Materials Science Forum Vols. 495-497

Abstract: Materials of ultra-fine grained microstructure (sub-micrometer grain size) exhibit large strength, hardness and ductility and also the increased toughness in comparison with conventional coarse-grained ones. In these materials also the super-plastic flow at lower temperatures is observed. This behaviour may be interesting when aluminium alloys like AlCuZr, used in superplastic forming, are considered. In the paper, the methods of preparing such materials by equal-channel angular pressing (ECAP) is proposed and the texture analysis, based on neutron diffraction pole figure measurements and calculated orientation distribution function of two alloys AlCu4SiMn and AlCu5AgMgZr is discussed. The influence of short time recrystallization is discussed in relation with TEM and SEM observations.

Abstract: Various processing routes have been studied to develop the most efficient route toward microstructure refinement and texture homogenization. Most studies have focused on the central shear zone in round or square cross-section rods. However, the utility or application of these materials is subject to conditions across the entire rod. This study begins to investigate the development of recrystallization textures and microstructures across copper ECAE processed via route Bc through 16 passes. Although the recrystallized condition appears to be reasonably homogeneous after 4 or 8 passes, additional passes lead to stronger, heterogeneous recrystallization textures and coarsened microstructures.

Abstract: In the work orientation distribution functions (ODF) were determined for wires drawn in pressure and roller dies from a high carbon steel wire rod with a diameter 5.5 mm to wires with a diameter 3.8 mm and 3.0 mm. For a comparison ODFs for wires drawn conventionally were also determined. The texture was measured on the cross sections of investigated wires prepared in a form of squares to eliminate the effect of the surface layer. In the first stage of a drawing with a total reduction of 54.3% it has been found that in wires drawn conventionally (KI), in pressure dies (HI) and in roller dies (RI) a strong <110> fibre-texture exist with a value of the ODF equal to about 3.2 for all tested wires. At an increase of the total reduction from 54.3% to 71.5% values of ODF were different for different methods of drawing. For wires with a diameter 3.0 mm drawn conventionally (KF) it was equal 4.25 and for wires drawn in pressure dies (HF) the ODF value was the highest and equal to 4.4. For wires drawn in roller dies the ODF value was the lowest and equal only to 2.6. It means that in spite of the increase of the total reduction roller die drawing results in a decrease of the sharpness of the fibre texture <110>. In conventional drawing and in pressure dies drawing an increase of the <110> texture has been noticed with the increase of the total reduction. In addition to a strong <110> texture component, specimens K and H also featured weak <311> and <310> components. In R specimens there were more of such additional components after the first stage of drawing i.e. <311>, <310>, <210>, <211> and after the second stage of drawing (total area reduction 71.5%) - <311>, <310>.

Abstract: Deformation and recrystallization texture has been investigated in Oxygen free high conducting (OFHC) copper wires drawn at room temperature to true strain of 2.31, and isothermally annealed at various temperatures between 150°C and 750°C. Local orientations of the microstructures were measured by means of electron backscattered diffraction (EBSD) technique. While the drawn wire was characterized by a major<111> + minor<100> duplex fiber texture, recrystallization occurred at annealing temperatures between 250°C and 400°C and resulted into a major<100>+minor<111> recrystallization texture. At temperatures above 500°C, the <100> dominated recrystallization texture changed to the <111> dominated growth texture due to secondary recrystallization, which favored the <111> orientation at the expense of the <100> component.

Abstract: Deformed under optimum conditions of temperature and strain rate, coarse-grained aluminum alloys show elongation to failure in excess of 300%. The strain rate sensitivity index and the activation energy point to solute drag creep as the principal mechanism, a mechanism that has virtually no grain size dependence. The present study summarizes microstructural effects that are grain size dependent and which can influence the values of the maximum tensile elongation that can be obtained in coarse-grained aluminum alloys. Such effects like inhomogeneous refinement of the microstructure accompanied by the increase of the ratio of low/high angle grain boundaries and that of the texture contributes to flow stress instabilities leading to necking and premature failure.

Abstract: Texture evolution and superplastic deformation behavior of a quasi-single phase Zn-0.3wt%Al have been investigated. It was attempted to produce a stable and fine-grained microstructure in a dilute Zn-Al alloy through a proper thermomechanical treatment process (TMTP). The grain size of about 1 µm was obtained in the Zn-0.3 wt.% Al alloy and a relatively coarse grain size of 10 µm was also obtained through a subsequent aging treatment. The fine-grained material showed typical rolling texture with basal poles tilted about 30 degrees away from the ND toward RD, while the coarse-grained material showed a typical recrystallization texture with basal poles parallel to ND. A series of load relaxation and tensile tests were conducted at room temperature. According to the internal variable theory of structural superplasticity, the grain boundary characters of fine and coarse-grained materials were different from each other. A large elongation of about 1400% was obtained in fine-grained material at room temperature.

Abstract: This work presents the results of a study on textural and microstructural inhomogeneities that develop during annealing of heavily drawn Oxygen free high conducting (OFHC) copper wire. The wire was drawn at room temperature to a true strain of 2.31 and isothermally annealed at 750°C for annealing times ranging from 10s to 1hr. The inhomogeneity of microstructure across the wire was clearly visible as three distinct concentric regions, which were classified as: the inner core, the mid section, and the outer surface. Two texture transitions were observed. At shorter annealing time, recrystallization which originated from the mid section, resulted into a strong<100>+weak<111> duplex fiber texture. However, prolonged annealing gave rise to abnormal grain-growth that proceed from the mid section to the outer surfaces with a dominant <111> fiber component at the mid and inner region, and mixed components of <111>, <100>, and <112> at the outer surfaces.

Abstract: Microstructural characteristics of friction-stir-welded Al 6061-T651 with varying rotating and advancing speed were examined by the electron backscattering diffraction (EBSD) installed in field emission-scanning electron microscopy (FE-SEM). It was found that FSW produced an equiaxed fine-grained microstructure in weld zone and the grain size in weld zone decreased up to about 4~6 µm with decreasing rotating speed. The primary textures developed in weld zone were {100}<001>, {110}<001> and {111}<110>. In thermo-mechanical affected zone, the change in grain size was not significant, however, large number of low angle grain boundaries were observed, which seems to be concerned with the formation of subgrains due to the development of dislocation cells.

Abstract: This paper studies the microstructure of drawn gold wires to equivalent strain of 10 and to equivalent strain of 8.5 then heat-treated. The texture of gold wire drawn to strain of 10 is mainly composed of <100> and <111> fibers. Tensile strength of the gold wire increases with <111> fiber fraction, while the grain size does not appear to affect the tensile property. With an exception at heat treatment at 600oC, the texture of gold wire drawn the strain of 8.5 is replaced with <100> fiber component by heat treatment process at 400~700oC. Heat treatment at 600oC produces <110> fiber or <112> fiber, depending upon annealing time.