Twin-roll Cast Sheets Research Articles

Improvement of strength and ductility synergy in a room-temperature stretch-formable Mg-Al-Mn alloy sheet by twin-roll casting and low-temperature annealing

• Twin-roll casting leads to the formation of uniform and fine grain structures. • The microstructure feature is effective to improve strengths-ductility synergy. • In-plane isotropic tensile property and good RT formability have been obtained. Strength and ductility synergy in an Mg-3mass%Al-Mn (AM30) alloy sheet was successfully improved via twin-roll casting and annealing at low-temperature. An AM30 alloy sheet produced by twin-roll casting, homogenization, hot-rolling, and subsequent annealing at 170 °C for 64 h exhibits a good 0.2% proof stress of 170 MPa and a large elongation to failure of 33.1% along the rolling direction. The sheet also shows in-plane isotropic tensile properties, and the 0.2% proof stress and elongation to failure along the transverse direction are 176 MPa and 35.5%, respectively. Though the sheet produced by direct-chill casting also shows moderate strengths if the annealing condition is same, the direct-chill casting leads to the deteriorated elongation to failure of 23.9% and 30.0% for the rolling and transverse directions, respectively. As well as such excellent tensile properties, a high room-temperature stretch formability with an Index Erichsen value of 8.3 mm could be obtained in the twin-roll cast sheet annealed at 170 °C for 64 h. The annealing at a higher temperature further improves the stretch formability; however, this results in the decrease of the tensile properties. Microstructure characterization reveals that the excellent combination of strengths, ductility, and stretch formability in the twin-roll cast sheet annealed at the low-temperature annealing is mainly attributed to the uniform recrystallized microstructure, fine grain size, and circular distribution of (0001) poles away from the normal direction of the sheet.

Through-thickness shear texture of the twin-roll cast AA6016 sheet after asymmetric rolling and its recrystallization behavior

In this study, we investigate the through-thickness shear texture F{111}<112> and r-cube {001}<110> of the AA6016 twin-roll cast sheet under asymmetric rolling (ASR) via simulation and experiments and its recrystallization behaviors after annealing at 330 °C for 60 min. ASR can be achieved by controlling the velocity ratio of the upper and lower rollers to 2.0. Finite element (FE) simulations in case of ASR are used to determine the shear strain through the sheet thickness. Polycrystal simulations are conducted based on the FE results to predict the shear texture. Subsequently, the crystallographic texture of the sheet obtained with unidirectional ASR processes is evaluated. The experimental results show that the F-texture is obtained and that the inhomogeneity was distributed. The F-texture intensity of the sample near the lower roller (sample A) was greater than that of the sample near the upper roller (sample B). The simulation results are in good agreement with the measured results. However, the simulation results obtained with respect to the r-cube texture are greater than the measured results, resulting in considerable deviation. Further, the different recrystallization behaviors of the F-oriented grains (F-grains) are determined based on the sheet thickness. The F-grains associated with sample A can be obtained based on the rolling texture contributed by continuous recrystallization, whereas those associated with sample B can be achieved via discontinuous recrystallization. A considerably inhomogeneous microstructure and texture are observed through the sheet thickness after annealing.

Relieving segregation in twin-roll cast Mg–8Al–2Sn–1Zn alloys via controlled rolling

Abstract Twin-roll casting (TRC) of Mg alloys with high Al content has unique advantages and broad development prospects. However, the severe segregation of high-alloyed Mg caused by TRC technology is difficult to solve at present, which restricts its practical application. In this work, the homogenization of coarse segregated phases in a twin-roll cast Mg–8Al–2Sn–1Zn (ATZ821) alloy was successfully achieved by a method combining solid-solution heat treatment and controlled rolling, which is suitable for industrial-scale production. In addition, the evolution of the microstructure was studied in detail. It was found that phases dynamically precipitated and dissolved repeatedly during the hot rolling process, and the evolution of entire second phases can be classified into three stages, i.e., the net dissolution, balancing and net precipitation stages. During the process, the large-size chain-like eutectic phases evolved into a fine and nearly spherical (∼0.4 µm) morphology that was uniformly dispersed in the Mg-matrix due to the thermodynamic coupling and the Ostwald ripening effect. Moreover, a fine grain microstructure (∼4 µm) was obtained. The formidable segregation problem of twin-roll cast Mg alloys with high Al content was solved, which is an important finding for the industrial application of high-alloyed twin-roll cast sheets.

Effect of Mn/Fe ratio on the microstructure and properties of 6061 sheets obtained by twin-roll cast

The effect of the Mn/Fe mass ratio on the microstructure and mechanical properties of vertical twin-roll cast 6061 sheets were investigated. The microstructure and morphology of the iron-rich phase of cast and rolled sheets were investigated using optical microscope, scanning electron microscopy, energy dispersive x-ray spectroscopy and transmission electron microscope. The effect of Mn on the equilibrium phase of 6061 aluminum alloy was analyzed by CALPHAD thermodynamic simulation. In addition, the mechanical properties of 6061 twin-roll cast sheets were tested using tensile tests. The results showed that as the Mn/Fe mass ratio increased, the iron-rich phase at the edge of 6061 twin-roll cast plates gradually transformed from acicular β-Al5FeSi phase to granular α-Al12(FeMn)3Si phase. The core gradually aggregated from a needle-like β-Al5FeSi phase to a star-like Al6(FeMn) phase, and finally to an irregular network and petal-like α-Al15(FeMn)3Si2 phase. When the mass ratio of Mn/Fe was 2.0, the twin-roll cast plates exhibited the best mechanical properties, with a tensile strength, yield strength and elongation of 204.80 MPa, 180.59 MPa and 17.83%, respectively.

Improvement of Spatial Inhomogeneity of Solute Elements and Mechanical Properties of Twin-Roll Cast Al-Mg-Si Alloy in Presence of Electromagnetic Fields

The objective of this work is to investigate the effects of electromagnetic external fields on the spatial distribution of alloying elements and the mechanical properties of Al-Mg-Si alloy prepared using twin-roll casting. The formation mechanism of macro/microsegregation and mechanical properties were examined, and the results indicated that the amount of centerline segregation defects was significantly reduced with the application of an external field. When a pulsed electric field and static magnetic field were applied simultaneously, the distribution of alloying elements in the thickness direction of the twin-roll cast sheet was the most uniform and the segregation was obviously suppressed. By virtue of the Lorentz force, the content of alloying elements in the matrix clearly increased, suggesting that such application of external fields can reduce segregation defects and improve the uniformity of the spatial distribution of alloying elements, ultimately improving the overall mechanical properties of AA6022 aluminum alloy.

Interfacial Reaction in Twin-Roll Cast AA1100/409L Clad Sheet During Different Sequence of Cold Rolling and Annealing

Besides cold rolling reduction and annealing temperature and time, sequence of cold rolling and annealing also affects interfacial reaction in twin roll cast (TRC) clad sheet. This is because of short contacting time between Al melt and steel and small rolling reduction in as-cast TRC sheet, which results in small and uneven distribution of metallurgical bonding in the sheet. In as-cast sheet, no intermetallic compound (IMC) appears at the bonding interface after 510 °C × 1.5 h annealing and the sheet has a high peeling strength of 21.5 N/mm. However, incubation period of IMC is shortened in the 40% cold rolled sheet. A 2.2 μm thick IMC layer appears in the 40% sheet after 510 °C × 1.5 h annealing and the peeling strength decreases to 15.5 N/mm. 25% reduction cannot reduce the incubation period. This is because the bonding interface becomes tight enough and its energy storage increases after 40% cold rolling and as a result, the inter-diffusion of Al and Fe atoms is enhanced during annealing.

Effects of shot peening parameters on gradient microstructure and mechanical properties of TRC AZ31

Microstructural variation along the depth of twin-roll cast sheet AZ31 Mg alloy was achieved by applying severe plastic deformation via intensified shot peening on the surface of the work-piece. Mechanical incompatibility between different layers from the ultra-fine crystallized structure on the peened surface to the un-deformed layers on the specimen interior introduces enhanced mechanical properties. AZ31 has shown distinct sensitivities to various parameters of the shot peening procedure such as pressure, shot size, and processing time. Thus, shot peening with shot sizes from less than 0.4 mm (conventional) to 3.18 mm for different processing times and under various pressures were performed to characterize their roles in controlling the microstructure and mechanical properties. Microstructural analysis revealed a direct relation between the thickness of the ultra-fine grained layer and severe shot peening parameters whereas each of them has a distinct effect on grain size. Electron backscatter diffraction data were used to define three distinct deformed layers wherein grain size and texture were changed during the process. Furthermore, microhardness tests demonstrated how pressure and shot size control fine grains at the surface. Tensile test results revealed that the best mechanical properties were obtained by maximum shot size and pressure at minimum processing time. Adding post-annealing treatment to the severely shot peened specimens enhanced ductility without a noticeable loss of ultimate strength. Consequently, this process has improved strength and ductility simultaneously.

Microstructure and texture development during deformation and recrystallisation in strip cast AA8011 aluminum alloy

In the present work, microstructure and texture development during deformation and recrystallisation of a twin roll cast (TRC) AA8011 aluminum alloy was investigated. TRC AA8011 alloy with initial thickness 7.2 mm and Fe:Si ratio ∼0.93 was cold rolled in a laboratory rolling mill to 2 mm final thickness. The cold rolled sheet was recrystallized at 375 °C and 450 °C for different times. The hardness decreased with increase in recrystallisation time for both temperatures, but there was no effect on centre line segregation (consisting predominantly of Al-Fe-Si intermetallics). XRD confirmed the presence of β-AlFeSi particles at all the stages of recrystallisation. The initial TRC sheet had a very weak texture close to brass ({110}<112>). After 72% cold rolling (final thickness, 2 mm), strong brass, copper ({112} <111>) and S ({123}<634>) texture i.e. metal type texture developed. Low temperature annealing (4 h at 375 °C) was found to give optimum combination of deformation texture and cube recrystallisation texture ({100} <100>) expected to improve the forming behavior of cold rolled and annealed sheet.

Effect of Electromagnetic Field on the Micromorphology of Twin-roll Cast 7075 Alloy

Abstract The micromorphology and the grain size of 7075 Al alloys were investigated by optical microscopy (OM). The rolled sheets were fabricated by electromagnetic field. It is found that the dendritic crystal of 7075 alloy sheet by alternating oscillating twin-roll cast (TRC) is severely broken, stretched, refined and equiaxed under the condition of pouring temperature 670 °C, compared with that of traditional TRC sheets. Meanwhile, the microstructures of the rolled sheets by static magnetic field (MF) process are also refined and stretched to some degrees with exciting current of 100 A. Segregation bands in center of TRC sheets are dramatically alleviated under the conditions of DC magnetic field and alternating oscillation field, while the influence of alternating oscillation TRC process is much more powerful. Hardness of 7075 sheets both on transverse and surfaces increases in turn along with traditional, static MF and alternating oscillation TRC. With increasing of electromagnetic intensity, the hardness and the properties of sheets are further improved. No matter wherever in the sheets, the influence of electromagnetic field will be further improved by elevated temperature.

Microstructural and Mechanical Characterization of ARB AZ31

In this work the influence of accumulative roll bonding (ARB) process on the microstructure and the mechanical characteristic is investigated. Therefore, AZ31 magnesium sheets were successfully deformed through ARB for a maximum of three passes. Twin roll cast sheets and twin roll cast sheets with subsequent heat treatment (480 °C, 1 h) were used as initial materials. After one ARB pass, the highest microstructure changes were measured. Electron backscattered diffraction (EBSD) reveals a bimodal microstructure with an average grain size of ~1µm. In comparison to the initial material a strong basal texture was measured. The significant refinement of grain size after severe plastic deformation cause an increase of tensile and compressive strength, e.g. rising yield stress and ultimate tensile strength of 42% and 15%, respectively. However, the maximum formability remains nearly at the same level. Further ARB passes do not improve the mechanical characteristics further.

Microstructure and texture evolution of TRC A8006 alloy by homogenization

The microstructure and texture evolution of twin-roll cast A8006 alloy by homogenization were characterized using scanning and transmission electron microscopy, and the microhardness was tested as well. According to the relationship between dendritic arm spacing and cooling rate the cooling rate of the as-cast twin-roll cast A8006 sheet of 6 mm in thickness was estimated as 1.48×103 K·s−1. It is found that the grains and the nanostructural precipitates of the twin-roll cast sheet become coarser after homogenization at 580°C for 4 h in comparison with those after homogenization at 500°C for 8 h. The textures formed after cold rolling and became weaker during homogenization. The increase in hardness of the as-cast twin-roll cast sheets is related to the supersaturated α-Al solid solution and fine microstructure, but the decrease in hardness after homogenization can be attributed to the coarsening of grains and Al6Fe(Mn) precipitates.

AZ31B マグネシウム合金セミソリッドスラリーを用いて連続鋳造した薄板の加工特性

We produced AZ31B magnesium alloy sheet by our semisolid casting method to cast slurry produced using an inclined cooling plate into the twin-roll. In this paper, the sheet obtained by this process was examined for texture, roll workability and Erichsen value compared with the chill cast plate and commercial AZ31B sheet. The results are as follows. The microstructure of continuously cast sheet exhibits fine grains of primary Mg-crystals. A (0001) pole figure of the continuously cast sheet confirms that the crystal direction was random and there was little rolling anisotropy. Influence of different heating temperatures on accumulative rolling reduction of the twin-roll cast sheet was not appeared by different roll directions versus the casting direction. The accumulative rolling reduction of the twin-roll cast sheet is higher than chill cast sheet in case of heating temperature of 473 K or less. The Erichsen test indicated excellent value.

TEM Investigation of Precipitation in Al-Mn Alloys with Addition of Zr

Aluminium and its alloys belong to the most widely used metallic materials for industrial applications. One of the possible casting methods is twin-roll casting which produces sheets with high solid solution supersaturation. Decomposition of this supersaturated material during heat treatment was studied in aluminium alloys from the AW-3003 series – one standard grade and the other modified by addition of zirconium. Characterization by differential thermal analysis and observations by electron microscopy revealed that precipitation of –AlMnFeSi phase occurred in two steps around 360 and 450 °C in twin-roll cast sheets, firstly on subgrain boundaries and afterwards also within the grains. In cold-rolled sheets, precipitates formed directly within the grains. The zirconium addition shifts recrystallization to higher annealing temperatures in the cold-rolled Zr-containing alloy. –AlMnFeSi

Twinning, dynamic recovery and recrystallization in the hot rolling process of twin-roll cast AZ31B alloy

Hot-rolling experiments with a reduction from 10% to 60% in single pass were conducted on AZ31B twin-roll cast sheets. Optical microscope (OM), electron backscattered diffraction (EBSD) tests and transmission electron microscope (TEM) were used to investigate twinning and DRV/DRX behaviors at different stage in the hot-rolling process. Two types of twinning occurred in the initial stage of hot-rolling process. DRV and discontinuous recrystallization dominated at moderate strain while continuous DRX took place homogeneously throughout original grains at the largest strains.

Microstructure and mechanical properties of Mg–Al–Mn–Ca alloy sheet produced by twin roll casting and sequential warm rolling

Microstructural evolution and mechanical properties of twin roll cast (TRC) Mg–3.3 wt.%Al–0.8 wt.%Mn–0.2 wt.%Ca (AM31 + 0.2Ca) alloy strip during warm rolling and subsequent annealing were investigated in this paper. The as-TRC alloy strip shows columnar dendrites in surface and equiaxed dendrites in center regions, as well as finely dispersed primary Al 8Mn 5 particles on interdendritic boundaries which result in the beneficial effect on microstructural refinement of strip casting. The warm rolled sheets show intensively deformed band or shear band structures, as well as finely and homogeneously dispersed Al–Mn particles. No evident dynamic recrystallization (DRX) takes place during warm rolling process, which is more likely attributed to the finely dispersed particle and high solid solution of Al and Mn atoms in α-Mg matrix. After annealing at 350 °C for 1 h, the warm rolled TRC sheets show fine equiaxed grains around 7.8 μm in average size. It has been shown that the present TRC alloy sheet has superior tensile strength and comparative elongation compared to commercial ingot cast (IC) one, suggesting the possibility of the development of wrought magnesium alloy sheets by twin roll strip casting processing. The microstructural evolution during warm rolling and subsequent annealing as well as the resulting tensile properties were analyzed and discussed.

Orientation analyses for twinning behavior in small-strain hot-rolling process of twin-roll cast AZ31B sheet

Small-strain hot-rolling experiments have been conducted on AZ31B twin-roll cast sheets. Optical microscope (OM), transmission electron microscope (TEM) and electron backscattered diffraction (EBSD) tests were used to study the various twinning behaviors in the rolling process. After 10% hot-rolling, grains lying with C-axes perpendicular to the ND twinned on the { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 1 〉 system with the largest SF, and rotated to orientations with C-axes aligned with ND, causing a sudden increase in basal texture consequently. With the increase of rolling reduction, { 1 0 1 ¯ 1 } − { 1 0 1 ¯ 2 } twins began to form in the new oriented grains, following the Schmid law. No evident increase in basal texture was found as rolling strain increased from 10% to 20% due to the inhomogeneous strain located in { 1 0 1 ¯ 1 } − { 1 0 1 ¯ 2 } twinned regions.

Formability of Twin-Roll Cast Age-Hardenable Mg-Zn Alloys

The suitability of a twin-roll cast (TRC) age-hardenable alloy for wrought applications is explored. A Mg-4Zn (wt.%) alloy, 3mm thick, was cast using the TRC route. Deviating from the traditional practice of homogenization followed by age-hardening in die/sand cast parts, the TRC sheet, cut into small strips, was hot rolled and annealed after homogenization. They were then deep drawn and subsequently age-hardened. The rollability, mechanical properties and microstructure of the alloy at different stages of processing and after forming, are presented and discussed.

Effect of Processing Parameters on Microstructure and Properties of Continuously Cast Al-Mg Sheets

Inner panels of modern ecological cars are nowadays manufactured from Al-Mg alloys. Continuously twin-roll cast sheets are a cost effective substitution for direct-chill cast sheets. The effect of composition and down-stream processing on sheet properties should be well understood in order to produce high quality products, which exhibit good formability and high strength. Finegrained microstructure and well-balanced texture are the necessary pre-requisites. Results of the investigation of twin-roll cast AlMg2Mn0.8 and AlMg3 alloys are reported. Sheets of 1.0 mm gauge were prepared using different processing routes. The route involving homogenisation results in grain coarsening and anisotropy, however, deep-drawing ability is affected only a little.