Twin-roll Casting Research Articles

Microstructure of Al-2%Si and Al-6%Si Strips Cast Using Vertical-Type High-Speed Twin-Roll Caster

Al-2%Si and Al-6%Si were cast at a roll speed of 30 m/min and a roll load of 5 N/mm using a vertical-type high-speed twin-roll caster. The rolls were suddenly stopped during casting and the molten metal was solidified. The effect of Si content on the microstructure at the cross section near the roll bite was investigated using Weck’s reagent. The cross section of the Al-2%Si strip consisted of five layers (one center layer, two middle layers, and two surface layers) at the roll bite and that of the Al-6%Si strip consisted of three layers (one center layer and two side layers). The a-Al in the center layer was globular for both Al-2%Si and Al-6%Si. The relative thickness of the center layer for Al-6%Si was greater than that for Al-2%Si. In Al-2%Si, the surface layer had a very fine chill-zone microstructure. The Si solid-solution content in the α-Al in the surface layers and the center layer was less than that in the middle layers in the Al-2%Si strip.

Enhancing corrosion resistance of Mg-Al-Mn-Ca-Y dilute alloy via novel core-shell structured Al8Mn4Y-Al2Ca and controllable solute segregation

A novel core-shell structured Al8Mn4Y-Al2Ca phase and controllable solute-segregation are elaborately designed in dilute Mg-0.6Al-0.5Mn-0.1Ca-0.1Y alloy (wt.%), via incomplete peritectic transformation during twin-roll casting. When soaked in 3.5 wt.% NaCl solution, Al2Ca shell with a low electrochemical potential prevents direct contact of noble Al8Mn4Y with Mg matrix, mitigating the micro-galvanic corrosion and meanwhile accelerating the formation of uniform corrosion film. Thereafter, solute (Al, Ca)-segregation motivates the formation of heterogeneous multilayered corrosion product films, enhancing corrosion resistance and even achieving self-healing upon long-term corrosion. Notably, the dilute Mg alloy exhibits a corrosion rate as low as 0.22 ± 0.05 mm·y−1.

Mechanical properties of three typical aluminum alloy strips prepared by twin-roll casting

Twin-roll casting (TRC) is a near-net shape processing technology that has found widespread application across various series of Al alloys. In this study, the process-structure-property relationships of 2099, 3003, and 6082 Al alloy strips prepared by TRC and traditional rolling (TR) methods were investigated. It shows that the tensile strength and fatigue strength of 2099-TRC are lower than 2099-TR, which is attributed to the reduced solid solubility of copper (Cu) elements resulting from the precipitation of Cu-rich micron phases and the presence of microstructure inhomogeneities. While both 3003-TRC and 3003-TR materials exhibit similar yield and tensile strength, the occurrence of casting micro-void defects in 3003-TRC leads to an accelerated accumulation of fatigue damage, consequently diminishing its fatigue strength. Conversely, 6082-TRC demonstrates an enhanced fatigue strength relative to 6082-TR. This improvement is primarily linked to the higher yield strength and comparable fatigue resistance observed in the former. In light of these findings, the TRC process holds promise for enhancing the fatigue performance of 6xxx Al alloy strips with good elongation. However, for 2xxx and 3xxx alloy strips with comparatively lower elongation, the TRC process enhancements may be necessary to realize similar benefits. The insights gleaned from this study could offer valuable reference and guidance for optimizing both the TRC process itself and the fatigue performance of Al alloy strips.

Magnetic properties and crystallization behavior of Fe-based nanocrystalline strips fabricated by twin-roll casting

In this study, the Fe78.4B12.3Si7.6C1Cu0.7 MG strip with a thickness of 157 µm was produced via twin-roll casting. The increased thickness resulted in a lower colling rate, lower energy state, and smaller free volume content. Moreover, the tremendous squeezing force applied during casting caused significant residual stress. Dense atomic stacking with high stress residual suppressed the magnetic domain rotation and domain-wall movement, producing a great coercivity (Hc). Two-pass rapid annealing(TPRA) was explored to improve the soft magnetic properties. Low-temperature annealing eliminated the residual stress, reducing the stress anisotropy and magnetic domain pinning of strips. A co-existing structure of residual amorphous and α-Fe(Si) phase was produced after high-temperature annealing. Fine α-Fe(Si) grain size of 24 nm decreased the magnetocrystalline anisotropy, and a great volume fraction of 71.3 % reduced the magnetostriction coefficient from 30 to 4.33 ppm. Finally, the Hc decreased from 27.4 to 6.4 A·m−1 after TPRA.

Measurement of Molten Steel Level Using a Single Camera in Top Side-Pouring Twin-Roll Casting

The molten steel level in twin-roll strip casting (TRC) has a significant impact on the heat transfer process between the molten steel and the rolls, as well as the subsequent solidification process of the steel. Therefore, ensuring a specific and stable molten steel level is crucial for the quality of as-casting strips. To achieve this, a precise and real-time molten steel level detection system is required. This paper utilizes machine vision technology to measure the molten steel level. A general mathematical model for the molten steel level in the TRC process is established. An image processing method for measuring the molten steel level using a single camera is proposed, including image segmentation, edge detection, and multiple coordinate transformations of the molten pool contour. The adverse effect of the inlet or nozzle is taken into account. Experimental measurements were conducted, and the results indicate that a single camera can accurately measure the molten steel level. Potential sources of error or limitations that may impact the accuracy of the proposed method is discussed.

Effect of Low Degree Electromagnetic Field on Solidification Mechanism and Mechanical Properties of Twin Roll Cast Al 7075 Alloy

Effect of Low Degree Electromagnetic Field on Solidification Mechanism and Mechanical Properties of Twin Roll Cast Al 7075 Alloy

Effect of Roll Load on Microstructure of Roll Cast Al-10%Mg Strip

The effect of roll load on the microstructure of an Al-10%Mg strip cast using a vertcal-type high-speed twin-roll caster was investigated using roll stop and etching with Weck’s reagent. Roll stop was adopted to investigate the transformation of the microstructute near the roll bite. Weck’s reagent was used to visually determine the of the Mg solid-solution content. The roll load was 2, 88, or 420 N/mm and the roll speed was 30 m/min. A band zone formed at the center of the thickness direction for all roll loads. The Mg solid-solution content in the αAl in the band zone obtained at a roll load of 2 N/mm was greater than that obtained at roll loads of 88 and 420 N/mm. Recrystalization migh occur in the band zone of the strip at a roll load of 2 N/mm. The Mg solid-solution content in αAl near the surface was greater than that inside the strip in the thickness direction. The Mg solid-solution content in αAl near surface obtained at a roll load of 2 N/mm was greater than that obtained at roll loads of 88 and 420 N/mm.

Twin-Roll Casting as a Grain Refinement Method and Its Influence on the Microstructure and Deformation Behavior of an AZ31 Magnesium Alloy Wire

Due to a combination of casting and rolling in one process step, twin-roll casting is an effective grain refinement method. This study compares the direct-chill cast (DC) state and the twin-roll cast (TRC) state of an AZ31 magnesium alloy in different steps regarding the microstructure, deformation behavior, and mechanical properties. In the initial state, the TRC AZ31 exhibits a significantly finer grain size and a slight rolling texture compared to the DC AZ31. Therefore, the TRC materials exhibit higher strengths and ductility. After a short heat treatment of 400 °C and 12 h for the DC state and 460 °C and 15 min for the TRC state, cylindric compression tests of the heat-treated samples were conducted at different temperatures (300–400 °C) and strain rates (0.1–10 s−1). To reproduce the deformation behavior at higher strain rates, hot rolling tests (350 °C, 15 s−1) of the heat-treated samples were performed. For both alloys, discontinuous dynamic recrystallization and twinning-induced dynamical recrystallization could be detected. A fine grain size and similar strengths were present after five passes. The AZ31 TRC exhibited a higher ductility due to a higher texture intensity, as the stress direction corresponds to the rolling direction in the case of tensile testing.

Detoxification of impurity elements in recycled aluminum alloys using vertical-type high-speed twin-roll casting and remaining problems for upgrade recycling

Detoxification of impurity elements in recycled aluminum alloys using vertical-type high-speed twin-roll casting and remaining problems for upgrade recycling

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.

High Speed Roll Casting of Al-5%Mg Strip at Semisolid Condition

Semisolid Al–Mg alloy strips were cast using high-speed twin-roll casting under very low roll loads to investigate the effect of low roll loads on surface cracking and center segregation of Mg. In the conventional twin-roll caster for aluminum alloys, the roll speed is usually less than 2 m/min, and the roll load is typically greater than 1 kN/mm to solidify the aluminum alloy and reduce casting defects. In the vertical type high-speed twin-roll caster, the roll speed can range from 10 to 90 m/min, and strips can be cast at roll loads below 500 N/mm, down to loads as low as 2 N/mm. Strips cast at 2 N/mm in this study did not completely solidify when released from the rolls; this means that the strips were semisolid. Al–Mg strips can be continuously cast without breaking when they are semisolid. The surface cracking and center segregation of these strips were compared with those of strips cast at a higher load of 88 N/mm. The effect of the small load on the presence of Mg at cross sections of the strip was investigated using etching with Weck’s reagent.

Effect of casting conditions on surface defect and segregation of strips cast by a high-speed twin-roll caster

Effect of casting conditions on surface defect and segregation of strips cast by a high-speed twin-roll caster

Microstructure Characteristics, Mechanical Properties and Strain Hardening Behavior of B2 Intermetallic Compound-Strengthening Fe-16Mn-9Al-0.8C-3Ni Steel Fabricated by Twin-Roll Strip Casting, Cold Rolling and Annealing.

In this study, the Fe-16Mn-9Al-0.8C-3Ni (wt.%) lightweight steel was fabricated by novel twin-roll strip casting technology. The microstructure, tensile properties and strain-hardening behavior of the present steel have been investigated and compared to those of conventionally processed steels with similar chemical compositions. After annealing, a unique gradient microstructure of intermetallic compound (B2)-austenite was obtained along the thickness direction, consisting of granular B2 (average: 430 nm) and fine austenite (average: 1.82 μm) at the surface layer, blocky B2 (average: 1.03 μm) and medium austenite (average: 3.98 μm) at the quarter layer and polygonal B2 (average: 1.94 μm) and coarse austenite (average: 6.13 μm) at the center layer. The cooperative action of B2 pinning dislocation, plane slip and back stress led to stronger strain hardening, among which the strong back stress effect originated from the multistage discontinuous austenite deformation and the mechanical incompatibility between austenite and B2 is believed to be the most important reason, thereby achieving an excellent balance of strength (ultimate tensile strength: 1147 MPa) and ductility (total elongation: 43.2%). This work not only developed a new processing way to fabricate Ni-containing Fe-Mn-Al-C lightweight steel with outstanding mechanical properties, but also provided a potential solution for manufacturing some other metallic materials accompanied by brittle B2 intermetallic.

Sustainability Study of a New Solid-State Aluminum Chips Recycling Process: A Life Cycle Assessment Approach

Nowadays, reducing greenhouse gas emissions in all human activities has become crucial. This article presents a life cycle assessment (LCA) investigation conducted to evaluate the environmental benefits of a newly developed solid-state recycling process for aluminum chips, involving two steps: direct rolling and accumulative roll bonding. A comparison was made between this process and two current industrial methods of recycling aluminum scraps to obtain wrought products, which involve melting, casting, and subsequent rolling. The LCA analysis considered a scenario where 50% of the total electric requirement was met by photovoltaic energy. The results of the study indicate that in all examined impact categories, direct rolling has a lower environmental footprint compared to both traditional recycling and twin-roll cast technology. These results suggest that this new solid-state recycling procedure has significant potential to replace environmentally harmful melting processes.

Mechanical and Microstructure Characterisation of the Hypoeutectic Cast Aluminium Alloy AlSi10Mg Manufactured by the Twin-Roll Casting Process

Multi-material designs (MMD) are more frequently used in the automotive industry. Hereby, the combination of different materials, metal sheets, or cast components, is mechanically joined, often by forming joining processes. The cast components mostly used are high-strength, age-hardenable aluminium alloys of the Al–Si system. Here, the low ductility of the AlSi alloys constitutes a challenge because their brittle nature causes cracks during the joining process. However, by using suitable solidification conditions, it is possible to achieve a microstructure with improved mechanical and joining properties. For this study, we used the twin-roll casting process (TRC) with water-cooled rollers to manufacture the hypoeutectic AlSi10Mg for the first time. Hereby, high solidification rates are realisable, which introduces a microstructure that is about four times finer than in the sand casting process. In particular, it is shown that a fine microstructure close to the modification with Na or Sr is achieved by the high solidification rate in the TRC process without using these elements. Based on this, the mechanical properties increase, and especially the ductility is enhanced. Subsequent joining investigations validate the positive influence of a high solidification rate since cracks in joints can be avoided. Finally, a microstructure-property-joint suitability correlation is presented.

Numerical Modeling and Experimental Study of Solidification Behavior of Al-Mg2Si Composite Sheet Fabricated Using Continuous Casting Route

Abstract Owing to manufacturing challenges, the fabrication of thin sheets of metal matrix composites has been an area of concern for sheet manufacturers. Converting a billet of composite into a sheet using rolling and extrusion is quite energy-intensive and prone to cracking using the conventional casting route. To address this issue, this study explores the development of particle-reinforced near eutectic Al-Mg2Si composite sheets using a vertical twin-roll continuous casting process. The numerical simulation involves fluid flow, solidification, and heat transfer analysis of the twin-roll continuous casting process for producing thin strips. Processing parameters such as the velocity of rolls and superheat temperature of the melt are optimized to successfully convert the melt into a sheet of composite material. A combined numerical and experimental study show that the continuous casting process is more sensitive to the casting speed. A small change in roller speed (2 rpm) significantly affects the solidified fraction at the roller exit. Optimizing the casting speed to 0.072 m/s and inlet temperature to 886 K, an in situ Al-Mg2Si composite sheet of 3 mm thickness is successfully cast. The particle distribution along the casting direction of the sheet is uniform, ensuring the homogeneous mechanical properties reported in terms of hardness. The entire process does not require external stirring to get uniform distribution of the reinforced particles.

Cast-rolling force model of multi-roll solid–liquid cast-rolling bonding process for fabricating metal cladding materials

Based on twin-roll casting technology and multi-roll groove rolling technology, a Multi-Roll Solid-Liquid Cast-Rolling Bonding (MRSLCRB) process was proposed to fabricate Cu/steel cladding bars, which processes the advantages of short flow and high-efficiency. However, it is a typical 3-D thermal-fluid-mechanics coupled problem, and determining cast-rolling force is difficult during the equipment design. Therefore, the geometrical evolution of the cast-rolling area was studied, laying the foundation to establish contact boundary equations and analyze mechanical schematics and metal flow. Then, a 3-D steady-state thermal-fluid coupled simulation model, including casting roll, substrate bar, and cladding metal, was established. The Kissing Point (KP) height, average outlet temperature, and process window were predicted, and simulation results of the three-roll layout indicate that the KP distribution along the circumferential direction can be considered uniform. Hence, the engineering cast-rolling force model was derived based on the differential element method and plane deformation hypothesis. The accuracy was verified by the 3-D finite element model, and the influences of process layouts and technological parameters on the cast-rolling force were analyzed. Through the indirect multi-field coupled analysis method, the temperature–pressure evolution and reasonable process window can be predicted, which provides a significant basis for guiding equipment design and improving product quality.

Effectively mitigated macro-segregation and improved tensile properties of twin-roll cast Al–Mg–Si (6022) alloy strips via Zr addition

It is a great challenge to avoid the central macro-segregation during the solidification process of twin-roll casting (TRC), which seriously limits the mechanical properties of 6xxx series Al alloys. In this study, we find that the trace addition of 0.08 wt% Zr to Al-1.0Mg-1.2Si (6022) alloy can effectively promote the columnar-to-equiaxed transition and refine the solidification microstructure (particularly α-Al dendrites and π-AlFeMgSi phase). More importantly, the macro-segregation of the as-cast TRC strip is well mitigated with Zr addition. The refinement of α-Al dendrites and π-AlFeMgSi phase may be attributed to the formation of (Al, Si)3Zr phases when introducing Zr element, which can act as heterogeneous nucleation sites for both of them. The secondary dendrite arm spacing (SDAS) in the central region of strips is sharply decreased from ∼33 to ∼16 μm, which facilitates the incorporation of more solute elements into the Al matrix, thus increasing the partition coefficients of Mg (kMg) and Si (kSi) elements. As a result, there are fewer solute atoms in the residual liquid phase during the final stage of solidification, leading to the alleviation of central macrosegregation. The tensile properties of the as-cast, solid solution treated (T4) and paint baking treated (T6) alloys are synchronously optimized with Zr addition. In particular, the fracture elongation of the T4 alloy is increased from ∼30.9% to ∼33.4%, indicating excellent formability. The yield strength of the T6 alloys is increased from ∼227 MPa to ∼239 MPa, satisfying the more demanding service requirements. This work can provide a strategy for the effective control of macro-segregation and produce alloy strips with high performance by the TRC process.

Effect of Mg and Si contents and TiC nanoparticles on the center segregation susceptibility of twin-roll cast Al–Mg–Si alloys

Center segregation during the twin-roll casting (TRC) has always been a barrier to the fabrication of high-performance Al–Mg–Si strips. In this work, Al–Mg–Si alloys with different Mg and Si contents were fabricated by vertical-type twin-roll caster to investigate the effect of Mg and Si contents on central segregation susceptibility. Alloys that undergo a eutectic reaction to form Si would lead to the enrichment of eutectic Si in the central region due to the low reaction temperature of eutectic Si, resulting the severe central segregation. For alloys with the same eutectic reaction during the solidification, the alloy with higher |ⅆT/ⅆ(fs1/2)| showed agglomeration of the eutectic phases due to its lower solidification rate. For the alloys with the same Mg/Si ratio, the width of central segregation increased with the increase in Mg and Si contents due to the increase in the proportion of near-equiaxed grains in the central region. The introduction of TiC nanoparticles could mitigate the central segregation band due to the control of solute diffusion by the fine near-equiaxed grain structure.

Experimental Evaluation on the Microstructural and Mechanical Response of Ce Microalloying AZ31 Fabricated by Multi-Pass Unidirectional and Cross Rolling after TRC

Conventional billet rolling is being widely used in magnesium (Mg) alloys products, but this method gives rise to biological and environmental problems. The advantages of the short process on sheet fabrication have been widely proved in Mg alloy twin-roll casting (TRC). In this study, an attempt is made to create high-performance Mg alloy sheets via multi-pass unidirectional and cross hot rolling (UR, CR) after TRC for purposes of lowering edge defects and energy consumption. Then, the microstructural and mechanical response of Ce when microalloying AZ31 was observed using UR and CR, respectively. The mechanism of the performance improvement after the AZ31 microalloying is disclosed. In addition, the effect of the rolling parameters on the microstructural and mechanical properties are discussed. Experimental results revealed that the homogenization effect of the AZ31-0.2Ce alloy was the best after being kept at 440 °C for 24 h. The CR-rolled sheet had a more uniform and finer microstructure in the horizontal and center, while for the UR-rolled sheet, it was the opposing edge microstructure. This research is expected to prepare and optimize the microstructural and mechanical properties of microalloying AZ31 in a sheet-rolling process, a material that has important theoretical significance and engineering application value.