Key Engineering Materials Vols. 353-358

Abstract: The texture evolution of polycrystalline AA 7055 aluminum alloy during rolling about 15% and 50% at room temperature and cryogenic temperature has been investigated by electron back-scattered diffraction (EBSD). With increasing the rolling reduction, the intensities of the components of the β fiber increase at both rolling temperature and simultaneously, the shear textures disappear gradually. The lattice rotation paths from the {001}<110> orientation to β fiber was discussed.

Abstract: The superplastic deformation and microstructure evolution of solid solution treated 7050 aluminum alloy has been investigated. Tensile were conducted at 420 and 460 °C with the strain rate of 1.0×10-4 ~ 1.0×10-1 s-1, and the deformed samples were characterized using optical microscopy, scanning electron microscopy and electron backscatter diffraction. The results show that the solid solution treated 7050 aluminum alloy gained the maximum elongation of 273% at 460 °C with the strain rate of 1.0×10-2. At the deformation condition, a large part of plastic deformation was completed at an invariable stress. The microstructure transformed from coarse grains to a bimodal microstructure and then to a nearly uniform fine microstructure and the dynamic restoration process is from dynamic recrystallization plus dynamic recovery to dynamic recrystallization with the increasing deform strain during superplastic deformation.

Abstract: Combined extrusion experiment (including direct and indirect extrusion) at 440 for large amount of deformation was carried out with the solution treated AA7050 aluminum alloy. Qualitative description and quantitative characterization were conducted employing electron backscattered diffraction (EBSD) technique on the microstructure of typical regions with different filler contents. These characteristic regions were filled at the following stages: ahead of filling (AF), beginning of filling (BF), mid stage of filling (MF) and the end of filling (EF). EBSD results showed that recrystallization fraction during direct extrusion were 8.3%, 13.5%, 9.3% and 11.2%, for AF, BF, MF and EF, respectively. Recrystallization fraction during indirect extrusion were 15.5%, 9.1% 5.2% and 9.9%，for AF, BF, MF and EF, respectively. It shows that the mode and the amount of deformation played an important role in DRX. DRX grains were formed continuously during direct extrusion, while during indirect extrusion, fewer DRX grains generated, and only originally generated DRX grains grew larger gradually.

Abstract: The stochastic nature of aluminum foam structure, having a random distribution of voids, makes it difficult to model its compressive deformation behavior accurately. In this paper, a 2-dimensional simplified modeling approach is introduced to analyze the compressive deformation behavior that occurs in Alporas aluminum foam (Al foam). This has been achieved using image analysis on real undeformed aluminum foam images obtained by VHX-100 digital microscope. Finite element mesh for the cross sectional model is generated with Object Oriented Finite element (OOF) method combined with ABAQUS structural analysis. It is expected that OOF modeling enable prediction of the origin of failure in terms of localized deformation with respect to the microstructural details. Furthermore, strain concentration sites leading to the evolution of the deformation band can be visualized. Thus, this investigation addresses the local inhomogeneity in the Al foam structure. This study implies that the OOF modeling approach combined with experimental observations can provide better insight into the understanding of aluminum foam compressive deformation behavior.

Abstract: Microscopic deformation of each crystal of duplex phases of Ni-Ti-Nb alloy due to hydrogen absorption was investigated by X-ray diffraction technique. Ni30Ti30Nb40 which is hydrogen permeation alloy and consists of the primary phase, NbTi, and the eutectic phases, NiTi + NbTi, was used as a specimen. The change of lattice spacing of the specimen during hydrogen absorption was measured by Cu-Kα characteristic X-ray. As a result, the lattice spacing of crystal of NbTi phase increased extremely, while that of NiTi phase increased slightly. It was pointed out that the NbTi phase is responsible for hydrogen absorption in the Ni-Ti-Nb alloy. When hydrogen gas was released from the specimen at high temperature, both lattice spacing returned nearly to those of them before hydrogen absorption, and the specimen kept its original shape. Therefore, it was confirmed that the volume expansion of crystal of the Ni-Ti-Nb alloy due to hydrogen absorption was elastic deformation.

Abstract: In order to study the texture effects on the anelastic recovery behavior of magnesium alloy, basal plane textured AZ31B alloy was compressed parallel and vertical to the extrusion direction. AE measurement was applied to characterize the deformation and the anelastic recovery behaviors. A model for the correlation between applied strain and the cumulative AE counts in detwinning was proposed. The effects of loading direction to the deformation and twinning behavior were discussed.

Abstract: Formability of AZ31 (aluminium 3%, zinc 1%) magnesium alloy sheets was studied by tensile test and deep drawing test. Effects of the working anisotropy and temperature on the alloy’s mechanical properties were first investigated. Test temperatures are 160, 180, 200 and 220°C, and specimens’ directions are 0°, 45° and 90° to the rolling direction. The deep drawing of cylindrical cups of 100mm in diameter were done for the same temperatures in order to discuss the effects of the test conditions (temperature, punch speed, lubricant and blank holding pressure) on the formability. The experimental results show that the formability of AZ31 alloy sheets (1mm in thickness) at 200°C is better than that of other tested temperatures. The highest drawing speed was also achieved for an operating temperature of 200°C.

Abstract: In this paper, the effects of collision velocity and collision angle on bullet deformation were discussed and performance of protection board made of PC (polycarbonate) plate was estimated. After gun firing experiments, the shape of the bullet and PC were measured using three dimensional measurement machine and deformed the bullet and PC plate shapes were reconstructed by using 3D-CAD as digital data. Furthermore, crash simulation of the bullets were performed by FEM analysis code “LS-DYNA”, and the results of simulation and measurement were discussed.

Abstract: Stress-assisted atomic migration occurs in thin films due to thermal stress development, followed by hillock and void formation on a film surface. Relation between thermal stresses and hillock formation was investigated on copper films with and without passivation layer. Copper films with a thickness of 10, 50 and 100 nm on oxidized silicon wafer were prepared for investigating thermal stress and hillock formation. In-situ thermal stress observation by X-ray measurement revealed that compressive stresses develop in an early stage of heating followed by a sudden decrease in the temperature region between 100 and 200 deg. In a cooling stage, stresses in a film linearly changed with decreasing temperature to form a tensile residual stress state. Surface morphology is observed by optical microscope and SEM after the heat cycle as well as at elevated temperatures in a vacuum chamber. Dome-like swells were formed on an AlN passivation layer. Almost of all of the swells on 100 nm thick film collapsed after the heat treatment up to 350 deg whereas the swells on 10 nm thick film had no collapse excepting a few case. Comparing with the film without passivation, the swell is considered to be the result of atomic migration of copper film to form hillocks in the interface between copper film and AlN passivation film during heating. Atoms are considered to migrate reversibly into the copper film in the cooling stage, resulting to make vacant hall in the swell of AlN film and then collapse due to tensile stress development.

Abstract: This paper presents an experimental work on the cyclic behavior of bolted and welded beam-to-column connections in steel portal frame. Three types of connection were used; tests for each specimen were performed twice in order to maintain test reliability. Specimen 1 (DWA) had only a double web angle connection, specimen 2 (TSD) had a top and seat angles with double web angle connection, and specimen 3 (FW) had a fully welded connection. All specimens were tested under cyclic loading conditions in order to simulate the effects of earthquakes. We also conclude that with appropriate design and careful consideration of connection strength and stiffness, the steel project economy may be maximized.