This paper presents the fabrication condition of TiNi alloy powder by mechanical alloying and shape memory characteristics of the sintered alloy. The effect of mechanical alloying condition on the characteristics of mechanically alloyed powder (MA powder) was investigated. Also, the difference in sintering behavior between the MA powder and the elementally mixed powders by V-blender and the shape memory characteristics of the sintered alloys were also examined. The MA powder was fabricated by milling using a planetary ball mill in a rotational speed between 200 and 500 min À1 for various milling times in an atmosphere of Ar gas. These two types of powders prepared in different processes were sintered using a pulse-current pressure sintering equipment at various sintering temperatures. The powder agglomerated and its particle size became larger with an increase in milling time. The mixture of Ti and Ni powders changed into an amorphous state by processing for 3.6 ks over 300 min À1 . The sintered alloy of the MA powder showed more uniform phase of TiNi than that of the elementally mixed powders sintered in a same manner, however, the former showed a lower density than the latter due to a larger particle size of the MA powder of before-sintering. It was found from the measurement of the transformation temperature of the sintered alloy of the MA powder using DSC that the alloy has shape memory characteristics, and the transformation temperatures of the alloy are higher than those of the alloy of the elementally mixed powders due to waste of Ni powder.
Lap joints of an upper Al alloy (1.0-mm-thick A5052) and lower hot dip galvanized steel (1.2-mm-thick GI steel) were welded by a novel spot welding process for dissimilar metal lap joints using a new tool with the tip made of spherical ceramics, i.e., "Friction Anchor Welding." As a result, the rotating tool was plunged only to 1.3-1.4 mm from the Al alloy surface, and accordingly, a steel projection was not formed in the Al alloy sheet. Further, the Al alloy near the rotating tool was removed. However, near this removed area, the Zn layer on the GI steel melted and was removed by friction heat, and consequently, the GI steel and the Al alloy were welded. Thus, the tensile shear strength reached about 2.6 kN/point.
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