Sub-rapid Solidification Research Articles

Understanding thermal compression and deformation behavior of 3.15 wt.% Si non-oriented electrical steels prepared by sub-rapid solidification

Understanding thermal compression and deformation behavior of 3.15 wt.% Si non-oriented electrical steels prepared by sub-rapid solidification

Sub-rapid solidification microstructure characteristics and control mechanisms of twin-roll cast aluminum alloys: A review

Rapid growth in industrial sectors such as automotive and shipbuilding has highlighted the significance of strip casting technology to produce lightweight alloys, particularly aluminum alloys widely used in both industrial production and daily life. Twin-roll casting (TRC), as an economically and environmentally friendly method for slab/strip production and processing, has attracted significant interest from researchers. However, the development of TRC aluminum alloys faces many challenges due to limited understanding of microstructural characteristics and control mechanisms. To further enhance comprehension of TRC aluminum alloys, this article reviews the influencing parameters, control methods, and existing issues related to TRC sub-rapid solidification (SRS) microstructure. It firstly summarizes TRC equipment types and their solidification characteristics, followed by a detailed analysis on key parameters affecting the evolution of TRC microstructure including rolling speed, roll separation force (RSF), and heat transfer coefficient (HTC). Finally, solutions to TRC defects are summarized and evaluated alongside their underlying mechanisms. This article provides a comprehensive review of the characteristics and control mechanisms of TRC microstructure while offering valuable insights for the future production of high-quality TRC aluminum strips.

Atomic-scale compositional complexity ductilizes eutectic phase towards creep-resistant Al-Ce alloys with improved fracture toughness

Hierarchical microstructures spanning from micro-sized eutectic structure to nano-sized precipitates are promisingly engineered in lightweight Al alloys to improve the high-temperature creep resistance that is increasingly required for rapid industrial development. However, the intrinsically-brittle eutectic phase is ready to fracture upon applied loading, which, dramatically reducing room-temperature ductility and fracture toughness, greatly hampers practical applications of the creep-resistant Al alloys. Here, through the combination of Sc microalloying with sub-rapid solidification, we observe the ductilization of Al11Ce3 eutectic phase in cast heat-resistant Al-Ce-Sc alloys due to the formation of atomic-scale compositional complexity. High-concentration Sc atoms are frozen within the Al11Ce3 intermetallic phase by the sub-rapid solidification, which then assemble into unusual atomic-scale compositional dipoles with the Sc atoms enriched at one pole and the Al atoms at the opposite during subsequent heat treatment. The dispersed Sc-Al compositional dipoles induce local lattice distortions that stimulate dislocation activities, as temporally and spatially visualized by in-situ neutron diffraction tensile test and microstructural characterizations. The unexpected plastic deformation triggered in Al11Ce3 improves the deformation compatibility between the eutectic phases, enabling the sub-rapidly-solidified Al-Ce-Sc alloy to reach a room-temperature tensile elongation 3 times and fracture toughness over 8 times of its counterpart derived from traditional solidification. In addition, the sub-rapidly-solidified Al-Ce-Sc alloy exhibits an excellent creep resistance at 300 °C, achieving a tensile creep stress threshold of ∼ 70 MPa. These findings provide new perspectives on the design of ductile intermetallic phases and the development of creep-resistant Al alloys with application-level ductility.

Simple route to produce excellent mechanical properties of 9Mn steel with heterostructure induced by pre-existing austenite with sub-rapid solidification

Medium-Mn steels have garnered significant interest due to their unique combination of high strength and exceptional ductility. However, a high Mn content inevitably causes the macro-segregation of Mn, which can significantly compromise the mechanical properties. This study effectively prevented the formation of Mn macro-segregation by employing the sub-rapid solidification. It resulted in the distribution of Mn micro-segregation bands within dendritic gaps in Fe-9Mn-2Si-0.5Al-0.1C steel. Mn micro-segregation bands results in a high proportion of pre-existing austenite (γpre) with small size and suitable stability in the as-cast strip, forming a lamellar structure with alternating distribution of lath martensite and austenite on the micrometer scale. The as-cast strip necessitates only basic simple hot rolling control without the need for any tempering treatment to achieve excellent mechanical properties comparable to conventional lengthy processes (ultimate tensile strength (UTS) of 1762 MPa, total elongation (TE) of 20 %, and product of strength and elongation (PSE) up to 35 GPa%). Utilizing this structure as a foundation, a simple austenite reverse tempering (ART) treatment can lead to additional enhancements in comprehensive mechanical characteristics with the UTS of 1529 MPa, TE of 25 % and PSE of 38 GPa%.

The effect of multi-scale second-phases on the microstructure evolution of a Mg–Al–Sn–Ca alloy during friction-stir processing

In the present work, the type, morphology and size of secondary phase particles in a Mg–4Al–2Sn-0.5Ca (ATX420) alloy are tailored through sub-rapid solidification (SRS) and aging treatment before friction stir processing (FSP) to systematically investigate their impact on microstructures and mechanical properties of the FSP ATX420 Mg alloy. The smaller eutectic CaMgSn phase with micro-defects in the as-cast SRS alloy is more likely to be broken during FSP, compared to the as-cast conventional solidification (CS) alloy. Additionally, nano-sized CaMgSn and Mg17Al12 particles precipitate in as-aged SRS alloy due to a high supersaturation solubility of solutes in the as-cast SRS alloy. These densely-distributed nano-sized precipitates in the as-aged SRS alloy increase the processing temperature by 60 °C during FSP, which results in less nano-sized precipitates in the stirring zone and grain growth of the α-Mg matrix. This leads to a decrease in hardness in the FSP-aged-SRS alloy (∼10 HV). Besides, the grain structure evolutions in the stirring zone and transition zone are systematically investigated for understanding the microstructure evolution during FSP in Mg alloys with eutectic phase.

Substantial grain refinement of Al-Mn-Si alloys mediated by collaborative effect of Al-5Ti-1B refiner and sub-rapid solidification

The mechanical properties of as-cast metallic materials depend strongly on the size and shape of grains, which are critical microstructural parameters dictated by the interplay of nucleation and growth of crystalline solids during solidification. In our experiments, the microstructure transition from coarse columnar crystals into fine equiaxed crystals for dilute Al-Mn-Si alloys was achieved by using sub-rapid solidification with the addition of Al-5Ti-1B grain refiner. The average grain size of Al alloy was reduced from a millimeter size to 73 µm. Through temperature gradient calculation, we found that the acquisition of fine equiaxed crystals could be attributed to the existence of a high number density of TiB2, acting as effective nucleation sites with an increase in total undercooling. Furthermore, the curvature supercooling, constitutional undercooling, thermal undercooling, and kinetic undercooling during sub-rapid solidification were quantitatively determined for given solidification rates. Our results showed that constitutional undercooling, rather than thermal undercooling, was primarily responsible for the formation of fine equiaxed grains, with the assistance of Al-5Ti-1B grain refiner. This work provides a new insight into the grain refining mechanism under sub-rapid solidification.

Investigation of the Effect of Sub-rapid Solidification Processes on the Microstructure and Mechanical Properties of Al86Cu6Co2Y6 (at.%) Alloy

Investigation of the Effect of Sub-rapid Solidification Processes on the Microstructure and Mechanical Properties of Al86Cu6Co2Y6 (at.%) Alloy

Response of partitioning to cooling rate for different solutes in aluminum alloys

It is commonly recognized that the cooling rate has a substantial effect on solute partitioning and its resultant microsegregation during solidification. The classical dendrite tip undercooling theory clarifies the mitigation of microsegregation by increasing the cooling rate. However, most of the studies focused on binary alloys, leaving an open question as to whether the microsegregation of different solutes in a multi-component alloy system exhibits a relieving degree similar to increasing cooling rate. Taking a widely used 6022-type Al alloy (Al-0.76Mg-0.93Si-0.2Fe) as a model alloy, the current study reveals that the microsegregation of Mg gets alleviated to the greatest extent, followed by those of Si and Fe when the cooling rate increases from 5 to 128 K/s. This phenomenon is attributed to the solute-based difference in response to partitioning to cooling rate (denoted as Rk). We propose a theoretical equation to quantify Rk, and the Rk values of solute Mg, Si, and Fe successfully explain the rank of solute partitioning in experiments. Furthermore, a broad range of Rk values of other commonly used alloying elements in Al alloys were calculated and ranked, delivering a handy tool to predict the microsegregation behavior and solubility of different solute elements upon sub-rapid solidification, which is consistent with experimental observation. This framework can also be extended to other multi-component alloy systems.

Evolution of the Microstructure and Mechanical Properties of As-Cast 22MnB5 Hot-Stamping Steel Processed by a Novel Sub-rapid Solidification Technique

Evolution of the Microstructure and Mechanical Properties of As-Cast 22MnB5 Hot-Stamping Steel Processed by a Novel Sub-rapid Solidification Technique

The influence of cooling rate on microstructure and magnetic properties of cast Fe-6.5wt%Si steel

Fe-6.5wt%Si steel samples of different thicknesses (1 mm, 2 mm, and 5 mm) were prepared by arc-melting and suction-casting with sub-rapid solidification rates. The microstructures and magnetic properties of the samples were studied, and the effect of solidification rates were discussed. Results show that columnar crystals are generated with a <100> fiber texture after casting. Ordered phases B2 and D03 are inhibited by sub-rapid solidification, and such an effect is clear in the 1 mm thick sample with the largest cooling rate. With decreasing cooling rate, the grain size increases, with the mean values being 66.6±30.8 μm, 93.0±42.8 μm, and 149.7±66.8 μm, and the intensity of the <100> texture increases, with the values being 3.14 mrd, 3.56 mrd, and 5.85 mrd, respectively. The 5 mm thick sample with the lowest cooling rate exhibits the best magnetic properties (B8=1.30 T, B50=1.55 T, P1/50=2.19 W/kg, P1/400=37.85 W/kg).

Superior strength-ductility synergy of wire-arc directed energy deposited Mg-Al-Si alloys mediated by sub-rapid solidification

Here we propose to employ wire-arc directed energy deposition (WA-DED) to tune the microstructure and the mechanical property of Mg-Al-Si alloys, on the basis of its sub-rapid solidification effect. According to finite element analysis, WA-DED shows higher cooling rate than conventional casting, reaching 598.3 K/s for Mg-Al-Si alloy, and the lower heat input, the larger cooling rate of WA-DED. Significant microstructure refinement is thus achieved, with reduced grain size and Mg2Si particle diameter. The transition from hypereutectic to fully eutectic microstructure is triggered by reducing the heat input. Compared with the as-cast alloy, WA-DED alloys demonstrate higher ultimate tensile strengths (UTS) at both room- and high-temperature (150 ℃) properties, increasing by 50.1% and 30.3%, respectively. The superior strength-ductility synergy for Mg-Al-Si alloys results from the microstructure tuning via sub-rapid solidification of WA-DED.

Influence of Ce micro-alloying on the microstructure and corrosion behavior of sub-rapid solidified Mg-4.5Al-1.5Sn-0.5Ca alloys

The effect of Ce micro-alloying (0, 0.05, 0.1 and 0.2 wt.%) on the microstructure and corrosion resistance of as-cast Mg-4.5Al-1.5Sn-0.5Ca (ATX521) alloys was investigated. The results reveal that the corrosion resistance of ATX521-0.1Ce alloy is remarkably improved by one order of magnitude via trace Ce addition in comparison to Ce-free alloy. The reduced electrochemical potential, refined and homogeneously distributed Ce-rich CaMgSn eutectic particles, effectively alleviate micro-galvanic corrosion and block the corrosion propagation. Furthermore, 0.1 wt.% Ce addition improves the compactness and protectiveness of product film, contributing to the enhanced corrosion resistance. The current work proposes a high-efficiency and low-cost route, i.e., sub-rapid solidification combined with Ce micro-alloying, towards fabricating a corrosion-resistant ATX521-0.1Ce alloy with improved mechanical properties.

Evolution of interfacial heat transfer, contact behavior and microstructure during sub-rapid solidification of molten steel with different hydrogen contents

Evolution of interfacial heat transfer, contact behavior and microstructure during sub-rapid solidification of molten steel with different hydrogen contents

A novel method for preparing ODS steel using precursor powder combining with sub-rapid solidification

Due to the expensive cost and challenges of batch mass production, the large-scale industrial application of oxide dispersion strengthened (ODS) steel is restricted. In this work, a novel method for preparing ODS steel using precursor powder combining with sub-rapid solidification was introduced. Herein, an ODS steel based on 316L stainless steel was prepared by this method and aged at 800 °C for 3 h to achieve massive diffuse precipitation of nano-scale oxides. The results indicated that the novel method successfully triggered the co-precipitation of nano-scale TiO2 and Er–Ti composite oxides with a number density of 6.58 × 1023 m−3 in the 316L stainless steel. After further aging at 800 °C for 3 h, a large number of Ti-rich oxide clusters with a size of less than 10 nm precipitated in the strips. With the precipitation of multiscale oxides, the aged 0.25% strip exhibited a yield strength and tensile strength of 411 MPa and 730 MPa, respectively, while maintaining an elongation of 33%. This work provided an alternative method for ODS steel fabrication.

Microstructure evolution and precipitation behaviour of the Cu-Ni-Si-Cr alloy based on twin-roll strip casting

ABSTRACT The twin-roll strip casting (TRSC) process was introduced because of its sub-rapid solidification characteristics, and the element segregation and ageing precipitation of the Cu-6Ni-1.4Si-0.1Cr alloy were studied. The results are as follows: TRSC can effectively refine grain size and inhibit the segregation of the Cu-6Ni-1.4Si-0.1Cr alloy. Two types of precipitates are formed mainly during the ageing process: disk-shaped δ-Ni2Si and rod-shaped β-Ni3Si. The comprehensive properties of the alloy are improved, and the precipitation strengthening mechanism is either from the dislocation shearing mechanism or the Orowan mechanism in different stages of ageing. The Cu-6Ni-1.4Si-0.1Cr alloy achieves optimum performance after ageing at 350°C for 4 h, where the tensile strength and conductivity are 1112 MPa and 27.35% IACS, respectively. The Avrami equations were established for the alloy to describe the kinetics of phase transformation and electrical conductivity during ageing, and the calculated results are consistent with the experimental data.

Phase Transformation Behaviors of Medium Carbon Steels Produced by Twin Roll Casting and Compact Strip Production Processes

Medium carbon steels have been widely used in the fields of tool and die manufacturing due to their outstanding hardness and wear resistance. In this study, microstructures of 50# steel strips fabricated by twin roll casting (TRC) and compact strip production (CSP) processes were analyzed to investigate the influences of solidification cooling rate, rolling reduction, and coiling temperature on composition segregation, decarburization, and pearlitic phase transformation. The results show that a partial decarburization layer with a thickness of 13.3 μm and banded C-Mn segregation were observed in the 50# steel produced by CSP, leading to the banded distributions of ferrite and pearlite in the C-Mn poor regions and C-Mn rich regions, respectively. For the steel fabricated by TRC, owing to the sub-rapid solidification cooling rate and short processing time at high temperatures, neither apparent C-Mn segregation nor decarburization was observed. In addition, the steel strip fabricated by TRC has higher pearlite volume fractions, larger pearlite nodule sizes, smaller pearlite colony sizes and interlamellar spacings due to the co-influence of larger prior austenite grain size and lower coiling temperatures. The alleviated segregation, eliminated decarburization and large volume fraction of pearlite render TRC a promising process for medium carbon steel production.

Precipitation of ceramic particles in Fe-TiB2 and Fe-Ni-TiB2 cast steels during the sub-rapid solidification process

Titanium diboride (TiB2) particle reinforced steels were prepared by a sub-rapid solidification process using the in-situ method. Effects of the Ni concentration on the precipitation of TiB2 ceramic particles were studied and modified in detail. The results show that the mechanically unfavorable-block TiB2-morphologies and the matrix constitutions change with the addition of alloy Ni. The Ni concentration in the iron matrix closes the primary δ-Fe ferrite phase zone, retards the precipitation of the primary TiB2 particles, changes the residual interfacial lattice strain in α-Fe ferrite from tension to compression and promotes the ordered adoption of Fe atoms in (Ti, Fe)B2, which results in the ceramic particles growth into the vermicular-shaped morphologies. Strongly coherent interfaces between a-Fe matrix and TiB2 particles form in Fe-Ni-TiB2 high-modulus steels (HMS) according to the generation of the compression lattice strains at α-Fe ferrite interfaces. The mechanical favorable interfaces are believed to be responsible for the obvious improvements in the mechanical properties, especially the tensile elongation, of Fe-Ni-TiB2 HMS.

Generalized stability criterion for controlling solidification segregation upon twin-roll casting

• Systematical framework integrating dendritic growth model, overall solidification kinetic model and generalized stability was constructed. • Processing parameters of the casting speed and the flow speed of cooling water in twin-roll casting are coupled. • Sub-rapid solidification kinetics, concentration and segregation by different processing parameters couple were established. • New strategy was proposed: high initial driving force suppresses centerline segregation, and high final generalized stability suppresses edge segregation. Macro- and micro-segregation formed upon twin-roll casting (TRC) can be inherited from sub-rapid solidification to solid-state transformation, even to plastic deformation, thus deteriorating drastically mechanical properties of as-produced thin sheets. Although many works focusing mainly on controlling fields of thermal, concentration and convection have been reported, how to control artificially and quantitatively the segregation using a theoretical connection between processing parameters and solidification models, has not been realized, yet. Regarding it, a systematical framework integrating non-equilibrium dendritic growth and overall solidification kinetics with the TRC parameters, was constructed applying a generalized stability (GS) conception deduced from transient thermodynamic driving force Δ G t and transient kinetic energy barrier Q eff t evolving upon solidification. Departing from this framework considering synergy of thermodynamics and kinetics (i.e., thermo-kinetic synergy), a criterion of high Δ G t -high GS guaranteed that the macro (i.e., the centerline) and the micro (i.e., the edge) segregation can be suppressed by increasing Δ G t and GS at the beginning and the ending stage of sub-rapid solidification, respectively. This typical thermo-kinetic combination producing the microstructure can be inherited into the plastic deformation, as reflected by corresponding strength-ductility combinations. This work realized quantitative controlling of TRC by a theoretical connection between processing parameters and solidification models, where, an optimization for sub-rapid solidification segregation using the GS conception including Δ G t and Q eff t has been performed.

Kinetics of austenite growth and bainite transformation during reheating and cooling treatments of high strength microalloyed steel produced by sub-rapid solidification

Kinetics of austenite growth and bainite transformation during reheating and cooling treatments of high strength microalloyed steel produced by sub-rapid solidification

Effect of chromium coating roughness and thickness on interfacial heat transfer behaviour of sub-rapid solidification process

ABSTRACT The comparisons of wear resistance and heat transfer behaviours of chromium and brass were conducted. The effects of different values of chromium coating average roughness (1.240, 4.576, 7.388, 9.323 μm) and thickness (15, 35, 55 μm) on the interfacial heat transfer behaviours were investigated with a novel droplet solidification technique. The results revealed that, compared with the brass, the chromium material has a significant improvement in the Vickers hardness and wear performance and a reduction of 25 percent interfacial heat transfer rate. Moreover, with the increase of the coating average roughness from 1.240 to 7.388 μm, the maximum heat flux between molten steel and cooling substrate decreases from 8.27 to 5.56 MW/m2 due to the enlargement of the air gap. As the coating average roughness further increases to 9.323 μm, the maximum heat flux increases to 6.50 MW/m2 because of the increasing contact area between molten steel and the cooling substrate. In addition, the maximum heat flux was reduced from 8.47 to 5.87 MW/m2, considering the enhancement of interfacial thermal resistance when the coating thickness increases from 15 to 55 μm. The results obtained have important implications for heat transfer control of the strip casting process by adjusting the coating average roughness and thickness.