A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the in...A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the increasing number of droplet ejection experiments,the peak heat fluxes between droplet and substrate decreased firstly(1rd–5th ejection),then increased(5th–7th ejection),and finally decreased again(>7th ejection).In the first five experiments,the interfacial thermal resistance between the droplet and the substrate improved with increasing film thickness.However,at the onset of the 6th droplet ejection experiment,the deposited film initiated its melting process due to the accumulated thermal resistance,which has the potential to eradicate the cavity or air space existing between the droplet and the substrate.Consequently,the interfacial contact condition was improved gradually with the increasing melting area from 5th to 7th droplet ejection experiments,leading to an increase in heat fluxes.Increased SiO_(2) content in deposited films for 3.5 wt.%Si steel led to lower peak heat fluxes than for 2.5 wt.%Si steel.The solidification structure of the 2.5 wt.%Si steel droplet sample comprised a fine grain zone at the base,a columnar grain zone in the center,and an equiaxed grain zone at the top.However,the solidification structure of the 3.5 wt.%Si steel droplet only contained columnar grains and equiaxed grains,with a larger average grain size due to the lower interfacial heat flux.展开更多
Al-Mg-Si(AA6xxx)series alloys have been used widely in automotive industry for lightweight purpose.This work focuses on developing a short process for manufacturing Al-0.5Mg-1.3Si(wt.%)alloy sheets with good mechanica...Al-Mg-Si(AA6xxx)series alloys have been used widely in automotive industry for lightweight purpose.This work focuses on developing a short process for manufacturing Al-0.5Mg-1.3Si(wt.%)alloy sheets with good mechanical properties.Hereinto,a preparation route without homogenization was proposed on the basis of sub-rapid solidification(SRS)technique.The sample under SRS has fine microstructure and higher average partition coefficients of solute atoms,leading to weaker microsegregation owing to the higher cooling rate(160℃/s)than conventional solidification(CS,30℃/s).Besides,Mg atoms tend to be trapped in Al matrix under SRS,inducing suppression of Mg2Si,and promoting generation of Al Fe Si phase.After being solution heat treated(T4 state),samples following the SRS route have lower yield strength compared with that by CS route,indicating better formability in SRS sample.After undergoing pre-strain and artificial aging(T6 state),the SRS samples have comparable yield strength to CS samples,satisfying the service requirements.This work provides technological support to industrially manufacture high performance AA6xxx series alloys with competitive advantage by a novel,short and low-cost process,and open a door for the further development of twin-roll casting based on SRS technique in industries.展开更多
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 crys-talline ...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 crys-talline solids during solidification.In our experiments,the microstructure transition from coarse colum-nar crystals into fine equiaxed crystals for dilute Al-Mn-Si alloys was achieved by using sub-rapid so-lidification with the addition of Al-5Ti-1B grain refiner.The average grain size of Al alloy was reduced from a millimeter size to 73μm.Through temperature gradient calculation,we found that the acqui-sition 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 su-percooling,constitutional undercooling,thermal undercooling,and kinetic undercooling during sub-rapid solidification were quantitatively determined for given solidification rates.Our results showed that con-stitutional 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.展开更多
A hypereutectic Al-3Fe(wt.%)alloy was subjected by rheo-extrusion,and the effect of sub-rapid cooling and shear deformation on the refinement of Fe-rich phase was investigated.The results showed that both the primary ...A hypereutectic Al-3Fe(wt.%)alloy was subjected by rheo-extrusion,and the effect of sub-rapid cooling and shear deformation on the refinement of Fe-rich phase was investigated.The results showed that both the primary Fe-rich phase and eutectic Fe-rich phase in the solidified Al-Fe alloy were finer than the platelike Fe-rich phase in the as-cast Al-Fe alloy with the same content of Fe.The solidified Al-Fe alloy was subjected to three stages of shear deformation,and both the primary Fe-rich phase and eutectic Fe-rich phase were fractured and the average length was refined to 400 nm,while Fe-rich phase in the as-cast Al-3Fe(wt.%)alloy was platelike and its average length was 40 pm.The tensile strength and elongation of the hypereutectic Al-3Fe(wt.%)alloy containing nanosized Fe-rich phase were 162 MPa and 25.78%while those of the as-cast AI-3Fe(wt.%)alloy containing coarse platelike Fe-rich phase were 102 MPa and 16.84%,respectively.In the refineme nt of Fe-rich phase in hypereutectic Al-Fe alloy during rheo-extrusion,the three stages of shear deformation contributed more than sub-rapid cooling.展开更多
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...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 Mg_(2)Si 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.展开更多
Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels.However,research on the hot deformation behavior of sub-rapid solidified non-oriented electri...Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels.However,research on the hot deformation behavior of sub-rapid solidified non-oriented electrical steel,particularly at varying strain rates,has yet to be fully understood.The effect of thermal compression on the microstructure and mechanical properties of 3.15 wt.%Si non-oriented electrical steel strips produced through a strip casting simulator was systematically investigated.The findings reveal that increasing the deformation temperature enhances grain recrystallization,while the peak stress decreases with higher temperature.Furthermore,a lower strain rate favors dynamic recrystallization and reduces thermal stress.It can be seen that sub-rapid solidification can effectively reduce the thermal activation energy of non-oriented electrical steel,and the thermal activation energy is calculated to be 204.411 kJ/mol.In addition,the kinetic models for the dynamic recrystallization volume fraction of the studied 3.15 wt.%Si non-oriented electrical steel were established.展开更多
The microstructure of sub-rapid solidification processed AZ61A magnesium alloy was presented and discussed.The results show that the grain size of the foil is significantly refined,and the grain morphology is cellular...The microstructure of sub-rapid solidification processed AZ61A magnesium alloy was presented and discussed.The results show that the grain size of the foil is significantly refined,and the grain morphology is cellular or globular.The eutectic transformation L→α-Mg+β-Mg_(17)Al_(12) and microsegregation in conventionally solidified AZ61A alloy are suppressed to a great extent Theβ-Mg_(17)Al_(12) phases located in theα-Mg grain boundaries are largely decreased due to high solidification cooling rate.As a consequence,the alloying elements Al,Zn,Mn show much higher solid solubility and the sub-rapid solidification microstructure dominantly consists of supersaturatedα-Mg solid solution.The mechanical properties and fractographic analysis reveal that the fracture mechanism and corresponding morphology of the rapture surface of tensile bars are linked to the microstructure obtained and depend on the sub-solidification processes.展开更多
The strip casts of cobalt-free maraging steel were fabricated using a twin-roll strip casting simulator,and its characteristics of sub-rapid solidification were studied.Subsequently,the confocal laser scanning microsc...The strip casts of cobalt-free maraging steel were fabricated using a twin-roll strip casting simulator,and its characteristics of sub-rapid solidification were studied.Subsequently,the confocal laser scanning microscope(CLSM)was employed to in situ observe the phase transformation during the heat treatment of maraging steel strip cast such as austenitization,solution treatment,and aging processes.It was found that due to the high cooling rate during the twin-roll strip casting process,the sub-rapid solidified strip cast possessed a full lath martensitic structure,weak macrosegregation,and evident microsegregation with a dendritic morphology.During austenitization of strip cast,the austenite grain size increased with the austenitization temperature.After holding at 1250℃for 250 s,the austenite grain size at the high temperature owned a high similarity to the prior austenite grain size of the strip cast,which effectively duplicates the microstructure of the strip cast after sub-rapid solidification.During the solution treatment process,the martensitic structure of the strip cast also underwent austenitic transformation,subsequently transformed into martensite again after quenching.Due to the low reheating temperature during solution treatment,the austenite grain size was refined,resulting in the fine martensitic microstructure after quenching.During the aging process of strip cast,some of martensite transformed into fine austenite,which was located in the interdendritic region and remained stable after air cooling,resulting in the dual-phase microstructure of martensite and austenite.The solute segregation of Ni and Mo elements during the sub-rapid solidification of strip cast caused the enrichment of Ni and Mo elements in the interdendritic region,which can expand the austenite phase region and thus enhance the stability of austenite,leading to the formation of austenite in the interdendritic region after aging treatment.展开更多
基金supports from National Natural Science Foundation of China(Nos.52304361 and 52130408)Natural Science Foundation of Hunan Province(2023JJ40737)are great acknowledged.
文摘A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the increasing number of droplet ejection experiments,the peak heat fluxes between droplet and substrate decreased firstly(1rd–5th ejection),then increased(5th–7th ejection),and finally decreased again(>7th ejection).In the first five experiments,the interfacial thermal resistance between the droplet and the substrate improved with increasing film thickness.However,at the onset of the 6th droplet ejection experiment,the deposited film initiated its melting process due to the accumulated thermal resistance,which has the potential to eradicate the cavity or air space existing between the droplet and the substrate.Consequently,the interfacial contact condition was improved gradually with the increasing melting area from 5th to 7th droplet ejection experiments,leading to an increase in heat fluxes.Increased SiO_(2) content in deposited films for 3.5 wt.%Si steel led to lower peak heat fluxes than for 2.5 wt.%Si steel.The solidification structure of the 2.5 wt.%Si steel droplet sample comprised a fine grain zone at the base,a columnar grain zone in the center,and an equiaxed grain zone at the top.However,the solidification structure of the 3.5 wt.%Si steel droplet only contained columnar grains and equiaxed grains,with a larger average grain size due to the lower interfacial heat flux.
基金Financial supports from The National key research and development program(No.2016YFE0115300)The Natural Science Foundation of China(Nos.51790483,51625402,51790485 and 51801069)are greatly acknowledged+2 种基金Partial financial support came from The science and technology development program of Jilin Province(No.20190901010JC)The Changjiang Scholars Program(T2017035)the Program for JLU Science and Technology Innovative Research Team(JLUSTIRT,2017TD-09).
文摘Al-Mg-Si(AA6xxx)series alloys have been used widely in automotive industry for lightweight purpose.This work focuses on developing a short process for manufacturing Al-0.5Mg-1.3Si(wt.%)alloy sheets with good mechanical properties.Hereinto,a preparation route without homogenization was proposed on the basis of sub-rapid solidification(SRS)technique.The sample under SRS has fine microstructure and higher average partition coefficients of solute atoms,leading to weaker microsegregation owing to the higher cooling rate(160℃/s)than conventional solidification(CS,30℃/s).Besides,Mg atoms tend to be trapped in Al matrix under SRS,inducing suppression of Mg2Si,and promoting generation of Al Fe Si phase.After being solution heat treated(T4 state),samples following the SRS route have lower yield strength compared with that by CS route,indicating better formability in SRS sample.After undergoing pre-strain and artificial aging(T6 state),the SRS samples have comparable yield strength to CS samples,satisfying the service requirements.This work provides technological support to industrially manufacture high performance AA6xxx series alloys with competitive advantage by a novel,short and low-cost process,and open a door for the further development of twin-roll casting based on SRS technique in industries.
基金Financial supports from the National Natural Science Foun-dation of China(Nos.52222409,52074132,U19A2084,and U22A20109)are greatly acknowledgedPartial financial support came from the National Key Research and Development Program(No.2022YFE0122000)+1 种基金the Interdisciplinary Integration and Inno-vation Project of JLU(No.JLUXKJC2021ZZ08)the Fundamental Research Funds for the Central Universities,JLU.
文摘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 crys-talline solids during solidification.In our experiments,the microstructure transition from coarse colum-nar crystals into fine equiaxed crystals for dilute Al-Mn-Si alloys was achieved by using sub-rapid so-lidification with the addition of Al-5Ti-1B grain refiner.The average grain size of Al alloy was reduced from a millimeter size to 73μm.Through temperature gradient calculation,we found that the acqui-sition 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 su-percooling,constitutional undercooling,thermal undercooling,and kinetic undercooling during sub-rapid solidification were quantitatively determined for given solidification rates.Our results showed that con-stitutional 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.
基金the National Key Research and Development Program under Grant No.2018YFB2001800the National Natural Science Foundation of China under Grant Nos.51674077 and 51871184+1 种基金Joint fund between Shenyang National Laboratory for Materials Science and State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals under Grant No.18LHPYO13High-Level Talent Support Program of Liaoning under Grant No.XLYC1802128。
文摘A hypereutectic Al-3Fe(wt.%)alloy was subjected by rheo-extrusion,and the effect of sub-rapid cooling and shear deformation on the refinement of Fe-rich phase was investigated.The results showed that both the primary Fe-rich phase and eutectic Fe-rich phase in the solidified Al-Fe alloy were finer than the platelike Fe-rich phase in the as-cast Al-Fe alloy with the same content of Fe.The solidified Al-Fe alloy was subjected to three stages of shear deformation,and both the primary Fe-rich phase and eutectic Fe-rich phase were fractured and the average length was refined to 400 nm,while Fe-rich phase in the as-cast Al-3Fe(wt.%)alloy was platelike and its average length was 40 pm.The tensile strength and elongation of the hypereutectic Al-3Fe(wt.%)alloy containing nanosized Fe-rich phase were 162 MPa and 25.78%while those of the as-cast AI-3Fe(wt.%)alloy containing coarse platelike Fe-rich phase were 102 MPa and 16.84%,respectively.In the refineme nt of Fe-rich phase in hypereutectic Al-Fe alloy during rheo-extrusion,the three stages of shear deformation contributed more than sub-rapid cooling.
基金National Natural Science Foundation of China (52105319)。
文摘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 Mg_(2)Si 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.
基金The National Natural Science Foundation of China(Nos.52130408 and 52204356)the Natural Science Foundation of Hunan Province,China(2023JJ40762)the National Key Research and Development Program of China(No.2021YFB3702401)are greatly acknowledged.
文摘Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels.However,research on the hot deformation behavior of sub-rapid solidified non-oriented electrical steel,particularly at varying strain rates,has yet to be fully understood.The effect of thermal compression on the microstructure and mechanical properties of 3.15 wt.%Si non-oriented electrical steel strips produced through a strip casting simulator was systematically investigated.The findings reveal that increasing the deformation temperature enhances grain recrystallization,while the peak stress decreases with higher temperature.Furthermore,a lower strain rate favors dynamic recrystallization and reduces thermal stress.It can be seen that sub-rapid solidification can effectively reduce the thermal activation energy of non-oriented electrical steel,and the thermal activation energy is calculated to be 204.411 kJ/mol.In addition,the kinetic models for the dynamic recrystallization volume fraction of the studied 3.15 wt.%Si non-oriented electrical steel were established.
基金Projects(50274017,50674018)supported by the National Natural Science Foundation of China
文摘The microstructure of sub-rapid solidification processed AZ61A magnesium alloy was presented and discussed.The results show that the grain size of the foil is significantly refined,and the grain morphology is cellular or globular.The eutectic transformation L→α-Mg+β-Mg_(17)Al_(12) and microsegregation in conventionally solidified AZ61A alloy are suppressed to a great extent Theβ-Mg_(17)Al_(12) phases located in theα-Mg grain boundaries are largely decreased due to high solidification cooling rate.As a consequence,the alloying elements Al,Zn,Mn show much higher solid solubility and the sub-rapid solidification microstructure dominantly consists of supersaturatedα-Mg solid solution.The mechanical properties and fractographic analysis reveal that the fracture mechanism and corresponding morphology of the rapture surface of tensile bars are linked to the microstructure obtained and depend on the sub-solidification processes.
基金supported by National Natural Science Foundation of China(Nos.52130408 and 52304361)Natural Science Foundation of Hunan Province(No.2023JJ40737)the Open Project Program of Anhui Province Key Laboratory of Metallurgical Engineering&Resources Recycling(No.SKF23-02).
文摘The strip casts of cobalt-free maraging steel were fabricated using a twin-roll strip casting simulator,and its characteristics of sub-rapid solidification were studied.Subsequently,the confocal laser scanning microscope(CLSM)was employed to in situ observe the phase transformation during the heat treatment of maraging steel strip cast such as austenitization,solution treatment,and aging processes.It was found that due to the high cooling rate during the twin-roll strip casting process,the sub-rapid solidified strip cast possessed a full lath martensitic structure,weak macrosegregation,and evident microsegregation with a dendritic morphology.During austenitization of strip cast,the austenite grain size increased with the austenitization temperature.After holding at 1250℃for 250 s,the austenite grain size at the high temperature owned a high similarity to the prior austenite grain size of the strip cast,which effectively duplicates the microstructure of the strip cast after sub-rapid solidification.During the solution treatment process,the martensitic structure of the strip cast also underwent austenitic transformation,subsequently transformed into martensite again after quenching.Due to the low reheating temperature during solution treatment,the austenite grain size was refined,resulting in the fine martensitic microstructure after quenching.During the aging process of strip cast,some of martensite transformed into fine austenite,which was located in the interdendritic region and remained stable after air cooling,resulting in the dual-phase microstructure of martensite and austenite.The solute segregation of Ni and Mo elements during the sub-rapid solidification of strip cast caused the enrichment of Ni and Mo elements in the interdendritic region,which can expand the austenite phase region and thus enhance the stability of austenite,leading to the formation of austenite in the interdendritic region after aging treatment.
