Ichinori Shigematsu

Joining of 5083 and 6061 aluminum alloys by friction stir welding

Friction stir welding (FSW) has emerged as a new solid state joining technique [1], especially for aluminum alloys [2–6]. In this process, a rotating tool travels down the length of contacting metal plates, and produces a highly plastically deformed zone through the associated stirring action. The localized heating zone is produced by friction between the tool shoulder and the plate top surface, as well as plastic deformation of the material in contact with the tool [1]. At the present time, FSW is used mainly for joining similar materials. For dissimilar welding, there have been few systematic studies aimed at clarifying the effect of material combination and welding conditions on weld properties [7, 8]. However, FSW of dissimilar materials will be required in the near future for advanced aircraft design. In the present research, we have tried to apply the FSW technique to dissimilar light metals such as 5083 and 6061 aluminum alloys. Then, we have examined the microstructure and the mechanical properties of the FSWed aluminum alloy joint. 3 mm thick plates of cold-rolled 5083 (0.4%Si, 0.4%Fe, 0.4%Mn, 4%Mg, balance Al) and 6061T6 (0.7%Si, 0.7%Fe, 0.1%Mn, 1.0%Mg, 0.4%Cu, 0.1%Cr, balance Al) aluminum alloys were used in this experiment. Fig. 1 shows a schematic illustration of the experimental apparatus. The test piece was fixed onto a steel plate horizontally. Welding direction was perpendicular to the rolled direction of the aluminum plates. The diameter of the tool shoulder was 10 mm. The diameter of the insert pin and height were 3.0 mm and 2.8 mm respectively. The tool rotation speeds were 890 rpm and 1540 rpm. The traverse speeds of the moving table were 118 mm/min and 155 mm/min. Fig. 2 shows combinations of test pieces. Following FSW, microstructures of the samples were observed by optical microscopy. Vickers microhardness profiles

Mechanical properties of fine-grained aluminum alloy produced by friction stir process

The hardness and tensile strength of the friction stir-processed 1050 aluminum alloy increased significantly with decreased tool rotation speed. It is noteworthy that, at 560 rpm, these characteristics increased as a result of grain refinement by up to 37% and 46% respectively compared to the starting material.

Billet temperature rise during equal-channel angular pressing

AbstractTheactualbillettemperatureduringequal-channelangularpressingwasmeasuredanddiscussed.Thetemperaturerisesofaluminumalloysandamagnesiumalloyat573Kwerebetween4and6Kat673K,whenthedeformationratewas1mms 1 .Adiabaticcompressionisresponsibleforabout10–20%ofthetotalgeneratedheat. 2002ActaMaterialiaInc.PublishedbyElsevierScienceLtd.Allrightsreserved. Keywords:Equal-channelangularpressing;Temperaturerise;Mechanicalwork;Adiabaticcompression;Heattransfer 1. IntroductionEqual-channelangularpressing(ECAP)isanattractivedeformationprocessthatcanproduceultrafine-grained bulk materials without chang-ingthecross-sectionaldimensionsofabillet.InECAP,abilletisrepeatedlypassedthroughtwodiechannelsofequalcross-sectionconnectedatanangle[1–10].MostofthestudiesonECAPpub-lishedtodateareconcernedmainlywiththeabilityto produce ultrafine-grained microstructures [1]andtheuniquedeformationgeometry[6]oftheECAPprocess.Numericalsimulationsofthede-formationduringECAPhavealsobeenpresented[8]. The production of an ultrafine-grained mi-crostructure in ECAP results from the intenseplastic strains introduced in the material thatdriverecrystallizationinthestrainedmaterial.ThemechanismsofmicrostructuralevolutioninECAPwere discussed for four different deformationgeometriesbyLangdonetal.[11].OneofthefactorsthataffectthegrainsizeinECAPis thetemperatureofthebillet inwhichdeformationandrecrystallizationtakeplace.Prac-tically,thebillettemperatureiscontrolledthroughthe billet preheating temperature. However, theexactbillettemperatureduringanECAPopera-tion may be significantly above the preheatingtemperatureduetotheheatgeneratedbytheme-chanicalwork.Itisthereforenecessarytomeasurethe actual billet temperature during ECAP forprecisecontrolofrecrystallization,andhenceofthegrainsize.ThetemperatureriseduringECAPisconsideredtodependonboththebilletmate-rial and the deformation rate. This study was

Superplasticity in Mg–Li–Zn Alloys Processed by High Ratio Extrusion

Superplastic behavior of Mg-8.5Li-1Zn and Mg-8.5Li-3Zn alloys has been investigated. Dynamic recrystallization occurs in the Mg–Li–Zn alloys during extruding with high ratio after stir casting. Mg-8.5Li-1Zn alloy exhibits an elongation of about 400% at the high strain rate of 1.1 × 10−2 S−1 at 623 K, while the Mg-8.5Li-3Zn alloy shows maximum elongation of more than 540%. The apparent activation energy for superplastic flow of both Mg-8.5Li-1Zn and Mg-8.5Li-3Zn alloys at 573–673 K is about 86 kJ/mol and 79 kJ/mol, respectively, so that the dominant deformation mechanism in Mg–Li–Zn alloys is grain boundary sliding (GBS) controlled by grain boundary diffusion.

Recycling of 6061 Aluminum Alloy Cutting Chips Using Hot Extrusion and Hot Rolling

Possibilities of the consolidation process using hot extrusion and subsequent hot rolling were investigated in order to recycle the cutting chips of the aluminum alloy efficiently. For the rolling process, differential speed rolling (DSR) was also applied in addition to normal rolling. Several kinds of cutting chips with different size and cleanliness were collected through turning 6061 aluminum alloy round bars. From these cutting chips, recycled material sheets were produced under various processing conditions via hot extrusion and subsequent hot rolling. Non-recycled material sheets were also prepared for comparison. All samples were characterized by optical microscopy, SEM(EBSP), X-ray texture analysis, tensile test and corrosion test. As a result, it was found that the recycled material sheets produced under optimum processing conditions had smaller grain sizes than those of the non-recycled ones, therefore the mechanical properties and the corrosion resistance of the recycled material sheets were almost comparable to those of the non-recycled ones. Moreover, concerning the DSR processed sheets, the traces of the chip interface, which were clearly observed in the normally rolled ones, almost disappeared, and the appearances were remarkably improved. Then the DSR processed sheets significantly surpassed the non-recycled ones in the tensile properties and the corrosion resistance.

Preparation of Three Dimensional Products Using Flow Deformability of Wood Treated by Small Molecular Resins

To investigate the effect of the additive agents such as polyethylene glycols (PEGs), melamine formaldehyde resin (MF-resin) and phenol formaldehyde resin (PF-resin) on the flow deformability of solid wood, free compression tests during heating were performed. Various molecular weights ranging from 200 to 20,000 for PEGs and almost similar molecular weight around 380 for MF-resin and PF-resin were applied. It was found from the compression tests that the yield stress indicating wood cell deformation resistance was drastically decreased with smaller molecular PEGs in wood, whereas the initiation of flow behavior, which is derived from detachment/slippage between cells, occurred at lower pressure with larger molecular PEGs. For generating the flow behaviors of solid wood, smaller molecular resin/substance was not always suitable. Thermosetting agents also act as a plasticizer during heating and especially the PF-resin showed better softening effect as well as a promoter of flow behavior than the MF-resin with almost similar molecular weight. This indicates that it is important for generating flow behavior to consider affinity/compatibility of resin to wood constituents. A maximum flow deformation ratio in the tangential direction of wood reached 180 % when using PEG 20,000 and MF-resin as an additive agent. It was also demonstrated that using PF-resin and MF-resin deep cup products shaped by a backward extrusion process had a better size stability against water, steam, and acetone.

溶液含浸木材の養生過程における細胞壁への溶質拡散機構の検証: 相対湿度がポリエチレングリコール水溶液含浸木材の膨潤・収縮挙動に及ぼす影響

To control the amount of solute in cell walls of solution impregnated wood using the conditioning process, the mechanisms of solute diffusion into the cell walls and of solvent evaporation from wood under the process were verified. The effect of relative humidity (RH) on temporal variability of swelling, shrinkage, and mass of wood impregnated with an aqueous solution of polyethylene glycol (PEG1540) was examined. The impregnated wood specimen swelled under the conditioning at the RH over 75%. The specimen was indicated to swell when the amount of the PEG polymers in the cell walls increase in this RH range. On the basis of this indication, the temporal variability of increasing rate of the polymers in the cell walls and of evaporating rate of water from the specimen under the conditioning was well explained by the mechanisms of the solute diffusion and the solvent evaporation, respectively. In the RH range, the increasing amount of the polymers in the cell walls increased with the evaporating amount of the water, which increased with the decrease in the RH. These results were supported by the mechanisms of the solute diffusion and the solvent evaporation, respectively. The diffusion mechanism also supported the effect of the history of the RH on the polymer amount in the cell walls throughout the conditioning and subsequent drying in a vacuum. It was concluded from these findings that the solute diffusion into cell walls is able to be controlled by the surrounding vapor pressure of solvent when the polymers (PEG1540) and water are employed as the solute and solvent, respectively.

Superplastic deformation of solid wood by slipping cells at sub-micrometre intercellular layers

In order to facilitate the generation of a flow phenomenon due to the slipping of wood cells under a specific temperature condition, a phenol formaldehyde resin of low molecular weight was introduced into wood cells. The effects of the presence of phenol formaldehyde molecules in wood cells on the flow behaviour of solid wood were investigated experimentally by means of a free compression test. The effectiveness of using phenol formaldehyde resin as an adsorbent to act as both binding and plasticising agents in the proposed wood flow forming shaping technique was examined, and an application to wood flow forming was demonstrated. The results revealed that the flow phenomenon of solid wood occurred at a certain resin content, even under compression at less than 25 MPa. An increase in the moisture content led to further improvement of the flowability of solid wood, which resulted from weakened facial strength among wood cells and intercellular layers due to a local increase in the volume of nano-level pores. Finally, the effectiveness of introducing phenol resin into wood for wood flow forming through backward extrusion was confirmed.

Solute diffusion into cell walls in solution-impregnated wood under conditioning process II: effect of solution concentration on solute diffusion

This study focused on solute diffusing into cell walls in solution-impregnated wood during conditioning, process of moderate drying of solvent. To clarify the effect of solution concentration on the diffusion during the conditioning, weight percent gain (WPG) and relative swelling of the wood sample impregnated with an aqueous solution of polyethylene glycol (PEG) polymers at a concentration of 10, 20, 30, 40, or 50 mass% were examined during the conditioning and subsequent drying processes. The relation between the concentration and the relative swelling after all processes, an indicator of the amount of the polymers in cell walls, exhibited a concave-downward curve with a maximum value at 20 mass%. The estimated mass of the polymers in cell walls just before conditioning increased with the concentration. This indicates that the distribution of the polymers changed during conditioning. The estimated mass just before conditioning and the relative swelling after all processes were normalized to the packing ratios of the polymers in cell walls. The ratio after all processes subtracted by that just before conditioning was larger than the ratio just before conditioning, and increased with the concentration up to 20 mass%; after which it decreased. This indicates that the majority of the polymers in cell walls increased during conditioning, and that the amount of the polymers that diffused into cell walls was at the maximum at concentration of 20 mass%. This was explained by two factors: the decrease in the diffusivity into cell walls and in the concentration difference of the polymers between cell walls and cell cavity with the concentration, based on the behavior of WPG during conditioning; and the estimated minimum concentration at which the solution contains the least amount of polymers to fill the cell walls.

Optimization method of FGM compositional distribution profile design by genetic algorithm

The progress of technologies requires high performance materials. However it is sometimes difficult to achieve the required high performance by homogeneous material. Therefore composite materials have been developed so far. Functionally graded materials (FGM), which is a kind of composite materials, can change the material property in each area for its objective such as heat transfer property, stiffness, and so on, by controlling a compositional distribution ratio of materials. Therefore we can make a product which has two or more different desirable properties in one body. However it is difficult to design a compositional distribution ratio of an FGM as a desired one, because material properties of one part relates to the other part and its shapes and surroundings also affect the properties. In this paper, we propose the automatic compositional distribution profile design system for FGM. The proposed system optimizes the compositional distribution profile to satisfy requirements. The design system consists of two parts: Analyzer and Optimizer. We employ the Finite Element Method as Analyzer for analysis of the state of the product and Genetic Algorithms as Optimizer for optimization of the compositional distribution profile. To show the effectiveness of the proposed design system, we apply the proposed system to thermal stress relaxation problem.