Weld pool profile characteristics of Al alloy in double-pulsed GMAW

Abstract

In order to better understand the influence of thermal pulse in double-pulsed gas metal arc welding on weld pool of Al alloy, a filter-reflection observation system is developed and used to image the weld pool profile during welding process. Meanwhile, the electrical waveform is recorded by a signal acquisition card. This method is proved to be valid and the clear weld pool images are captured effectively. Under double-pulse condition, the weld pool is influenced by high frequency and thermal frequency simultaneously. The weld pool geometry is varied with thermal frequency (F), and the weld joint ripple size has a close relation with the number of high-frequency pulse (N p and N b) in thermal pulse. The weld pool size at thermal peak (T p) is larger than that at thermal base (T b), the weld pool keeps an “expanding–shrinking” mode between T p and T b, and its fluidity is improved significantly. The variation of weld pool size decreases with an increase in thermal frequency (F). After droplet transfer into the weld pool, the fluid flows to the root of the weld pool and a concave is formed. When the thermal frequency is relatively low, the weld pool oscillation amplitude is high; otherwise, the weld pool oscillation amplitude is low. The effect of thermal pulse on weld pool tends to vanish finally with the thermal frequency increasing continuously.