Multi-pass Cold Rolling Research Articles

Regulating the grain refinement and rolling properties of coarse-crystalline Mg-Zn-Gd-Ca-Mn alloy through multi-pass cold rolling and annealing

The newly developed Mg–Zn-RE (rare earth) alloy sheet shows significant prospects for 3C applications due to its superior room-temperature malleability compared to the commercial AZ31 alloy. However, the casting ingots of these alloys often exhibit coarse grains due to low alloying element content and the absence of the grain-refining element Zr, making them susceptible to significant cracking while hot-rolling. This study applies a multi-pass cold rolling technique with minimal reduction to a cast Mg–Zn-Gd-system alloy characterized by coarse grains, followed by a static annealing process to enhance its rolling capability. The impact of cold rolling and annealing temperatures on microstructure, plastic deformation mechanism, and static recrystallization (SRX) behavior were studied. It was found that multi-pass cold rolling with minimal decrease promoted the generation of more twins and slip lines, resulting in more uniform deformation and a substantial accumulated rolling strain of 10 %. Consequently, the significant accumulated strain, coupled with stress concentration at positions such as grain boundaries, twin boundaries, and dislocation tangles, acted as nucleation sites for complete static recrystallization at a specific annealing temperature of 375 °C. As a result, the coarse cast grains were successfully refined from 400 μm to 37 μm. Fortunately, this improvement has significantly enhanced the hot-rolling qualities, removing fractures throughout the process. This advancement not only enables industrial-scale rolling but also enhances production efficiency.

Texture evolution and strengthening mechanism of CuCrZr alloys during cold rolling

The evolution of microstructure and crystallographic texture in Cu–1Cr-0.061Zr alloy strips during multi-pass cold rolling deformation was studied. The results showed that the tensile strength of Cu–1Cr-0.061Zr alloy increased from 507 MPa to 683 MPa with increasing rolling strain, while the conductivity decreased from 84.1 to 68.1 of the International Annealed Copper Standard. When the strain is 1.86–3.85, the elongation is effectively stable at 7.5%–8.5%. The local strain and grain dislocation angle inside the alloy gradually increase with the increase in strain, and the grain orientation distribution becomes more uniform and stronger. The dislocation slip generated during the rolling process leads to the concentration of grain orientation toward the <11−1> direction, causing the Goss texture ({110}<001>) to gradually transform into a Copper texture ({112}<11−1>) with relatively stable grain orientation, which significantly improves the mechanical properties at the macro level. In addition, the heat generated during the cold rolling process causes the cancellation of heterologous dislocations on a certain slip surface, resulting in a decreased dislocation density and a slight growth of nanoprecipitates. Nanoprecipitation strengthening and grain boundary strengthening are the main strengthening mechanisms in the Cu–1Cr-0.061Zr alloy, while the strength contribution of banded Cr phase dispersion is relatively small.

Texture evolution during multi-pass cold rolling and annealing of Ti-2Al-1.5Mn alloy

In this contribution, the underlying mechanisms of microstructure evolution and texture development during the cold rolling and annealing of a Ti-2Al-1.5Mn alloy were investigated and elucidated comprehensively. As a result of the heightened dislocation density and grain boundary, the hardness ascended as the successive reductions applied. However, the annealing treatment reinstated the structure through complete recrystallization. During cold working, the dominant basal <a> and prismatic <a> glide inclined the c-axis and <101̅0> axis towards the compressive direction and the rolling direction (RD), respectively. The primary rolled orientation consisted of <101̅0> fiber, the orientation of {1̅21̅3}<101̅0> with Euler angle {10°, 45°, 0°}and {1̅21̅7}<101̅0> with Euler angle {5°, 25°, 0 °} were predominant. Schmid Factor (SF) analysis and orientation rotation related to various textures demonstrated that basal <a> slipping resulted in a descendingϕangle in the Bunge system and <101̅0> pole parallel to the RD was the stable orientation. It was revealed that the recrystallized grains preponderantly exhibited textures inherited from the rolled matrix, but a new T-type texture also emerged. This implies that both the strain-induced boundary migration (SIBM) mechanism and selective grain growth, which nucleates at different sites, manipulate the annealing process. The study enhances our comprehension of texture evolution mechanisms involved in the plastic forming and helps ascertain the most effective operational parameters for producing high-performance titanium plates.

Effects of Stacking Number on Microstructure and Mechanical Properties for Cold Roll Bonding Process of Dissimilar Aluminum Alloy Sheets

A cold roll-bonding (CRB) process is applied to study the effects of stacking number on the microstructure and mechanical properties of roll-bonded and age-treated Al sheets. Commercial AA1050 and AA6061 sheets with a thickness of 2 mm were stacked alternately on each other to two and four layers, and roll-bonded by multi-pass cold rolling. The roll-bonded Al sheets were then subjected to natural aging (T4) and artificial aging (T6) treatments. The as roll-bonded Al sheets showed a typical deformation structure, where the grains are elongated in the rolling direction regardless of the stacking number. However, after the T4 and T6 aging treatments, the Al sheets had a recrystallization structure consisting of coarse grains in both the AA5052 and AA6061 regions with different grain sizes in each. In addition, the sheets showed an inhomogeneous hardness distribution in the thickness direction, with higher hardness in AA6061 than in AA1050 after the T4 and T6 age treatments. The tensile strength of the T6-treated specimen was higher than that of the T4-treated one for both the 2 and 4-layer CRBs. In addition, both the tensile strength and elongation of the specimens processed by the 4-layer stack CRB were higher than those of the 2-layer stack CRB for all experimental conditions.

Role of unusual double-peak texture in significantly enhancing cold rolling formability of AZ31 magnesium alloy sheet

Multi-pass cold rolling experiments were performed on AZ31 magnesium alloy sheet with unusual double-peak texture, where basal poles tilt about ±40° away from normal direction to rolling direction. This adopted sheet was fabricated by a novel technology of equal channel angular rolling and continuous bending process with subsequent annealing. Experimental results confirm that such an unusual double-peak texture contributes to a huge improvement of accumulated reduction up to 39.2%, which is over twice as much as that (18.3%) in sheet with strong basal texture. Optical microscopy and electron backscatter diffraction measurements demonstrate that the evolution of microstructure and texture in sheet with unusual double-peak texture is quite different from that in sheet with strong basal texture. Schmid factor (SF) analysis confirms that sheet with unusual double-peak texture possesses obviously large SF values for basal 〈a〉 slip {1012} and extension twin (ET) and remarkably small SF values for prismatic 〈a〉 slip and pyramidal 〈c+a〉 slip during cold rolling process. Therefore, basal 〈a〉 {1012} slip and {1012} ET will be activated more frequently in sheet with unusual double-peak texture to sustain plastic strain, leading to significant enhancement in cold rolling formability.

The influence of microstructure and texture on the hardening by annealing effect in cold-rolled titanium

The purpose of this study was to compare the influence of microstructural and textural changes on the hardening by annealing effect in cold-rolled titanium. Ultrafine-grained (UFG) Ti Grade 2 was produced by multi-pass cold rolling (or warm rolling at 400 °C at the final stage) to different thickness reductions (90%, 95% and 97%) aimed at varying both the microstructural features of the material (dislocation density, grain size distribution and grain boundary characteristics) and its texture (the intensity and volume fraction of texture components). The hardening effect of UFG Ti Grade 2 sheets was obtained by a short-time annealing at 250 °C for 15 min. The highest strengthening, of about 4–5%, was observed for the UFG Ti Grade 2 sheet rolled to 90%; the strengthening gradually decreased for higher thickness reductions (down to ∼ 2% for 97%). The texture intensity and volume fractions of texture components for the annealed UFG Ti Grade 2 sheets were very close to their as-rolled counterparts, so this did not demonstrate any clear reason for the hardening effect. Instead, the dislocation substructure recovered during annealing at 250 °C, i.e. the dislocation density declined significantly, the remaining dislocations became rearranged, and it was easier to differentiate more nanosized subgrains of about 50–150 nm. The hardening by annealing effect was a result of the annihilation of mobile dislocations and the ordering of the dislocation substructure, mostly within coarse grains (>500 nm). The level of strengthening by low-temperature annealing was mainly affected by the fraction of coarse grains with a tangled-dislocation substructure in the as-rolled state, i.e. a higher fraction of coarse grains favored more pronounced strengthening. These observations seem to be very promising for optimizing the cold rolling process and short-time annealing of the UFG Ti Grade 2 sheets, which could be a simple and cost-effective way of enhancing their mechanical properties.

Thermal Stability and Mechanical Behavior of Ultrafine-Grained Titanium with Different Impurity Content

Ultrafine-grained (UFG) commercially pure (Ti Grade 2) and high-purity (Ti 99.99%) titanium can be a good alternative to less biocompatible Ti alloys in many biomedical applications. Their severe plastic deformation may lead to a substantial increase of strength, but their highly refined microstructure show a lower thermal stability which may limit their range of applications. The purpose of this study was to investigate the effect of interstitial elements on the thermal stability of UFG Ti Grade 2 and high-purity Ti 99.99% processed by a multi-pass cold rolling to the total thickness reduction of 90%. The severely cold rolled Ti sheets were annealed at temperature in the range of 100-600 °C for 1 h and, subsequently, they were evaluated in terms of microstructure stability, mechanical performance as well as heat effects measured by differential scanning calorimetry (DSC). It was found that the microstructure and mechanical properties were relatively stable up to 200 and 400 °C in the case of UFG Ti 99.99% and Ti Grade 2, respectively. DSC measurements confirmed the aforementioned results about lower temperature of recovery and recrystallization processes in the high-purity titanium. Surprisingly, the discontinuous yielding phenomenon occurred in both investigated materials after annealing above their thermal stability range, which was further discussed based on their microstructural characteristics. Additionally, the so-called hardening by annealing effect was observed within their thermal stability range (i.e., at 100-400 °C for UFG Ti Grade 2 and 100 °C for UFG Ti 99.99%).

Investigation on the corrosion behavior of Alloy 800H at various levels of deformation

The corrosion behavior of Alloy 800H in deaerated supercritical water was investigated. Multi-pass cold rolling was used to achieve thickness reductions of up to 80%, and the weight gain vs. time (up to 1000 h) in supercritical water at 600 ℃ and 25 MPa were obtained for specimens in the polished vs. ground surface condition. Polished specimens without rolling showed the highest corrosion rates, and surface grinding or cold rolling significantly increased the corrosion resistance. A thick oxide film develops, with an outer moderately uniform layer of magnetite (Fe3O4) with crystallites along the surface, and areas of uneven oxidation into the metal that incorporate Cr (e.g., FeCr2O4). Very few Cr2O3 particles exist, and preferentially near the grain boundaries. Continuous Cr-rich oxide films were found in the thin oxide films on the surface of ground specimens and heavily rolled specimens, and an associated Cr depleted zone in the metal under the oxide of ground specimens, but not in heavily rolled specimens. This indicates that the high density of dislocations accelerates the diffusion of elements and enhance the formation of Cr-rich oxide film, which promotes passivity.

Multi-pass cold rolling and wire drawing process of gadolinium and its magnetocaloric effect

Owing to low ductility of magnetocaloric material (MCM)s, the plastic deformation process is quite challenging, and information available on the deformation process of MCMs is limited. In this study, the cold rolling and wire drawing processes of Gd wire including heat treatment were conducted. Uniaxial compression test of as-cast and heat treated Gd rod was conducted to evaluate the material property. The magnetocaloric effect (MCE) of drawn Gd wire was indirectly measured using a vibrating sample magnetometer (VSM). Pass schedule of cold rolling and wire drawing process for the Gd wire of Ø1.0 was designed. Finite element (FE) simulation of drawing process was conducted to investigate the drawing force for each drawing pass and strain distribution. Friction coefficient between the drawing die and Gd wire was evaluated via FE simulation and drawing experiments using a lubricant. Magnetic properties of the deformed and annealed Gd wire were evaluated and compared. The evaluated magnetic properties have shown that the presented process schedule is reasonable for manufacturing magnetocaloric wire without diminishing the magnetocaloric effect.

Microstructure and Texture of an Aluminum Plate Produced by Multipass Cold Rolling and Graded Annealing Process

In order to explore the microstructure, texture, individual performance, and grain size characteristic evolution law during the process of multipass cold rolling, graded annealing process, the experimental design, research approach, and methodology were investigated using the equipment of optical microscope (OM), X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and transmission electron microscope (TEM). The results show that a low interannealing temperature could strengthen the cubic texture after finished product annealing, and a high volume fraction of cubic texture components was subsequently obtained. In view of the nucleation advantage of cubic texture, the Cube-{001}&lt;100&gt; texture formation after annealing was promoted by the cold-rolled texture of Cu-{112}&lt;111&gt; and S-{123}&lt;634&gt;, which mainly depended on the decomposition of Cu and S textures, finally, they were consumed and transformed from Cu and S textures into a cubic texture. In addition, the dislocation configuration and corrosion pit density were clearly visible and distinctive in the observation space of aluminum foil.

The cold rolling load distribution of the nuclear power zirconium alloy based on the self-adaptive particle swarm optimization algorithm

Aiming at the problem of load distribution during multi-pass cold rolling of nuclear zirconium alloy strip, the load distribution model with good plate shape is established by the self-adaptive particle swarm optimization (SAPSO) algorithm, considering the main constraint conditions including rolling force, reduction, and torque in cold rolling process. Based on the penalty function method transforming the constraint problem into the unconstrained problem, the particle swarm optimization algorithm (PSO) combined with self-adaptive inertia weight factor optimized the load distribution model is developed to improve the local search ability of the particle swarm optimization algorithm. Compared with the original nuclear zirconium alloy cold rolling schedule, the simulation results of load distribution based on the SAPSO algorithm can keep good plate shape in multi-pass cold rolling process with the high prediction accuracy. The industrial experiments demonstrate that the proportional crown difference value is consistent, and the plate shape flatness is good.

Enhanced cold deformability of a marine Cu-Ni-Al–Fe-Mn alloy produced by HCCM vertical continuous casting: effect of deformation mechanism and second phases

ABSTRACT Cu-Ni-Al–Fe-Mn alloy billets were prepared by heating–cooling combined mould (HCCM) continuous casting at different casting speeds. Then, the cold deformation behaviour of billets was studied by multi-pass cold rolling, and the effects of HCCM continuous casting on cold deformability were discussed by comparing with the mould casting (MC) alloy. The results show that HCCM continuous casting significantly improves the cold deformability of Cu-Ni-Al–Fe-Mn alloy billets. When the rolling reduction is 94%, HCCM continuous casting samples have good edge quality without obvious crack, while the MC sample has severe edge cracks. With the rolling reduction increasing from 40% to 94%, the elongation of the MC samples decreases from 6% to 2%, while that of HCCM continuous casting samples maintains in 6%∼9%, showing good continuous deformability. The HCCM continuous casting samples with lower casting speeds have [001] oriented columnar grains along the casting direction, which make the deformation mechanism change from nano-crystallization to parallel stacking faults. In the meanwhile, HCCM continuous casting improves deformation coordination of as-cast grains and restrains intergranular cracking, which is reflected in the influence on misorientation between as-cast grains and distribution of coarse NiAl phases. In addition, nano-twins found in the rolled MC sample promote the initiation and propagation of cracks.

Autowave Criteria of Fracture and Plastic Strain Localization of Zirconium Alloys

Plastic deformation and fracture of Zr–1% Nb alloys exposed to quasi-static tensile testing have been studied via a joint analysis of stress-strain curves, ultrasound velocity and double-exposure speckle photographs. The possibilities of ductility evaluation through the εxx strain distribution in thin-walled parts of zirconium alloys are shown in this paper. The stress-strain state of zirconium alloys in a cold rolling site is investigated considering the development of localized deformation bands and changes in ultrasound velocity. It is established that the transition from the upsetting to the reduction region is accompanied by the significant exhaustion of the plasticity margin of the material; therefore, the latter is more prone to fracture in this zone exactly. It is shown that traditional methods estimating the plasticity margin from the mechanical properties cannot reveal this region, requiring a comprehensive study of macroscopically localized plastic strain in combination with acoustic measurements. In particular, the multi-pass cold rolling of Zr alloys includes various localized deformation processes that can result in the formation of localized plasticity autowaves. Recommendations for strain distribution division over the deformation zone length in the alloy in the pilger roll grooves are provided as well.

Effect of Prior Austenite Grain-Size on the Annealing Twin Density and Hardness in the Austenitic Stainless Steel

The present study examined the effect of prior austenite grain size on twin density and hardness of austenitic stainless steels (ASS). The 253 MA and 316L ASS were subjected to multi-pass cold rolling to reduce thickness up to 2.3 mm. Subsequently, the rolled steels were heat treated at 1100°C at 0, 900, 1800, 2700, and 3600 seconds in a tubular furnace in a hydrogen atmosphere. At the end of the annealing time, the rolled steel was quenched in the cooled zone of the tubular furnace until it reached room temperature in a hydrogen atmosphere. Then, microstructure observation of ASS was done to identify the austenitic grain size and annealing twin, and a hardness test was performed using the micro-Vickers hardness scale. The line intercept method was used to measure the changes in 253 MA and 316L austenitic grain sizes. ImageJ software was used to measure grain size and twin length. The results showed that austenite grains of both steels grew normally; 253 MA ASS had a lower SFE and K value than 316L ASS, which indicated that 253 MA ASS had sluggish grain growth, smaller grains, more easily formed annealing twins, and higher twin density. The Hall–Petch coefficient, K’, of 253 MA ASS was higher than 316L ASS, which resulted in a higher hardness value. The Sellars, Pande and Hall-Petch models were shown to predict austenite grain sizes, twin density, and hardness in 253 MA and 316L ASS.

Role of effective strain on the deformability of brittle Hf-based bulk metallic glass

Numerical finite element method (FEM) calculation results reveal that the effective strain differs between the ductile Zr-based bulk metallic glass and brittle Hf-based bulk metallic glass (BMG) during rolling at room temperature. The current results demonstrated that the deformation mechanism of ductile Zr-based bulk metallic glass can be explained by perceptibility of multiple shear bands formation, however, the deformation mechanism of brittle Hf-based bulk metallic glass is represented by uniformly distribution of effective strain through overall specimen rather than localized into shear band. The variation of stress and the distribution of effective strain change significantly near the surface region of a Hf-based bulk metallic glass plate with increasing number of rolling passes. Under elasto-plastic deformation by cold rolling, the brittle Hf-based BMG has a thickness strain (εt) of −0.012, and the neutral effective strain (εeff) is 0.011 at the thickness direction, respectively. We present experimental confirmation that when the applied effective strain can be adjusted to below 1.1% during elasto-plastic deformation then even the brittle as-cast Hf-based BMG can be deformed up to 44% thickness reduction and 23% width expansion after multi-pass cold rolling without fracture by localization of shear stress.

Formation of Heterogeneous Microstructure in AA1050/AA5052/AA6061/AA1050 Layered Sheet Processed by Cold Roll-Bonding and Subsequent Annealing.

A cold roll-bonding process was applied to fabricate an AA1050/AA6061/AA5052/AA1050 four-layer clad sheet and subsequently annealed. Three types of aluminum alloy sheets such as AA1050, AA6061 and AA5052 with 2 mm thickness, 40 mm width and 300 mm length were stacked up each other after such surface treatment as degreasing and wire brushing, then reduced to a thickness of 2 mm by multi-pass cold rolling. The rolling was performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 400 mm at rolling speed of 6.0 m/sec. The roll bonded AA1050/AA6061/AA5052/AA1050 clad sheet was then annealed for 0.5 h at 200~400 °C. Microstructures of the as-roll bonded and subsequently annealed aluminum sheets are investigated by electron back scatter diffraction (EBSD) measurement. After rolling, the roll-bonded AA1050/AA5052/AA6061/AA1050 sheet showed a typical deformation structure that the grains are largely elongated to the rolling direction. However, after annealing, it exhibits a very heterogeneous structure consisting of both deformation structure and recrystallization structure containing nanometer order grains. The formation of this heterogeneous structure and texture with annealing is investigated in detail through EBSD analysis.

The Effect of a Composite Nanostructure on the Mechanical Properties of a Novel Al-Cu-Mn Alloy through Multipass Cold Rolling and Aging

An effective approach composed of solution treatment, multipass cold rolling and aging was developed to improve the strength and ductility of novel Al-Cu-Mn alloys. This approach increased the yield strength by 214 MPa over that of the conventional peak-aged samples while maintaining a good elongation of 8.7%. The microstructure evolution was examined by confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). During postaging, deformed structures underwent a considerable decrease in dislocation density and typical dislocation network structures were formed. At the same time, highly dispersed nanoprecipitates and extensive ultrafine grains and nanograins were generated. These nanoprecipitations enabled effective dislocation pinning and accumulation during tension deformation. Therefore, composite nanostructures containing ultrafine grains, nanograins, dislocation network structures and nanoprecipitates were responsible for the simultaneous increases in strength and ductility. This paper provides a new understanding of designing composite nanostructure materials for achieving high strength and good ductility that is expected to be used for other age-hardenable alloys and steels.

Stress states of a tool and a billet during multi pass cold rolling of rectangular splines on shafts

It is proposed to use the contact stresses that arise when rolling splines on the shafts to predict the complex profile of the part, resources and moments of failure of the tool and the shaft. Keywords contact stresses, plastic deformation, rolling, knurling roller. AWA-adakin@yandex.ru

Effects of annealing temperature on the interfacial microstructure and bonding strength of Cu/Al clad sheets produced by twin-roll casting and rolling

Abstract In this paper, Cu/Al clad sheets were prepared by twin-roll casting and multi-pass cold rolling. Annealing treatment was performed at temperatures of 250 °C, 300 °C, 350 °C and 400 °C, separately. The influences of the annealing temperature on the interface layer structure, peel strength and peeled surface microstructure of the clad sheets were studied. The crack propagation behavior in the peeling process of the clad sheets was revealed, and the strengthening mechanism of the interface was explained. The results showed that the Cu/Al interface metallurgical bonding rate increased and the intermetallic compound layer thickness could be controlled within 550 nm after annealing at 250 °C, which encouraged more cracks to propagate along the Al matrix, and the average peel strength could reach approximately 39 N/mm. However, after high-temperature annealing treatment (350 °C and 400 °C), the clad sheet broke completely in the intermetallic compound layer, and a large number of cleavage fractures appeared, which caused the bonding strength to decrease sharply.

Microstructure and Mechanical Properties of AA6061/AA5052/AA6061 Complex Sheet Fabricated by Cold-Roll Bonding Process

A cold roll-bonding process is applied to fabricate an AA6061/AA5052/AA6061 three-layer clad sheet. Two AA6061 and one AA5052 sheets of 2 mm thickness, 40 mm width, and 300 mm length are stacked, with the AA5052 sheet located in the center. After surface treatment such as degreasing and wire brushing, sample is reduced to a thickness of 1.5 mm by multi-pass cold rolling. The rolling is performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 400 mm at rolling speed of 6.0 m/sec. The roll bonded AA6061/AA5052/AA6061 complex sheet is then hardened by natural aging(T4) and artificial aging(T6) treatments. The microstructures of the as-roll bonded and age-hardened Al complex sheets are revealed by optical microscopy; the mechanical properties are investigated by tensile testing and hardness testing. After rolling, the roll-bonded AA6061/AA5052/AA6061 sheets show a typical deformation structure in which grains are elongated in the rolling direction. However, after T4 and T6 aging treatment, there is a recrystallization structure consisting of coarse equiaxed grains in both AA5052 and AA6061 sheets. The as roll-bonded specimen shows a sandwich structure in which an AA5052 sheet is inserted into two AA6061 sheets with higher hardness. However, after T4 and T6 aging treatment, there is a different sandwich structure in which the hardness of the upper and lower layers of the AA6061 sheets is higher than that of the center of the AA5052 sheet. The strength values of the T4 and T6 age-treated specimens are found to increase by 1.3 and 1.4 times, respectively, compared to that value of the starting material.