High-frequency pulse-modulated square wave AC TIG welding of AA6061-T6 aluminum alloy
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RESEARCH PAPER
High-frequency pulse-modulated square wave AC TIG welding of AA6061-T6 aluminum alloy Yajie Wang 1,2 & Maoai Chen 1 & Chuansong Wu 1 Received: 20 March 2020 / Accepted: 28 June 2020 # International Institute of Welding 2020
Abstract Bead-on-plate welding of 6-mm thick AA6061-T6 aluminum alloy is used to characterize the high-frequency (HF) pulsemodulated square wave AC TIG (HFPM AC TIG) welding. The modulation HF pulse reduces the reignition voltage of negative half-wave arc. However, its effectiveness on increasing weld penetration is not evident until the penetration rate (penetration-toworkpiece thickness ratio) exceeds 45%. Above this value, the weld penetration increases significantly with increasing peak current of the HF pulse, and first increased and then decreased with increasing pulse frequency from 10 to 40 kHz. Maximum penetration achieved at optimal welding condition increases by 120% compared with that of conventional AC TIG welding. The grain size and width of partially melted zone are visibly reduced. The average equiaxed grain size, pore number density, and average pore size in HFPM AC TIG weld metal decrease with increasing pulse frequency. Keywords HFPM AC TIG welding . Weld penetration . Porosity . Microstructure
1 Introduction AA6061-T6 aluminum alloy has been widely used in various fields such as aerospace, automobile, high-speed train, and pressure vessel industries thanks to its good forming performance and physical and chemical properties. TIG welding is one of the main welding processes for this kind of material so far, since it possesses many advantages, such as good weld appearance, high flexibility, excellent control of root pass weld penetration and spatter-free, etc. However, it suffers from low welding penetration, low productivity, high porosity, and significant HAZ softening. Recently, researchers have Recommended for publication by Commission II - Arc Welding and Filler Metals * Maoai Chen [email protected] 1
MOE Key Laboratory for Liquid-Solid Structure Evolution and Materials Processing, Institute for Materials Joining, Qianfoshan Campus of Shandong University, 17923 Jingshi Road, Jinan 250061, People’s Republic of China
2
Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, People’s Republic of China
been trying to solve these problems through introducing ultrasonic vibration energy into the arc and molten pool. Sun et al. [1] developed an ultrasonic-assisted TIG system in which a specially designed welding torch was used to couple ultrasonic vibration energy directly into TIG arc. The penetration of U-TIG weld in AISI 304 was increased by 300% due to the increase of arc push force. Dai [2] introduced ultrasonic wave into 7075-T6 aluminum alloy workpiece through an ultrasonic welder ahead of the TIG welding gun. The heating and cooling rates were significantly increased by the transmission waves, and the dwell time and peak temperature of the thermal
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