained with GMAW. Fig. 8 — XRD analysis of the secondphase particles for different welding processes: A — GMAW; B — UGMAW; C — PUGMAW. Table 2 — Mg and Zn Contents (wt%) in Different Welding Processes and Different Locations to the Same Weldment Processes Locations Mg Zn Upper 03.53 00.98 GMAW Middle 03.56 01.02 Lower 03.86 01.60 Upper 03.54 02.24 UGMAW Middle 03.51 02.48 Lower 03.50 02.62 Upper 03.54 03.23 PUGMAW Middle 03.95 03.79 Lower 03.60 04.10
Welding Journal | July 2016
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