Twin-roll Casting Research Articles

High-Speed and Low-Load Twin-Roll Casting of Al–5%Mg Strip

A conventional twin-roll caster usually casts strips at a speed slower than 2 m/min and a roll load greater than 2 kN/mm. A vertical-type high-speed twin-roll caster can cast aluminum alloy strips at a speed higher than 10 m/min and a roll load smaller than 550 N/mm due to the effect of the large thermal conductivity of copper alloy rolls, compared with that of steel rolls. However, the properties of an aluminum alloy strip cast at a roll load smaller than 140 N/mm and at a roll speed higher than 30 m/min are not clear. In this study, Al–5%Mg strips were cast at a roll speed of 30 m/min and roll loads of 2 and 88 N/mm using a vertical-type high-speed twin-roll caster. The effects of roll load on cracking at the strip surface, the tensile mechanical properties, and the microstructure were investigated. Rotating rolls were stopped during casting, and the progression of centerline segregation and the microstructure between the rolls was investigated. Centerline segregation and surface cracking were lower at 2 N/mm than at 88 N/mm. In the strip cast at 2 N/mm, elongation in the width direction was greater than that cast at 88 N/mm, due to decreased surface cracking. The results demonstrate that a very low roll load improves the properties of the cast strip.

Effect of Al/Mn ratio on corrosion behavior of lean Mg-Zn-Ca-Al-Mn alloy processed by twin-roll casting

Adopting twin-roll casting (TRC) technique, lean Mg-1.2Zn-0.3Ca-0.3Al-xMn (x = 0.25, 0.38, 0.5 wt%) alloys with different Al/Mn ratio were prepared. The stoichiometric ratio of Al8Mn5 is taken as dividing line. Under Al/Mn>1.6, rhombohedral Al8Mn5 is formed, while under Al/Mn≤1.6, cubic β-Mn is generated. Because of lower Volta potential of Al8Mn5 than β-Mn, the alloy with Al/Mn>1.6 shows the lowest average corrosion rate (4.55 mm y−1). The formation of fine rather than coarse Al8Mn5 weakens micro-galvanic corrosion and relieves stress concentration, thus simultaneously endowing the alloy (Al/Mn>1.6) with admirable corrosion resistance and mechanical properties (UTS:∼266 MPa, YS:∼193 MPa, EF:∼20 %).

The effect of combined cold rolling and homogenization on the microstructures and mechanical properties of twin-roll casted 8021 aluminum alloy

The microstructures and mechanical properties of the twin-roll casting (TRC) 8021 alloy strip under different homogenization processes (direct homogenization, cold rolling + homogenization) have been systematically investigated by optical microscope, tensile testing, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) technique. It was revealed that due to the severe microstructural gradient throughout the full strip thickness, the coarse grain layer is readily formed in the strip surface due to the high stored energy involved. Although the introduction of cold rolling before homogenization reduces the strain inhomogeneity in the strip, the rather high deformation level produces fully recrystallized structures after homogenization at 580 °C. After cold rolling and final annealing, recrystallized grains are formed in the interior of the sheets for most the homogenization temperatures. Compared with direct homogenized samples, the average recrystallized grain sizes in the “cold-rolled + homogenized” samples are larger due to the small thickness reduction. Therefore, the combination of cold rolling and homogenization can improve the elongation and decrease the strength of the strip. Homogenization at 530 °C is selected as the optimum parameter for both the two homogenization processes as it provides a good combination of strength and elongation.

Fabrication and interface optimization of continuous CF/Al composites with different reinforcement volume fraction

Interface is the key factor to determine the properties of composites. In this work, the Ni coated continuous CF/Al composites were fabricated via twin-roll casting method. After interface optimization, the interfacial bonding strength was enhanced and the dispersion of carbon fibers was improved. The effect of reinforcement volume fraction on microstructure, mechanical properties and strengthening mechanism of CF/Al composites was studied. The microstructural showed that the increase of reinforcement volume fraction was easy to cause more defects in composites. Transmission electron microscopy (TEM) and thermodynamic calculation were used to characterize the interfacial phase composition of composites after interface optimization. The results revealed that the exterior of carbon fibers bundle was mainly composed of Al3Ni intermetallic phase, and there was no obvious Al4C3 phases were found interior of the CFs bundle. In addition, the composites with 13.6 vol% CFs had the best UTS of 218.7 MPa and well dispersion. Furthermore, Vickers hardness test and Nano-indentation results showed that Al-Ni intermetallic compound can enhance the whole hardness of CF/Al composites. Dislocation strengthening in the Al-Ni intermetallic compound region was observed by TEM. The interface evolution mechanism of CF/Al composites were revealed for the first time.

Center Line Globular Structure of Strip Cast Using High Speed Twin Roll Caster

Formation of a centerline globular structure in an aluminum alloy strip cast using a vertical type high-speed twin-roll caster was investigated. The theory that the crystals form at tip of the nozzle and are conveyed to the roll gap was investigated by roll casting using a cooling slope and clad-strip-casting in this study. In high-speed roll casting, the center of the strip thickness is semisolid, and the temperature gradient in the thickness direction is small. The latent heat of the semisolid metal heats the dendrite structure, which is divided by melting. The dendrite structure was divided as in thixocasting, which is the mechanism of formation of a globular crystal form. The zone of the semisolid metal becomes narrow as the roll load increases or the pouring temperature of the molten metal decreases. As result, the zone containing globular crystal structures becomes thinner.

Microstructural and Textural Investigation of an Mg-Zn-Al-Ca Alloy after Hot Plane Strain Compression.

The formability of magnesium alloys can be significantly improved by Ca as an alloying addition. Compared to conventional alloy sheets such as AZ31, texture modification can be found in rolled Mg-Ca sheets, which reveal a randomized orientation distribution. The hot deformation behavior of a twin-roll cast and homogenized Mg-2Zn-1Al-0.3Ca (ZAX210) alloy was characterized during hot compression at a temperature of 350 °C and strain rates of 0.1 s-1 and 10 s-1. Electron backscatter diffraction (EBSD) analysis was performed in order to describe the microstructural and texture evolution. The ZAX210 alloy exhibits a pronounced dynamic recrystallization (DRX) behavior during compression at high strain rates, while at lower strain rates DRX hardly occurred. This effect can be attributed to different DRX mechanisms that take place as a function of strain rate. At low strain rates, DRX occurred locally at the grain boundaries of the original microstructure, forming a so-called necklace structure. Increasing strain rate results in an increased fraction of recrystallized grains from 18% (0.1 s-1) to 39% (10 s-1). The microstructure revealed that twin boundaries act as nucleation sites for the DRX (TDRX). The recrystallized areas exhibit a weaker texture compared to the deformed microstructure.

Microstructure and Crystallographic Texture in Twin-Roll Casting of AA1050 Aluminum Alloy: Simulation and Industrial Validation

Twin-roll casting (TRC) is a process in which liquid metal is introduced directly between counter-rotating water-cooled rolls, where it solidifies and is rolled to a strip having final thickness of 3 to 8 mm. TRC for aluminum is best suited to those alloys having a narrow freezing range with little susceptibility to hot tearing, such as 1XXX, 3XXX, 5XXX, and 8XXX. TRC offers advantages over conventional DC casting followed by hot and cold rolling for these alloys due to its lower capital cost, and decreased downstream processing operational cost and energy consumption, since hot rolling is not required. The microstructure formed in the strip must be carefully controlled, because as a near-net shape product used mostly for non-age-hardenable alloys, there is limited opportunity to modify it by subsequent processing. In particular, the near-surface microstructure has a strong effect on performance in forming applications. In this article, we present a computational model of TRC, and validate it for AA1050 aluminum alloy in a production environment. The novel aspect of this work is that the model is used to predict the final microstructure and crystallographic texture of the cast strip. The model is validated in plant trials for strip cast at a range of thicknesses, casting speeds, and caster setup by comparing the predicted microstructure, texture, and process outcomes such as roll separating force and forward slip to their corresponding measured values. We then apply the validated model to explore process parameters outside the standard practices, including feed inlet setback, casting speed, metal inlet temperature, and changing roll material to demonstrate how the microstructure and texture can be controlled via these parameters.

Variation Law of Thickness Fraction of Three-Laminated Aluminum Composite Plate by Solid–Liquid–Solid and Liquid–Solid–Liquid Twin-Roll Casting

Solid–liquid–solid twin-roll casting (SLS-TRC) and liquid–solid–liquid twin-roll casting (LSL-TRC) are two processes for manufacturing three-laminated aluminum composite plates by using solid–liquid cast-rolling composite technology. In order to study the variation law of thickness fractions, a 1060/3003/1060 three-laminated aluminum composite plate was taken as the manufacturing product, and the thickness of the solid strip was used as the variable. Based on the “uactive” user subroutines of MSC.MARC software, the 2D thermomechanical coupling models of SLS-TRC and LSL-TRC were established respectively, and the thickness variation law of the solid strip under the two processes was obtained and verified by experiments. Finally, the recommended process was given according to the target thickness fraction. The results show that with an increase in the cladding thickness, the KISS point (complete freezing point of molten metal) height of the SLS-TRC process increases, the coordinated deformation position decreases relative to the KISS point, and the strain increases. In the LSL-TRC process, as the thickness of the core increases, KISS point height increases, the coordinated deformation position decreases relative to the KISS point, and the strain decreases. The formation process of the composite interface of the two processes is consistent with the N. Bay theory. Finally, through the comparison of cast-rolling forces, it was found that when manufacturing a three-laminated aluminum composite plate with a relatively small thickness fraction (the thickness fraction is less than 30%), the SLS-TRC process requires less load; when the thickness fraction of the three-laminated aluminum composite plate is large (the thickness fraction is greater than 30%), the load required for the manufacturing of the LSL-TRC process is small. The results of this research can provide practical guidance for the manufacturing of three-laminated metal matrix composite panels.

Tribological and texture analysis in Twin-roll casting 2060 Al-Li alloy

In this work, the wear behaviors of a 2060 Al-Li alloy prepared by the twin-roll casting (TRC) process was analyzed and supplemented with coupling simulation calculations. As the load increased from 2 N, 5 N, 10 N, and 20 N at room temperature, the friction coefficient decreased due to the oxidation lubrication triggered by heat accumulation, which was calculated via the simulation; the wear volume decreased; and the decrease in wear volume rise rate was a result of dynamic recrystallization and grain rotation. Observing the grain rotation and analyzing the texture evolution law during wear tests with scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) was an innovation. To support the rotation behavior, a method for calculating the Schmid factor of rotating grains was developed. As the load rose, the R-Cube {001} 〈110〉 texture rotated to the rotating cube {001} 〈310〉 texture towards the α-fiber line. The modification decreased the maximum Schmid factor along the sliding and rolling directions, indicating an increase in initial strength and wear resistance. In addition, at a 2 N load, the TRC-3 sample with higher substructure and deformation texture exhibited less wear volume than the TRC-6 sample.

Effect of Roll Material on Strip Solidification between the Rolls of a Vertical-Type High-Speed Twin-Roll Caster

Tool steel for hot working is usually used for the rolls of conventional twin-roll casters for aluminum alloys. In a vertical high-speed twin-roll caster, copper rolls are used to rapidly solidify the aluminum alloys and to increase the casting speed, since the thermal conductivity of copper is higher than that of tool steel. However, the degree of superiority of copper rolls over steel rolls is not clear. In the present study, the effect of the roll material on strip solidification between the rolls of a vertical high-speed twin-roll caster was investigated by inserting a thermocouple in the strip during casting. The Al-4.8%Mg alloy was used, since it does not stick to the steel rolls in the absence of a parting material. Both copper rolls and mild steel rolls were used. The cooling rate, the supercooling of the liquidus temperature, and the temperature of the strip cast using the copper rolls were superior to those of that cast using the mild steel rolls. The copper rolls were better than the steel rolls in terms of achieving high-speed roll casting, rapid solidification of the strip, and high productivity.

Microstructure evolution and recrystallization behavior of hot rolled AA6061 twin-roll casting plate with different manganese contents

AA6061 twin roll casting plate was annealed and then the hot rolling experiment was carried. Effect of Mn content on microstructure evolution and recrystallization behavior was investigated. The results show that Mn element can significantly change the recrystallization behavior of the alloy and produce particle induced recrystallization (PSN) effect. The mechanical properties of the plate would be effectively improved with appropriate Mn content. With the increase of Mn content in cast rolling plate, the number of recrystallized grains in the alloy increases; The strength and hardness of 6061 cast rolled plate increases first and then decreases with the increase of Mn content in the alloy, and the elongation decreases gradually with the increase of Mn content. Comprehensively considered, when the Mn content is 0.46%, the mechanical properties of the plate are optimal, i.e., tensile strength 197.36 MPa, yield strength 157.89 MPa and elongation 6.23% respectively.

Mechanical Properties and Joinability of AlSi9 Alloy Manufactured by Twin‐Roll Casting

AlSi casting alloys combine excellent castability with high strength. Hence, this group of alloys is often used in the automotive sector. The challenge for this application is the brittle character of these alloys which leads to cracks during joint formation when mechanical joining technologies are used. A rise in ductility can be achieved by a considerable increase in the solidification rate which results in grain refinement. High solidification rates can be realized in twin–roll casting (TRC) by water‐cooled rolls. Therefore, a hypoeutectic EN AC–AlSi9 (for European Norm ‐ aluminum cast product) is manufactured by the TRC process and analyzed. Subsequently, joining investigations are performed on castings in as‐cast and heat‐treated condition using the self‐piercing riveting process considering the joint formation and the load‐bearing capacity. Due to the fine microstructure, the crack initiation can be avoided during joining, while maintaining the joining parameters, especially by specimens in heat treatment conditions. Furthermore, due to the extremely fine microstructure, the load‐bearing capacity of the joint can be significantly increased in terms of the maximum load‐bearing force and the energy absorbed.

Interfacial pressure distribution and bonding characteristics in twin-roll casting of Cu/Al clad strip

The mechanical properties and product thickness specifications of bimetallic clad strip prepared by twin-roll casting are tightly related to the mechanical behavior of bonding interface interaction. The thermal−flow coupled simulation and the interface pressure calculation models are established with the cast-rolling velocity as the variable. The results show that the interface temperature decreases, the interface pressure and the proportion of the thickness of the Al side increase with the decrease in cast-rolling velocity. The thinning of Cu strip mainly occurs in the backward slip zone. The higher pressure and longer solid/semi-solid contact time make the interface bonded fully, which provides favorable conditions for atomic diffusion. The inter-diffusion zone with a width of 4.9 μm is attained at a cast-rolling velocity of 2.4 m/min, and the Cu side surface is nearly completely covered by aluminum. Therefore, the ductile fracture occurs on the Al side, which prevents the propagation of interface delamination cracks effectively. Meanwhile, shear effect becomes more significant at high interfacial pressure and large plastic strain, and the microstructure on Al side is composed of slender columnar crystals. Thus, the metallurgical bonding and refinement of grains on the Al side can result in higher bonding strength and tensile properties of the clad strip.

The effect of Mg/Si ratio on the microstructure and tensile properties of twin-roll casting Al-Mg-Si alloys

In this work, two types of Al-Mg-Si strips with different Mg/Si ratios were fabricated by vertical-type twin-roll casting (TRC), and the effect of the Mg/Si ratio on microstructure and tensile properties of the TRC strips was investigated. The TRC strips show the heterogeneous structure, composed of columnar dendrites near the surface of both sides and near-equiaxed grains in the central region. Serious central segregation of eutectic phases occurred in the TRC strips with Mg/Si = 0.5 (S0.5), while no obvious central segregation was found in the strips with Mg/Si = 2.9 (S2.9), which was ascribed to the different solidification path. The low Mg/Si ratio promoted precipitation during aging, which resulted in an increase of 85 MPa in yield strength compared to the S2.9 sample. However, intergranular fracture occurred in the S0.5 sample, lowering uniform elongation.

Effect of Large Particles in Central Band of Al–4%Mn–1%Si High-Speed Twin-Roll Cast Strip on Elongation of Cold-Rolled and Annealed Sheets

Effect of Large Particles in Central Band of Al–4%Mn–1%Si High-Speed Twin-Roll Cast Strip on Elongation of Cold-Rolled and Annealed Sheets

Modeling effect of cooling conditions on solidification process during thermal cycle of rollers in twin-roll strip casting

Modeling effect of cooling conditions on solidification process during thermal cycle of rollers in twin-roll strip casting

Fabrication of Mg/Al Clad Strips by Direct Cladding from Molten Metals

This work describes the fabrication of AZ91D/A5052 clad strips by direct cladding from molten metals using a horizontal twin roll caster. Subsequently, the effects of roll speed, pouring sequence, and solidification length on the AZ91D/A5052 clad strips were investigated. The AZ91D/A5052 clad strips with a thickness of 4.9 mm were successfully cast at a roll speed of 9 m/min and with a 5 mm roll gap. The cladding ratio of AZ91D/A5052 was about 1:1. The single-roll casting results showed that the experimental solidification constants of AZ91D and A5052 were 62 mm/min0.5 and 34 mm/min0.5, respectively. The twin-roll casting results showed that the effect of rolling speed on the surface condition of A5052 was greater than that of AZ91D. In addition, the high melting point A5052 alloy poured into the lower nozzle could solve the remelting problem of the low melting point AZ91D. Moreover, extending the upper solidification distance could reduce the generation of intermetallic compounds. The EDS analysis results showed no voids at the bonding interface, while three intermetallic compound layers were also found at the bonding interface of AZ91D/A5052 strips, namely α-Mg + Mg17Al12, Mg17Al12, and Al3Mg2. This study could be instructive for dissimilar sheet metal bonding.

Microstructure, Precipitates Behavior, and Mechanical Properties of Age-Hardened Al-Mg-Si Alloy Sheet Fabricated by Twin-Roll Casting.

Twin-roll casting (TRC), as a near-net-shape technology, is employed to fabricate age-hardened Al-Mg-Si alloy. Compared with conventional direct chill (DC) casting, the TRC method is much more economical and efficient. In this work, the microstructure, precipitates behavior, and mechanical properties of age-hardened Al-Mg-Si alloy sheet fabricated by TRC were investigated by hardness measurements and tensile tests, metallographic microscopy, field emission gun scanning electron microscope, electron backscatter diffraction, transmission electron microscopy, and differential scanning calorimetry analyses. It was found that the size of recrystallized grains for DC casting alloy with finely dispersed particles was larger than that of TRC alloy with coarse particles. Typical CubeND texture accompanied by P texture formed after solution treatment made the value of r reach ~0.7 in the TRC alloy due to the PSN effect caused by the segregation of particles. More GP zones resulted in the strength of TRC alloy being higher than that of DC casting alloy after T8X treatment. With the time of paint-bake hardening extended to 8 h, few segregation particles remained in the TRC alloy. This decreased the concentration of supersaturated atoms. The hardness of the TRC alloy with the lower density of the β″ strengthening phase was lower compared to the DC casting alloy.

Segregation behavior, microstructure and properties of TA2/AA7005 composite plates manufactured by horizontal twin-roll casting under the effect of an electromagnetic oscillation field

Three TA2/AA7005 composite plates were manufactured by horizontal twin-roll casting (HTRC) under various external fields, and the formation mechanism of segregation in the cast-rolling clad process as well as the effect of external fields on the segregation behavior, microstructure and properties of the composite plates were studied. In the non-field (NF) plate, due to the high cooling rate and asymmetric heat transfer in the cast-rolling clad process, a central macro-segregation band and an interface segregation band were formed in the aluminum matrix. After applying the electromagnetic oscillation field (EMOF), the electromagnetic oscillation stirring effect was induced in the melt of the cast-rolling zone. The dendrites grown at the solidification front were broken by a shearing force and re-entered the melt. In addition, the temperature gradient at the solidification front decreased, which inhibited the growth of dendrites and avoided blocking the equilibrium distribution of solute elements due to the “bridging” of dendrite arms. After applying the EMOF, the central and interface segregation bands of the composite plate were nearly eliminated and the microstructure became more homogeneous. As a results, under the action of the EMOF, the tensile strength, yield strength, effective elongation, and interfacial bonding strength of the TA2/AA7005 cast-rolling composite plate were 303.8 MPa, 204.7 MPa, 21.6%, and 25.3 N/mm respectively, which were significantly improved in comparation with the NF plate.

Alleviating segregation and enhancing tensile properties of Inconel 718 superalloy by twin-roll casting and two-stage cold rolling

A novel processing route involving twin-roll casting and two-stage cold rolling was proposed to manufacture Inconel 718 alloy. Due to the sub-rapid solidification rate (412.5 °C/s) of as-cast strip, the element segregation can be alleviated and the growth of Laves phase was effectively suppressed. It was also observed that the dissolution of Laves phases during subsequent homogenization was significantly accelerated because of their refined size. The corresponding homogenization time can be shortened from dozens of hours to 1 h. Additionally, the non-uniform microstructure of cold-rolled and annealed samples caused by coarse grains from homogenization treatment can be eliminated by two-stage cold rolling method. Furthermore, a large amount of granular δ phases precipitated during intermediate annealing. After double aging treatment, the final products exhibited an excellent combination of strength and elongation. The ultimate tensile strength when deformed at room temperature and at 650 °C were about 1475 and 1120 MPa, and the corresponding total elongation were ∼ 15% and ∼ 22%. These results indicated that the twin-roll casting was a promising route to produce Inconel 718 alloy.