The friction stir processing is applied in mixing elemental thin sheets of Mg, Al, and Zn in various portions to result in hard intermetallic alloys with Vicker¡¦s hardness in excess of 350. The Mg3Al2Zn3

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In this study, the fundamental mechanism of friction stir welding was investigated to establish the relationship among the three components of the forces acting on the work pieces, the variation of the stirring energy, and the joint characteristics of the materials. A dynamometer designed by Chiou et al., was used to measure the axial force (z-direction), the feed force (x-direction), and the clamping force (y-direction). The output energy of servo motor was monitored by power meter. Experimental results show that with increasing welding speed, the feed force increases obviously, the axial force increases slightly, and the energy almost remains constant for the fixed rotation speed of the spindle. At the rotation speed of spindle of 800 rpm, the spindle angle of 1¢X, the pre-clamping force of 2kN and the welding speed of 60 mm/min, results show that the feed force is about 1kN when the probe is plunged into the specimens but the shoulder does not be in contact with the surface of the specimen. However, when the probe is plunges into the specimens entirely and the shoulder is in contact with the surface slightly, the feed force is reduced to 0.48kN. Moreover, when the shoulder is in contact with the surface heavily, the feed force is reduced to 0.2kN. This result indicates that the contact force between the shoulder and the specimen causes the material to become soft and to backfill into the weld, and then decreases the feed force. After the specimen of the 6061-T6 aluminum has been welding, the micro hardness measurements are made. Results show that the distribution of the hardness is quite consistent along the welding as the feed force approaches to 0.2kN. Furthermore, the appearance on the surface of the weld is quite fine, and thereby it is able to get the high and uniform quality. The spacing distance of the weld surface can be theoretically analyzed. It is found that the spacing distance increases with welding speed and decreases with rotation speed of spindle. The theoretical predictions are in very good agreement with the experimental measurements.

In this study, billet of a binary Al-10at%Fe alloy was prepared from pure Al and Fe powders by the use of conventional press and sinter route. The sintered billet was then subjected to multiple passages of friction stir processing (FSP). After FSP, the structure of a binary Al-10at%Fe alloy can be refined to sub-micrometer scale. Transmission electron microscopy (TEM) showed that particles of Fe-containing phase were distributed uniformly in the aluminum matrix, and the mean size of these second phase particles was about 100nm. From the results of X-ray diffraction and energy dispersive spectroscopy (EDS), the Al-Fe second phase was identified as Al13Fe4. We also observed obvious reaction zone around iron particles in the friction-stirred zone. Apparently, a rapid in-situ reaction between Al and Fe had occurred in FSP. In order to reduce the reaction time and the heat input, the higher traversing speed was used. In addition, a higher sintering temperature was used to promote Al-Fe reaction. Furthermore, micro-hardness, tensile and compressive tests were performed to evaluate the mechanical properties of the Al-10at%Fe alloy fabricated by FSP.

To investigate the fundamental mechanism of friction stir welding to form a butt joint, two additional tests are performed, one using the rotating probe pin only, the other using the rotating shoulder only. In the first case, the pin tool is plunged into the joint interface, but the shoulder is not in contact with the workpiece. When the pin tool is feeding, the material in the vicinity of the pin tool is scratched and piled on the retreating side, but a butt joint is not formed by this test on two thin plates of aluminum alloy 6061-T6. In the second case, when the shoulder is feeding, the plastic shear deformation of the material in the vicinity of the shoulder can be observed and then it is joined together due to the heat generated from the shoulder to cause the material diffusion. According to these additional experiments and the friction stir welding process, the mechanism to form a butt joint is as following. When the probe plunge into the material and the shoulder is in contact with the workpiece, a large amount of frictional heat is generated from the shoulder and the pin. When the tool moves forward, the soft material in front of the pin is squeezed, so that the material is refilled into the space behind the pin by the rotating pin and shoulder. According to the observation of cross-section of butt joint, an interface curve can be found. This curve is formed by the plastic shear deformation of the material in the vicinity of the shoulder and the pin at high frictional temperature. It can be explained by the boundary layer theory.

A scanning reference electrode technique (SRET) apparatus has been designed and commissioned to investigate the corrosion of friction stir spot welds (FSSW) made in AZ31 magnesium alloys. The operational parameters of the apparatus have been calibrated to give good spatial resolution. By combining the SRET data with material flow data and immersion test data it was found that the FSSW process caused the formation of distinct noble and active regimes within the weld area. The noble region was aligned with the stir zone (SZ) and was caused by a dynamically recrystallized grain structure which is void of dislocations / twins, and β Mg17Al12. Localized corrosion attack was observed in both SRET and immersion testing along the thermo-mechanically affected zone (TMAZ). The same effect was consistently observed with a flat versus concave shoulder tool, and dwell times of 1s and 4s.

A scanning reference electrode technique (SRET) apparatus has been designed and commissioned to investigate the corrosion of friction stir spot welds (FSSW) made in AZ31 magnesium alloys. The operational parameters of the apparatus have been calibrated to give good spatial resolution. By combining the SRET data with material flow data and immersion test data it was found that the FSSW process caused the formation of distinct noble and active regimes within the weld area. The noble region was aligned with the stir zone (SZ) and was caused by a dynamically recrystallized grain structure which is void of dislocations / twins, and β Mg17Al12. Localized corrosion attack was observed in both SRET and immersion testing along the thermo-mechanically affected zone (TMAZ). The same effect was consistently observed with a flat versus concave shoulder tool, and dwell times of 1s and 4s.

Thesis (M.S.)--University of Texas at El Paso, 2007. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (M.S.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 9, 2009) Includes bibliographical references (p. 118-127).

Thesis (M.S.)--Brigham Young University. School of Technology, 2007. / Includes bibliographical references (p. 73-75).