Increasing Thickness Reduction Research Articles

Study on microstructure evolution mechanism and inhomogeneous characteristic of 2219 aluminum alloy in hot flow forming

In order to reveal the evolution mechanism of the deformation microstructure of 2219 aluminum alloy tube under compression-shear stress, in this paper, flow forming tests and their numerical simulations were carried out, respectively, at temperatures from 250 °C to 400 °C. Meanwhile, a midrange layer index was proposed to analyze the gradient of deformation microstructure. The results show that multiple recrystallization mechanisms of the 2219 aluminum alloy are presented simultaneously during hot flow forming. The shear stress during forming is the main factor that generated the microstructure gradient along the thickness direction, and the recrystallization level is higher with higher shear strain. In addition, it is beneficial to improve microstructure homogeneity and mechanical properties by increasing thickness reduction or decreasing the temperature. This study provides guidance for microstructure control of the 2219 aluminum alloy tube flow forming process.

Strain-dependent heterogeneity of microstructure and mechanical properties of 2195 Al–Li alloy during power spinning and heat treatment

The effect of thickness reduction (20 % in each pass) on microstructure evolution and mechanical properties of 2195 Al–Li alloy during hot power spinning and the subsequent heat treatment were investigated. As a result, high-performance 2195 Al–Li alloy tube with a thickness of 1.56 mm was successfully fabricated. The results showed that the strain localization of spinning led to the heterogeneity of microstructure and mechanical property along the wall thickness direction of the spun tube. With the increase of thickness reduction, dynamical recrystallization set up from the outer surface and propagated to the inner surface, and thus refined the microstructure, improved the mechanical properties, and reduced the heterogeneity in the microstructure and mechanical properties of the spun tube. However, after heat treatment, abnormal grain growth appeared in the microstructure near the inner surface of the spun tube with a moderate thickness reduction, triggering a severer inhomogeneity in the microstructure and mechanical properties. A large enough thickness reduction could induce sufficient dynamic recrystallization, which led to the disappearance of abnormal grain growth of spun tube during heat treatment. Grain boundary strengthening and precipitation strengthening were the dominant strengthening mechanisms of 2195 Al–Li alloy spun tube.

Quantitative characterization of Zr60700 alloy plate rolling in different directions based on electron back-scatter diffraction

Fully annealed Zr60700 alloy plates with a thickness of 15 mm were rolled at 15%, 30%, 45%, 60%, and 75% thickness reductions, and the rolling paths were unidirectional rolling (UR) and cross-rolling (CR), respectively. Electron back-scatter diffraction (EBSD) experiments revealed that the texture developed gradually towards the basal texture with increased thickness reduction. Severe orientation hardening enhanced the deformation resistance of the CR sample, resulting in a higher grain size than the UR sample. The plastic deformation during the rolling process was dominated by dislocation slip. The results of the prediction based on the Schmid factor (SF) and the calculation based on the in-grain misorientation axis (IGMA) showed that the prismatic <a> slip was the primary deformation mode in the early stages of the UR and CR processes. With the increase in thickness reduction, the basal <a> and pyramidal <c+a> slip played an increasingly important role. Compared with the UR process, the CR process was more accessible to activate the basal <a> slip and more conducive to forming the basal texture. Mechanical tests showed that the CR samples exhibited higher isotropy than the as-received and UR samples.

Synergistic effect of B2 phase and O phase in hot-rolled Ti2AlNb alloy and its influences on mechanical properties

The Ti2AlNb alloy, solution-treated at 1070 °C, underwent hot rolling at 960 °C with different thickness reductions to investigate the synergistic effects of the O phase and B2 phase and their impact on its properties. The results reveal that after solution treatment, the Ti2AlNb alloy consists of nearly spherical O, lath O, and B2 matrix at 30% and 50% thickness reductions during hot rolling. However, at a 70% thickness reduction, the alloy exhibits spherical O, worm-like O, and a continuously distributed B2 phase. The α2 phase formed during solution treatment decomposes during hot rolling. As the thickness reduction increases from 30% to 70%, the O phase content initially rises and then declines, accompanied by an increase in the average dimension of the O phase from 0.25 ± 0.16 μm to 0.36 ± 0.18 μm. Additionally, the B2 phase in the alloy undergoes dynamic recrystallization (DRX) during hot rolling, coinciding with the growth and spheroidization of the O phase. With an increase in the thickness reduction during hot rolling, the elongation of the alloy increases from 5.9% at 30% reduction to 12.47% at 70% reduction. Meanwhile, the ultimate tensile strength reaches its peak value of 1092.2 MPa at 30% reduction, decreases to 936 MPa at 50%, and then increases to 970 MPa at 70%. The tensile strength of the alloy improves due to the interaction and accumulation of dislocations at the phase interface. The continuous distribution of the B2 matrix, dislocation movement, rotation of the O phase, DRX of the B2 phase, and interface slip all contribute to enhanced ductility. Furthermore, the fracture behavior of the Ti2AlNb alloys under various hot rolling conditions was elucidated.

Effect of cold rolling on microstructure and mechanical property of a novel (Fe50Mn30Co10Cr10)97C2Mo1 high entropy alloy

Effect of cold rolling on microstructural evolution and mechanical properties of a novel (Fe50Mn30Co10Cr10)97C2Mo1 high entropy alloy has been investigated via electron microscopy and tensile testing. The results show that the alloy is mainly deformed via dislocation and twinning due to its low stacking fault energy. With increasing thickness reduction, the dislocation density first increases, up to a maximum of ∼29.3 × 1014 m−2 at CR 60 %, then reduces, to 21.1 × 1014 m−2 at CR 90 %. The width and spacing of the deformation twins gradually decrease with an increase of thickness reduction. TEM examination also reveals that shear bands produce in CR 40 % sample, and that its volume fraction gradually increases with increasing thickness reduction. Such microstructural evolution with cold rolling, gives rise to a quick enhancement of yield strength of the alloy (1926 MPa for CR 90 % vs. 239 MPa for the as-homogenized sample) whereas a clear loss in ductility. However, the cold-rolled samples at low to medium strains show a good combination of strength and ductility, e.g., CR 20 % sample has a yield strength of 800 MPa (, which is 3.3 times higher than that of as-homogenized HEA) and an elongation of 30 %, while 1300 MPa yield strength and 15 % elongation for CR 40 % sample.

Microstructural Considerations of a Multi-Pass Rolled Ti-Nb-Ta-Zr Alloy.

The microstructural characteristic evolution was investigated during thermomechanical processing of Ti-29Nb-9Ta-10Zr (wt %) alloy, which consisted of, in a first stage, in a Multi-Pass Rolling with increasing thickness reduction of 20%, 40%, 60%, 80%, and 90%; in step two, the multi-pass rolled sample with the highest thickness reduction (90%) was subjected to a series of three variants of static short recrystallization and then to a final similar aging. The objective was to evaluate the microstructural features evolution during thermomechanical processing (phase's nature, morphology, dimensions, and crystallographic characteristics) and to find the optimal heat treatment variant for refinement of the alloy granulation until ultrafine/nanometric level for a promising combination of mechanical properties. The microstructural features were investigated by X-ray diffraction and SEM techniques through which the presence of two phases was recorded: the β-Ti phase and the α″-Ti martensitic phase. The corresponding cell parameters, dimensions of the coherent crystallite and the micro-deformations at the crystalline network level for both recorded phases were determined. The majority β-Ti phase underwent a strong refinement during the Multi-Pass Rolling process until ultrafine/nano grain dimension (about 9.8 nm), with subsequent slow growing during recrystallization and aging treatments, hindered by the presence of sub-micron α″-Ti phase dispersed inside β-Ti grains. An analysis concerning the possible deformation mechanisms was performed.

Nonlinear ultrasonic characterization of joint structures using backscatter guided waves

Abstract Joint structures made from plates or shells are frequently used in large constructions, such as oil storage tanks in petrochemical industries. The corrosion-induced metal loss often appears on the back side of the bottom plate supported by ground or sand. The welding residual stress and weight of shell walls accelerate the corrosion. Determining the severity of metal loss under the joint is challenging. This work uses the mode pair technique for nondestructive inspection of inaccessible regions in joint structures. A finite element analysis model simulates the transient responses of the incident and mode-converted fundamental and second harmonic plate waves. The second harmonic s0 plate wave satisfying the phase velocity matching condition accompanies the transmitted fundamental SH0 plate wave. A directional filter identifies every mode-converted plate wave by comparing the frequency spectra with the dispersion curves. Linear ultrasonic guided waves can detect inaccessible regions using mode-converted reflections. The symmetry of the linear mode-converted fundamental plate waves depends on the defect position and geometry, not the size. The mode-converted second harmonic guided wave can achieve better spatial resolution for defect sizing. The nonlinear parameter shows a proportional trend with an increasing thickness reduction. Experimental and numerical evidence reveals nonlinear ultrasonic guided wave technique has the potential for defect detection in joint structures.

The Rollers’ Offset Position Influence on the Counter-Roller Flow-Forming Process

Background: The general counter-roller flow-forming (CRFF) process rarely considers the roller’s offset position for the symmetric rollers. However, the rollers’ offset position can regulate the tube shape, force, and other features. Studying the novel asymmetric CRFF process, which is the CRFF process with the rollers’ offset position, is essential. Methods: The influence of the rollers’ offset position, the tube blank thickness, thickness reduction on the material deformation, flow-forming force, final tube middle radius, and thickness in the CRFF process are studied using AA5052 aluminum tube experiments and numerical simulation. Result: The final tubes with three tube blank thicknesses, four thickness reduction, and four rollers’ offset positions were obtained by the symmetric and asymmetric CRFF processes. Conclusions: AA5052 aluminum alloy tube can be made by the novel asymmetric CRFF process using a small rollers’ offset position (−17.5–0%). Different rollers’ positions could change the tube’s middle radius. With negative rollers’ offset position, the outer roller force is larger than the inner roller force. The force differences increase with the increase of tube blank thickness, the increase of thickness reduction, and the decrease of rollers’ offset position. The asymmetric CRFF process helps design and construct large tube flow-forming equipment.

The dependency of work hardening on dislocation statistics in cold rolled 1050 aluminum alloy

In this contribution, the phenomenon of work hardening is studied as a function of the nature of dislocation evolution with change in the level of deformation for commercially available 1050 Al alloy. To investigate the nature of dislocations in the cold-rolled aluminum alloy, total dislocation density was calculated using the indentation technique as well as by implementing two numerical approaches. For estimation of a statistically representative value of geometrically necessary dislocations (GND), electron backscattering diffraction measurements were performed over a large area (~ 0.5 mm2). The GND density of deformed samples was quantified by the implementation of a modified kernel average misorientation technique as well as by using Nye's dislocation density tensor for corresponding lattice curvature. The values of statistically stored dislocations (SSD) are obtained based on the assessment of the total dislocation density and GND values after different straining levels. The study provides both qualitative and quantitative illustrations of the mechanism of dislocation multiplication as thickness reduction increases, thereby, increasing the hardness of the samples. The results obtained reveal that the hardening of rolled materials is majorly governed by the SSD density at lower deformation. However, as the deformation level approaches the value of ~0.4, the density of GNDs rises and its contribution becomes significantly accountable for the strain hardening of the material. On the other hand, it has been observed that at lower straining levels the generated GNDs are trapped at grain boundaries and have a high contribution towards forest dislocations but with an increase of strain, the GNDs have a tendency to contribute nearly equally to mobile and forest dislocations. The estimated stored energies for samples subjected to rolling reduction ranging between 5.3 and 76% tend to change between the 5.6 kJ/m3 and 343.3 kJ/m3.

XFEM Simulation of Tensile and Fracture Behavior of Ultrafine-Grained Al 6061 Alloy

In the present work, the tensile and fracture behavior of ultra-fine grained (UFG) Al 6061 alloy was simulated using extended finite element method (XFEM). UFG Al 6061 alloy processed by cryorolling (CR) and accumulative roll bonding (ARB) was investigated in this work. Numerical simulations of two-dimensional and three-dimensional models were performed in “Abaqus 6.14” software using an elastic-plastic approach, and the results obtained were validated with the experimental results. The specimens corresponding to the three-point bend test, compact tension test with center crack, and double edge cracks were analyzed using XFEM (eXtended Finite Element Method) approach. In XFEM, the partition of unity (PU) was used to model a crack in the standard finite element mesh. The tensile and fracture properties obtained from the simulation were in tandem with the experimental data. UFG Al alloy showed higher tensile strength and fracture toughness compared to their bulk solution treated counterparts. Fracture toughness was measured in terms of stress intensity factor and J integral. In CR Al alloys, with increasing thickness reduction, an increase in stress intensity factor and a decrease in the J integral was observed. This behavior is attributed to the increase in strength and decrease in ductility of CR samples with increasing thickness reduction. In ARB Al alloys, the strength and ductility have increased with an increase in number of cycles. It also revealed an increase in both the stress intensity factor and J integral in ARB processed Al alloys with increase in number of cycles, as evident from XFEM simulation results.

Evolution of microstructure and electrochemical corrosion behavior of CuZn-based alloys induced by cold rolling

In this work, we investigated the influence of thickness reduction on the microstructure, mechanical properties and electrochemical corrosion resistant of the cold-rolled CuZn-based alloy. With the increase of thickness reduction from 50% to 80%, the <111> orientation degree, the content of Sn-rich phase and pore defects of the alloys were all increased. While the compressive stress, tensile strength, electrochemical corrosion potential and corrosion current density were firstly increased with the increase of thickness reduction, then decreased when the thickness reduction was further increased to 70%. The variation of the mechanical properties and electrochemical corrosion resistant of the CuZn-based alloys was due to the variation of orientation, compressive stress, the content of precipitated phase and pore defects which was induced by the increase of dislocation density and vacancies, and the dynamic recovery and recrystallization during cold rolling process.

Asymmetric cold rolling of AA7075 alloy: The evolution of microstructure, crystallographic texture, and mechanical properties

In the present work, for the first time, the effect of asymmetric rolling at room temperature on the microstructural evolution, texture, hardness, tensile properties, and fracture surface of AA7075 alloy was investigated. It was found that the width of grains significantly decreased to 2.6 μm by 60 % asymmetric rolling. Also, shear bands in the RD-ND (rolling direction – normal direction) plane of AA7075 after 40 % and 60 % asymmetric rolling were evident. In addition, the size of iron-rich intermetallic particles was reduced with increasing thickness reduction. Microstructure and texture revealed that new grains through continuous dynamic recrystallization (CDRX) are created after 40 % and 60 % strain. On the one hand, after applying only 10 % thickness reduction, average hardness demonstrated 75 % enhancement. On the other hand, maximum yield (611 MPa) and ultimate tensile (644 MPa) strengths achieved in the 60 % deformed sample, demonstrating 287 % and 73 % improvement compared to the initial sample. These results were due to strain hardening, dynamic/static precipitation, and Fe-rich particle fragmentation. The Portevin-Le Chatelier (PLC) effect is reduced with increasing the strain. Interestingly, the 40 % deformed sample revealed the serrated flow. For this reason, the 40 % rolled sample has a lower total elongation (4.4 %) than the 60 % deformed sample (11.1 %). The tensile strength of the 40 % deformed sample (575 MPa) was lower than the 10 % and 20 % rolled samples (581 and 594 MPa, respectively). This result was owing to the occurrence of softening mechanisms, strengthening the Goss {110}⟨001⟩ component, and weakening the Copper {112}⟨111⟩ orientation after 40 % asymmetric rolling. By increasing the thickness reduction up to 40 %, the number of dimples decreased. However, the fracture surface of the 60 % deformed sample showed a noticeable amount of small dimples.

Computational modelling of cold rolling of ferritic iron containing ε-Cu precipitates

The precipitation strengthening of ferritic iron using copper particles was studied using a molecular dynamics model. The developed model simulated the cold rolling of a ferrite sample containing copper precipitates at three different thickness reductions. The dislocation density and the amorphous structure in the ferrite sample increased as the thickness reduction increased. The copper particles experienced severe elongation, and their aspect ratios increased as the thickness reduction increased. It was found that the copper particles lose the fcc structure and transform to amorphous and bcc structures. As the thickness reduction increases, a fraction of the atoms changing to the bcc structure dissolved into the ferrite matrix. The remaining bcc structure atoms were at the interface between the copper particles and the ferrite matrix. Tensile testing of the deformed samples confirmed that the copper particles strengthened the ferrite for up to 30 % thickness reduction, while above 30 % resulted in lower strength due to copper particles’ dissolution.

Investigation of Flow-Formability of an AZ31 Magnesium Alloy

Flow-formability of a Ca-added AZ31 magnesium alloy tube is investigated. The flow-forming process is conducted at various temperatures (100–500 °C), thickness reductions (30–85%), and feed rates (0.1–0.56 mm/rev). Inner and outer surfaces of the tubes are heated by means of a thermal element embedded inside the mandrel and a radiation element, respectively. The formed tubes are visually inspected for the occurrence of cracking and fractures. Microstructures and tensile properties of the samples are analyzed by optical microscopy and tensile test, respectively. It is shown that deformation above 200 °C is required for sound processing with the occurrence of dynamic recrystallization (DRX). Up to 200 °C, the twinning-induced shear banding is the dominant phenomenon in microstructural evolution and responsible for the early strain localization and subsequent fracture. By increasing the temperature, the maximum achievable thickness reduction increases. However, at about 300 °C, the maximum thickness reduction reaches a limit value of about 76%. A twist in the deformed part of the tube occurs at greater thickness reductions. A simple analytical model is presented to analyze the occurrence of the twist phenomenon. Accordingly, a flow-formability map is proposed for the alloy. The DRX grain size is shown to follow a power law with the temperature compensated strain rate known as the Zener–Hollomon parameter. While the grain size is not affected by the feed rate, dimensional accuracy is deteriorated at feed rates over 0.2 mm/rev due to the diametral growth of the workpiece. Based on the tensile test results, by increasing the deformation temperature, the tensile strength increases and the ductility decreases, so that the sample processed at 500 °C shows a brittle fracture. The impacts of temperature on the strength and ductility are attributed to the combined effects of microstructural and texture evolutions during the flow-forming process.

Combined effects of low temperature nitriding and cold rolling on fatigue properties of commercially pure titanium

The combined effects of low-temperature nitriding (LTN) and cold rolling on the microstructure of commercially pure titanium (CP titanium) were investigated. The grain size of the LTN-treated CP titanium decreased with increasing thickness reduction due to the cold rolling pre-treatment and with decreasing the nitriding temperature. The fatigue limit for the nitrided CP titanium depended on the grain size beneath the nitrided layer and increased with decreasing the nitriding temperature because of the suppression of grain-coarsening. Furthermore, the LTN at 873 K decreased the friction coefficient and reduced the wear loss of CP titanium during the ball-on-disk dry friction tests.

Influence Research of Al and Zn Addition for Twin Roll Casting Magnesium During Multi-Pass Hot Rolling

This study was aimed at revealing the influence of Al and Zn additions on microstructure, texture evolution and mechanical properties of twin roll casting Mg during multi-pass hot rolling. Firstly, both pure Mg and AZ31 sheets were rolled 9 passes with ∼80% thickness reduction. More effective grain refinement in AZ31 compared to pure Mg after hot rolling, which caused by the pinning effect from fine Mg17Al12 particles present in AZ31 alloy. Meanwhile a strong basal texture gradually formed with increasing thickness reduction in pure Mg. With Al and Zn adding, the texture intensity of AZ31 was much lower than pure Mg in each rolling-pass. The 5th AZ31 sample features a maximum intensity of ∼12.9, which is reduced by 50.6% as compared to the value of ∼26.1 for pure Mg. Compared to pure Mg, the Al and Zn solutes and weakened texture in AZ31 favor the strong work hardening, which promotes a simultaneous high ultimate tensile strength of ∼270 MPa and ductility of ∼22% in the 5th AZ31 sample. The results will be helpful for the TRCed Mg alloys with huge potential for industrial application.

EBSD Study of the Effect of Hot Deformation on Low Carbon Bainitic Structure

The effect of deformation temperature (DT) and thickness reduction on the bainitic structure was investigated under various test conditions by using hot compression on a Gleeble-1500 thermo-mechanical simulation machine, and electron back scattering diffraction (EBSD) technique. In the case of the bainitic structure consisting of granular bainite (GB), lath bainite (LB) and a little ferrite (AF) under the given deformation conditions, DT and thickness reduction have remarkable effect on the transformation kinetics, starting temperature (B) of bainite fast transformation, and the type of bainitic structure. With the decreasing of DT from 810 °C to 730 °C, the starting temperature of transformation B increase from 585 °C to 595 °C. When the thickness reduction was 0 % and 20 %, the microstructure consists of GB, LB and a little AF, whereas as the thickness reduction increase to 40 %, large grain size of LB and GB disappear, and only AF and M/A remained. With the thickness reduction increases from 0 % to 40 %, the effective grain size decreases from 4 μm to 2 μm, and the fraction of HGB increases from 48 % to 57 %.

Delamination analysis in single-point incremental forming of steel/steel bi-layer sheet metal

Layered metallic materials (LMMs) offer superior properties in comparison to their counterpart monolithic sheets. Single-point incremental forming (SPIF) has emerged as an economical solution to produce LMM parts. However, delamination can limit the formability of such parts. In this study, the delamination analysis during SPIF of layered sheets was performed. Steel/steel bi-layer sheets were fabricated by roll bonding. These sheets were produced at thickness reduction ratios of 47%, 58% and 70%. The bond strength and fracture toughness in mode I and mode II were determined by T-peel and tensile shear tests, respectively. When the thickness reduction ratio was increased from 47 to 70%, an increase in bond strength was observed with 572% increase in mode I and 15.6% in mode II, respectively. On the other hand, with the same percent increase in thickness reduction, the critical strain energy release showed an increase of 3992% in mode I and 20% decrease in mode II. Surface-based cohesive zone model was used to define the interface between layers during numerical simulation of SPIF for delamination analysis. To validate the numerical results, SPIF of given bi-layer sheet was performed experimentally and a good agreement between the numerical and experimental results was observed.

Effect of Warm Rolling and Annealing on Microstructure, Texture, and Mechanical Properties of a 2205 Duplex Stainless Steel

The effect of warm rolling and annealing processes on the microstructure, microtexture, and mechanical properties of a 2205 duplex stainless steel is investigated in this work. To evaluate the microstructure, scanning (SEM) and transmission electron microscopy (TEM) and electron backscatter diffraction are used as the main techniques. The mechanical properties are assessed through tensile tests. A transition from a bamboo type into a pearl structure is observed as the thickness reduction increases. Furthermore, the ferrite phase presents a weakening of the α‐fiber (&lt;011&gt;//rolling direction, RD) and a development of γ‐fiber (&lt;111&gt;//normal direction, ND), whereas the austenite has a reduction in the intensity of the {110}&lt;112&gt; brass component and a strengthening of the {110}&lt;001&gt; Goss and {112}&lt;111&gt; copper components. Multistage work hardening behavior is observed by Jaoul–Crussard analysis, which indicates the presence of secondary deformation mechanisms during the plastic deformation of the steel. Post‐deformation SEM and TEM results reveal the formation of α′ and ε‐martensite at deformed regions. The orientation relationship that develops between γ‐ and ε‐martensite is Shoji–Nishiyama (S–N) &lt;110&gt;γ//&lt;2110&gt;ε.

Evolutions of the microstructure, texture and mechanical properties of a cold rolled Al-0.8Mg-0.8Si-0.66Cu-0.1Fe-0.12Cr alloy

The evolutions of microstructure, texture and mechanical properties of an Al–Mg–Si–Cu alloy subject to cold rolling were investigated by scanning electron microscope, transmission electron microscope, electron backscattering diffraction and x-ray diffraction in this study. The evolution of the shape of grains was characterized by EBSD. TEM was used to observe the distribution of the dislocations. The texture of the rolled alloy was analyzed using x-ray diffraction. In addition, the fracture morphologies of the samples after tensile deformation were observed by SEM. The results revealed that the grain size decreases during the cold rolling process, accompanied by increase of the dislocation density. High density of the dislocations and dislocation tangles resulted in the formation of subgrains. In addition, when the thickness reduction is large enough, about 70%, β fiber formed run though the Euler angle space from the Copper orientation {1 1 2}〈1 1 1〉 through the S orientation {1 2 3}〈6 3 4〉 to the Brass orientation {0 1 1}〈2 1 1〉 according to the x-ray diffraction results. The intensity of β-fiber increases with the increase of the thickness reduction. With the thickness reduction increases to 90%, the intensity of β fiber increases to the highest value. The cold rolled Al–Mg–Si–Cu alloy with a rolling reduction of 90% has excellent comprehensive mechanical properties along 45° to the rolling direction, with the yield strength and tensile strength being about 265 MPa and 280 MPa, respectively, and the elongation being about 12.6%. The yield strength and elongation have improvements of about 12% and 52% compared to the sample stretched along the rolling direction.