none

A novel surface modifying technique, friction stir processing¡]FSP¡^, has been developed for fabrication of surface composite. Al-Al2O3 surface composites with different volume fractions of particles were successfully fabricated. The Al2O3 particles were uniformly distributed in the aluminum matrix. The surface composites have excellent bonding with the aluminum alloy substrate. The microhardness of the surface composite reinforced with 40 vol% Al2O3 of ~50nm, average particle size was ~150 HV, almost doubt that of the 5083 Al alloy substrate¡]86HV¡^. The distribution curves showed that the SD was increased steeply when the volume fractions of Al2O3 particles of SZ attained to about above 30 vol%. In addition, it is difficult to reduce the grain size of SZ stirring with powder by increasing traveling speed or adding more volume fractions of Al2O3 particles because the processing temperature is higher than 0.5 Tm.

We applied the Friction-Stir Process (FSP) to make the ZrO2 /5083 Al alloy composite material, and analyzed its physical properties in different aspects. Different weight percents of nanometer composite materials, ZrO2/Al, with well distributed strengthening grains were manufactured with the FSP which was used for five runs on ZrO2 along with the matrix material, aluminum, at 505¢XC, and created reactants of Al3Zr, tetragonal D023 structure, and Al2O3, identified with X-ray diffraction analysis. The grain size of 5083 Al-alloy could be finer, around 2.6£gm, by the FSP. This study suggests that increasing the addition of ZrO2 into the Al matrix could make the grain size of aluminum finer. We found that the Al grain size would be able to down to 0.66£gm, as 15.3 wt% of ZrO2 powder was reached. The mechanical properties of the Al-matrix material could be also modified by adding ZrO2 that reduces the ductility but boosts the strength of the matrix material. When we put 15.3 wt% of ZrO2 powder, 5083 Al-alloy attained the hardness of 158Hv, almost twice of hardness of the original alloy material, and its yield strength also increased from 125MPa to 400MPa as well.

Al-Al2O3 precipitated alloys and Al-Zn solid solution alloys fabricated by friction stir process are investigated in this study. The mechanical specimen cutting from stir zone were tested by Instron machine. Micro-structure was observed by Scanning Electron Microscopy and Transmission Electron Microscopy. Phase composition was measured by X-ray diffraction. Different Grain sizes sample were obtained at condition with constant traverse speed of 1.0mm/s, different RPM(500rpm, 550rpm, 700rpm, 1500rpm and 1500rpm with subsequent annealing treatment) and pin shape. Mechanical properties and ductility improvement on grain size effect are discussed in this research. In Al/Al2O3 composite materials, mechanical strength is enhanced by Al2O3 precipitation distributed homogeneously in Al matrix and ductility is improved simultaneously by increment of work hardening rate due to interaction between obstacles and dislocations. In Al-Zn solid solution alloys, ductility enhancement takes place not only in refining grain sizes but also occurs obviously with different weight fraction of Zn addition.

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Vita. Includes bibliographic references (p.107-111).

Thesis (Ph. D. in Electrical Engineering)--Vanderbilt University, May 2009. / Title from title screen. Includes bibliographical references.

Friction Stir Processing (FSP) of aluminium alloys has been used to modify and improve the microstructure and relevant properties of fusion welded aluminium alloys. The effect of FSP on MIG-Laser Hybrid (MLH) welded aluminium alloy 6082-T6 mechanical and microstructural properties has been studied in this research. The FSP process was used on 6mm thick aluminium alloy plates and a tool was designed specifically for FSP, and the effect of varying speeds was analysed before the final FSP welds were made. The effect of FSP was analysed by optical microscopy, tensile, microhardness and fatigue testing. The aim of the study was to determine whether the FSP process has a beneficial influence on the mechanical properties and metallurgical integrity of MIG-Laser Hybrid welded 6082-T6 aluminium alloy with varying gap tolerances. Three welding processes were compared, namely combined Friction Stir Processing on MIG-Laser hybrid process (FSP-MLH), MLH and Friction Stir Welding (FSW) as part of the analysis. (FSP was carried out on MLH components when it was found that FSP is not an entirely complete welding process but rather a finishing process per se.) The aim of this dissertation is to investigate the effects of the FSP process on the weld quality of MLH welded joints and also to compare this to individual processes like FSW and MLH. This investigation was undertaken in order to gain an understanding of the effect of these processes on fatigue performance and microhardness distribution on aluminium alloy 6082-T6 weld joints.

This Master Thesis was performed in terms of robotic three dimensional friction stir welding with T-butt joint. Friction stir welding (FSW) is a solid state welding method that achieves the weld temperature by friction of a rotating non-consumable tool with the workpiece. Science and technology fast developing requires for higher seam quality and more complex welding joint geometry like 3D welds. In order to acquire high productivity, capacity and flexibility with acceptable cost, robotic FSW solution have been proposed. Instead of the standard FSW machine, using a robot to perform complicated welds such as, three-dimensional. In this report, a solution for weld a 3D T-butt joint, which located in an aluminium cylinder with 1.5 mm thickness using a robot, was developed. Moreover, two new paths were investigated in order to avoid the use of two welds to perform this type of joint. The paths were tested on 2D and on 3D (with a 5050 curvature radius) geometries. Both paths had good results. What is more, the parameter developing methods of FSW process, which is composed of necessary parameter setting, positional compensation was introduced. Specially,the study demonstrates how complicate geometry can be welded using a robot. Also,it shows that TWT temperature control is able to acquire high quality 3D welds. In addition, an analysis of the 2D welding and 3D welding was performed, which exposed that, keeping exactly the same welding conditions, higher lateral forces on the tool were found during 3D welding. Basis on the special case in this paper, when the tool goes like "climbing" the sample, the suffering force of tool decreasing with increasing the height(Z position); nevertheless, when the tool goes like "downhill", the suffering force of tool decreasing with decreasing the height (Z position). What is more, in 2D weld, increasing the downforce (Fz) results increasing the lateral forces which can be Fx and/or Fy. Finally, the future works suggestions were presented in terms of (1) performing the new paths into a real cylinder, (2) performing tensile test on the paths and comparing it with conventional path which weld twice, (3) researching how the downforce (Fz) influence the Fx and Fy during welding of different 3D geometries, (4) how the cooling rate of backing bar influence the seam quality when it is use the same welding parameters and (5) the effect of performing welds in the same welding temperature achieved with different combination of the tool rotational speed and downforce on the material properties

Dissimilar metals joining have been used in many industry fields for various applications due to their technique and beneficial advantages, such as aluminum-steel and magnesium-steel joints for reducing automobile weight, aluminum-copper joint for reducing material cost in electrical components, steel-copper joints for usage in nuclear power plant, etc. The challenges in achieving dissimilar joints are as below. (1) Big difference in physical properties such as melting point and coefficient of thermal expansion led to residual stress and defects. (2) The miscibility issues resulted in either brittle intermetallic compound layer at the welded interface for miscible combinations (such as, aluminum-steel, aluminum-copper, aluminum-titanium, etc.) or no metallurgical bonding for immiscible combinations (such as magnesium-copper, steel-copper, etc.). For metallurgical miscible combinations, brittle intermetallic compounds formed at the welded interface created the crack initiation and propagation path during deformational tests. (3) Stress concentration appeared at the welded interface region during tensile testing due to mismatch in elastic properties of dissimilar materials. In this study, different combinations of dissimilar metals were joined with friction stir welding. Lap welding of 6022-T4 aluminum alloy/galvanized mild steel sheets and 6022-T4 aluminum alloy/DP600 steel sheets were achieved via friction stir scribe technology. The interlocking feature determining the fracture mode and join strength was optimized. Reaction layer (intermetallic compounds layer) between the dissimilar metals were investigated. Butt welding of 5083-H116 aluminum alloy/HSLA-65 steel, 2024-T4 aluminum alloy/316 stainless steel, AZ31/316 stainless steel, WE43/316 stainless steel and 110 copper/316 stainless steel were obtained by friction stir welding. The critical issues in dissimilar metals butt joining were summarized and analyzed in this study including IMC and stress concentration.

Nanoscaled-Al2O3 particles reinforced 1050 Aluminum composites by FSP were successfully fabricated in this study. The grain size of 1050 aluminum was obviously refined to about 0.5£gm by friction stir process(FSP), and there was a tendency that grain size decreased with increasing of Al2O3 content, where grain size of 0.84£gm was achieved with 24.7vol% of Al2O3. Nanoscaled-Al2O3 particles reinforced 1050 Al alloy by FSP revealed an excellent strengthening effect and excellent ductileity, Where hardness and UTS of the composite with 24.7vol% nanoscaled-Al2O3 particles were increased up to Hv113 and 310MPa respectively. The tensile result showed a 400% of increase in UTS comparing to the pure Al after FSP.