WELDING RESEARCH Pulsed UltrasonicWaveAssisted GMAW of 7A52 Aluminum Alloy A comparative study was conducted on pulsed and continuous ultrasonicwaveassisted gas metal arc welding JULY 2016 / WELDING JOURNAL 239-s Introduction Arc welding, characterized by advantages such as simple operation, high production efficiency, and being prone to automation, has been extensively BY W. F. XIE, C. L. FAN, C. L. YANG, AND S. B. LIN applied in welding manufacturing, including in the automobile, aviation, shipbuilding, national defense, petroleum, and electron industries. As the technology and the theory develop, arc welding has become a systematic discipline (Ref. 1). However, with the continuous development of modern industry and the variation in the diversity of products, materials, and their service conditions, the requirements for welding quality become more strict. Excellent welding technology of high efficiency and low consumption is an inevitable development trend in the field. Considering the advantages of ultrasonic, such as mechanical effect, acoustic streaming, and cavitation effect, many researchers have done some distinctive work to introduce it into the process of arc welding. Dai (Ref. 2) imposed ultrasonic frequency vibration to the side surface of a workpiece to be welded in the gas tungsten arc welding (GTAW) of 7075- T7 aluminum alloy and found that the grain size in the overheated and heataffected zones decreases. By exerting ultrasonic to the back of the workpiece of AL-6XN austenitic stainless steel, Cui et al. (Ref. 3) discovered that the corrosion resistance was improved. In conventional gas metal arc welding (GMAW), Watanabe et al. (Ref. 4) introduced into the weld pool by the ultrasonic frequency oscillation of filler metal and found that the elongation of the stainless steel joint increased by more than 40% compared to those obtained in conventional GMAW. Wu et al. (Ref. 5) reported this arc ultrasonic as the result of excitation of arc by high-frequency current. He et al. (Ref. 6) and Morisada et al. (Ref. 7) also demonstrated the effectiveness of this method in improving the performance of the joint. Yang et al. (Refs. 8, 9) proposed the continuous ultrasonic-wave-assisted arc welding method, where the noncontact ultrasonic vibration is imposed along the coaxial direction of the arc to form an acoustic radiation field in the arc zone. The ultrasonic field acted on the arc and the weld pool. Under the action of ultrasonic radiation force, both GTA and GMA welding arcs can be compressed and therefore generate certain arc acoustic binding effects (Refs. 10, 11). During the continuous ultrasonic-wave-assisted GMAW (U-GMAW) process, it was ABSTRACT As a new welding process, pulsed ultrasonicwaveassisted gas metal arc welding (PUGMAW) was first proposed. The peak power output of pulsed ultrasonic is higher than that of continuous ultrasonic. In theory, the effect of ultrasonic treatment on the molten metal should be more pronounced during the welding process. To prove the feasibility of this idea, three groups of comparative experiments, including gas metal arc (GMA), continuous ultrasonicwaveassisted GMAW (UGMAW), and PUGMAW of 7A52 aluminum alloy were conducted. A highspeed camera and a spectrometer were employed to detect the welding process in real time. The weldments were evaluated by performing a variety of testing methods. In PUGMAW, when the smallest droplet size and the largest metal transfer frequency were obtained, the weld area increased significantly. The grains refined by pulsed ultrasonic were much finer than those refined by continuous ultrasonic. The microhardness tests revealed the degree of softening of the joint decreased. The microstructure and element analysis showed the presence of the coarse secondphase particles, which was a cause of softening in the fusion zone, and due to enhanced ultrasonic agitation there was a significant inhibitory effect to the Zn element gasification loss. Compared with the ultimate tensile strength (UTS) and elongation of the GMA joint, those of the PUGMA joint increased 23 and 62%, respectively. The UTS and elongation of the UGMA joint were 8.34 and 15.43% lower than those of PUGMA joint, respectively. KEYWORDS • Pulsed UltrasonicWaveAssisted Gas Metal Arc Welding (PUGMAW) • 7A52 Aluminum Alloy • Microstructure • Mechanical Properties W. F. XIE, C. L. FAN (fclwh@hit.edu.cn), C. L. YANG, and S. B. LIN are with the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, China.
Welding Journal | July 2016
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