In order for the edge cracks during the AZ31 Mg alloy rolling to be reduced, the hot-rolling microstructure and texture were modified through multi-cross rolling (MCR) during the deformation. The ...AZ31B magnesium alloy sheets were hot rolled at a temperature ranging from 250 °C to 400 °C and at a rolling speed of 0.5 m/s. Four different multi-cross rolling (MCR) routes were selected in the test. The macroscopic morphology, microstructure and texture of the as-rolled AZ31B sheets were characterized to investigate the edge-crack behavior during the rolling with various rolling routes and temperatures. Through the various rolling routes comparison, the grain size, the texture and the twins were the main factors that affected the cracks. It was demonstrated that the grain refinement and weak basal textures obtained by RII where the rolling direction was changed by 90° between two adjacent passes, could significantly reduce the edge cracks during the rolling at an elevated temperature. When rolling with RII at 400 °C, no apparent edge cracks appear on the sheet rolled with four passes. The propagation mechanism of the crack tips was studied in details at the temperature of 350 °C, whereas the results demonstrated that a high-sized area of grain boundaries in-between the finer grains could increase the crack propagation resistance.
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The aluminium alloy wire 2319 is commonly used for Wire + Arc Additive Manufacturing (WAAM). It is oversaturated with copper, like other alloys of the precipitation hardening 2### ...series, which are used for structural applications in aviation. Residual stress and distortion are one of the biggest challanges in metal additive manufacturing, however this topic is not widely investigated for aluminium alloys. Neutron diffraction measurements showed that the as-built component can contain constant tensile residual stresses along the height of the wall, which can reach the materials' yield strength. These stresses cause bending distortion after unclamping the part from the build platform. Two different rolling techniques were used to control residual stress and distortion. Vertical rolling was applied inter-pass on top of the wall to deform each layer after its deposition. This technique virtually elimiated the distortion, but produced a characteristic residual stress profile. Side rolling instead was applied on the side surface of the wall, after it has been completed. This technique was even more effective and even inverted the distortion. An interesting observation from the neutron diffraction measurements of the stress-free reference was the significantly larger FCC aluminium unit cell dimension in the inter-pass rolled walls as compared to the as-build condition. This is a result of less copper in solid solution with aluminium, indicating greater precipitation and thus, potentially contibuting to improve the strenght of the material.
In order to promote the magnetically favourable //ND texture (θ-fibre) and minimize the unfavourable //ND fibre (γ-fibre) in non-oriented electrical steel, an unconventional cold rolling scheme was ...employed in this study, in which the cold rolling was carried out at an angle (i.e. 30°, 45°, 60°, and 90°) to the hot rolling direction (HRD). After annealing, two steel sheets (i.e. those after cold rolling at 60° and 45° to the HRD) were found to have considerably different textures from other sheets, i.e. showing the strongest and the weakest θ-fibre textures, respectively. These two sheets were then subjected to skin pass rolling to various reduction rates from 5–20% to investigate the effect of rolling reduction on the evolution of texture. It was found that during skin pass rolling, the cube texture ({001} ) was gradually weakened and the rotated cube orientation ({001} ) was strengthened. With the increase of the reduction rate, the {112} orientation on the α-fibre became a major component. Upon final annealing, the cube texture was slightly restored, but the volume fraction was considerably lower than that before skin pass rolling.
•Inclined cold rolling optimizes the textures of non-oriented electrical steels.•A 60° angle to the hot rolling direction results in the largest improvement of the favorable texture.•Skin pass rolling weakens the cube texture and promotes the {112} texture.•Final annealing restores some of the cube texture and strengthens the rotated cube texture.•Low Taylor factor of the cube orientation leads to its easy deformation in skin pass rolling.
The aim of a massive reduction of CO2-emissions results in a move away from fossil fuels. In the hot strip production of steel, almost exclusively gas-fired furnaces are currently used due to the ...lower energy costs. On the contrary, it is imperative to convert existing fossil heated processes to CO2-free (green) technologies in the context of the energy-transition. Obvious alternatives are electrical heating or hydrogen combustion, both strongly dependent on the specific electricity generation mix that determines the CO2-emissions. In this case study, different process heat generation options for continuous reheating furnaces in steel hot rolling mills are discussed by a quantitative approach. A state-of-the-art reheating furnace fired with natural gas is used as reference case, while electrical heating, hydrogen-air heating and hydrogen-oxygen heating are the alternatives investigated. The energy balances, the primary energy consumption and the resulting CO2-emissions are compared for the three countries of France, Poland and Germany with regard to the country-specific electricity generation mix. Additionally, the possible development until 2050 is analysed. The results show the high impact of continuous reheating furnaces in steel hot rolling mills on the total CO2-emissions of downstream steel processing. Furthermore, the massive increase in electrical energy consumption of the whole steel production process is highlighted. Each investigated alternative shows a significant potential to save CO2-emissions, depending on the country specific electricity generation mix and the future expansion of renewable energy sources. An increase in H2-production efficiency will both lead to a lower primary energy consumption and lower CO2-emissions for reheating furnaces.
•Reheating furnaces have a high impact on CO2-emissions in downstream steel processing.•Primary energy consumption changes based on process heat generation alternative.•Alternative technologies show big potential to emit less CO2 than state-of-the-art.•Potential savings depend on technology and country-specific electricity generation mix.•CO2-emissions could be further reduced by increased H2-production efficiency.
Based on the analysis of the influence of roll vibration on the elastoplastic deformation state of a workpiece in a rolling process, a dynamic rolling force model with the hysteresis effect is ...established. Taking the rolling parameters of a 1780 mm hot rolling mill as an example, we analyzed the hysteresis between the dynamic rolling force and the roll vibration displacement by varying the rolling speed, roll radius, entry thickness, front tension, back tension, and strip width. Under the effect of the dynamic rolling force and considering the nonlinear effect between the backup and work rolls as well as the structural constraints on the rolling mill, a hysteretic nonlinear vertical vibration model of a four-high hot rolling mill was established. The amplitude-frequency equations corresponding to 1/2 subharmonic resonance and 1:1 internal resonance of the rolling mill rolls were obtained using a multi-scale approximation method. The amplitude-frequency characteristics of the rolling mill vibration system with different parameters were studied through a numerical simulation. The parametric stiffness and nonlinear stiffness corresponding to the dynamic rolling force were found to have a significant influence on the amplitude of the subharmonic resonance system, the bending degree of the vibration curve, and the size of the resonance region. Moreover, with the change in the parametric stiffness, the internal resonance exhibited an evident jump phenomenon. Finally, the chaotic characteristics of the rolling mill vibration system were studied, and the dynamic behavior of the vibration system was analyzed and verified using a bifurcation diagram, maximum Lyapunov exponent, phase trajectory, and Poincare section. Our research provides a theoretical reference for eliminating and suppressing the chatter in rolling mills subjected to an elastoplastic hysteresis deformation.
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This work aimed to alter the texture components and enhance the stretch formability of rolled AZ31 sheets by developing the rolling technology. In this study, a continuous bending ...channel was introduced into an equal channel angular rolling apparatus and a new rolling technology was successfully developed. Microstructure evolutions during hot-rolling, equal channel angular rolling and subsequent continuous bending were investigated. Results showed that hot-rolling generated a strong basal texture component. Single pass equal channel angular rolling cannot eliminate the basal texture component, while can greatly weaken basal texture intensity. After continuous bending, basal texture component was almost eliminated. Meanwhile, a strong c-axis//RD texture component and a weak double-peak texture component with symmetrical splitting of the {0002} basal texture were formed. After recrystallization annealing, symmetrical double-peak texture whose {0002} pole peak located at about 40° from normal direction towards the rolling direction was enhanced with the disappearance of c-axis//RD texture. The AZ31 sheets with double-peak texture exhibited excellent stretch formability at room temperature (with an Erichsen value of 7.4 mm). Finally, the relevant mechanisms were discussed.
The objective of this study is to evaluate the effect of slip ratio on the wear and rolling contact fatigue (RCF) of wheel/rail materials using a rolling–sliding wear testing apparatus. The results ...indicate that two wear types are presented in terms of wear rate: type I (mild wear) and type II (severe wear). In type I wear, cracks propagate parallel to the surface. While in type II, the peeling is aggravated and spalling can be observed. With the slip ratio increasing, the wear mechanism of rollers transforms from slight oxidation wear and peeling to severe fatigue wear and spalling. Due to the mild wear and light plastic deformation in type I, the angle and depth of cracks show no obvious differences between the wheel and rail rollers. The crack depth and angle increase in type II wear owing to severe plastic deformation, while the depth is smaller on the wheel rollers. The size of flake wear debris presents an increasing trend and the main composition is Fe2O3 and metallic iron, and the content of iron diminishes with increasing oxidation.
•Two wear types are defined in terms of wear rate of wheel/rail rollers.•The slip ratio has a significant effect on the hardness and friction coefficient.•Two wear types present different subsurface damages.•The size of debris with flake structure has a downtrend with slip ratio increasing.
•Infeasibility of cold and warm rolling for large-size AlCoCrFeNi2.1 is demonstrated.•High-temperature rolling is feasible to severely deform the large-size AlCoCrFeNi2.1.•The hot-rolled tensile ...properties are excellent and comparable to cold rolling.•The proposed process paves the way for engineering application of AlCoCrFeNi2.1.
Improving the strength and ductility of small-size AlCoCrFeNi2.1 eutectic high-entropy alloy by thermo-mechanical processing has been successfully achieved; whereas, its feasibility for large-size AlCoCrFeNi2.1 has not been evaluated yet. The current study demonstrates that both cold-rolling and warm-rolling cannot severely deform large-size AlCoCrFeNi2.1 probably due to large intrinsic deformation resistance and increased casting defects. Instead, hot-rolling successfully deforms large-size AlCoCrFeNi2.1 and achieves outstanding tensile properties comparable to the cold-rolling. This finding paves the way for engineering application of AlCoCrFeNi2.1.
•MBN was used to characterize local anisotropy of non-oriented electrical steel.•The MBN results are directly compared to the texture factors of the steel sheets.•The overall MBN signal changes ...substantially throughout various processing stages.•A cosine function was observed between the MBNrms and the angle of magnetization.•Residual stress changes the cosine relationship in partially recrystallized steel.
Magnetic Barkhausen noise (MBN) signals were measured on a non-oriented electrical steel through all the thermomechanical processing stages, i.e. hot rolling, hot band annealing, cold rolling and final annealing. The temperature of the final annealing was varied from 600 °C to 750 °C so that the steel consisted of partially or completely recrystallized microstructures and different levels of residual stresses. The angular MBNrms (root mean square) values were compared to the texture factors in the same directions, the latter being calculated from the crystallographic texture measured by electron backscatter diffraction (EBSD). It was found that, in the cold-rolled, hot-rolled and completely recrystallized steels, the angular MBNrms followed a cosine function with respect to the angle of magnetization, while in partially recrystallized state such a relation does not exist. After cold rolling, the maximum MBNrms was observed in the rolling direction (RD) and the minimum MBNrms was in the transverse direction (TD), which was inconsistent with the magnetocrystalline anisotropy as indicated by the texture factor. After hot rolling, the maximum and minimum MBNrms values were observed in the TD and RD, respectively, exactly opposite to the cold-rolled state. If the steel was completely recrystallized, the maximum MBNrms was normally observed at a direction that was 15–30° from the minimum texture factor. If the steel was partially recrystallized, both the magnetocrystalline anisotropy of the material and the residual stress contributed to the angular MBNrms, which resulted in the deviation of the relationship from a cosine function. The relative strength of the two factors determined which factor would dominate the overall magnetic anisotropy.
ZK61 magnesium-alloy plate with high tensile strength and elongation is obtained by combined multipass symmetric hot rolling and asymmetric warm rolling. Deformation history considering varying ...strain rate obtained from the macro-finite element analysis of the selected passes are introduced into the viscoplastic self-consistent model (VPSC) as initial boundary conditions for macro- multiscale and micro-multiscale coupling analysis. VPSC simulation results show that in the initial stage of rolling deformation, the basal slip is the dominated deformation mode, supplemented by prismatic slip and pyramidal <c+a> slip. With increased rolling strain, the pyramidal <c+a> slip presents competitive relationship with basal slip, and the activation amount of {101-1} compression twins is limited. During asymmetric rolling, the basal slip is dominant, followed by the pyramidal <c+a> slip. Experimental results show that the basal texture is gradually strengthened after symmetric rolling, and grain size is refined due to the activation and recrystallization of twins. Asymmetric rolling makes the basal texture deflect 10° to the rolling direction and further refine the grain size. With the ongoing of symmetric rolling, the mechanical anisotropy of the plate weakens, and the yield strength, tensile strength, and plasticity of the material improves. In particular, after asymmetric rolling, the tensile strength in the RD and TD directions of the plate reaches 391.2 MPa and 398.9 MPa, whereas the elongation reaches 19.8% and 25.5%.
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