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.

Abstract Friction stir processing (FSP) is modified to produce various grain sizes of aluminum matrix composites (Al-Al2O3, Al-Zn-Al2O3 and Al-Zn) ranging from 300 nm to 3£gm. The microstructures of the composites were characterized using SEM and TEM. Tensile tests were performed to evaluate the mechanical properties of these composites. In the Al-Al2O3 system, it was found that the nano-scale alumina made it very effective to accumulate dislocations within grains during deformation, and resulted in increasing working hardening rate which is very critical to extend uniform elongation for materials with submicron grain sizes. In the Al-Zn-Al2O3 system, addition of Zn which dissolved into Al matrix to form solid solution and subsequently uniformly distributed G-P zones can improve strength and uniform ductility to some extent, comparing to those without addition of Zn. In addition, the relaxed and dislocation-free boundaries were observed regardless the existence of Al2O3 particles on boundaries. As a result, ko derived from Hall-Petch equation from various strain region decrease as Zn increases. In the Al-Zn system, experimental evidence suggests that increasing Zn content from 0 to 15wt% can enhance the total elongation but not uniform elongation as a result of the uniform spreading of the fine slip bands all over the gauge length and the contribution of grain boundary sliding (GBS) at RT. The relaxed and dislocation-free boundaries and GBS are attributed to the combination of high fraction of high-angle GBs and high GB diffusion to help fast dislocations annihilation at boundaries.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xii, 135 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 106-112).

The study of defect formation and identification is important to the further application of friction stir welding in industry. To better understand the topic, a systematic study was undertaken to describe material flow effects on the formation of defects, to list the various types of defects encountered across a parameter window, and to identify features in the weld force data that can then be used to recognize defects within the weld without destructive testing. Tracer studies were used to determine the impact of the material flow on defect formation with a determination that proper shoulder contact is necessary to obtain sufficient material flow to fully consolidate the weld. A series of welds across a range of rotational speeds was used to identify mechanisms that led to variations in the mechanical properties of the welded panels. A balance between the x- and yorces on the tool is needed to produce robust welds that were defect free. UMF was shown to identify regions of changing material flow conditions; however, the identification of intermittent defects was not as successful.

Process forces arising during Friction Stir Welding (FSW) have become of interest to investigators interested in obtaining weld quality information from recorded weld data. Successful analysis of process forces require the separation of force signals stemming from material flow mechanisms within the weld from signals influenced by the FSW machine. Three modes of FSW control were characterized for system response: Servo Position (SPC), Electronic Deflection Compensation (EDC), and Constant Load Control (CLC). The gain value of the feedback loops associated with EDC and CLC modes were altered and characterized. SPC mode response to vertical changes in the tool position was also characterized. Machine-specific force signatures associated with the motor transmission assembly and spindle resonance were also identified. Characterization of the influence of machine control modes and other machinespecific frequencies on process force signals will allow future investigators to identify segments of welds during which machine actions influenced recorded force data.

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Este estudo apresenta uma investigação sobre a possibilidade de adotar o processo de solda por agitação e fricção, ou \"friction stir welding\" em substituição ao processo usual de fixação por rebitagem, na construção de um painel de fuselagem aeronáutica de dimensões compatíveis com uma aeronave regional com capacidade aproximada de cinqüenta assentos. A investigação avalia aspectos técnicos de engenharia, tais como capacidade de unir materiais heterogêneos, resistência mecânica, vida em fadiga da estrutura, aspectos de produtividade e custos associados. O processo de solda por agitação e fricção ocorre em estado sólido, não requer a introdução de um terceiro material ou qualquer tipo de arco elétrico ou atmosfera de gás inerte. Os materiais a serem unidos não atingem o ponto de fusão, mas são submetidos à severa deformação plástica, sendo misturados sem que haja fusão. As características mecânicas resultantes dos componentes soldados são equivalentes ou superiores às características dos componentes rebitados. Sob o ponto de vista econômico, existem ganhos em redução de custos de mão de obra e aumento na velocidade de produção, quando comparado ao processo de rebitagem. / This study presents an investigation about the possibility of use friction stir welding process to replace the usual riveting process to build an aeronautic fuselage panel which has its dimensions compatible to a fifty seats regional aircraft. The investigation evaluates engineering technical aspects as the capability to join dissimilar materials, the mechanical strength, structure\'s fatigue life, productivity aspects and associated costs. Friction stir welding is a solid state process where a third material deposition is not required, as well is not required any electric arc or inert gas atmosphere. The materials to be joined do not reach the fusion point, but are subjected to severe plastic deformation, being mixed without melting. The mechanical behavior of welded components is equivalent or better than the behavior of riveted components. From financial standpoint, there are benefits on labor costs reduction and increased production rate, when compared to the riveting process.

Aluminum and Zinc oxide powder were blended by friction stir processing (FSP) with threaded pin of 6mm in diameter under conditions of traverse speed, 1mm/sec and rotation speed, 1500rpm. Different thermal analysis (DTA) was conducted to reveal that the melting point of the stir zone decreased to 592oC from 660oC of the green compact specimen containing 20wt%ZnO. X-ray diffraction (XRD) identified that Zn from ZnO dissolved into Al matrix, and did not resolve redox products, alomina. Scanning electron microscopy (SEM) with filed emission gun was employed with EDS analysis. It is interesting to note that many redoxed products with oxygen concentration higher than that of the matrix can be seen as dark and gray phases in BSE images. Evidently, a chemical reaction in Al/ZnO system is possible during FSP and results of the reduced Zn dissolving into the Al matrix and the expected but not detectable nanoscale alumina uniformly being dispersed into the matrix can be attributed to the excellent 22% elongation, and 350 MPa tensile strength in the stir zone from stirred Al-25wt% ZnO.

In this paper, Friction Stir Welding(FSW) experiments are conducted using similar and dissimilar metals of 6061-T6 Aluminum alloy, AZ-31 Magnesium alloy, JISC-1100 pure copper as specimens. Thermalcouples of type D are used to measure temperature history at different postions of workpiece duing Fsw. Form the temperature history, the preheating temperature and the tool rotation and tool moving speed can be found for a successful welding process. The experimental results show that the temperature ranges for the tool starting to move after preheating are 250-2500C, 200-2500C and 300-3500C for silimar metals of Al alloy, Mg alloy and pure copper and that for of dissimilar of Al alloy and Mg alloy is 200-2500C. Vickers hardness test and tensile test of the welded products are also conducted. The hardness testing results show that the vickers hardness of similar Al alloy, Mg alloy and pure copper sheets beforing weldig are about, 102, 70 and 105HV, respectively. The hardness of the nugget region of similar Al alloy, Mg alloy and pure copper sheets after welding are about 60, 62 and 65 HV, respectively and that for dissimilar of Al alloy and Mg alloy sheets is 138HV. The tensile testing results shows that for similar of Al alloy, Mg alloy and pure copper sheets beforing weldig are about, 320, 300 and 280MPa, respectively. The tensile strenghts of similar Al alloy, Mg alloy and pure copper sheets after welding, are about 160, 250 and 200 MPa, respectively, and that for dissimilar Al and Mg alloys is 100 MPa. The above experimental results can provide information for Fsw of Al, Mg alloys and pure copper. Keywords¡GFriction Stir Welding¡Fthermalcouple¡Ftemperature career

In this study, the experimental apparatus with a friction stir welding dynamometer was employed to investigate the joint characteristics of Cu-Ni alloy plate in thickness of 3.6mm lap-welding to low carbon steel plate in thickness of 4 mm using cylinder type tool (without probe) under the welding parameters of rotating speeds (800~1400 rpm) and traveling speed of tool (10~80 mm/min). To prevent the joint interface from oxidizing during the welding process, the joint interfaces of Cu-Ni alloy and low carbon steel respectively were electroplated with Ni coating layer in different thicknesses before the welding. The effect of the thickness of Ni coating layer on shear strength of joint interface and the mechanism of welding are also investigated. Experimental results show that under the rotating speed of 1000 rpm and travelling speed of 10 mm/min, the shear strength for without Ni coating layer is measured about 100 MPa. On the other hand, the shear strength is increased to saturated value of 290 MPa with increasing the thickness of Ni coating layer. Especially, the shear strength of joint interface for the Cu-Ni alloy with 5£gm thickness of Ni coating layer lap-welding to low carbon steel with thickness of 20£gm thickness of Ni coating layer is about 2.9 times of that for without Ni coating layer. Moreover, the downward force (Fd) is decreased and the maximum interface temperature (Tmax) and shear strength (£n) are increased with increasing the rotating speed (N). The downward force is increased and the maximum interface temperature and shear strength are decreased with increasing the traveling speed (f). This complex relationship is discussed by the new parameter of Fd¡EN/f, the relationship among Fd¡EN/f, maximum interface temperature and shear strength shows that the maximum interface temperature is increased and shear strength is increased to saturated value of 290 MPa with increasing Fd¡EN/f. The phenomenon is explained that the diffusion bonding between the joint interface of two plates become more homogeneous.