Materials Science Forum Vols. 702-703

Abstract: The effects of the 12T magnetic field on transformed morphology and crystallographic characteristics of high purity Fe-1.1C (wt.%) alloy during diffusional decomposition of austenite are studied by SEM/EBSD. With the applied field, the lamellar spacing of pearlite is greatly enlarged and the spheroidization tendency of the pearlitic cementite is enhanced. This can be attributed to the thermodynamic effect of the field on phase equilibrium by elevating the eutectoid temperature; hence the eutectoid transformation happens at higher temperature that favors carbon diffusion. As a consequence, the eutectoid cementite that is usually in lamellar shape spheroidizes to reduce its specific surface area. In addition, three orientation relationships between ferrite and cementite in pearlite, namely Isaichev ORs and two near Pitsch-Petch ORs (P-P1 and P-P2), are found both in non-field and field treated specimens. The magnetic field favors the occurrence of P-P2 OR due to the promotion of nucleation of the pearlitic ferrite. However, there is no obvious effect of the field on the crystallographic orientation of pearlitic ferrite, and that is probably related to the quick saturation of magnetization that results in the disappearance of magnetization anisotropy.

Abstract: Friction stir processing (FSP) is an emerging grain refinement technique for magnesium alloys. In this study, a cast AZ91 alloy was processed by a single-pass FSP to achieve an average grain size of ~6 mm in the nugget zone. The FSP is found to introduce texture in the alloy due to preferred alignment of basal poles in the processing direction. The mechanical behavior is significantly influenced by texture. After FSP, the alloy was aged at different temperatures and times for continuous and discontinuous precipitation of b-Mg₁₇Al₁₂. A high anisotropy in yield stress is observed in the processing and transverse direction after FSP. It is shown that this anisotropy can be minimized under optimum ageing conditions. The observed yield asymmetry is correlated with the texture variation after FSP. The role of b-Mg₁₇Al₁₂ precipitates in reducing the yield anisotropy is also discussed.

Abstract: In order to develop favorable textures for deep drawing of Al-Mg-Si and Mg-Al-Zn alloys that are promising as automotive body panels, we have adopted the symmetric/asymmetric combination rolling (SACR) process consisting of conventional symmetric rolling and subsequent asymmetric rolling at relatively low reduction. The combination of symmetric cold rolling and asymmetric warm rolling for AA6022 sheets leads to the formation of “TD-rotated β-fiber texture”, resulting in the evolution of {111} recrystallization texture after solution treatment at a high temperature. The SACR processed and solution-treated sheets show a high average r-value with small in-plane anisotropy, and consequently the limiting drawing ratio increases significantly, compared to that of the cold-rolled and solution-treated sheets. In the case of AZ31 magnesium alloy, the SACR process by hot rolling causes the formation of a unique texture, which shows two (0001) poles with tilt angles of 0 and −40 degrees from the normal direction (ND) toward the rolling direction (RD). In addition, subsequent annealing weakens intensity of the double-peak texture, so that the drawability is greatly improved in comparison with that of the conventional warm-rolled sheets with a strong basal texture. At the same time, yield strength decreases to some extent, but the SACR processed and annealed sheets exhibit a good balance of strength and formability due to a mixed texture with basal and tilt components.

Abstract: Magnesium alloys have attracted a great deal of attention and have been extensively studied, but there is still a major obstacle to their practical application, namely, their poor formability at room temperature, which basically originates from their insufficient number of slip systems. The development of a microstructure and/or texture that is more conducive to formability is one promising solution that could improve their formability. In the present work, the microstructures, textures, and tensile properties of AZ31 Mg alloys are studied following extrusion and full annealing and rolling at 100 and 300°C. After full annealing, a strong ∥ED fiber texture and a weak + ∥ED fiber texture (c-axes in the radial direction) were developed. After 40% rolling at 100°C, many deformed twins were observed and a relatively weak texture was developed. The basal poles were split and rotated about 20° to the rolling direction (RD). During 60% rolling at 300°C, dynamic recrystallization (DRX) took place and a strong ∥ND fiber texture was developed, and this had an influence on the alloys’ poor formability at room temperature.

Abstract: The viscoplastic self-consistent (VPSC) formulation is by now a well established approach for simulating texture development and constitutive response during plastic forming of high and low-symmetry polycrystals. In this work we have used the VPSC approach to model the uniaxial tensile and compressive deformation characteristics of pure magnesium with random and extruded texture. We compare our results with experimental data and find that they are in good agreement with the available experimental evidence.

Abstract: In the present work, Mg - 9wt. % Li - 7% wt. Al – 1 wt. % Sn (LAT971) alloy was cast and hot rolled at ~573K. Phase analysis of LAT971 revealed the presence of dual phase structure namely Mg-rich α- and Li-rich β-phase. After hot rolling, it was observed that dynamic recrystallization led to refinement of the α-phase grain structure. Significant crystallographic texture evolution, characterized by electron backscatterd diffraction, revealed increased activity of the non-basal (101 ̅0) slip plane after conventional hot rolling process.

Abstract: Development of microstructure and texture in alloy Al5052 deformed at room and cryogenic temperatures in an equal channel angular pressing (ECAP) die has been investigated. Billets were deformed using the Bc route up to 14 passes. Billets pressed at room temperature showed almost a 4 fold increase in the yield strength, which increased to about 320 MPa from about 90 MPa, while it increased to about 230 MPa in billets deformed at cryogenic temperature. At two deformation temperatures, grains were refined at more or less similar size reduction rate as a function of number of passes. However, for a given amount of strain, billets pressed at the two temperatures showed subtle differences in their microstructures and texture.

Abstract: The present study reports the microstructure evolution and mechanical behaviour of severe plastically deformed pure Cu under cryogenic conditions. The samples were severely deformed by cryo rolling upto 50%, 75% and 95% deformation. Microstructure evolution of cryo rolled samples has been characterized by using optical, TEM and EBSD technique. The rolled samples were heat treated at various temperatures so as to control the recrystallization in the severely deformed samples. The effect of recrystallization on the mechanical behaviour was investigated in detail by tensile testing. The EBSD analysis performed on 95% rolled + heat treated samples showed that partial recystallized microstructure demonstrate an optimum combination of strength and ductility in cryo rolled Cu.

Abstract: Present work addresses the evolution of texture and microstructure of equal channel angular extrusion (ECAE) processed AA 2014 Al alloy upto four passes at room temperature by adopting route B_C. TEM is used to assess the microstructural changes during each ECAE pass. Texture measurements on samples of each pass were carried out by XRD technique. The evolution of texture components after each ECAE pass are analyzed and the changes are discussed with respect to the initial texture.

Abstract: The crystallographic alignment of microbands in a Goss oriented single crystal was investigated by two and three dimensional electron back scatter diffraction. The microband boundaries were found to be curved instead of being perfectly flat interfaces, and the overall alignment closely matched a potential slip plane. The bumps and curved were created during subsequent deformation and, thus, deviates the microband boundaries from crystallographic nature.