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World Journal Of Engineering EXPLOSIVE WELDING OF MAGNESIUM ALLOY WITH ALUMINUM AND STAINLESS STEEL Palavesamuthu Manikandan﹡, Joonoh Lee﹡, Akihisa Mori﹡﹡ and Kazuyuki Hokamoto﹡﹡﹡ ﹡ Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan ﹡﹡ Shock Wave and Condensed Matter Research Center, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan ﹡﹡﹡ Department of Mechanical Engineering, Sojo University, 4-22-1 Ikeda, Kumamoto 860-0082, Japan for all the experiments. The explosive SEP (density and detonation velocity, 1310 kg/m3 and 6970 m/s respectively), provided by Kayaku Japan Corporation, Japan, was used for the experiments. The thickness of the explosive was 5 mm. The experimental setup and the different parameters affecting the process have been described elsewhere [3]. In this work, parameters such as thickness of flyer plate, distance between the explosive and the center of the sample, D, and the initial angle of the experimental setup was varied to attain an optimum microstructure for the welded combinations. Microstructural characterization was done by optical microscope, scanning electron microscope and electron probe micro analyzer. Introduction There is a growing trend in automotive industry to substitute light weight materials such as aluminum and magnesium in an effort to improve fuel economy and reduce emissions. Magnesium alloys are gaining attention due to its low density and good mechanical properties [1]. By combining magnesium with another light metal aluminum or with stainless steel, the cost can be effectively decreased with good mechanical properties. For practical applications, a good bonding strength of the clad is required. Conventional joining techniques are not suitable for the joining of magnesium with other metals due to the difference in the properties and the formation of brittle intermetallic compounds. Explosive welding is an alternate approach for the joining of dissimilar materials [2]. Underwater explosive welding is a variation by which any difficult to join materials can be joined [3]. In this work, underwater explosive welding technique was used to join magnesium alloy with aluminum alloy and stainless steel. The microstructural variations and the conditions for obtaining a good welding are reported. Results and Discussion Fig.1 shows the cross sectional optical micrograph of the explosion welded A5052/AZ31. The transition is seen as a clear wavy interface between the participant metals associated with the vortices. In explosive welding, when the collision parameters are in the required range, a wavy interface is formed. When the collision velocity is high, vortices are formed. These vortices contain the intermetallic compounds of magnesium and aluminum as this combination is a metallurgically incompatible one. The presence of these intermetallic compounds is undesirable as it may degrade the bonding strength of the clad. Hence, it is necessary to vary the welding conditions so that a minimum or nil intermetallics are formed. In underwater explosive welding, the conditions can be changed by varying the initial angle and the distance between the explosive and the center of the sample. Fig. 2 shows the microstructure of the explosive welded A5052/AZ31 for the increased distance, D. When the distance is increased, the shock pressure on the sample is less. This reduced energy causes less Experimental Underwater explosive welding was employed for the experiments. For all combinations, magnesium alloy AZ31 was used as base plate. Aluminum alloy A5052 and stainless steel SUS 304 was used as flyer plate. The length and width of the welded plates were 70 mm x 50 mm. The thickness of the base plate was fixed as 3 mm, whereas the thickness of the flyer plate was varied as 0.5 mm and 1 mm. A 0.2 mm thick stainless steel was used as a cover plate for Al/Mg combination only. The stand off distance between the plates was 0.2 mm 773 World Journal Of Engineering plastic deformation along the interface which in turn favors the formation of small waves with small or nil vortices. By reducing the vortices, it is expected that the bonding strength is high for this clad. SUS 304 A5052 AZ 31 100 mm Fig.3 Welded interface of 0.5 mm stainless steel/AZ31 for D=25 mm, = 30° AZ 31 SUS 304 100 mm Fig.1 Welded interface of 0.5 mm A5052/AZ 31 for D=25 mm, =30° A5052 AZ 31 100 mm Fig.4 Welded interface of 0.5 mm stainless steel/AZ31 for D=60 mm, = 30° Conclusion AZ 31 100 mm Underwater explosive welding was used to clad magnesium alloy with aluminum alloy and stainless steel. A wavy interface with vortices was formed for A5052/AZ31. The vortices containing intermetallic compounds were reduced by changing the welding conditions. In case of SUS304/AZ31, a flat interface with a thin resolidified interlayer was formed. The welding conditions were changed to obtain an interlayer free interface. Fig.2 Welded interface of 0.5 mm A5052/AZ 31 for D=60 mm, =30° Fig.3 shows the microstructure of magnesium alloy/ 0.5 mm stainless steel. The welded interface exhibits a flat interface between the participant metals. In general, the explosive welded interface exhibits a wavy structure. However, in cases, when the participant metals have a vast difference in the properties, a flat interface is formed similar to the ones reported for metal/ceramic. Further, a thin layer is formed along the interface. This is due to the presence of a resolidified interlayer formed by the difference in the melting points of the participating components. Though magnesium and stainless steel does not form any intermetallic compounds, it is necessary to make an interlayer free interface. Hence, the experiments were conducted by changing the distance, D. Fig. 4 shows the microstructure of the AZ31/SUS304 when the distance is increased. The microstructure reveals a clear flat interface with no resolidified interlayer. It is also possible to make an interlayer free interface by changing the initial angle. Acknowledgements The authors acknowledge the support of funding by Global COE program on Pulsed Power Engineering, Kumamoto University. References 1. Chen, Y.C. and Nakata, K. Scripta Mater. 58 (2008) 433-436. 2. Crossland, B. “Explosive Welding of Metals and Its Application”, Oxford Univ. Press, UK (1981). 3. Hokamoto, K., Nakata, K., Mori, A., Tsuda, S., Tsumura, T., and Inoue, A., J. Alloy Compd 472 (2009) 507-511. 774