Twin-roll Casting Research Articles

Microstructural evolution and mechanical properties of titanium-alloying high borated steel sheets fabricated by twin-roll strip casting

High borated steels have been applied in the nuclear power industry as excellent neutron-shielding materials, but their ductility was relatively low due to the large and brittle borides, restricting their wider utilization. In this work, the high-performance borated steels containing 2.40 wt% B were fabricated through a designing combination of titanium-alloying along with twin-roll strip casting technology. It was found that titanium addition facilitated the increasing boron content of eutectic point for steels. The TiB2 particles solidifying firstly from molten steel depleted massive boron atoms in advance, leading to an as-cast microstructure consisting of more γ-Fe and less M2B-type borides comparing with titanium-free steels. Besides, TiB2 particles were 200–240 nm, and they could act as heterogeneous nucleation cores for M2B borides. Thus dispersive and fine M2B borides smaller than 5 μm were produced in as-cast microstructure. After subsequent hot-rolling and solution-treating, ultra-fine borides were obtained with more than 80% of which in a size range of 0.1–2 μm. In this case, the steels exhibited an excellent total elongation of 16.2% that was twice as high as that of titanium-free steels. Additionally, the relations between microstructure and mechanical properties of hot-rolled and solution-treated steels were clarified. The ductility of steels was determined by the volume fraction of γ-Fe matrix that could accommodate large deformation, but the strength of steels was dominated by the volume fraction of borides that provided the strengthening effects including grain refinement, load transfer term and hindering the dislocation slip. This work provided a new promising method to enhance the ductility of such high borated steels.

Analysis of defects in a twin roll cast Mg‐Y‐Zn magnesium alloy

AbstractTwin roll casting (TRC) enables the production of magnesium strips in an economic manner. TRC has enormous potential for the production of thin strip material from magnesium alloys. However, a range of defects may arise during casting. Internal and surface defects also influence the final properties of TRC strips. In this work, the magnesium alloy Mg‐6.8Y‐2.5Zn‐0.4Zr (WZ73) containing long‐period stacking ordered (LPSO) structures was twin roll cast with different process parameters, and the defects that arose were investigated. In particular, defects such as surface bleeds, center‐line segregations and deformation segregations in the mid‐thickness of the strip were observed and analyzed with regard to the TRC parameters applied. The latter may have developed due to the solidification of solute‐rich liquid in the center of the strip. X‐ray diffraction analysis was carried out to determine the phase compositions within the casting defects. A (Mg,Zn)3Y phase was found to precipitate in a blocky or lamellar shape within large, plate‐like LPSO phases. Wavy lines resulting from high specific rolling forces can be avoided if specific rolling force does not exceed a value of 8 kN/mm. Casting speed of 1.5 m/min has proven to be favorable to prevent the occurrence of center‐line segregation.

Effect of second-phase particle evolution in a twin-roll-casted Al-Mg-Si alloy on recrystallization texture and mechanical anisotropy

In this study, the evolution of second-phase particles in a twin-roll-casted (TRC) Al-Mg-Si alloy is analyzed, and the influence of this evolution on recrystallization texture and mechanical anisotropy is investigated. Based on the obtained results, homogenization significantly affects second-phase particles by promoting dissolution of Mg2Si phases, transformation of the Fe-rich intermetallic phase, and precipitation of AlMgSi dispersoids. During TRC and homogenization, different distributions of second-phase particles (coarse intermetallic phases and fine dispersoids) are achieved. These distributions control the recrystallization texture intensity and components and have a great impact on mechanical anisotropy. For example, the TRC sheet that has a large number of coarse intermetallic particles is characterized by very weak Cube-ND {001} 〈310〉 texture. This sheet has the highest average normal anisotropy r (0.71) and lowest planar anisotropy ∆r (0.077) among the investigated samples. Compared to the non-homogenized sheet, the homogenized counterparts exhibit enhanced texture intensity due to the dissolution or transformation of the intermetallic phase and increase in the number of fine dispersoids. Moreover, the main texture component in these sheets gradually changes to Cube {001} 〈100〉 orientation. To improve the application prospects of the TRC Al-Mg-Si alloy, further studies must be conducted regarding the effects of alloy designing and short process optimization on the material.

Novel Direct Cladding of Magnesium and Aluminum Alloys Using a Horizontal Twin Roll Caster

This study introduces the direct cladding of magnesium and aluminum alloys using a horizontal twin roll caster in one step. A horizontal twin roll caster can cast a Mg/Al clad strip with thickness exceeding 5mm at a roll speed of 8m/min in one step, which is difficult for a vertical twin roll caster. Therefore, it is possible to cast a thick clad strip with different melting point alloys using a horizontal twin roll caster at low speed. It is also possible to cast clad strips using as the overlay an alloy that has a higher melting point than that of the base strips. The thickness of the Mg/Al clad strip is 6.5mm, and the ratio of the Mg layer to the Al layer is 3:2. The surface of the clad strip is good, and there is no void between bonding interfaces. The mixing layer of the bonding interface is deeply related to the reduction rate. As the reduction rate increases, the mixing layer becomes more balanced and the thickness of the mixed layer decreases to 68μm. By observation of the interface of the cladded material, the mixed layer of the bonding interface is divided into two layers. It has been found the mixed layer near the Al layer has the highest hardness (up to 228HV), and the tensile shearing strength of the manufactured Mg/Al clad strip was 44MPa.

Cast-rolling force model in solid−liquid cast-rolling bonding (SLCRB) process for fabricating bimetal clad strips

Based on twin-roll casting, a cast-rolling force model was proposed to predict the rolling force in the bimetal solid−liquid cast-rolling bonding (SLCRB) process. The solid−liquid bonding zone was assumed to be below the kiss point (KP). The deformation resistance of the liquid zone was ignored. Then, the calculation model was derived. A 2D thermal−flow coupled simulation was established to provide a basis for the parameters in the model, and then the rolling forces of the Cu/Al clad strip at different rolling speeds were calculated. Meanwhile, through measurement experiments, the accuracy of the model was verified. The influence of the rolling speed, the substrate strip thickness, and the material on the rolling force was obtained. The results indicate that the rolling force decreases with the increase of the rolling speed and increases with the increase of the thickness and thermal conductivity of the substrate strip. The rolling force is closely related to the KP height. Therefore, the formulation of reasonable process parameters to control the KP height is of great significance to the stability of cast-rolling forming.

Roll Casting of Al-Mg-Si Alloy

The aluminum alloy Al–5%Mg–2%Si, the chemical content of which is close to that of the Magsimal-59 aluminum alloy commonly for die casting, was successfully cast into strips using a vertical high-speed twin-roll caster at a speed of 30 m/min. This means that Al–5%Mg–2%Si is suitable for the high-speed twin roll-casting. The as-cast Al–5%Mg–2%Si strip was then successfully cold-rolled to a thickness of 0.7 mm. Tension and cup tests were conducted on the cold-rolled annealed strips. The tensile stress was 205 MPa and the elongation was 20% for a thickness of 1 mm. The limiting drawing ratio was 2.0 at a 0.7 mm thickness. The present results demonstrates that Al–5%Mg–2%Si can be used for die casting and sheet forming. This means that use of this alloy for both sheet forming and die casting could eliminate the need for the separation of wrought aluminum alloys from cast aluminum prior to processing at recycling plants.

Casting of Al-Mg Strip Using Single Roll Caster Equipped with a Scraper

A scraper was attached to an unequal-diameter twin-roll caster without requiring large modifications. This caster was used as a 1000 mm diameter single roll caster equipped with a scraper, and its strip casting ability was tested. The effects of the scraper angle and load, the roll speed, and the pouring temperature of the molten metal on the scribed surface, thickness distribution and average strip thickness were investigated. The scribed surface characteristics were sound and the thickness distribution was flat when the scraper angle was 60° and the scraper load was in the range of 1 to 4 kg. When the scraper load was more than 1 kg, the thickness distribution was uneven. The average strip thickness decreased as the roll speed increased. The pouring temperature of the molten metal influenced the evenness of the solidified layer thickness. The solidified layer became even as the molten metal temperature was decreased. A strip cast with the determined optimal conditions was then cold rolled down to 1 mm to improve its surface quality.

Thermal, magnetic and mechanical behavior of large-sized Fe-based amorphous alloy ribbons by twin-roll strip casting

Fe-based amorphous alloys are characteristic of high saturation magnetization, low coercivity, and low core loss, which holds a grand promise for several engineering applications, such as soft magnetic, corrosion-resistant and wear-resistant coatings. However, poor amorphous forming ability (AFA) and size limit remain the main obstacles in applications. This study aims to address those scientific-technical challenges through a twin-roll strip casting method to yield two cost-effective Fe-based amorphous alloy (Fe73Mo4B5Si5P8C5 and Fe80Al2B5P9C4) ribbons with ca. 200-μm thickness and promising soft magnetic functions. Their crystallization behavior, thermal stability, magnetic properties, and mechanical performance for melt-spun and annealed alloys were studied systematically. Results demonstrate that Fe73Mo4B5Si5P8C5 and Fe80Al2B5P9C4 present good thermal stability, a large temperature interval between Tg and Tx1(61.7 °C for Fe73Mo4B5Si5P8C5 and 43.1 °C for Fe80Al2B5P9C4) infers that both the alloys have good processability. Meanwhile, Fe80Al2B5P9C4 amorphous alloy subjected to annealing at 450 °C for 300 s exhibited high saturation magnetization greater than 1.5 T, low coercivity of 5.3 A/m and high hardness of 989 Hv, which were attributed to the utterly amorphous structure and superior thermal stability achieved by twin-roll strip casting. Integrating the favorable mechanical, magnetic characteristics and high manufacturability of ultra-thick Fe73Mo4B5Si5P8C5 and Fe80Al2B5P9C4 amorphous alloys indicates that twin-roll strip casting is a sound solution to tackle the poor AFA and size limit in production of amorphous ribbons.

Physical and computational study of a novel submerged entry nozzle design for twin-roll casting process

With significant emphasis on reducing the turbulence in the bath and the need for effective distribution of metal along the roller length in twin-roll casting, a novel submerged entry nozzle (SEN) configuration with two “gap regions” was provided. The “gap regions” of the new SEN divide the bath into two parts, the “upper melt bath” (casting region) and the “lower melt bath” (rolling region). The newly designed SEN was tested by using both full-scale water modeling experiments and numerical simulations. Results demonstrated that the turbulence could only be found near the rotating roller surfaces. The “gap regions” can make the near-wall flows more uniform. They can also prevent the instabilities in the “upper melt bath” to be transferred to the “lower melt bath”, thus improving the stability of the process. Moreover, the novel SEN can stabilize the meniscus where the initial solidification occurs. This is achieved by increasing the SEN immersion depth, which in turn, can enlarge the volume of the upper part of the bath.

Cracking Possibility Evaluation of 304 Stainless Steel During Twin Roll Casting by 3D Simulation

The crack morphologies of 304 stainless steel strip after twin roll casting were observed by scanning electron microscope (SEM). Its phase transformation was calculated by Jmatpro software. Then a 3D stress model of twin roll cast stainless steel strip was developed by ANSYS software. The simulation results show good accordance with the crack observation. Then the stress fields with different casting speeds were simulated, and the cracking possibilities were evaluated. The results show that the stress mainly distributes on the contact surface between molten pool and roll. The risky points are located at the outlet, specifically, close to the side dams and the center of molten pool. With the increase of casting speed, the stress decreases and the stress peak caused by phase transformation disappears gradually. When the optimized casting speed is 0.2-0.4 m/s, no crack initiates on the stainless steel strip during twin roll casting process.

The evolution of Σ3 grain boundaries in the strip-cast Hi-B grain orientated Fe-6.5% Si alloy

A novel high magnetic induction Fe-6.5%Si alloy with B800 that reached up to 1.77 Telsa was prepared by twin-roll strip casting. Electron backscattered diffraction (EBSD) investigations demonstrated that Σ3 grain boundaries formed in the body-centered cubic (BCC) metal solidified microstructure without phase transition where the ratio of grain boundaries was greater than 20%. Transmission electron microscopy (TEM) revealed that the partial Σ3 grain boundaries are BCC structured twinning. A certain amount of Σ3 boundaries were inherited from the process of warm rolling, cold rolling and annealing, which acted to stabilize the matrix grain boundaries, resulting in the formation of a perfect Goss microstructure with excellent magnetic properties.

Hot Deformation and Dynamic Recrystallisation Behaviour of Twin-Roll Cast Mg-6.8Y-2.5Zn-0.4Zr Magnesium Alloy.

In this work, the deformation behaviour of a twin-roll cast (TRC) Mg-6.8Y-2.5Zn-0.4Zr alloy during plane strain compression was characterised by high-temperature testing. Based on the experimental data, the values of strain-rate sensitivity, the efficiency of power dissipation and the instability parameter were investigated under the conditions of various hot deformation parameters. In contrast to conventionally cast material, no lamellae of the LPSO (long period stacking ordered) phase were precipitated in the magnesium matrix after TRC. The precipitation of fine lamellar LPSO phases only occurred during cooling to forming temperature after the heat treatment. Dynamic recrystallization (DRX) hardly occurred during deformation at temperatures between 350 °C and 400 °C. This can be attributed to the precipitation of the lamellar LSPO phases, which contribute to retardation of the DRX process. At higher deformation temperatures and strain rates DRX is pronounced and the twin-induced (TRDX) as well as continuous dynamic recrystallization could be identified as the dominant softening mechanisms. The processing maps were established by superimposing the instability map over the power dissipation map, this being associated with microstructural evolution analysis in the hot deformation processes. Two instability zones could be recognised for the twin-roll cast and heat-treated Mg-6.8Y-2.5Zn-0.4Zr alloy: (1) 350 °C to 460 °C and 0.01 s−1 to 0.3 s−1 and (2) 485 °C to 525 °C and 2.5 s−1 to 10 s−1, where deformation is not favourable.

Improving Mechanical Properties of Twin-Roll Cast AZ31 by Wire Rolling

Since 2018, the institute of metal forming has been studying the novel twin-roll casting (TRC) of magnesium wire at the pilot research plant set up specifically for this purpose. Light microscopic and scanning electronic investigations were carried out within this work and show the unique microstructure of twin-roll cast AZ31 magnesium alloy with grain sizes of about 10 μm ± 4 μm in centre and 39 μm ± 26 μm near the surface of the sample. By means of a short heat treatment (460 °C/15 min), segregations can be dissolved and grain size changes in centre to 19 μm ± 12 μm (increase) and near the surface to 12 μm ± 7 μm (decrease). Further, the mechanical properties of the twin-roll cast and heat-treated wire were analysed by tensile testing at room temperature. By heat treatment, the total elongation could be increased by a third whereas the strength decreases slightly. In heat-treated state, no preferred orientation is evident. In addition to the twin-roll cast and the heat-treated condition, the rolled state was analysed. For this purpose, the twin-roll cast wire was hot rolled using an oval-square calibration. After hot rolling, a dynamic recrystallization and grain refinement of the twin-roll cast wire could be achieved. It can be seen, that an increase in strength as well as in total elongation occur after wire rolling. Beside this, a rolling texture is evident.

Microstructure and Precipitate Evolution in Cu-3.2Ni-0.75Si Alloy Processed by Twin-Roll Strip Casting

Given the sub-rapid solidification characteristics of twin-roll strip casting (TRSC), the solidification structure and growth process of precipitates during aging treatment were studied. The results showed that TRSC could refine the solidification structure and inhibit the microsegregation of Cu-3.2Ni-0.75Si alloy. During aging treatment, the precipitates mainly consisted of rod β-Ni3Si and disk δ-Ni2Si. The precipitate size was increased by increasing the aging time, which altered the mechanism of precipitation strengthening. Also, the experimental results indicated that precipitate strengthening arises either from the cutover mechanism or from the Orowan mechanism. Furthermore, the Avrami equation, which describes the kinetics of phase transformation and electrical conductivity during aging were established for the Cu-Ni-Si alloy, and the calculated results are consistent with the data. The Cu-3.2Ni-0.75Si alloy after aging treatment at 450 °C for 4 h exhibited optimum performance, and the tensile strength and electrical conductivity were as high as 711 MPa and 43.2% IACS, respectively.

Processing and characterization of vertical twin roll cast aluminium alloy sheets of A356, A6061 and A6005

Aluminum alloys A356, A606 and A6005 were twin roll cast in sheets 3 mm thickness using a vertical twin roll caster. Microstructure, hardness and wear characteristics of the cast sheets were investigated. VTRC processed sheets showed finer grain size depending upon the solidification range of alloy. It was observed that hardness values of VTRC alloys were significantly higher than those of corresponding ingot cast alloy products. Approximate Hall-Petch calculations show possibilities of additional strengthening mechanisms other than grain boundary for VTRC processed alloys. Extensive wear studies were performed using a pin on disc wear testing machine. The parameters like wear constant, specific wear rate and average friction coefficient were determined to understand the wear behaviour. The wear results show that all the alloy sheets exhibit wear in the mild wear regime.

Preparation of Papers for IFAC Conferences & Symposia: Soft sensor control for twin roll casting processes of magnesium alloys

Increasing lightweight constructions ensures a growing interest in economically produced magnesium sheets. The process of magnesium twin roll casting makes this possible by combining several different process steps into one process. However, due to the harsh process conditions, it is not possible to directly record the relevant process parameters to control product properties. Therefore, in this article will be discussed, how twin roll casting process can be transformed into a property-controlled process with a soft sensor. The digital image of the process is created by usage of an extended layer model, developed as a digital twin for offline computation and whose calculation times are many times shorter than in the FEM method. This makes it possible to train the digital twin and use it for online controlling in the TRC process. As a result, from the sensor data on the roller surface, which in turn forms the computational core of the required soft sensor, conclusions can be drawn about the state of the material in the rolling gap.

PRECIPITATE EXTRACTION FROM 3003 ALUMINUM ALLOY PRODUCED BY TWIN ROLL CASTING/ EXTRAÇÃO PRECIPITADA DE 3003 LIGAS DE ALUMÍNIO PRODUZIDAS POR FUNDIÇÃO EM ROLO DUPLO

In the present study four different precipitate extraction techniques were investigated on a 3003 aluminium alloy samples (twin-roll cast and homogenized conditions). The dissolution product was analyzed with the help of X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The performance of four chemical solutions (iodine solution, perchloric acid, oxine solution, and phenol solution) was compared, and the phenol solution presented the best precipitate extraction results. The phases in the cast and homogenized microstructures were identified, explaining some aspects of the phase transformation during the homogenization.

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.

Evolution of microstructure and texture during homogenization in a strip cast AA8011 aluminum alloy

The present study investigates the effect of homogenization on microstructures and texture evolution in a TRC i.e. twin roll cast Al-Fe-Si aluminum alloy (AA8011). TRC AA8011 alloy with an initial thickness of 7 mm was cold rolled upto 50% thickness reduction and homogenized at 580 °C for different times (4h, 8h, and 12h). The initially elongated grains (due to TRC) were further deformed and transformed into a banded structure after cold rolling and the large Al-Fe-Si particles in the as-cast microstructure also reduced in size. After homogenization, the elongated banded grain structure changed to an equiaxed structure and the second phase particles Al-Fe-Si became finer (~2 μm) and more uniform. The near needle shaped second phase particles present in the deformed structure became rounded, which is beneficial for deformability. However, the centerline segregation (CLS) was not removed even after homogenization. Initial TRC AA8011 alloy had a very weak texture consisting of Brass ({110} <112>), Goss ({110} <001>), S ({123} <634>) and Cube ({100}<100>). After cold rolling, Brass, Goss, and S strengthened, while Cube ({100}<100>) decreased at mid-thickness of the samples. At the surface, the deformation texture was predominantly near Brass. At mid-thickness, homogenization at 580 °C improved Cube in general, and the maximum Cube texture was obtained for 8 h (~7.7%) along with weak Brass and Goss. The deformation texture components were absent at the surface with minor variation in Cube.

Effect of casting speed on microstructure, corrosion behaviour and in vivo bone reaction of Mg-rare earth alloys

In this study, two casting speeds of 10 and 30 r/min were used in vertical twin-roll casting (TRC) to obtain Mg-rare earth (Mg-RE) alloys, and their microstructures, corrosion behaviours and in vivo bone reactions were investigated in detail. The results indicated that the roll-castings of TRC-30 r/min exhibited a finer grain size and higher volume fraction of non-crystallization than those in castings of TRC-10 r/min. Moreover, the results of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization indicated that the castings of TRC-30 r/min displayed a higher corrosion resistance compared with those in the castings of TRC-10 r/min. Animal tests showed that a higher degree of newly formed bone tissues was achieved by implants of TRC-30 r/min. Additionally, in vivo tests displayed that degradation properties of the TRC-30-r/min implants were better than those of the TRC-10-r/min implants; furthermore, the degradation layer was a two-layer structure, and P and Ca were enriched in the outer degradation layer. In summary, these findings elucidated that casting speed has a substantial effect on the microstructure and degradation property of Mg-based implants, and the degradation property performs better with increased casting speed.