Vertical Twin-roll Casting Research Articles

Generalized stability criterion for columnar to equiaxed grain transition during solidification upon vertical twin roll casting

To promote the columnar to equiaxed grain transition (CET) to obtain uniform equiaxed grain, most of the available theoretical works mainly focus on the growth but ignore the nucleation. Regarding it, a systematical framework integrating nucleation catalyzed by refiners with dendritic growth, was constructed, where, a new conception of generalized stability (GS), considering evolving thermodynamic driving force (ΔG) and kinetic energy barrier (Q) upon solidification of VTC, was adopted to study the CET position, the grain radius and the mechanical properties. By adding the refiners, especially the Al–5Ti–1B refiner, the larger thickness of 5–6 mm for equiaxed grain and finer grain radius of 19 μm are exhibited by increasing the ΔG for nucleation and the GS for growth, possessing simultaneously improved strength and plasticity. Following a criterion of high ΔG–high GS, the refiner diameter is optimized to be 0.3 μm.

Influence of Mg/Si ratio on the microstructure and formability of 6061 cast-rolled sheets

Three kinds of 6061 aluminum alloy cast-rolled plates with Mg/Si mass ratios of 1.23, 1.45, and 1.7 are prepared using NF6–300 vertical twin-roll casting and rolling mill. Metallurgical microscope (OM), x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), room temperature tensile test, and other analysis methods studied the influence law and mechanism of Mg/Si ratio on the microstructure and texture of 6061 cast-rolled sheet. The best Mg/Si ratio cast-rolled sheet is then analyzed for formability. Research indicates that with increasing Mg/Si ratio, the grain size shows first decreasing and then increasing trend. Morphology of precipitated phases at the edge and the central of the sheet are different, however, the texture type has no obvious change, and a strong {112} 〈110〉 texture and weaker rotating cube {001} 〈110〉 texture is always observed. When the Mg/Si ratio is 1.45, the average grain size is the smallest, the edge size is 39.78 μm, the central size is 31.31 μm, and the precipitated phase is evenly distributed at the edge and central of the cast-rolled sheet. In addition, the elongation reaches 8.9%, the n-value is 0.072, and the r-value is 1.161 when the cast-rolled sheet reaches 90° along the cast-rolled direction under T6 state heat treatment.

Effects of casting speed on microstructural and tensile properties of Al–Mg–Si alloy fabricated by horizontal and vertical twin-roll casting

For the development of Al–Mg–Si strips with high mechanical performance via twin-roll casting (TRC) technology, it is necessary to understand through comparative analysis of traditional horizontal twin-roll casting (HTRC) and promising vertical twin-roll casting (VTRC) technologies. In this study, two types of Al–Mg–Si alloys (denoted as H-alloy and V-alloy) were fabricated by HTRC and VTRC using different casting speeds (0.69 and 20 m/min, respectively). The microstructural evolution and mechanical properties of the two alloys were comprehensively assessed and compared. To reveal the microstructural characteristics, various techniques including energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), texture calculation and differential scanning calorimetry (DSC) were utilized. Center segregation occurred in H-alloy and V-alloy in the form of channel segregation and segregation bands, respectively. Moreover, the texture components of H-alloy showed rolling and shear textures, indicating continuous casting with hot-rolling during HTRC; however, those of V-alloy showed a random texture, indicating the absence of hot-rolling during VTRC. Therefore, the amount of plastic deformation in H-alloy was greater than that in V-alloy, which increased the yield strength through dislocation strengthening. Furthermore, solid-solution strengthening and precipitation strengthening primarily helped improve the strength of V-alloy, whereas pre-existing voids caused premature fracture. Our comparative analysis of the microstructural evolution and tensile properties realized by HTRC and VTRC is anticipated to broaden the understanding of twin-roll-cast strips.

Examination of conditions for producing thin sheets of aluminum alloy A6061 by vertical twin roll casting

Examination of conditions for producing thin sheets of aluminum alloy A6061 by vertical twin roll casting

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.

In vivo degradation behaviour and bone response of a new Mg-rare earth alloy immobilized in a rat femoral model

A new type of Mg-rare earth (Ce, La) and the AZ31 alloy sheets were prepared by vertical twin-roll casting (TRC) technology under identical casting conditions, and their microstructural features, degradation behaviours and bone responses were investigated. The microstructural characterization showed that the Mg-RE (rare earth) exhibited a higher amorphous forming ability than the AZ31. Moreover, the results of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization indicated that the Mg-RE sheets displayed a higher corrosion resistance compared with the AZ31 sheets. Additionally, the Ti, Mg-RE and AZ31 sheet implants were immobilized and implanted in a rat femur model to observe degradation behavior during 16 weeks. in vivo tests showed that no significant change in the femur surrounding the Ti group, which excluded the external factor that the new bone formation resulting from bone remodeling. Furthermore, the Mg-RE group induced more newly formed bones, which met the necessary conditions for the prevention of pathological fractures. Therefore, the novel Mg-RE alloy appear to hold a healing candidate as the biodegradable implant material.

Application of non-equilibrium dendrite growth model considering thermo-kinetic correlation in twin-roll casting

Upon non-equilibrium solidifications, dendrite growth, generally as precursor of as-solidified structures, has severe effects on subsequent phase transformations. Considering synergy of thermodynamics and kinetics controlling interface migration and following conservation of heat flux in solid temperature field, a more flexible modeling for the dendrite growth is herein developed for multi-component alloys, where, two inherent problems, i.e. correlation between thermodynamics and kinetics (i.e. the thermo-kinetic correlation), and theoretical connection between dendrite growth model and practical processing, have been successfully solved. Accordingly, both the thermodynamic driving force ΔG and the effective kinetic energy barrier Qeff have been found to control quantitatively the dendrite growth (i.e. especially the growth velocity, V), as reflected by the thermo-kinetic trade-off. Compared with previous models, it is the thermo-kinetic correlation that guarantees quantitative connection between the practical processing parameters and the current theoretical framework, as well as more reasonable description for kinetic behaviors involved. Applied to the vertical twin-roll casting (VTC), the present model, realizes a good prediction for kissing points, which influences significantly alloy design and processing optimization. This work deduces quantitatively the thermo-kinetic correlation controlling the dendrite growth, and by proposing the parameter-triplets (i.e. ΔG - Qeff - V), further opens a new beginning for connecting solidification theories with industrial applications, such as the VTC.

Vertical twin-roll cast Al-50Si alloy with different Mg content

In the present work, the sheets of Al-50Si alloys with different Mg content (0, 5, and 10 wt% Mg) are fabricated by vertical twin-roll casting (VTRC) technology at different roll-casting speeds. The size and morphology of primary Si are studied systematically. The central congregation mechanism of primary Si and the central fracture mechanism as well as the relationship between thickness and roll-casting speed are illuminated in detail. The thickness of the sheet increases with decreasing of roll-casting speed. The central congregation phenomenon of primary Si and the layer phenomenon caused by crack will appear when the roll-casting speed is slow. The size of primary Si and the hardness of alloy are mainly influenced by roll-casting speed and Mg content. The min size of primary Si and the max value of hardness obtained at the speed of 30 m min−1 with 10% Mg content are 7.0 μm and 384, respectively.

Mechanical properties and reinforced mechanism of the stainless steel wire mesh–reinforced Al-matrix composite plate fabricated by twin-roll casting

Taking the 304 stainless steel wire mesh as reinforcement, Al 1060 as matrix, a solid–liquid cast-roll bonding process based on the vertical twin-roll casting was presented to fabricate the stainless steel wire mesh–reinforced Al-matrix composite plate. Optical microscope and scanning electron microscope were used to observe the microstructure of bonding interface, and the mechanical properties were investigated through tensile test and three-point bending test. The observation results show that there is no macroscopic defect at the bonding interface. Furthermore, atom diffusion occurs between the steel wire and aluminum matrix under the high temperature and contact pressure in the cast-rolling zone during solid–liquid cast-roll bonding process. The thickness of interfacial reaction diffusion layer is about 5 µm, and no separation was observed in the interface after three-point bending. The tensile test results indicate that the tensile strength and elongation rate of composite plate are improved with the increase in orientation angle of the steel wire relative to rolling direction, and the tensile strength and elongation are maximum when the orientation angle is 45°. In addition, there are two stress platforms in the tensile curve of the as-rolled composite plate due to the asynchrony of fracture between the reinforcement and matrix, but only one in the curve of as-annealed composite.

Numerical analyses of cladding processes by twin-roll casting: Mg-AZ31 with aluminum alloys

Two types of cladding process by vertical twin-roll casting were analyzed in two dimensions. Mg-AZ31 sheet was cladded with molten AA3003 in Type I while molten Mg-AZ31 was cladded with two AA1100 sheets in Type II. Assuming the viscosity of a fluid and the proportional constant of the flow rule of a Mises material to be equivalent, the rigid-thermoviscoplastic finite-element method was applied to these analyses. Steady-state solutions were achieved after a number of non-steady state solutions for continuously updated configurations by using small time-steps. As a result, the Mg-AZ31 sheet was found to be pulled in tension under roll pressure and thinned with a risk of fracture in Type I. However, the Mg-AZ31 melt was found to be incompletely solidified because of low IHTC at the interface between the roll and the AA1100 sheet in Type II. Details of flow, temperature distribution, plastic deformation and possibility of fracture were predicted by the analyses.

405 縦型双ロール法による銅合金の薄板連続鋳造(OS4-(2),OS4 オーガナイズドセッション≪材料・組織と加工≫)

405 縦型双ロール法による銅合金の薄板連続鋳造(OS4-(2),OS4 オーガナイズドセッション≪材料・組織と加工≫)

Finite-element analysis of a vertical twin-roll casting

Metallic strips can be produced by twin-roll casting, in which the melt is cooled, solidified, and rolled to a specific thickness. In the present study, the rigid-thermoviscoplastic finite-element method was applied to the analysis of complex phenomena including melt flow, heat transfer, solidification, and plastic deformation occurring in a vertical twin-roll casting of magnesium alloy AZ31. The melt was found to be confined in rotational motions of two symmetric vortexes developed at the roll entrance, and thus only the melt near the nozzle wall became solidified and rolled to a sheet. As the nozzle thickness increased, the vortex increased in size resulting in more bifurcation and instability, which are definitely adverse to material properties of the strip. The maximum cooling rate of 600 °C/s was found at the centerline as solidification took place at the roll exit. Other findings are also discussed including roll force, roll torque, and pressure distribution, which were greatly dependent upon the plastic deformation after solidification.

415 縦型双ロールキャスターを用いたリン青銅薄板の製造(OS4-(4),OS4 オーガナイズドセッション《材料・組織と加工》)

In recent years, because of the expansion of the digital consumer electronics market and automotive electronics, demand for personal computers and mobile phones is increasing. Copper alloys are used as the lead frame members mounted on the IC chip of the electronic device. In this study, we attempted the production of copper alloy sheet by using a vertical twin roll caster. As a consequence, we have achieved the production of Cu-Sn-P and Cu-Ni-Si alloy thin plate by using vertical twin roll casting.

Finite-Element Analysis of Melt Flow in a Vertical Twin-Roll Casting

Twin-roll casting is an efficient and economical process to fabricate metal sheets since it combines solidification and rolling in one process. However, this process requires a careful control because several phenomena, such as heat transfer, solidification, fluid flow and solid deformation, occur simultaneously. In the present study, a rigid-thermo-viscoplastic finite-element analysis was utilized to understand these complex phenomena occurring in a vertical twin-roll casting of an aluminum alloy. As a result several interesting findings were obtained including the development of two symmetrically identical vortexes at the roll entrance.

Effects of Al and Ca on microstructure and surface defect of magnesium alloy thin strip

Mg-Al-Zn alloy thin strips were prepared by vertical twin-roll casting. Effects of Al and Ca on the microstructure and the surface defects of the thin strips were investigated. The results show that with the increase of Al content, the quantity of surface cracks of the thin strips increases rapidly and their locations are moved to the center of the thin strips. The alloy melts with more than 0.10% Ca (mass fraction) stick on the roller and a poor surface quality of the thin strips appears. With the increase of Al content, the microstructure of the thin strips evolves from single α-Mg phase, characterized by the uniform and equiaxed recrystallization grains, to the combination of dendritic α-Mg with Al supersaturated α-Mg. The minor addition of Ca can obviously refine the grains of Mg-3Al-1Zn thin strip because the formation of Al 2Ca and the finest grains are obtained by adding 0.08% Ca.

Research on the Rolling of AZ31 Strip Prepared by Twin Roll Casting

The AZ31 thin sheet (minimum thickness less than 1mm) was obtained by rolling the cast strip which was prepared by vertical twin roll casting in this paper. Since the absolute deformation during rolling was smaller,due to the small thickness of the strip of 3mm, the rolling of cast strip was different from the conventional rolling process. It was found that homogenizing time at 400°C for the cast strip was 4h and reduction per pass should be 8-10% for producing thinner (1-1.5mm) rolled AZ31 sheet at 350°C. Mechanical properties of the sheet were equivalent to conventional rolling sheet’s.

Twin-roll strip casting of magnesium alloys in China

The development status of twin-roll strip casting for magnesium alloys in China was summarized as well as the new progress when several kinds of twin-roll strip casting technologies were developed and used. Horizontal twin-roll casting (HTRC) of magnesium alloys has attracted much attention and has been industrialized in China. Vertical twin roll casting (VTRC) of the magnesium alloys can reach a speed of higher than 30 m/min and its research and development are just beginning and exhibit exciting potential. By comparing the process characteristics of the two technologies, the process stability of HTRC for the magnesium alloys is better, and the casting speed and the cooling rate of VTRC for the magnesium alloys are higher. The quality of the products by the two technologies needs to be improved and further investigated.