Accelerated Bonding of Magnesium and Aluminum with a CuNi/Ag/CuNi Sandwich Interlayer by Plasma-Activated Sintering
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rts on joining dissimilar magnesium alloys and aluminum alloys focus on two approaches, developing advanced welding processes and modifying the surfaces of the base metals. Diffusion bonding (DB)[1] and friction stir welding (FSW)[2] as the conventional solid-state welding processes have been widely used in joining Mg and Al. The long-term heating process by radiation heat transfer mode in DB usually results in the formation of brittle Mg-Al intermetallic compounds (IMCs) at the joint interface.[3–5] Formation of oxide layers (MgO and Al2O3 for Mg and Al) on base metals is another issue for long-term bonding process.[6,7] Large local heat generated during FSW process promotes the formation of Mg-Al intermetallics, which YIYU WANG, Ph.D. Student, is with the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, P.R. China, and also with the Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 2V4, Canada. MEI RAO, Master Student, GUOQIANG LUO, Associate Professor, and QIANG SHEN and LIANMENG ZHANG, Professors, are with the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology. Contact e-mail: [email protected] LEIJUN LI, Professor, is with the Department of Chemical and Materials Engineering, University of Alberta. Manuscript submitted October 21, 2014. Article published online December 1, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
is believed to cause the nucleation of microcracks during the cooling cycle.[2,8] To prevent the intermetallics from forming, lower temperatures and shorter diffusion times would be preferred. Other welding processes that produce more rapid thermal cycles, such as laser beam welding (LBW)[9] and ultrasonic welding (UW),[10] have been successfully attempted in bonding Mg and Al. However, the formation of Mg-Al IMCs that lowers the joint bonding strength still cannot be entirely avoided. Surface modification of base metals provides an alternate way to solve the intermetallic problem. Bonding barrier interlayers, mostly pure metal thin foils such as Ni, Cu, Ti, and Ag, have been reported to prevent the formation of IMCs by blocking direct inter-diffusion of Mg and Al.[11–13] Surface coating layers deposited on the base metals by physical and chemical deposition methods are proved to eliminate the formation of IMCs.[10,14] Combining a high efficient welding process and IMC-prevention effect from surface modification, the plasma-activated sintering process (PAS) appears to be an ideal candidate to achieve some synergistic effects in joining Mg and Al. In the PAS process, a pulsed current is applied directly to the material being sintered, leading to extremely high heating and cooling rates. The highest heating rate in PAS can reach 2000 K/minute (2000 °C/ minute) and the highest cooling rate can reach 400 K/ minute (400 °C/minute). A strong electric discharge field forms in the small gaps between the bonding surfaces of material
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