Fusion and friction stir welding of aluminum-metal-matrix composites
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I. INTRODUCTION
THE joining of aluminum-metal-matrix composites is indeed a challenge, and limits the widespread application of these materials.[1,2] In the past, fusion welding, diffusion bonding, resistance welding, and friction welding have been used to evaluate the feasibility of joining these materials.[1–13] Among the fusion-welding processes, the arc, electron beam (EB), and laser beam (LB) methods have been considered, with and without filler wire. Resistance spot welding was performed, with and without a soft aluminum interlayer. Among the solid-state processes, capacitor discharge, friction, and diffusion bonding have been investigated before. Most of these investigations focused either on alumina (Al2O3)reinforced composites[11,13] or on silicon carbide (SiC)-reinforced composites, in a wide range of cast- or wroughtaluminum alloys.[5] It is generally known that the fusion-welding processes often leads to the deterioration of these metal-matrix composites. In the case of Al2O3-reinforced composites, the Al2O3 decomposes to aluminum and gas on contact with liquid aluminum.[13] Similarly, in the case of SiC-reinforced composites, the SiC reacts with molten aluminum to form Al4C3 carbide.[2] A review of the literature shows that the tendency toward the formation of Al4C3 can be reduced in certain arcwelding conditions.[13] During laser welding, it is very difficult to avoid these decompositions. However, Dahotre et al.,[4] in their elegant work, showed that decreasing the specific energy during laser melting could reduce the formation of Al4C3. Based on these two works and on other published research on Al-SiC composite welding, one can speculate that the tendency to form these Al4C3 carbides can be related to peak temperatures achieved in the melt, i.e., a
D. STORJOHANN, Graduate Student, is with the Metallurgical and Materials Engineering Department, Colorado School of Mines, Golden, CO 80401. O.M. BARABASH, S.A. DAVID, P.S. SKLAD, and E.E. BLOOM are with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. S.S. BABU, formerly with the Metals and Ceramics Division, Oak Ridge National Laboratory, is with the Edison Welding Institute, Columbus, OH 43017. Contact e-mail: [email protected] Manuscript submitted February 2, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
low specific energy leads to less superheating above the melting point of the aluminum alloy. Therefore, in the first part of this research, the tendency to form carbides was evaluated with three different fusionwelding processes, and the weld-microstructure evolution was compared with the computational thermodynamic calculations. The autogenous fusion-welding processes were performed on two different aluminum-metal-matrix composites, i.e., an Al-Al2O3 composite and an Al-SiC whisker composite. The tendency toward the degradation of the reinforcing particles was investigated, using optical microscopy and hardness. It is also well established that friction- and capacitancedischarge-welding processes have mo
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