Low-Power Laser/Arc Hybrid Welding Behavior in AZ-Based Mg Alloys
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INTRODUCTION
AS light structural materials, Mg and its alloys have recently attracted more attention, especially in the automotive industry, because of their low density and high specific strength. It is well known that the manufacturing techniques, such as welding, play an important role in exploiting the new fields of the applications of new alloys. The excellent welding technology is an effective solution for simplifying product design and decreasing production cost. To date, however, the literature published on Mg alloys welding is limited. Since Mg alloys have properties such as higher vapor pressure, lower viscosity, and lower surface tension as compared with Fe-based alloys, the fusion zone (FZ) of Mg alloys will be less stable, with spattering effects resulting in Mg loss during welding.[1,2] Therefore, while welding Mg alloys the energy input into the filler material has to be regulated in such a way that the wire will melt but not vaporize.[3] Gas tungsten arc welding (GTAW) alone has been commercially employed at present. Due to the high-energy input of the arc welding, a broad FZ and heat-affected zone (HAZ) would be formed, which is harmful to the mechanical properties. The typical joint efficiency for Mg alloys subjected to GTAW could be as high as 70 to 90 pct.[4,5] However, GTAW would be most suitable for thin sheets since the FZ depth-to-width aspect ratio is typically low. For especial delicate applications, laser-beam welding and L.M. LIU, Professor, G. SONG, Instructor, and M.L. ZHU, Associate Professor, are with the State Key Laboratory of Materials Modification & School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, P.R. China. Contact e-mail: [email protected] Manuscript submitted July 17, 2006. Article published online April 22, 2008 1702—VOLUME 39A, JULY 2008
electron-beam welding have been also selectively applied, and have been considered to be powerful for welding thick plates due to their much higher FZ aspect ratio.[6] Although the high-energy beam welding has a very narrow HAZ, high FZ aspect ratio, and welding speeds, the gap bridging ability is very low due to its small focus diameter. Besides, because of low material absorptivity for laser beam, much laser energy would be reflected during laser welding, especially for aluminum alloy, Mg alloy, etc. These would, in turn, decrease energy utilization ratio and reduce practical application. The previous discussion leads us to put forward a new welding process for Mg alloys: the laser/arc hybrid welding. The laser/arc hybrid welding process was first reported by Steen, to jointly use a laser beam and an electric arc for welding and other kinds of metal treatment, so that both heat sources would affect the metal within the same heating zone.[7–9] They found that with the laser and arc on opposite sides of the workpiece, a 300 pct increase in speed was obtained for an arc current of 25 A on 0.2-mm-thick mild steel, and 100 pct increase in speed at the same arc current was achieved on 0.8-mm-thick titanium wi
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