Forge Welding of Magnesium Alloy to Aluminum Alloy Using a Cu, Ni, or Ti Interlayer
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IN view of more efficient, energy-saving measures, the expanded application of magnesium (Mg) alloy to automobiles and other transport vehicles has been eagerly anticipated. To date, Mg alloy application has experienced significant limitations related to its corrosion resistance and strength. This issue has been addressed by combining Mg alloy with Al alloy, which is widely utilized in industry as a joint or cladding material. However, welding of these two alloys produces a weak joint, attributed to the brittle intermetallic layer that forms at the joint interface.[1–4] From a productivity perspective, the welding process itself presents several disadvantages. For example, in conventional diffusion bonding processes, the bond requires long loading times (several hours) under a reduced pressure or in an inactive gas atmosphere. In laser welding or friction stir welding (FSW), the workpiece is restricted basically to line or spot welding, i.e., the conventional processes are
HIDEKI YAMAGISHI, JUNJI SUMIOKA, SHIGEKI KAKIUCHI, Senior Research Engineers, and SHOGO TOMIDA, Director of Administration, are with the Central Research Institute, Toyama Industrial Technology Center, Takaoka 933-0981, Japan. Contact e-mail: [email protected] KOUICHI TAKEDA, and KOUICHI SHIMAZAKI, are with the BBS Japan Co., Ltd, Takaoka 933-0313, Japan. Manuscript submitted November 26, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
difficult to adapt to curved surfaces in short processing times. In this study, we developed a technique based on forge welding under a high pressure load, using pressures 100- to 1000-fold of that used in conventional diffusion bonding.[5] To prevent direct reaction between the Al and Mg alloys, an insert material, composed of pure copper (Cu), pure nickel (Ni), or pure titanium (Ti), separated the alloys. The insert material provided a good diffusion reaction layer, having a thickness on the order of nanometers. High-strength bonding in air was achieved with relatively short bonding durations, suggesting the applicability of this approach to large-scale production. Additionally, microscopic plastic flow was observed using this bonding method,[6] which created an anchor effect and increased the reactive area, in addition to avoiding direct reaction between Al and Mg, associated with brittle joints. We confirmed the suitability of the transition metals for the insert material, with pure Ti demonstrating the greatest potential. We also compared the resulting tensile strengths and bond qualities among the inserts tested.
II.
EXPERIMENTAL PROCEDURES
Cast billets of AZ80 Mg alloy and A6151 or A2017 Al alloys were used for the base metals. Sheet metals of Cu (99.96 wt pct), Ni (99.69 wt pct), or Ti (99.86 wt pct) were used for the interlayer materials. The chemical
compositions of the alloys are listed in Table I, and the mechanical properties of the materials are given in Table II. The configuration of the assembled specimen after forge welding using a mold is shown in Figure 1(a). The bonding surfaces of the mate
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