Comparative Study on the Weld Formation and Pore Distribution Characteristics, Microstructure, and Mechanical Properties of High-Strength Al-Mg-Si-Cu Aluminum Alloy Cold Metal Transfer Mix Synchro-Pulse Welded Joints

The cold metal transfer mix synchro-pulse (CMT + SP) processes consist of the low-frequency pulse (LFP), high-frequency pulse (HFP), and CMT stages. Compared to the pulse stage (fP = 70 Hz) of the traditional CMT plus pulse (CMT + P) process, the high pulsed frequency (fH = 80 Hz) of the HPF stages increased by 14.0%, increasing the arc force and the impact of droplets on the surface of the molten pool, enlarging the molten pool, and promoting the escape of bubbles. For the same heat input, using the CMT + SP produced a full penetration weld seam and decreased the number density and porosity of micropores to 0.6 pieces/mm2 and 0.1%, respectively. Due to the lack of unfused zone and low porosity, the average tensile strength, yield strength and elongation of the CMT + SP welded joints increased to 240, 173 MPa and 4.0%, respectively.