A research on the deformation behavior of Al–Cu–Mn alloy sheets was conducted under a biaxial stress state at cryogenic temperatures to determine fundamentals of a novel forming method for ...complicated components. The strength, ductility, strain hardening exponent and work hardening rate of an Al–Cu–Mn alloy sheet were compared with uniaxial tension tests at different cryogenic temperatures. The deformation of a dome specimen was analyzed by using a newly-designed bulging device and an optical three-dimensional (3D) deformation measuring system at temperatures of 293 K and 113 K. The limiting dome height (LDH) at 113 K was 37.1% higher than that at 293 K. The strain and thickness distribution of the bulged specimens were more uniform at 113 K owing to a higher strain hardening capacity. Compared to room temperature, the cryogenic bulging results revealed that the formability of the Al–Cu–Mn alloy could be enhanced under a biaxial stress state. Likewise, the resistance to the micro-deformation of the aluminum alloy was increased due to the harder formation of the slip bands and fewer slip localizations at cryogenic temperatures. The increased dislocation density and strength of the alloy were resulted from numerous netted dislocation substructures with interactive dislocation walls (DWs) and dislocation tangles (DTs). Furthermore, more uniformly distributed dislocation cell structures with continuous ridges could facilitate multiple dislocation glides and diminish localized deformation, which resulted in the improvement of the ductility of the Al–Cu–Mn alloy during the cryogenic deformation process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•A newly-designed digital image correlation (DIC) testing device at cryogenic temperatures was developed.•The cryogenic FLDs and FLSDs of the solution-treated Al-Cu-Mn alloy sheet ...were experimentally obtained.•The cryogenic FLD and FLSD ductile fracture models were determined to predict the drawing limits of the Al-Cu-Mn alloy sheet.
In this paper, the analysis of the necking and limit strains of a solution-treated aluminum alloy sheet at extreme low temperatures is performed using a newly-designed test apparatus equipped with the digital image correlation (DIC) device. The forming limit diagram (FLD) and forming limit stress diagram (FLSD) ductile fracture models were used to predict the drawing limit and fracture resistance capacity of an Al-Cu-Mn alloy sheet under complex stress at room temperature (RT) and -160 °C. It was found that the FLD0 value at -196 °C increased to 0.32 as compared to 0.23 at RT. The Al-Cu-Mn alloy sheets at -160 °C and -196 °C were found to have significantly higher limit strains than those at RT. The drawing height and limit major strain at the round corner of the cryogenic deep-drawn cups were found to be increased by 21.3 % and 9.7 %, respectively, as compared to those at RT. Moreover, a larger necking amount and higher fracture resistance of the Al-Cu-Mn alloy sheet could be achieved during cryogenic deformations. The obtained cryogenic FLDs and FLSDs can be used to accurately predict the damage evolution and failure occurrence for the forming of complex-shaped aluminum alloy components at low temperatures.
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•La2O3 improved the temperature gradient and reduces crack susceptibility.•La2O3 promoted nucleation and grain refinement and increases dislocation density.•La2O3 doping increased the hardness of the ...coating and improved the wear pattern.
In this study, CoCrFeNiMoSi and CoCrFeNiMoSi + 0.5 % La2O3 High entropy alloy (HEA) coatings were prepared by laser cladding. The microstructure was consisted mainly of body-centered cubic structure, face-centered cubic structure and intermetallic compounds of Si. The addition of rare earth La2O3 resulted in the refinement and uniformity of the CoCrFeNiMoSi + 0.5 % La2O3 HEA coating grains, leading to an increase in microhardness from 430 HV to 520 HV. Additionally, the friction coefficient decreased by 0.15 and the wear rate decreased by 2/3. These findings indicate that the appropriate addition of La2O3 has significant potential in enhancing the friction and wear performance of HEA coatings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•A novel deep drawing process at cryogenic temperatures is developed to overcome the low drawability of Al-Cu-Mn alloy sheets at room temperature.•A special deep drawing system is ...designed for investigating the cryogenic deep drawability of the Al-Cu-Mn alloy sheet.•The superior deep drawability of the Al-Cu-Mn alloy sheet can be obtained as the temperature decreases to −160 °C. The LDR value at RT is 1.80, while the −160 °C is increased to 2.08, which has increased by 15.6%. The average cup height at −160 °C is 50.2% higher than that at RT.•The deformation mechanism for the enhanced formability and strength is illuminated by the microstructure observations on fracture morphologies and dislocation evolutions at cryogenic temperatures.
To overcome the low drawability of aluminum alloy sheets at room temperature (RT), a novel deep drawing process at cryogenic temperatures is proposed. Uniaxial tensile tests were carried out at RT, −130 °C, −150 °C, −160 °C and −196 °C, respectively, and the desired temperature of cryogenic deep drawing was obtained. Based on a newly-designed cryogenic deep drawing system, deep drawing experiments of an Al-Cu-Mn alloy sheet were conducted at different cryogenic temperatures. The material flow, drawing ratio, drawing load, thickness distribution and Vickers microhardness of the drawn cups at both RT and cryogenic temperatures were discussed in detail. It was found that the deep drawability was significantly enhanced as the temperature decreased to −160 °C. The limiting drawing ratio at RT was 1.80, while that at −160 °C increased by 15.6% to 2.08. Similarly, the average cup height (89.5 mm) at −160 °C was found to be 50.2% higher than that at RT (59.6 mm). The cryogenically drawn cups exhibited slight localized thinning, uniform thickness distribution, and a large drawing height and drawing load. In addition, the enhancement of the deep drawability was illuminated via microstructural observations of the fracture morphology and dislocation evolution at cryogenic temperatures.
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An experimental research was conducted on the enhanced ductility and strain-hardening of a solution-treated Al–Cu–Mn alloy for understanding its deformation mechanism at the cryogenic temperature of ...liquid nitrogen (LN2). Both quasi-in situ tensile and rigid punch bulging tests were performed, enabling the deformation behaviors under uniaxial stress and complex stress states to be considered comprehensively. The capabilities of resisting fracture and plastic deformation were evaluated at both room temperature (RT) and −196 °C. Based on the EBSD/SEM observations, the correlations were quantitatively elucidated between the macroscopic deformation and the microstructure evolution, underlying the slip band, local misorientation, geometrically necessary dislocation, stored strain energy and relative slip distance. It is concluded that the Al–Cu–Mn alloy exhibits cooperatively enhanced ductility and strain-hardening at −196 °C. The average limiting dome height (LDH) is increased from 20.6 mm to 26.8 mm as the temperature varies from RT to −196 °C. The maximum load is 2.25 times higher than that at RT under a biaxial stress state. Moreover, the capabilities of resisting crack propagation and localized thinning are also substantially improved. In terms of the observation of local misorientations at −196 °C, the enhanced ductility is primarily a result of the diminished accumulation of movable dislocations along the grain boundaries, and the increased storage capacity in grain interiors. The increased strain hardening is attributed to the decreased relative slip distance of the activated dislocations, and the inhibited massive collapses of the tangles and cells of dislocations during the cryogenic deformation.
•The capabilities of resisting fracture and plastic deformation were evaluated through a newly-designed bulging device at the temperature of LN2.•The strength-ductility combinations for a solution-treated Al-Cu-Mn alloy after the quasi-in situ tensile and rigid-punch bulging tests are enhanced collectively at -196 °C.•The relationships among the enhanced strength, ductility and strain hardening were quantitatively elucidated based on the quasi-in situ electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) observations.
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The cold semi-precision forging of a multi-row sprocket was investigated using upper-bound （UB） and finite element methods combined with experiments. Based on the design of a new tooth profile for ...the sprocket, a cold semi-precision forging process and a kinematically admissible velocity field for filling the die cavity were proposed. Using the UB method, the velocity fields of the sprocket billet in the forming process were divided theoretically and calculated. The process of forging a multi-row sprocket was simulated using the FEM package Deform-3D V6.1 to obtain the distributions of the velocity field and the effective stress field in filling the die cavity. Similar to the simulated results, the experiment on cold forging a 5052 aluminum alloy sprocket was successfully performed. By comparing the calculated （UB method）, experimental and simulated load-stroke curves, the calculated and simulated results were basically in accordance with the experimental results. The study provides a theoretical foundation for the development of the precision forging of multi-row sprockets.
•A novel testing device equipped with digital image correlation (DIC) measurements in a cryogenic environment was developed to obtain the flow stress curves of aluminum alloy sheets under biaxial ...stress state.•The flow stress curves under biaxial stress state are determined via the theoretical analyses and rigid punch bulging tests at RT, −140 °C and −160 °C.•The expansion ratio of surface and average deviation of thickness were proposed to analyze the effects of cryogenic temperatures on the formability and deformation uniformity of the Al-Cu-Mn alloy sheets.•The validity of calculated flow stress curves under biaxial stress state is illustrated by the cryogenic deep drawing simulations combined with the experiments.
To study the formability and flow stress of an Al-Cu-Mn alloy sheet under biaxial stress state at various cryogenic temperatures, a geometric model of the bulged dome and a calculation method of the flow stress curves were newly proposed. Based on a novel testing device equipped with digital image correlation (DIC) measurements, the strain, displacement, bulging height, punch force and wall thickness were obtained during the rigid punch bulging at RT, −140 °C and −160 °C. The evaluation indexes regarding the expansion ratio of surface area and average deviation of thickness were proposed to analyze the effects of cryogenic temperatures on the formability and deformation uniformity of the Al-Cu-Mn alloy sheet. The expansion ratio of surface area at −160 °C is approximately 2.3 times greater than that of the RT. The average deviations of thickness are decreased by 9.1% and 37.0% at −140 °C and −160 °C with an identical bugle height, respectively. Based on the geometrical and stress models, the flow stress curves of the Al-Cu-Mn alloy sheet are determined under biaxial stress state at RT, −140 °C and −160 °C. The validity of calculated flow stress curves is illustrated by the cryogenic deep drawing simulations combined with the experiments. Furthermore, potential applications of the calculated flow stress curves are suggested to accurately analyze the deformation behavior and formability of the Al-Cu-Mn alloy sheet at cryogenic temperatures.
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To further strengthen the AlCoCrFeNi high-entropy alloy (HEA) coating prepared by high-speed laser cladding (HLC), laser remelting (LR) was chosen to reprocess it. The effects of LR on the ...topography, microstructure, growth orientation, phase distribution, and properties were investigated. It was revealed that there were a large number of liquid phase separation (LPS) zones in the HLC coating because of an ultrafast cooling rate. After LR, the LPS zones were eliminated. Compared to HLC coating, the microhardness increased from 622 HV to 762 HV, and the friction coefficient and the wear weight loss were reduced by 0.1 and 0.5 mg, respectively. In electrochemical testing, the self-corrosion potential increased by 45.9 mV and the self-corrosion current density decreased by one order of magnitude. Meanwhile, EBSD analysis indicated that the LPS zones were prone to recrystallization. The LPS zones were nickel-poor, low hardness, also BCC phase, and had a clearer (101) orientation. With the elimination of the LPS zones, the kernel average misorientation values were reduced, Taylor factor values and high angle grain boundaries were increased, and the average grain size was reduced from 2.43 μm to 2.12 μm. Eventually, for LR coatings, the combination of fine grain strengthening, solid solution strengthening, spalling reduction, and Cr element segregation resulted in better wear and corrosion resistances. The overall results show that a reasonable LR application can induce the microstructure of the HLC coating and improve its service properties.
● The AlCoCrFeNi high-entropy alloy coatings were prepared by high-speed laser cladding (HLC) and reprocessed by laser remelting (LR).● There were a large number of liquid phase separation (LPS) zones in the HLC coating. After LR, the LPS zones were replaced by fine equiaxed crystals.● The LPS zones were nickel-poor and low hardness, had a clearer (101) orientation, and tended to spall off in the wear test, causing a decrease in the overall wear resistance of the coating.● As a result of the elimination of the LPS zones, the microhardness and wear resistance of the LR coating were improved by solid solution strengthening and fine grain strengthening.● Appropriate undercooling and more high angle grain boundaries caused by LR provided a larger driving force for grain boundary segregation. The elemental content of Cr at the grain boundaries became higher, and the corrosion resistance of the LR coatings increased significantly. Display omitted
•HLC led to a large number of the LPS zones in the AlCoCrFeNi HEA coating.•LR could successfully eliminate the LPS zones.•Recrystallization made the grains of the LPS zones coarse and soft.•The microhardness and wear resistance of the coating were improved by LR.•Higher Cr content at grain boundaries boosted corrosion resistance of LR coating.
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Modeling impacts of the construction area on the mixed traffic flow would be a challenge. It needs to figure out the traffic regulations near the construction area, which vehicles must comply with. ...Meanwhile it requires depicting the different driving behaviors of cars and trucks when they run into the construction area. To deal with these problems, we present a three-lane cellular automaton traffic model with a construction area, taking the traffic flow on Hangzhou Bay Bridge with the third lane closed as a case study. The different longitudinal position updating rules and the lateral lane-changing rules are proposed for cars and trucks respectively, which are driven by aggressive drivers and cautious drivers. The simulation results show that the traffic flow will reach the maximum value when the length of the work zone, i.e., the main part of the construction area, is appropriate. On the other hand, the construction area has a great negative impact on the traffic flow when the injection rate is high, and cause the serious traffic congestions. In order to optimize the traffic flow, the variation tendency of the total traffic flow and the delay time with the increasing length of the work zone and the injection rate are analyzed. And the recommended values of the work zone’s length under different injection rates are obtained. In addition, according to the variation trend of the merging rate with the increasing length of the merging area and the injection rate, the recommended values of the merging area’s length under different injection rate are obtained. The results are meaningful and expected to be applied in the traffic management during the period of highway construction.
•A heterogeneous three-lane CA traffic model with a construction area in Lane 3 is presented.•The impacts of the construction area on the traffic flow are investigated.•The reasonable work zone’s lengths under different injection rates are recommended.•The merging area’s length is optimized aiming for the high and smooth traffic flow.
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To strengthen face-centered cubic structured high entropy alloys, this paper explores a new method of ceramic reinforced CoCrFeNiMo0.2 high entropy alloy composite gradient coating. In this study, ...four sets of gradients were created by first preparing a pristine alloy coating without silicon carbide content on the substrate, followed by preparing composite coatings with varying silicon carbide mass fractions (8 %, 16 %, 24 %) on the pristine coatings. The coatings were then analyzed for their phase composition, microstructure, microstructure evolution process, and friction wear properties. The study reveals that the microstructure of the initial alloy coating consists of a single-phase face-centered cubic solid solution. It is observed that intragranular segregation occurs in the coating, resulting in the boundary enrichment of Mo and Cr elements. As the silicon carbide addition increases, the segregation behavior becomes more pronounced, and the generation of body-centered cubic phase is observed. The second, third, and fourth layers exhibit significantly higher average hardness, measuring at 594 HV, 722 HV, and 788 HV respectively. This can be attributed to the presence of body-centered cubic structure, carbide, and grain boundary strengthening effects. On average, the hardness of these layers is three to four times higher than that of the first layer. With an increase in the number of layers, the wear mechanism changes from adhesive wear to abrasive wear. The wear rates of the second, third, and fourth layers were all reduced by at least 87 % compared to the first layer. However, there were different forms of abrasive wear observed between these layers. The findings of this study have significant engineering implications.
•The microstructural evolution of columnar grains to equiaxed dendrites was studied.•The high-density of dislocations enhances the diffusion of Mo and Cr elements.•The tissue shows phase separation act containing the BCC structure.•The shift behavior of the wear mechanism of the gradient structure was studied.
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