Increasing Rolling Strain Research Articles

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.

Microstructure and Texture Evolution of Hot-Rolled Mg-3Gd Alloy during Recrystallization

An Mg-3Gd (wt.%) sample with gradient rolling strains (ε = 0–0.55) was prepared using a wedge-shaped plate after one-pass hot rolling, allowing a high-throughput characterization of microstructure and texture over a wide strain range within one hot-rolled plate. The microstructure and texture evolutions were characterized as a function of rolling strain for the as-hot-rolled sample and as a function of annealing temperature for the subsequently annealed samples. The deformed microstructure showed a gradual change with increasing rolling strain, i.e., from a deformation twins-dominant structure in the low strain range of 0–0.20, to a shear bands-dominant structure in the higher strain range of 0.20–0.55. The recrystallization behavior during annealing showed a clear correlation between the recrystallization nucleation site and the deformed microstructure. However, a weak recrystallization texture with non-basal texture components was formed over almost the entire strain range. This work demonstrates a high-throughput experimental strategy using a wedge-shaped sample to investigate the effect of various processing parameters, such as strain and annealing temperature, on the evolution of microstructure, texture, and mechanical properties, which could accelerate the optimization of processing parameters and microstructural design.

Study on Microstructure and Properties of Single‐Pass Online Heating Rolling of Mn‐Containing Magnesium Alloy Sheets

Mg–2.0Zn–1.5Mn (ZM21) alloy and Mg–1.0Mn–0.5Al (MA10) alloy extruded bars have excellent mechanical properties and low processing cost. Herein, these two alloys sheets are rolled at different temperatures and reductions by online heating rolling. In addition, their mechanical properties and microstructure characteristics are also studied through electron backscattered diffraction. The results show that the yield strength of rolled ZM21 sheets is gradually improved with increasing rolling strain and temperature and further exhibits good comprehensive mechanical properties. The mechanical properties of ZM21 rolled sheets are slightly lower than that of AZ31 rolled sheet and have the potential to substitute the AZ31 sheet. However, MA10 alloy rolled sheet herein exhibits poor mechanical properties, indicating that the mechanical properties of MA10 alloy highly depend on the microstructures resulting from the processing parameters. The mechanism of poor mechanical properties and different mechanical behaviors of extruded bars and extruded sheets are discussed.

Development of the fine-grained Mg-0.6Zr sheets with enhanced damping capacity by high strain rate rolling

Fine-grained Mg-0.6Zr sheets are successfully prepared by high strain rate rolling (HSRR) at different strain rates of 10, 20 and 30 s−1. Microstructure, mechanical properties and damping capacity of the as-rolled sheets are carefully investigated. The as-rolled Mg-0.6Zr alloys are featured with average grain size below 10 μm and have only a small amount of dislocation tangles. With the increasing rolling strain rate, the dynamic recrystallization (DRX) grain size increases and the basal plane texture is weakened, resulting in the increase of damping property but little change in mechanical properties. The damping mechanism of the fine-grained Mg-0.6Zr sheets fits with the Granato-Lücke theory.

Effect of cold rolling on microstructure and mechanical properties of a Cu–Zn–Sn–Ni–Co–Si alloy for interconnecting devices

A Cu–Zn–Sn–Ni–Co–Si alloy has been developed to meet the requirements of high thermal stability and good processing properties for interconnecting devices. The effects of cold rolling on the microstructure and mechanical properties are investigated. The tensile properties, thermal stability, and microstructure are characterized, complemented by electron back-scatter diffraction analysis and transmission electron microscopy. The precipitated phase of the orthorhombic (Ni, Co)2Si has been found in the rolled alloy, which is incoherent to the Cu matrix. With the increasing rolling strain, the alloy exhibits higher tensile strength and thermal stability while the electrical conductivity and strain rate sensitivity remain constant. The increasing rolling strain has a combined effect on the matrix and precipitates, leading to higher densities of dislocation and twin as well as more and finer precipitates. After cold rolling to 50% stain, the tensile strength, electrical conductivity and softening temperature of the Cu–Zn–Sn–Ni–Co–Si alloy are 650 MPa, and 33% IACS, and 325 °C, respectively.

The role of Al content on deformation behavior and related texture evolution during hot rolling of Mg-Al-Zn alloys

Effect of Al addition on microstructure and texture evolution during hot rolling of Mg alloys was investigated using Mg-(3, 6 and 9 wt%)Al-Zn series alloys. The results showed deformation behaviors, including twinning, dynamic recrystallization and activation of slip system, were affected by the increase of Al content. Compared with AZ31 Mg alloys, the rolled AZ91 sample exhibited strong basal texture and intensity of basal texture decreased by increasing rolling strain. Unlike double twins and contraction twins which were commonly observed in the hot rolling of AZ31 Mg alloys, twinning behavior was strongly suppressed by the addition of Al content. It was observed some grain-like extension twins nucleated inside unrecrystallized grains with ultrafine size in AZ91. The size of dynamic recrystallized grains in AZ91 was ultrafine compared to that of AZ31 due to pinning effect produced by small Mg17Al12 particles. These recrystallized grains were distributed along grain boundaries and would continuously coordinate further deformation strain after their nucleation. The increase of the area fraction of recrystallized grains resulted in a texture weakness during large strain rolling in AZ91. Geometrically necessary dislocation information was analyzed for the rolled samples. It showed prismatic <a> slip took an advantage in AZ31 rather than AZ91 during hot rolling, which may be a reason for the weaker basal texture of unrecrystallized grains in AZ31.

Evaluation of microstructure and mechanical properties of Al–Zn alloy during rolling

Solid solution-treated binary Al–20% Zn alloy was deformed by rolling and accumulative roll bonding in the equivalent strain range of 0.19–12.05 at room temperature. The grain size of the Al matrix decreases with the increase in deformation degree and reaches the nanometre range. The dislocation density initially increased with the deformation degree and then decreased. The Zn-phase particles were dynamically precipitated from the Al–Zn supersaturated solid solution and then coarsened during rolling. Rolling after the strain of 12.05 did not result in full decomposition of the solid solution. The hardness of the Al–Zn was also investigated. Results showed that the value reached up to 119.76Hv at a strain of 2.92 and then decreased with increasing rolling strain. At the early stage of rolling, the strengthening mechanism of the rolled Al–Zn alloy included work hardening by dislocations, precipitation strengthening by nanosized precipitates and boundary strengthening by grain refinement. When the strain was larger than 2.92, the Al–Zn alloy's consistent softening was attributed to the decomposition of supersaturated solid solution, coarsening of the precipitate phase and annihilation of dislocations during severe plastic deformation.

Dynamic precipitation of Al–Zn alloy during rolling and accumulative roll bonding

In this study, cold rolling was performed on a binary Al–20 wt%Zn alloy and dynamic precipitation identified for the first time in Al alloys under cold rolling. Zn clusters formed after application of 0.6 strain, and the Zn phase precipitated upon further increasing strain. Both grain refinement and rolling-induced defects are considered to promote Zn precipitation. The hardness of Al–Zn alloy initially increased with strain up to a strain of 2.9 and then decreased with increasing rolling strain. Dynamic precipitation greatly affects the strengthening mechanism of the rolled Al–Zn alloy under various strains.

Intercritical Rolling Induced Ultrafine Lamellar Structure and Enhanced Mechanical Properties of Medium-Mn Steel

The medium-Mn steel with ferrite and austenite structure was rolled in the intercritical region down to different rolling reduction. The microstructure and mechanical properties of the rolled steels were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile tests. It was found that the ferrite and austenite structure gradually evolved into an ultrafine structure from the random directional lath structure to lamellar structure with lath longitudinal direction parallel to the rolling direction with increasing rolling strain. It was found that the thickness of the laths was gradually refined with increasing rolling strain. The lath thickness is about 0. 15 μm stored with high density dislocations and the austenite volume fraction of the steel is about 24% after 80% rolling reduction. Furthermore, it was interesting to find that yield strength, tensile strength and total elongation of the 80% rolled medium-Mn steel are about 1000 MPa, 1250 MPa and 24%, respectively, demonstrating an excellent combination of the strength and ductility. Based on the microstructure examination, it was proposed that the grain refinement of the medium-Mn steels could be attributed to the duplex structure and the low rolling temperature. Analysis of the relationship between the microstructure and the mechanical properties indicated that the high yield strength mainly resulted from the ultrafine grain size and the high density dislocation, but the improved ductility may be attributed to the large fractions of austenite retained after intercritical rolling.

Intercritical rolling induced ultrafine microstructure and excellent mechanical properties of the medium-Mn steel

The medium manganese steel (0.2C5Mn) was first intercritically annealed and then intercritically rolled up to thickness reduction of 77.5%. It was found that intercritical rolling resulted in a microduplex microstructure with ferrite and austenite lath thickness continuously thinned and gradually rotated to be parallel to the rolling plane with increasing rolling strain, and during which the austenite was most retained after intercritical rolling. Mechanical properties examination indicated that the yield stress increased from 492MPa to 980MPa, and the tensile strength increased from 1030MPa to 1296MPa, but the failure elongation (31.7%) was almost the same with increasing rolling strain. Based on the experimental results, it was proposed that the microstructural refinement of the 0.2C5Mn steel was carried by the geometric thinning of laths and the suppression of recrystallization of ferrite phase and austenite phase. The significantly enhanced mechanical properties by intercritical rolling were attributed to the refined microstructure and the TRIP effects of the large fractioned austenite phase.

Microstructural evolution and its influence on creep and stress relaxation in nanocrystalline Ni

Indentation creep and stress relaxation tests were performed on rolled and annealed nanocrystalline (NC) Ni to study the influence of microstructure evolution on plastic deformation behavior. Dislocation density (ρ) increases with increasing rolling strain, reaching a maximum at 20% strain, followed by a decrease at larger strain. The ρ of Ni decreases significantly with increasing annealing temperature. Softening behavior is observed in NC Ni with grain size <40nm, i.e., an inverse-like Hall–Petch effect. For rolling NC Ni, both creep strain rate and rate sensitivity first increase and then decrease, while those of annealed Ni continuously decrease. With increasing grain size, creep activation volume unusually decreases first, then starts to rise, which is different from that of coarse-grained metal. A model involving dislocation annihilation and emission at grain boundaries under indenters is used to explain the anomalous behavior of rolled and annealed Ni, respectively.

Investigating the effect of rolling strain on fracture behavior of roll bonded Al6061 laminates under quasi-static and dynamic loading

Damage tolerance improvement has been reported by laminating aluminum alloys and composites by researchers. Three-layer laminates comprising Al6061 outer layers and Al1050 interlayer have been roll bonded in this research. While most of the works done have focused on fracture properties of roll bonded Al laminates in crack arrester geometry, this study explores their behavior in crack divider configuration. Rolling strain is varied to control the interfacial bonding in laminates. The fracture behavior of laminates and the constituent material was examined via three-point bending and impact tests. This study presents significant improvement in damage tolerance of laminates compared to their monolithic counterpart. This work also highlights the importance of debonding as an effective toughening mechanism in these laminates. At high strain rate condition, it is shown that improving the interfacial bonding by means of rolling strain can increase the damage tolerance of the laminate as far as delamination is not suppressed. Results of this study also show that increasing rolling strain can eliminate debonding at interfaces and reduce damage tolerance of laminate.

Texture Development in a Cold-Rolled and Annealed Body-Centered-Cubic Mg-Li Alloy

The rolling and annealing textures formed in bcc Mg 14 wt pct Li have been investigated and compared with interstitial-free (IF) and more heavily alloyed ferritic steel rolled at the same temperature. The α fiber texture component ( //rolling direction) is very strong after 90 pct rolling at room temperature; however, there is evidence that the γ fiber ({111}//rolling plane) weakens with increasing rolling strain to give a peaklike texture centered on {111} . A rarely found cold rolling fiber texture has been identified, which has {100}//rolling plane and peaks at {100} . Annealing at 200 °C very rapidly produces {554} , which gives way to components near {111} on grain growth. The α fiber is destroyed by recrystallization; however, the {100}//rolling plane fiber shifts intensity from the as-rolled orientation {100} to {100} . Since texture largely determines drawability, the best that can be achieved in terms of press performance of this alloy is most likely a Lankford parameter of unity.

Microstructural Evolution and Crystallographic Texture Formation of Cold Rolled Austenitic Fe‐30Mn‐3Al‐3Si TWIP‐Steel

The microstructural and texture evolution of cold rolled low stacking fault energy fcc Fe‐30Mn‐3Al‐3Si alloy was investigated as a function of the cold rolling strain. The alloy was melted and cast in a vacuum induction furnace, hot rolled and annealed before being cold rolled at three different strains: ε = 0.035, e = 0.2 and ε = 1.2. During the cold rolling process different deformation mechanisms became active depending on the strain. At low strain levels, ε = 0.035 and ε = 0.2, slip traces were observed whereas at higher strains shear bands appeared. The brass orientation {110}&lt;112&gt; spreading towards the Goss orientation {110}&lt;001&gt; was dominant at every strain level. The intensity of these texture components increased with increasing rolling strain. The increase of the brass component was more pronounced when e varied from 0.035 to 0.2, whereas the increase of the Goss component was more pronounced when ε varied from 0.2 to 1.2. Additional texture components developed: the E orientation {111}&lt;110&gt; lying on the γ‐fibre and the S orientation {123}&lt;634&gt; lying on the ß‐fibre. This evolution is comparable to other low SFE fcc materials exhibiting the brass‐type texture.

Microstructural evolution during accumulative roll-bonding of commercial purity aluminum

The microstructure in commercial purity aluminum deformed from medium to high strain ( ε vM=1.6–6.4) by accumulative roll-bonding (ARB) at 473 K was quantitatively examined by transmission electron microscopy. It was found that a sub-micrometer lamellar structure characterizes the microstructure at high strains ( ε vM>1.6), and that the lamellar boundary spacing decreases and the misorientation across the lamellar boundaries increases with increasing rolling strain. This characteristic evolution has also been observed during conventional cold-rolling of commercial purity aluminum. However, a comparison between the two processes shows a significant difference in the evolution of the microstructural parameters. These differences are discussed based on the different processing conditions characterizing ARB and conventional rolling, respectively.

Structure and properties of low-carbon steel after deformation to high strains

The results of tensile tests carried out at various stages of deformation of a low-carbon steel by cold rolling are compounded to show the overall changes in mechanical properties during the process, which are then interpreted in terms of microstructural and fracto graphic changes. The rise in tensile stress with increasing rolling strain is essentially linear, with a plateau over a narrow strain range corresponding to a break up of the pearlite structure and the loss of its contribution to the strength. The linear increase in stress with further strain is associated with the formation of an increasing number of microbands within the ferrite portion of the structure where most of the strain is accommodated. A model is proposed for the formation of the microbands which is consistent with the observations. The microstructural changes with increasing strain are similar but not identical to those reported recently in pure copper.