► Stage II strain length determined by the amount of grains favorable for twinning. ► Contribution to increasing strain hardening rate results from texture strengthening. ► Significant yield behavior ...can be induced by only a small amount of twins.
The effect of initial texture on the mechanical properties and strain hardening behavior of AZ31 magnesium alloy has been investigated. Cylindrical specimens of extruded and hot rolled AZ31 are compressed along different directions, with the compression axis (C) perpendicular or parallel to the extrusion direction (ED) or the sheet normal direction (ND), referred to as C⊥ED, C//ED, C⊥ND and C//ND specimen, respectively. The compression tests are conducted at room temperature with a strain rate of 0.01s−1. The results indicate that the yield strength and the strain hardening rate are highly anisotropic with respect to the initial texture. The significant yield behavior can be induced by only a small volume of twins. When the initial grain orientations are unfavorable for {101¯2} twinning, the strain hardening rate decreases gradually. When the initial grain orientations are favorable for {101¯2} twinning, the strain hardening behavior exhibits three distinct stages. The main contribution to increasing strain hardening rate (corresponding to the stage II) results from texture strengthening, which rotates grain orientations into hard orientations by the {101¯2} twinning. The length of the stage II is predominantly related to the volume fraction of grains which are favorable for {101¯2} twinning.
► Pr-rolling along TD initiates (10–12) twins which incline basal plane by 86°. ► Inclination of basal plane can effectively improve rolling capability at 300
°C. ► Non-basal slip of 〈a〉 dislocation ...in pre-rolled sample can accommodate strain in ND.
A method to weaken the strong basal texture of rolled magnesium alloy by twinning deformation is reported. Pre-rolling along the transverse direction at room temperature initiates extension twinning and reorients the basal plane. A dramatically increased maximum thickness reduction per pass during subsequent rolling at 300
°C is achieved in pre-deformed sample compared to that of the directly rolled one. The corresponding mechanisms are addressed and discussed.
Detection of cyclostationary primary user (PU) signals in colored Gaussian noise for cognitive radio systems is considered based on looking for single or multiple cycle frequencies at single or ...multiple time lags in the cyclic autocorrelation function (CAF) of the noisy PU signal. We explicitly exploit the knowledge that under the null hypothesis of PU signal absent, the measurements originate from possible colored Gaussian noise with unknown correlation function. Our formulation allows us to simplify the spectrum sensing detector and obviates the need for estimating an unwieldy covariance matrix needed in some prior works. We consider both single and multiple antenna receivers, and both nonconjugate and conjugate CAFs. A performance analysis of the proposed detector is carried out. Supporting simulation examples are provided to demonstrate the efficacy of the proposed approaches and to compare them with some existing approaches. Our proposed approaches are computationally cheaper than the Dandawate-Giannakis and related approaches while having quite similar detection performance for a given false alarm rate.
A novel annealing process of controlled heating rate is used to produce severe cold-formed aluminum plates, which are processed into aluminum foil and mainly used for high-voltage electrolytic ...capacitor anodes. The experiment in this study focused on various aspects such as microstructure, recrystallization behavior, grain size, and grain boundary characteristics. The results revealed a comprehensive influence of cold-rolled reduction rate, annealing temperature, and heating rate on recrystallization behavior and grain boundary characteristics during the annealing process. The heating rate applied plays a crucial role in controlling the recrystallization process and the subsequent grain growth, which ultimately determines whether or not the grains will become larger. In addition, as the annealing temperature rises, the recrystallized fraction increases and the grains size decreases; conversely, the recrystallized fraction decreases as the heating rate increases. When the annealing temperature remains constant, the recrystallization fraction increases with a greater deformation degree. Once complete recrystallization occurs, the grain will undergo secondary growth and may even subsequently become coarser. If the deformation degree and annealing temperature remain constant, the increased heating rate will result in a lower recrystallization fraction. This is due to the inhibition of recrystallization, and most of the aluminum sheet even remains in a deformed state before recrystallization. This kind of microstructure evolution, grain characteristic revelation, and recrystallization behavior regulation can provide effective help for enterprise engineers and technicians to guide the production of capacitor aluminum foil to a certain extent, so as to improve the quality of aluminum foil and increase the electric storage performance.
In this work, Mg−2Zn−0.5Ca (wt.%) alloy sheets fabricated according to various rolling parameters were evaluated to investigate the effect of rolling parameters on room-temperature stretch ...formability. The sheet rolled at 360 °C with a pass rolling reduction of 10~33% exhibited the worst I.E. value of 4.4 mm, while the sheet rolled at 360 °C with a pass rolling reduction of 20~50% exhibited the best index Erichsen (I.E.) value of 5.9 mm. Among the sheets, the (0002) basal texture intensity was the weakest, and the grain basal poles split away from the normal direction toward both the rolling direction and the transverse direction. Microstructural and deformation mechanism measurements of stretch forming to 2 mm for the sheet rolled at 360 °C with a pass rolling reduction of 20~50% by electron backscatter diffraction and in-grain misorientation axes showed that there was a higher activity of {10−12} extension twins and that a prismatic slip was initiated. As a result, the weakening of the texture and the broader distribution of basal poles in the plane contributed to the improved formability of the sheet rolled at 360 °C with a pass rolling reduction of 20~50%.
The isothermal deformation compression tests of AA7085 aluminum alloy were performed on Gleeble-1500 system in the temperature range from 250°C to 450°C and at strain rate range from 0.01s−1 to ...10s−1. The microstructure of samples was observed using optical microscopy (OM) and transmission electron microscopy (TEM) techniques. The results show that the peak stress levels decreased with the increase of deformation temperatures or the decrease of strain rate, which can be represented by the Zener–Hollomon parameter in the exponent-type equation with the hot deformation activation energy of 249.11KJ/mol. Dynamic recrystallization more obviously occurred in the sample with higher Z value than in the sample with lower Z value. Dynamic recrystallization is sensitively dependent on the deformation temperature.
In this work, the microstructure and texture evolution of an as-cast Mg-2Zn-2Gd alloy subjected to different hot rolling regimes (cross rolling (CR) and unidirectional rolling (UR), CR+UR and UR+UR, ...respectively) and subsequent annealing at 400 °C were systematically investigated. The hot CR helps to develop relatively homogeneous distribution of (0002) poles in a circle inclining about 40° away from the ND in the annealed sample. However, this type of texture cannot be retained after subsequent unidirectional rolling along the RD and annealing, forming a texture with (0002) poles inclining approximately 40° from the ND toward the TD. It is found that the (0002) poles of recrystallized grains generally distribute along the direction perpendicular to the rolling direction, irrespective of the orientations of parent grains. There is a intense in-plane anisotropy of yield strength in plates containing a TD-tilted texture, while the homogeneous distribution of (0002) poles along the TD and RD can completely remove this planar mechanical anisotropy.
As research and development of nanocomposites receive more attention in today's fast-paced world. SiC nanowires (SiC NWs) and their composites exhibit numerous unique and exceptional properties. As a ...result, they are widely used in various fields such as the chemical industry, optoelectronic devices, electronic products, aerospace, and military applications. In this paper, we present a comprehensive summary of the synthesis technology, distinctive properties, and potential applications of SiC NWs and the composite constructed from them. The introduction begins with an overview of the basic concept and characteristics of SiC. It then provides a detailed list of common synthesis methods, including precursor infiltration pyrolysis, chemical vapor deposition, solvothermal synthesis, carbothermal reduction, template method, other methods of molten salt, controllable chemical etching, and self-assembly synthesis. The advantages and shortcomings of these methods are also discussed in the context of specific applications. Then, the special performance and multidisciplinary applications are displayed after summarizing the previous studies. Eventually, this review concludes with an outlook on future research regarding SiC NWs and their composite materials, highlighting major prospects, challenges to be addressed, and possible solutions in a wide range of areas. A systematic overview of the topic of interest actually helps to reveal patterns in research cognition, plays a potential role in fostering awareness of scientific innovation and cross-thinking, and also serves as a guide for scientific research and interest development.
AZ31 magnesium alloy with two different forms of initial textures were extruded at 573K to investigate the effect of initial texture on dynamic recrystallization (DRX) and deformation mechanisms. It ...reveals that the initial texture significantly affected twinning behavior. Hardly any twins were found in the extruded and annealed (EA) rod while {10−12} extension twins were observed to be very active in the rolled and annealed (RA) rod. DRX in the RA rod was retarded compared with that in the EA rod. The delay of DRX in the RA rods was attributed to the different deformation mechanisms occurring before DRX initiation. For the EA rod, dislocation slip was considered as the main deformation mechanism at the initial stage of extrusion which resulted in a faster increasing of the stored energy within the grains and consequently DRX was initiated. For the RA rod, {10−12} extension twin was a dominant deformation mechanism at the initial stage of extrusion before DRX initiated which resulted in an extrusion texture with the basal planes parallel to the extrusion direction (ED). Because of the profuse twinning, the stored energy caused by dislocation motion was relatively small in the RA rod, which was considered as the main reason of the delay of DRX in the RA rod. However, although the initial texture had great influence on DRX and deformation mechanisms during extrusion it had no significant effect on final fully DRX extrusion microstructure. DRX is a texture weakening process during extrusion. A weak fiber texture with the basal planes parallel to ED but without any specific crystallographic direction parallel to ED was obtained in the fully DRX extrusion microstructure.
Two types of hot compression tests, namely, constant strain rate and strain rate jump, were carried out for Alloy 800 H within a wide temperature range of 450–900 °C and strain rate range of ...0.001–1 s−1. Following the above tests, we studied the effect of dynamic strain aging (DSA) on the mechanical properties and microstructure features to reveal the underlying mechanism responsible for DSA. The results indicated that three kinds of serrated yielding behavior (Type A, B and C) can be observed in the stress-strain curves of the DSA regime. The DSA temperature (TDSA) is located in the temperature range of 500–750 °C at a strain rate of 0.001 s−1, in 550–790 °C at 0.01 s−1, and in 600–840 °C at 0.1 s−1. The activation energy for the appearance of negative strain rate sensitivity was calculated to be 194 kJ/mol, and pipe diffusion of substitutional solutes (i.e. Cr, Ni and Ti) is regarded as the mechanism of DSA. TEM observations further elucidated a tendency of linear microstructure within the DSA regime, which also restricts the cross-slip of dislocations and promotes the strain localization along deformation bands.
