High-Productivity Forge Welding of AZ80 Magnesium Alloy to A2024 Aluminum Alloy Using an AC Servo Press
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TRANSPORTATION consumes vast amounts of energy. To reduce this energy consumption and realize a low-carbon society, drastic weight reductions are required for vehicles. However, there is a limit to the savings achievable by simply improving the current steels, and there is a growing trend toward multimaterial design to place the optimal material in the right location. Thus, focusing on the automobile field, the technical development of dissimilar welding to provide high strength and high reliability is of particular interest.[1–11] Examples of multimaterial designs include a front sub-frame of an automobile manufactured from an aluminum (Al) alloy and steel[12] and a space-frame made of steel, Al alloy, and carbon fiber reinforced plastic (CFRP).[13]
HIDEKI YAMAGISHI, SHIGEKI KAKIUCHI, and MASARU SATO are with the Central Research Institute, Toyama Industrial Technology Center, Takaoka, 933-0981, Japan. Contact e-mail: [email protected] Manuscript submitted December 15, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Magnesium (Mg) alloy is considered as a structural material for next-generation automobiles. However, applications of Mg alloys have been limited by their poor corrosion resistance and strength. This issue has been addressed by combining Mg alloys with Al alloys; this combination is widely used as a joint or cladding material. However, welding of these two alloys typically produces a weak joint, which has been attributed to the brittle intermetallic compound (IMC) layer that forms at the joint interface.[14,15] Currently, resistance-spot welding is used the most in automotive body welding process. This is a fusion welding method of joint boundary using joule heat and using a multiarticulated robot with c-type arm, realizing fast spot-joint and flexibility like a stapler. This is advantageous compared with other welding methods in the automotive field. Due to the fusion welding, however, this method cannot be generally expected to be applicable for a dissimilar bonding because of IMC generation. Furthermore, low electrical-resistance materials such as aluminum and magnesium, which are expected to serve as a multimaterial structure, need high current compared to steel, due to which early consumption of electrode occurs. Thus, this process is hard to be
practically applicable for the light-weight materials even in case of similar metals welding: hence, this process is generally restricted to similar welding of steel. Solid-phase bonding can control IMC growth and holds promise for dissimilar bonding. However, in general, solid-phase bonding requires very close control of processing conditions and the atmosphere; the bonding surfaces also typically require machining or polishing. Although friction stir welding (FSW) is a commercially viable process, some issues remain, such as figure restrictions of lines or spots, severe process conditions, specimen fixation, and processing time. In some situations, this process will never be suitable. For a dissimilar welding application of an automobile str
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