High-speed Twin-roll Casting Research Articles

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

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 Homogenization Heat Treatment on Elongation Anisotropy in Cold-Rolled and Annealed Al–Si Alloy Sheets Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strips

Effect of Homogenization Heat Treatment on Elongation Anisotropy in Cold-Rolled and Annealed Al–Si Alloy Sheets Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strips

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

Microstructure and Properties after Friction Stir Processing of Twin-Roll Cast Al–Mn–Cu–Be Alloy

We studied the effect of friction stir processing (FSP) on the microstructure and properties of high-speed twin-roll cast strips made of an experimental Al–Mn–Cu–Be alloy. The samples were examined using light, scanning, and transmission electron microscopy, microchemical analysis, X-ray diffraction, and indentation testing. During FSP, the rotational speed varied, while other parameters remained constant. The uniformity of the microstructure increased with the growing rotational speed. In the stir zone, several processes took place, and the most important were: recrystallisation of the matrix grains, fragmentation of the primary intermetallic particles Al15Mn3Be2 and their more uniform distribution in the stir zone, fracture, and dispersion of the eutectic icosahedral quasicrystalline phase (IQC), transformation of tiny Al15Mn3Be2 and IQC particles into the τ1-Al26Mn6Cu4 phase and precipitation of Al–Mn–Cu precipitates. In the thermomechanically affected zone, new dislocations formed as well as dispersion of the IQC eutectic phase and recrystallisation of the matrix grains. In the heat-affected zone, dissolution of θ’-Al2Cu precipitates occurred. The hardness variation was not severe between the stir and heat-affected zones.

Microstructure and Indentation Properties of Single-Roll and Twin-Roll Casting of a Quasicrystal-Forming Al-Mn-Cu-Be Alloy

In this investigation, strips of an experimental Al-Mn-Cu-Be alloy were manufactured by high-speed single-roll and twin-roll casting to stimulate the formation of a quasicrystalline phase during solidification. The strips were characterised by light microscopy, scanning and transmission electron microscopy, microchemical analysis, and X-ray diffraction. Indentation testing was used to determine the mechanical responses of the strips in different areas. A smooth surface was achieved on both sides of the twin-roll-cast strip, while the free surface of the single-roll-cast strip was rough. The microstructures in both strips consisted of an Al-rich solid solution matrix embedding several intermetallic phases Θ-Al2Cu, Be4Al (Mn, Cu), Al15Mn3Be2 and icosahedral quasicrystalline phase (IQC). The microstructure of the single-roll-cast strip was more uniform than that of the twin-roll-cast strip. Coarse Al15Mn3Be2 particles appeared in both alloys, especially at the centre of the twin-roll strip. These coarse particles adversely affected the strength and ductility. Nevertheless, both casting methods provided high-cooling rates, enabling the formation of metastable phases, such as quasicrystals. However, improvements in alloy composition and casting procedure are required to obtain enhanced microstructures and properties.

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.

Microstructure and mechanical properties of high-manganese-containing high-speed twin-roll cast Al-Mn-Si alloy strips and their cold-rolled sheets

Al-Mn based alloys with high-manganese content are expected to have improved mechanical properties due to solid solution hardening and/or dispersion hardening. However, the increase of Mn solubility of the alloy is difficult by using the conventional DC casting. In order to solve this problem, in the present study, we focused on the twin-roll casting method which is characterized by high cooling rates. Several kinds of high Mn-containing Al-Mn-Si alloy strips were fabricated by using a vertical-type high-speed twin-roll caster equipped with a pair of water-cooled copper rolls. Direct temperature measurement of the liquid melt during the casting was also performed. The alloy strips of various compositions containing up to 4 Mn and 2 Si (wt%) were successfully obtained. By observing the microstructure of the cross section of the strip, we found the characteristic solidified structure. The solidified structure consisted of three layers. Two solidified shells with a columnar dendrite structure grew from the roll surfaces toward the strip center. In the mid-thickness region, the band structure consisting of equiaxed dendrites and globular grains was observed between the solidified shells. Very fine primary particles were observed in the matrix near the strip surface, while, relatively coarse particles with blocky and needle-like shape were observed in the central band of the as-cast strip. The electric conductivity measurement was performed for the as-cast strips. Mn solubility in Al matrix was estimated from the obtained values. The estimated Mn solubility in the Al-2Mn-xSi strips was between 1.5 ~ 1.8wt% Mn. It was over 1.43wt%Mn for the Al-4Mn-xSi strips. We found that the Mn solubility of the as-cast strips was considerably high. The strips were cold-rolled to the sheets and then annealed at various conditions. They were subjected to the tensile tests, and the effects of solid solution hardening and dispersion hardening are discussed.

Mechanical Properties of Cold-Rolled and Annealed Al–12%Mg Alloy Sheet with High Mg Solid Solubility Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strip

Mechanical Properties of Cold-Rolled and Annealed Al–12%Mg Alloy Sheet with High Mg Solid Solubility Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strip

Center Segregation and Cross-Hatched Surface Pattern of Vertical-Type High-Speed Twin-Roll Cast Al–Si–Mg Alloy Strip Formed by Wide Rolls

Center Segregation and Cross-Hatched Surface Pattern of Vertical-Type High-Speed Twin-Roll Cast Al–Si–Mg Alloy Strip Formed by Wide Rolls

Role of Roll Separating Force in High-Speed Twin-Roll Casting of Aluminum Alloys

The role of the roll separating force in the high-speed twin-roll casting of aluminum alloys was examined. In horizontal-type twin-roll casting, as the casting speed increased upon decreasing the roll separating force, the strip texture changed from a shear and rolling texture to a random texture. Direct temperature measurements during high-speed twin-roll casting showed that the roll separating force played a significant role in maintaining a good contact between the strip and the roll surface. This resulted in a high cooling rate around the roll nip and enabled the fabrication of a sound strip with a fine microstructure. Moreover, the high casting speed and lowered roll separating force gave a band structure consisting of fine globular grains in the mid-thickness region of the strip, which could be considered beneficial in the formation of a well-dispersed center segregation.

Surface quality and microstructure of Al-Mg alloy strips fabricated by vertical-type high-speed twin-roll casting

Al-Mg alloy strips were fabricated by the vertical-type high-speed twin-roll casting. Periodic patterns on the strip surface were observed in the casting direction consisting of the shiny region and un-shiny region with cracks. The un-shiny region and cracks remain even after successive cold rolling. Therefore, formation of the periodic patterns during casting should be suppressed. In this study, the formation mechanism of the periodic patterns of the JIS-AC7A strips was examined by microstructural observation and compositional analysis. The cross-sectional observation in the un-shiny region revealed the inverse segregation of Mg and Fe from the mid-thickness area of the strip toward the surface along the grain boundaries. It is considered that the residual liquid is squeezed out from the mid-thickness area of the strip toward the surface through the grain boundaries, and results in the formation of the un-shiny region. Temperature measurement was performed at the gap formed between the roll surface and the nozzle tip by using thermocouples. The strips were also fabricated by using the nozzles with various tip shapes in order to change the contact conditions between the melt and roll surface. The oscillation of the molten metal meniscus in the gap between the roll surface and the nozzle tip is considered to be one of the possible reasons of the formation of the periodic patterns on the strip surface.

Influence of Cooling Rate on Primary Particle and Solute Distribution in High-Speed Twin-Roll Cast Al-Mn Based Alloy Strip

Influence of Cooling Rate on Primary Particle and Solute Distribution in High-Speed Twin-Roll Cast Al-Mn Based Alloy Strip

Microstructural Evolution of Al-Mn Based Alloy Fabricated by Vertical-Type High-Speed Twin-Roll Casting

For decades, twin-roll casting has been applied for manufacturing aluminum alloy sheets. This conventional process contributes to make thin aluminum sheets from the molten metal directly. Recently, vertical-type high-speed twin-roll casting (HSTRC) has been developed with much higher casting speed rather than the horizontal-type. Some modifications such as feeding nozzle and water-cooling system of copper rolls contribute to increase cooling rates. This characteristic leads to many metallurgical advantages like grain refinement, super-saturation of alloying elements and fine distribution of secondary particles. The objective of this study is to investigate the constituent particles in HSTRC aluminum alloy. The commercial Al-Mn alloy strip was successfully fabricated by HSTRC. Clearly different microstructure was found in thickness direction. Many constituent particles observed along the grain boundaries/cell boundaries as well as inside of Al matrix on the surface area, while eutectic structure around globular grain boundaries was observed in mid-central area. The morphology as well as chemical compositions of the constituent particles were investigated.

Application of Vertical-Type High-Speed Twin-Roll Casting for Up-Grade Recycling and Clad Sheets Fabrication of Aluminum Alloys

A horizontal-type twin roll casting method has been popular for producing aluminum alloy strips, however, it is characterized by a relatively low productivity (1~6 m/min). In contrast, a vertical-type high-speed twin-roll casting method possesses an extremely high productivity (60~120 m/min (1~2 m/s)) and an excellent heat extraction ability. The rapid cooling effect provided significant microstructure refinement and mechanical properties improvement in various kinds of cast aluminum alloy products. Not only “product to product recycling” but also “up-grade recycling” can be achieved by making good use of these merits. Two examples of application showing the potential of vertical-type high-speed twin roll casting method are presented. (1) Several kinds of Al-Si base alloy were cast into the strips. Not only strength and toughness but also formability was increased in the twin roll cast products. In particular, great improvement in deformability shows the potential of the twin-roll cast aluminum alloy products as substitutes for some wrought aluminum alloy products. (2) The vertical-type tandem twin-roll caster was able to fabricate a clad strip by single step. The A4045/A3003/A4045 aluminum alloy clad sheets produced by the twin-roll casting showed better mechanical properties than the conventional hot-roll bonded clad sheets.

Effect of nozzle shape on solidification behaviour in high-speed twin-roll strip caster: a simulation approach

In twin-roll strip casting process, the solidification characteristics of the strip are directly influenced by the process parameters, i.e. casting speed, roll gap and nozzle shape, etc. To obtain a defect free strip, optimisation of the process parameters is inherently required. In the present investigation, a comprehensive three-dimensional model for top side pouring high-speed twin-roll strip casting of Al-4.5wt.% Cu alloy with different nozzle shape has been carried out. ANSYS 13.0 was used to model fluid flow, heat transfer and solidification behaviour during the top side pouring of liquid Al-4.5wt.% Cu alloy in twin-roll strip caster with different nozzle shape. The model takes into account the coupled fluid flow, heat transfer and solidification characteristics in the molten pool. The variations of nozzle shape on flow feature and solidification characteristics were studied. From the simulation results, it was found that with circular shape nozzle, uniform solidification takes place which results defect free strip as compared to the square shape, triangular shape and elliptical shape nozzles. It was observed that, the nozzle with circular shape was most favourable for high-speed twin-roll strip caster.

Microstructure evolution of eutectic Al–Cu strips by high-speed twin-roll strip casting process

In the present investigation, microstructural evolutions of functionally graded eutectic Al–Cu strips prepared by high-speed twin-roll strip caster at different casting speeds and liquid melt superheats were studied. The as-cast sample was subjected to scanning electron microscope to study the evolution of microstructure of the strip at different casting speeds and liquid melt superheats. At different casting speeds, non-equilibrium eutectic structure observed on the Al–Cu eutectic strip consists of lamellar as well as wavy structure with a distinct boundary. The lamellar microstructure consists of alternating layers of well-bonded α-Al phase and θ-Al2Cu phase. The globular flowery structure within the eutectic matrix was observed on the strip at different liquid melt superheats. The microhardness of the as-cast strip was studied by Vickers hardness tester, and it was found that hardness value increases with increasing casting speed and decreases with increasing liquid melt superheat.

Solidification Structure and Casting Defects in High-Speed Twin-Roll Cast Al–2 mass% Si Alloy Strip

Al­2mass% Si alloy, which has wide freezing temperature range, was cast using a laboratory-scale vertical-type high-speed twin-roll caster. The solidification structure and several kinds of casting defects were examined using OM, SEM and SEM-EDS. The results showed that the unstable melt pool condition could cause the surface defects such as the ripple mark, “un-shiny” zone and the inverse segregation. In the present nozzle type, constructing a stable high melt pool level was seemed to be essential to obtain a sound strip with no defect on the strip surface. A large-scale internal cracking along the casting direction was also observed in the high-speed twin-roll casting of aluminum alloy. The present results revealed that the cracking was related to distribution of the residual liquid in the central band region, which could be controlled by the roll separating force near the roll nip. It is considered that the roll separating force caused the shear localization in the central band region and promoted a formation of continuous liquid film in the shear localized region. The liquid film was a cause of the internal cracking when the strip passed through the roll nip. [doi:10.2320/matertrans.L-M2013824]

Modeling and Experimental Validation of Rapid Cooling and Solidification during High-Speed Twin-Roll Strip Casting of Al-33 wt pct Cu

The numerical modeling of heat transfer and solidification during twin-roll strip casting involves incorporating fluid flow, heat transfer, and phase change in the liquid metals and knowledge of heat flux distribution at the liquid metal–roll interface. Although efforts have been put in the development of comprehensive modeling of the process simulation of the heat transfer, solidification during high-speed twin-roll casting and its experimental validation has not been attempted. In the current paper, the results of simulation of twin-roll strip casting up to high speeds has been reported for Al-33 wt pct Cu using FLUENT 6.3.16 (ANSYS, Inc., Canonsburg, PA). Further Jackson-Hunt plot for Al-33 wt pct Cu has been used to validate the simulation. It has been shown by simulation as well as experiment that high speed twin-roll casting can be a method for direct production of layered materials.

Effect of Cooling Rates during Solidification of Al-5.5%Mg-2.3%Si-0.6%Mn and Al-13%Mg<SUB>2</SUB>Si Pseudo-Binary Alloys on Their Secondary-Particle Morphology and Tear Toughness

Al–5.5%Mg–2.3%Si–0.6%Mn alloy and Al–13%Mg2Si pseudo-binary alloy were cooled at various cooling rates during solidification. Morphological change of secondary particle was examined. Solidified structure of Al–5.5%Mg–2.3%Si–0.6%Mn alloy consisted of primary α–Al dendrites, Al–Mg2Si eutectic structure and Al6Mn particles. The most significant morphological change was from lamella Al–Mg2Si eutectic structure in the permanent mold cast and the die-cast product to refined and globular Mg2Si phase in the high-speed twin-roll cast product. In contrast, no morphological change was observed for Al6Mn particles. In order to investigate the effect of morphological change of Mg2Si phase on tear toughness, tear toughness tests were performed for Al–13%Mg2Si pseudo-binary alloy cast products produced by permanent mold casting and high-speed twin-roll casting. Unit crack propagation energy (UEp) of the high-speed twin-roll cast products was 5 times higher than that of permanent mold cast products. For permanent mold cast specimens, crack propagation occurred along the interface of plate-like Mg2Si/matrix of the eutectic solidified region and in Al-matrix. But fracture surface of high-speed twin-roll cast specimens was covered with fine dimples. Such difference of fracture mode is due to morphological change of Mg2Si phase from plate-like to globular by rapid cooling.