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The influences of aging temperatures (160–200 °C) and 8% pre-rolling on the mechanical properties, and microstructures of the creep-aged AA2050 alloys were investigated. The results show that for the solid-solutioned alloys after the creep aging, the strength increased with an increase of aging temperatures. The ultimate tensile strength (UTS) and yield strength (YS) reached the highest value of 527 and 484 MPa at 200 °C, respectively, although the elongation (EL) reduced to 10.8%. At expense of σ phases, the temperature increase promoted the dislocation accumulation and the dense precipitation of θ′ and T1 phases, which increased the strength. It is noted that the strong oriented precipitation at 200 °C lost some strengthening effect. After the 8% pre-rolling, the strength of creep-aged alloys increased firstly and then decreased with the increase of temperature. The high strength (UTS = 574 MPa, YS = 535 MPa) at 180 °C was attributed to the dense precipitation of T1 phases under the action of diffusion kinetic and thermodynamic driving force. When the temperature reached 200 °C, the activated ledge mechanism significantly thickened T1 phases, thus decreasing the strength. The work revealed the critical roles of aging temperature and pre-rolling in tailoring precipitation behaviors and mechanical performance of Al–Li alloys, paving a way in designing creep-aged Al–Li alloys with the superb mechanical properties.

Ultraprecision positioning to better than nanometer in accuracy is of a great interest in various applications. The paper reports on recent pre-rolling experimental measurements of the moment friction during the phase of pre-rolling, i.e., at the start and at the finish. To discuss the case properly, the experiments are set for pure rolling without any external effect nor any slippage at the contact patch. The pendulum was designed to secure pure pre-rolling without slippage. Beside the fact that the experiments have shown extremely low values of rolling coefficients in the order of (× 10–7), it is possible to establish the appearance of real hysteresis curves showing the dependance of the friction moment on the displacement. The sensitivity of the measurement of rolling friction moments is in the order of 10–10 Nm, the measurement error does not exceed 10% with 125 nm minimum displacement of the ball peel adhesion density evaluated as 2.2 × 10–4 J/m2. [ABSTRACT FROM AUTHOR]

The effect of pre-rolling on the microstructure and fatigue crack (FC) propagation resistance of the Al-Cu-Li alloy was studied using tensile testing, fatigue testing, transmission electron microscopy (TEM), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The results revealed that reducing the alloy thickness through pre-rolling by up to 12% enhanced both tensile strength and yield strength, albeit at the expense of reduced elongation. In addition, the FC growth rate decreased by up to 9% pre-rolling, reaching the minimum, while the application of additional mechanical stress during the pre-rolling increases this parameter. Deformations in the Al-Cu-Li alloy with less than a 9% thickness reduction were confined to the surface layer and did not extend to the central layer. This non-uniform deformation induced a compressive stress gradient in the thickness direction and led to an inhomogeneous distribution of T1 phase, resembling the structure generated by shot peening. The superior FC propagation resistance in the 9% pre-rolled alloy could be primarily attributed to the optimum balance of compressive residual stress and work hardening. [ABSTRACT FROM AUTHOR]

The development results of a single-point contact system set up as a pendulum to study the laws of rolling resistance to contacting bodies at a distance significantly reduced compared to the elastic contact spot size. The designed device uses a physical pendulum sustained by only one ball on a flat polished surface. The problem of stability of the pendulum swing plane is solved. A phenomenological theory of rolling resistance is described. The surface tension of solids on the contact zone, parameters of the frequency-independent internal friction and the pressure of the adhesion forces are found. [ABSTRACT FROM AUTHOR]

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The development results of a single-point contact system set up as a pendulum to study the laws of rolling resistance to contacting bodies at a distance significantly reduced compared to the elastic contact spot size. The designed device uses a physical pendulum sustained by only one ball on a flat polished surface. The problem of stability of the pendulum swing plane is solved. A phenomenological theory of rolling resistance is described. The surface tension of solids on the contact zone, parameters of the frequency-independent internal friction and the pressure of the adhesion forces are found.

Present study aimed at investigating the effect of introducing pre-width reduction (Pre-WR) on microstructure evolution and rolling formability variation during both the break-down rolling and finish rolling of AZ31B alloy. Different rolling routes relevant to the above two rolling processes were performed and compared. Results show that pre-induced twins by pre-rolling (8% thickness reduction) can significantly reduce the edge-cracking depth level during subsequent super-high reduction rolling (SHRR) (80% thickness reduction) through replacing the formation of shear bands by the promotion of the twinning-induced recrystallization to coordinate the severe deformation. However, the dominant behavior of twinning and twinning-induced DRX within the edge region induced a unique partial recrystallization with coarse grains and further a poor rolling formability in SHRR. Introducing more {10 1 ¯ 2} tensile twins at the edge by Inter-WR (a Pre-WR type with 10% width reduction) before the SHRR can significantly refine the grains and obtain almost a recrystallized homogeneous microstructure. It can also weaken the basal texture of the edge material and further decrease the number/depth level of edge crack by enhancing the activity of both non-basal slips and dominant continuous dynamic recrystallization (CDRX). During finish rolling, heavy twins and shear bands resulted in the larger edge crack level. The improvement of Pre-WR on rolling formability can be inherited to the strip finishing rolling process by evidently reducing the twins and shear bands. [ABSTRACT FROM AUTHOR]

The coarse segregative eutectic phases, emerged in the twin roll casting (TRC) process of Mg strips, which cannot be resolved solely by controlling the processing variables or post heat treatment, are detrimental to the subsequent rolling deformation. Considering it, we introduce the pre-rolling steps on the TRC Mg-4Al-2Sn-1Zn (ATZ421) alloys, which is expected to facilitate the dissolution of these segregative phases by increasing distortion of crystal lattices and rolling stress, and further investigate the effect of a single pass or two passes pre-rolling on the microstructure evolution and tensile properties. It indicates that the pre-rolled alloy with two passes presents more uniform precipitates and higher twinning density in comparison with that using a single pass. The uniform distribution of precipitates in two passes pre-rolling is due to the increase in density of dislocations and deformed twins, which results in more distortion of crystal lattices with more stored energy, facilitating the diffusion of solutes. Moreover, the pre-rolling of two passes introduces more rolling stress into Mg matrix, which is beneficial for the crush of coarse eutectic phases, and further accelerates the sufficient dissolution of second phases. After the subsequent rolling and annealing processes, the sheet with pre-rolling deformation of two passes shows finer microstructure, which mainly benefits from the pinning effects of uniform nano-sized precipitates. As a result, the annealed sheet with two-pass pre-rolling deformation exhibits an advantageous combination of high strength and high ductility with fine microstructure, showing an ultimate tensile strength of ~297 MPa, a yield strength of ~ 205 MPa and an elongation of 25.0%. This work provides an effective method of dissolving the coarse segregative phases in the TRC Mg alloys with significant potential for industrial production. [ABSTRACT FROM AUTHOR]

Hysteresis friction behaviors of linear rolling bearings (LRBs) are important for precision positioning applications, which are related to the displacement and the traversed trajectory history within pre-rolling friction region. Although these behaviors have been pointed out in literature, the time dependence of transient hysteresis friction behaviors has not been reported before. In this work, the effects of initial conditions induced by the applied forces prior to commencement of the hysteresis motion are considered, which are denoted by the differences between the magnitudes of positive endpoints and the magnitudes of negative endpoints of virgin curves for the obtained asymmetrical hysteresis loops. The evolution of the time dependence is denoted by the decaying of the differences with the increasing dwell time. The effects of the damping and the junction growth during the dwell time are used to explain the time-dependent hysteresis friction behaviors of the LRB. The experiments of higher preload and lubrication-free conditions have been implemented as well, and the results indicate that the conditions are positive to diminish the time-dependent hysteresis friction behaviors. [ABSTRACT FROM AUTHOR]

The effects of pre-rolling treatment on the grain refinement, dynamic precipitation and mechanical properties of a Mg-6 wt%Zn-1 wt%Mn alloy (ZM61) processed by high strain rate rolling (HSRR) were investigated. The results indicate that: (1) a large number of twins and microbands formed during pre-rolling treatment, which provide plenty of nucleation sites for dynamic recrystallization (DRX) during subsequent HSRR. As a result, an average grain size of 0.8 µm and a DRX degree of 99% were obtained for the alloy after pre-rolling and subsequent HSRR; (2) the pre-rolling treatment also resulted in the formation of a high density of fine precipitates, distributing uniformly in the matrix; (3) an excellent balance of the strength and ductility was achieved for the alloy processed by pre-rolling and subsequent HSRR, which is superior to that of the alloy processed only by HSRR. [ABSTRACT FROM AUTHOR]

In this study, the traditional hot rolling to fabricate Al/Ti laminated metal composites (LMCs) was improved by using a pre-rolling diffusion process. The effect of the pre-rolling diffusion on microstructure and mechanical properties of Al/Ti LMCs were investigated by various methods, such as optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and tensile tests. The results show that, with increasing diffusion temperature, the thickness in diffusion layer was increased and the mechanical properties of LMCs were improved obviously, which was attributed to the optimized interfacial structure after diffusion process. In addition, the formation of TiAl3 intermetallic compounds (IMCs) was detected in the bonding interface, which played an important role in improving the mechanical properties for Al/Ti LMCs. The predicted results of stress-strain curves from rule of mixture (ROM) indicated that, there existed an extra interfacial strengthening in Al/Ti LMCs beside the mechanical properties provided by the contribution of constituent layers. The pre-rolling diffusion process is effective for the optimization of interfacial structure and improvement of mechanical properties in Al/Ti LMCs.

The damage tolerance of Al-Cu-Mg alloy sheet was successfully improved by pre-rolling with small reduction (6.1%) rather than large reduction (12.2% and 21.7%). By this 6.1% pre-rolling, most of deformation only occurs at the surface layer of sheet, but not at the center layer. A protected compressive stress gradient was created, i.e., compressive stress gradually decreased from surface to center layer. Besides, atom probe tomography analysis showed that compared to center layer, large Cu-Mg co-clusters (50–100 atoms) with higher number density formed at surface layer. This led to greater module hardening and ordering hardening in surface layer than in center layer. Both the distributions of compressive stress and Cu-Mg co-clusters were responsible for the enhanced damage tolerance of alloy sheet. [ABSTRACT FROM AUTHOR]

Pre-rolling combined with double aging (DAT8) and interrupted aging (IAT8) were carried out to improve the mechanical properties of rapidly solidified 2195 Al–Cu–Li alloy. For the DAT8 treatment (4% pre-rolling + 120 °C/12 h + 165 °C/16 h), low aging temperature (120 °C) in the first stage forms abundant δ′ phase, which grows into well-dispersed T 1 plates in the second stage (165 °C). The IAT8 treatment (165 °C/2 h + 4% pre-rolling + 65 °C/5 day + 165 °C/16 h) first produces some small GP zones, which are connected to dislocations generated by pre-rolling. Subsequent long-term low-temperature aging (65 °C/5d) results in the enrichment of Cu, Mg, Ag and Li atoms on dislocations, significantly enhancing the precipitation driving force of the T 1 phase. The results show that DAT8 and IAT8 treatments simultaneously improve the strength and ductility of the alloy. The increased strength is mainly due to the dense precipitation of the T 1 phase, generating higher precipitation strengthening, as well as the introduction of high dislocation density, yielding strain strengthening. The improved ductility is attributed to the fine and well-dispersed T 1 phase, decreasing the incongruous deformation between precipitates and matrix, and suppressing the formation of precipitation free zone (PFZ), weakening local stress concentration at sub-grain boundaries. [ABSTRACT FROM AUTHOR]

Linear rolling guideways (LRGs) play an important role in precision engineering. In the pre-rolling region, the hysteretic friction force exerts great impacts on the positioning accuracy. Numerical and experimental studies of the hysteresis of friction force are presented in this paper. A model, which is based on the stripe theory and the simplified theory of rolling contact, is built to describe the transient hysteresis of the friction force. Then, the model is modified by taking the anelasticity effect into consideration. Experimentally, a linear motor direct-drive setup is utilized to measure the transient asymmetrical hysteresis of the friction force in the pre-rolling region of an LRG. The influences of the pre-rolling displacement and the dwelling time on the asymmetrical hysteresis of the friction force are studied. The numerical and experimental results are well correlated, which shows good accuracy of the model. The transient asymmetrical hysteresis of friction force in the pre-rolling region of LRGs can thus be determined using the model. [ABSTRACT FROM AUTHOR]

AZ31 magnesium alloy plates were processed by pre-rolling followed by warm compression. The corresponding microstructure evolution and mechanical properties were investigated in the present paper. The pre-introduced twins by pre-rolling increased the number of nucleation sites for dynamic recrystallization (DRX) during subsequent warm compression, which resulted in a fine completely recrystallized microstructure. With the increasing warm compression, more grains were recrystallized and the basal texture intensity was greatly strengthened. Finally, the average grain size was significantly refined from 31.9 μm to 2.0 μm by pre-rolling followed by warm compression. As a result, the AZ31 alloy plates processed by pre-rolling followed by warm compression exhibited higher yield stress and ultimate stress resulting from grain refinement without a reduction in elongation. [ABSTRACT FROM AUTHOR]

Dynamics of small free swings of a pendulum supported by two spherical balls pre-rolling on a flat basis are considered to investigate the occurrence of micro-slippage at the contact interface between the balls and the flat surface. The basic mechanisms of this micro-slippage are investigated, showing how geometric conditions could initiate and magnify micro-slippage rather than assuming that these effects are core characteristics in any rolling system. This article also discusses the energy dissipation of a ball slipping on a flat surface at pre-rolling caused by three mechanisms and the conditions enabling the decrease of energy dissipation of the pendulum and the influence of the basis vibrations. [ABSTRACT FROM PUBLISHER]

Theoretical and experimental investigations of pre-rolling resistance of a ball on a flat surface were carried out. The cycling displacements of the ball were considered within a range much smaller than the radius of a contact patch. The method of free oscillations of a pendulum supported with two balls on a substrate is proposed for experimental investigations. It is proved that this method allows measurement of a set of parameters of pre-rolling resistance with high sensitivity and precision. The proposed setup has secured pure rolling measurement conditions. [ABSTRACT FROM PUBLISHER]

In this work, a novel texture modification, termed the ellipse texture, is introduced by the pre-rolling and subsequent annealing (PRA) process in as-extruded (AE) Mg-Gd-Zn (GZ21) alloy. The static recrystallization (SRX) mechanisms and the evolution of microstructure during the PRA process are investigated by electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) techniques. The results show that the introduction of the ellipse texture distribution leads to the improved planar isotropy of the mechanical properties compared with the AE sheets, when tensile along different directions. Accordingly, the Erichsen value (IE value) increases to 5.7 ± 0.1 mm. Furthermore, the activation of non-basal dislocations (prismatic and pyramidal dislocations) during the pre-rolled process induces preferred nucleation sites for the SRX grains with the c -axis oriented to TD. The co-segregation of Gd and Zn atoms at grain boundaries leads to the preferred growth of these TD texture component grains. Both the preferred nucleation and growth of the SRX grains contribute to the formation of ellipse texture distribution in the PRA GZ21 alloys. • A novel texture modification treatment which includes pre-rolled and subsequent annealing (PRA) process is operated on the as extruded Mg-Gd-Zn (GZ21) alloy sheets to introduce the ellipse textures. • The planar isotropy of the mechanical properties was enhanced due to the introduction of the ellipse texture distribution. • The static recrystallization mechanisms and the evolution of microstructure during the PRA process are revealed by the electron backscattered diffraction, transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy techniques. [ABSTRACT FROM AUTHOR]

Abstract: The effect of pre-annealing and pre-rolling (an initial rolling deformation prior to pre-annealing) on the final engineering critical current density J e of Ag-sheathed Bi-2223 tapes has been investigated. The optimization of pre-annealing process was found to be dependent on annealing temperature much more than on oxygen partial pressure or soaking time. The highest J e has been achieved for pre-annealing at 790°C for 20h in a flowing 8.5% O2-balance N2 atmosphere. Optical microscope and XRD rocking curve analysis show that pre-rolling improved the homogeneity of the tapes, reduced the sausaging effect and improved the texturing of the superconducting phase. All these effects strengthen the grain connectivity and further enhance the J e value of the tapes. Too large a pre-rolling reduction, however, decreased the J e owing to the introduction of more cracks that cannot be completely healed in subsequent heat treatment. [Copyright &y& Elsevier]

Ultra-precision positioning is contaminated by the non-linearities and hysteresis caused by Hertzian contact at pre-rolling due to the absence of accurate models that could be implemented by positioning controllers to compensate for it. In this paper an attempt is made to model such behaviour at low speed and dry conditions while taking into account the mechanical characteristics of the bodies in contact. The proposed model simulates the non-linear behaviour, called non-linear spring behaviour (NSB), from pre-rolling to the steady state rolling without a transitional function. The model is compared to experimental measurements performed with several materials. [ABSTRACT FROM AUTHOR]

In this study, the traditional hot rolling to fabricate Al/Ti laminated metal composites (LMCs) was improved by using a pre-rolling diffusion process. The effect of the pre-rolling diffusion on microstructure and mechanical properties of Al/Ti LMCs were investigated by various methods, such as optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and tensile tests. The results show that, with increasing diffusion temperature, the thickness in diffusion layer was increased and the mechanical properties of LMCs were improved obviously, which was attributed to the optimized interfacial structure after diffusion process. In addition, the formation of TiAl3 intermetallic compounds (IMCs) was detected in the bonding interface, which played an important role in improving the mechanical properties for Al/Ti LMCs. The predicted results of stress-strain curves from rule of mixture (ROM) indicated that, there existed an extra interfacial strengthening in Al/Ti LMCs beside the mechanical properties provided by the contribution of constituent layers. The pre-rolling diffusion process is effective for the optimization of interfacial structure and improvement of mechanical properties in Al/Ti LMCs. [ABSTRACT FROM AUTHOR]