Search

At present, there are few studies on the phase transition during the thermocompression plastic deformation of magnesium alloy. In this study, the evolution model of thermal compression plastic of AZ31 magnesium alloy was constructed by molecular dynamics, and the phase transition relationship between HCP and FCC at different thermal compression rates was studied. By combining GLEEBLE thermal compression experiment with transmission electron microscopy experiment, high-resolution transmission electron microscopy images were taken to analyze the transition rules between HCP and FCC during plastic deformation at different thermal compression rates, and the accuracy of molecular dynamics analysis was verified. It is found that the slip of Shockley's incomplete dislocation produces obvious HCP →FCC phase transition at low strain rate and base plane dislocation at high strain rate, which makes the amorphous phase transition of HCP→OTHER more obvious, which provides theoretical guidance for the formulation of forming mechanism and preparation process of magnesium alloy.

Herein, a novel dual-strengthening technology that combines the external second-phase nanoparticle addition method with the hot compression deformation tests was carried out to investigate the effects of surface-modified nanoparticles (NPs) and deformation conditions on the characteristics of inclusions and the evolution of microstructure in the micro-alloyed (MA) medium carbon steels. The results revealed that the inclusions in the steels were divided into single phase inclusions and composite phase inclusions. With the addition of NPs, Al2O3 inclusions were replaced by MgAl2O4 spinel, and the composite inclusions mainly consisted of TiN–VN, MgAl2O4–TiN and MgAl2O4–TiN–MnS inclusions, and the same types of inclusions became significantly smaller in size. According to the EDS results, some of the inclusions acted to induce ferrite nucleation, and the MgAl2O4–TiN–MnS composite inclusion was more favorable for the nucleation of acicular ferrite (AF). The deformation induced ferrite (DIF) started to form at the deformation temperature of 750 °C and the maximum stress peak in the NPs-bearing steel was 516 MPa, which was 28.4% higher than that in the original steel. The proportion of ferrite increased as the deformation temperature decreased. The dispersed NPs contributed to the ferrite nucleation and the grain refinement as the inclusion-modifying agent, which improved the material properties, and the relevant strengthening mechanisms were explained.

To explore the effect of temperature on the phase transformation of HCP→FCC during compression, the uniaxial compression process of AZ31 magnesium alloy was simulated by the molecular dynamics method, and the changes of crystal structure and dislocation evolution were observed. The effects of temperature on mechanical properties, crystal structure, and dislocation evolution of magnesium alloy during compression were analyzed. It is concluded that some of the Shockley partial dislocation is related to FCC stacking faults. With the help of TEM characterization, the correctness of the correlation between some of the dislocations and FCC stacking faults is verified. Through the combination of simulation and experiment, this paper provides an idea for the in-depth study of the solid-phase transformation of magnesium alloys and provides reference and guidance for the design of magnesium alloys with good plasticity and formability at room temperature.

Corrugated-flat rolling (CFR) process was employed to manufacture the Mg/Al clad plate at 400 °C. The CFR process can produce flat Mg/Al clad plate with excellent shape and corrugated interface. EBSD analysis and tensile-shear tests were conducted to study the corrugated interface characteristics of the flat plate, revealing its strengthening mechanism. After the second-pass flat rolling process, the interface intermetallic compounds (IMCs) layer formed by heat treatment between passes broke, causing new bonding interface observed in the gap between the fractured IMCs. Intermittently distributed IMCs played a “pinning” role on the Mg/Al interface and restrained each other with the new bonding interface, which can improve the cooperative deformation ability of Mg plate and Al plate, and enhance the interface bonding strength. The interface tensile-shear strength at trough position was 33.97 MPa, which was higher than that at the peak position (24.17 MPa). During the second-pass flat rolling process, strong compressive stress was applied, improving the stress uniformity of the flat plate and refining metal grains, resulting in an improvement in tensile properties. The rolling UTS of flat plate was 255.77 MPa, and the fracture EL was 5.72%.

JCOE is a progressively advanced forming process that encompasses J-forming, C-forming, O-forming, and expansion technology. This methodology constitutes an efficacious means of producing high-strength pipes. In recent years, this process has been utilized in the manufacturing of small-diameter, thick-walled welded pipes using nickel-based alloy N08810 plates. This study establishes a mathematical model for key parameters in the pre-bending process, rooted in JCOE forming and plastic bending theory, and introduces a process optimization approach. Initially, by refining the mold configuration and executing simulation analyses, we comprehensively delineate the stress–strain distribution and metal flow dynamics during pre-bending. Furthermore, we unravel the influence of varying plate thicknesses on both the pre-bending force and springback bending angle. Ultimately, the veracity of our theoretical model and simulation protocol is substantiated through rigorous experimentation. The findings indicate that the optimized mold configuration yields superior pre-bending forces and springback bending angles compared to conventional methods, thereby furnishing a solid theoretical foundation for industrial applications.

The plastic deformation of metal material is accompanied by surface defects, internal defects, damage cracks, etc., and these defects seriously restrict the processing of metal and its performance improvement. Therefore, the continuous damage mechanics theory and the fine view of the damage mechanics theory were reviewed, and then according to the damage model construction, to effectively predict the material crack damage, thus making a good foundation for the subsequent secondary development and simulation application. By comparison, the Johnson-Cook model has been widely used by researchers in its simple multiplication form, owing to its excellent ability to predict strain rate and mechanical behavior in the temperature range. The model is very suitable for finite element program simulation and its verification, and has been continuously improved and optimized.

As the demand for lithium-ion batteries increases, higher quality requirements are being placed on pure aluminum ultra-thin strips, one of the main materials used in lithium-ion battery current collectors. Roller vibration during the rolling process of pure aluminum ultra-thin strips is unavoidable and significantly affects the quality of the strips. This paper uses 1A99 pure aluminum ultra-thin strips as raw materials and employs a controlled vibration method during the rolling process to obtain products under two conditions: stable rolling and vibrational rolling. The surface and cross-section of the aluminum strips were characterized using scanning electron microscopy (SEM), and the microstructure of the surface and cross-section was studied using electron backscatter diffraction (EBSD) technology. The results show that, during stable rolling, the surface quality of the aluminum strip is good without defects. Under vibration, obvious vibration marks appear on the surface of the aluminum strip, showing characteristics of peaks and troughs. With the increase in strain at the trough position, there is a transition from low-angle grain boundaries to high-angle grain boundaries, and the grain size is uneven at the peak and trough positions, with noticeable grain refinement at the troughs. At the same time, under the influence of vibration, the aluminum strip induces a different texture morphology from conventional rolling. Due to the different plastic strains at the peak and trough positions, a texture alternation phenomenon occurs at these positions. The tensile test results indicate that aluminum strips exhibit poor mechanical properties under roller vibration, with the reduction in mechanical performance primarily attributed to the uneven microstructure distribution caused by roller vibration.

Abstract To develop and design mg-based nanoalloys with excellent properties, it is necessary to explore the forming process. In this paper, to explore the effect of different loading directions on the phase transformation of magnesium alloy, the model of AZ31 magnesium alloy was established, the process of Uniaxial Compression (UC) of magnesium alloy in different directions was simulated, the changes of atomic position and phase structure were observed, and the phase transformation mechanism of AZ31 magnesium alloy under uniaxial compression under different loading directions was summarized. The conclusions are as follows: the stress and strain, potential energy and volume change, void evolution, phase structure change and dislocation evolution of magnesium alloy are consistent, and there is no significant difference. In the process of uniaxial compression, the phase transformation of hexagonal closely packed (HCP) → face-centered cubic (FCC) is the main, and its structure evolves into HCP → Other → FCC. Shockley partial dislocations always precede FCC stacking faults by about 4.5%, and Shockley partial dislocations surround FCC stacking faults. In this paper, the phase transformation mechanism of AZ31 magnesium alloy under uniaxial compression under different loading directions is summarized, which provides a theoretical basis for the processing and development of magnesium-based nanoalloys.

To ensure the long service life of concrete buildings in the marine environment, it is urgent to develop building materials with good corrosion resistance and weatherability. Stainless steel cladding is suitable for a highly corrosive environment and provides cost advantages. This paper investigated the deformation coordination and the microstructure evolution near the cladding interface of stainless steel/carbon steel. The stress-strain curves at different temperatures and strain rates were analyzed on the basis of high-temperature compression experiments. In addition, the sin-hyperbolic constitutive model was constructed, and the optimized parameters were obtained using electron backscatter diffraction characterization technology. The results show that at the deformation temperature of 1100 °C and the strain rate of 1 s−1, the deformation coordination increases significantly near the interface, accompanied by a large number of recrystallized grains, which has a positive impact on the comprehensive performance of the materials.

The 347 stainless steel tube cold rolling test was carried out by a LG60 two-roll pilger mill. The microstructure evolution was examined by microscope, SEM, and XRD tests. The finite element software DEFORM-3D has been used to simulate the pilgering process, and the obtained equivalent stress and metal flow were analyzed. The experimental results showed that the internal slip line was randomly distributed, the deformation of the inner wall was more intense than the outer wall structure, and the austenite γ phase was transformed into the α′-martensitic phase. The simulation results indicated that the direction of metal flow was constantly changing, and the equivalent stress of the inner wall of the steel tube was greater than the equivalent stress of the outer wall. In addition, the slip zone of the inner wall of the characteristic section was more severe than that near the outer wall slip zone. The simulation verified the experimental results to some extent.

The viscoplastic self-consistent (VPSC) model is used to establish a combination of different deformation mechanisms. By using this model, axial tension and compression tests of extruded AZ31 magnesium alloy at room temperature are simulated. The influence of secondary deformation mechanism (prismatic slip, pyramidal slip, and 101¯1 compression twin) on mechanical response and texture evolution is expounded. Increased activity of the prismatic slip is conducive for the improvement of flow stress in mechanical response during axial tension and for the splitting of pole densities in the {0002} pole figure during axial compression. However, increased activity of the pyramidal slip causes the basal texture to transfer to the extrusion direction in the {0002} pole figure during axial compression. The 101¯1 compression twinning has a negligible influence on the plastic deformation and mechanical response of AZ31 magnesium alloy during axial tension and compression. However, the 101¯1 compression twinning should be included in VPSC modeling to predict the texture evolution accurately.

Based on the thermodynamic conversion mechanism and energy transition principle, a three-dimensional cellular automata model of grain growth is established from the aspects of grain orientation, grain size distribution, grain growth kinetics, and grain topology. Also, the effect of temperature on the three-dimensional grain growth process of AZ31 magnesium alloy is analyzed. The results show that the normal growth of three-dimensional grains satisfies the Aboav-weaire equation, the average number of grain planes is between 12 and 14 at 420°C and 2000 CAS, and the maximum number of grain planes is more than 40. Grains of different sizes are distributed normally at different times, most of which are grains with the ratio of grain diameter to average grain diameter R/Rm ≈ 1.0, which meets the minimum energy criterion of grain evolution. The grain of AZ31 magnesium alloy increases in size with the increase of temperature, and the number of grains decreases with the increase in time. The angle between the two-dimensional slices of three-dimensional grains is approximately 120°, which is consistent with that of the traditional two-dimensional cellular automata. The relative error of grain size before and after heat preservation is in the range of 0.1–0.6 μm, which indicates that the 3D cellular automata can accurately simulate the heat preservation process of AZ31 magnesium alloy.

In this paper, we focus on the bonding mechanism of bimetallic clad tube because of its low cost and comprehensive properties. The numerical simulation and the experiment are carried out from the diffusion behavior of carbon atoms in the metallurgical bonding process. Based on the dislocation density model of Kocks, the tube billets are rolled by pilger hot rolling; the outer tube is 06Cr19Ni10 stainless steel, the inner tube is Q235 carbon steel, and the wall thickness ratio is 1 : 1. The research shows that the diffusion ability of carbon atoms mainly depends on the degree of the plastic strain in the stainless steel hot rolling process; there is positive correlation between the thickness of bonding carburized layer and the dislocation density produced by plastic deformation of stainless steel. The thickness difference of circumferential carburized layer in the deformation zone is larger than that near the finishing zone. Furthermore, a lot of contaminants cannot be completely metallurgically bonded between 20% and 30% reduction ratios; the contaminants near the bonding layer are refined and completely bonded metallurgically between 30% and 60% reduction ratios; the contaminants are further refined above 60% to 70% reduction ratio.

Samples were cut from an extruded AZ31 magnesium alloy bar for uniaxial tensile and EBSD characterization tests. The long axis and bar extrusion directions were 0° (T0 sample), 45° (T45 sample), and 90° (T90 sample). The effects of loading direction on the tensile behavior, microstructure, and texture evolution of the magnesium alloy were studied. Results show that the obvious mechanical anisotropy of tensile behavior is affected by the loading direction, and the T0 sample with a grain c-axis perpendicular to the extrusion direction has a strong basal texture and high flow stress and yield strength. The loading direction has a significant influence on the microstructure characteristics of different samples, especially the number of {10–12} tensile twins and {10–11} compression twins. Texture evolution results show that the loading direction and the effect of deformation mode on the deformation mechanism lead to variations in texture evolution: the basal slip and prismatic slip during the plastic deformation of the T0 specimen, the compression twin of the T45 specimen, and the tensile twin of the T90 specimen.

Based on the stress characteristics of the instantaneous cross-section deformation of the wall reducing section during the cold rolling of two-roll Pilger pipes, the rectangular samples with 0° and 90° to the extrusion direction (ED) were cut from the extruded AZ31 magnesium alloy bar for 3% pre-deformation test to simulate its stress state equivalently. The sample was then cut from the pre-deformed sample by wire cutting for secondary compression, and the sample that is not pre-deformed is selected. The mechanical behavior and texture evolution of AZ31 magnesium alloy under different loading conditions were respectively studied by EBSD experiment and VPSC simulation. Results show that the true stress–strain curve and texture evolution characteristics of AZ31 magnesium alloy during the secondary compression process are in good agreement with the prediction of the VPSC model. The secondary compression behavior can be effectively explained by the relative activity of the deformation modes. The pre-deformation in the ∥ED (⊥ED) direction is conducive to the shift of the pole density of the {0001} basal surface texture to the positive and negative directions of the ED (TD). The pre-deformed sample exhibits a higher yield strength than the non-pre-deformed sample in the same loading direction. The high ductility of magnesium alloys can be achieved by activating pyramidal 〈c + a〉 slippage.

Cuboid samples with significant initial texture differences were cut from extruded AZ31 Mg alloy samples, whose long axis and bar extrusion direction ED were 0° (sample E0), 45° (sample E45), and 90° (sample E90). The relationship among the initial texture, deformation mechanism, mechanical properties, and texture evolution of the AZ31 Mg alloy was investigated systematically using a compression test, microstructure characterization, and the Viscoplastic Self-Consistent (VPSC) model. Results revealed a close relationship among them. By influencing the activation of the deformation mechanism, the deformation under different initial textures resulted in obvious mechanical anisotropy. Compared with E0 and E90, the initial texture of E45 was more conducive to the improvement of reforming ability after pre-compression. Meanwhile, the initial texture significantly affected the microstructure characteristics of the material, especially the number and morphology of the {10–12} tensile twins. Texture results showed that the priority of deformation mechanism depended on the initial texture and led to the difference in texture evolution.

The influence of the initial texture of the {10–12} twinning variants selection mechanism of the magnesium alloy was investigated using the compression test, the EBSD technology, the trace method, the orientation rotation method, and the Schmid’s law. Results show that various {10–12} twin patterns are observed in the AZ31 E90 sample subjected to compression. In the multi-twins inside a grain pattern, the high Schmid factor (SF) variant is activated first to coordinate the externally imposed strain, and the ortho-position (OP) variant with the best strain compatibility is activated. Typical case of paired twins in two neighboring grains usually have high SF, and the activation of corresponding variants follows the Schmid’s law. When E45 sample is compressed, the ${{\rm{SF}}}_{45^\circ }$ of a pair of relative variants among the six twin variants in the crystal is very large and favorable for local strong basal texture formed by the two adjacent grains for the twin-transfer phenomenon. When E0 sample is compressed, the activation of the corresponding variants follows the Schmid’s law and is linked to the stress fluctuation at the grain boundary.

Wrought AZ (Mg−Al−Zn) series alloys have attracted lots of researches, due to low cost, high strength and good formability. Few researches focus on creep characteristics of wrought AZ series alloys, which might be of significance to extensive use of low-cost wrought Mg−Al based alloy at elevated temperature. The microstructures, tensile properties and creep characteristics of as-extruded Mg-9Al-Zn-0.5RE-0.5Ca-0.5Si (wt.%, named AZXSE91000) alloy were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometer (XRD), TEM (transmission electron microscopy), tensile tests and tensile creep tests (40−100 MPa, 125−150 °C). The as-extruded AZXSE91000 alloy exhibited good tensile strength both at room temperature and elevated temperature. The co-addition of Si, Ca and rare earth elements can improve the heat resistance of as-extruded AZ91 alloy resulting from fragmented heat-resistant particles hindering grain boundaries sliding. The steady creep rates of as-extruded AZXSE91000 alloy can be comparable with that of as-cast AZ91 alloy under similar experimental conditions. Dislocation climbing and grain boundary slip should dominantly contribute to the creep of as-extruded AZXSE91000 alloy. The asymmetric discontinuous precipitation in crept samples revealed that diffusion played an unneglected role during the creep process.

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As a novel metal forming process, cross-wedge rolling (CWR) is widely used in the manufacture of large axles in the rail transportation industry. When the forming process of the axle is studied, its formability becomes one of the key issues in the metal forming process. This paper takes LZ50 axle steel as the research object. Through the application of ANSYS finite element simulation software, combined with previous research and literature, a dynamic simulation of the rolling process is carried out, and the stress, strain and temperature field of the axle steel in the forming process are analysed. The results show that with the deepening of rolling, the plastic deformation of the metal becomes increasingly obvious. When the finishing section is reached, the temperature on the surface and inside the rolled piece reaches relatively uniform distribution. [ABSTRACT FROM AUTHOR]

True strain-true stress curves of the LZ50 axle steel were obtained after hot compression tests had been performed on a Gleeble-3800 thermal simulator at strain rates of 0.01, 0.1, 1 and 5 s-1 and at deformation temperatures from 850 to 1,150. Following the data processing, the relationship between the flow stress and the deformation temperature of the material under different true strain conditions was analysed. On this basis and according to the influence of deformation factors, the constitutive equation of the Johnson-Cook flow stress model is established, and the model is modified according to the defects of the model, so that the improved model can effectively predict the mechanical behaviour in the range of high strain rates and temperatures. The dynamic material model (DMM) was used to generate the hot working diagram of the material. Through calculation and analysis, the optimum process area in terms of temperature was found to be in the range from 1,050 to 1,150 and in terms of strain rate in the rage from 1 to 5 s-1. Finally, the microstructure evolution of the compressed specimens under different strain rates and temperatures was studied in the metallographic analysis, which provided a theoretical basis and reference value for later damage. [ABSTRACT FROM AUTHOR]