Being used more and more widely in engineering,AlSi alloys comprise about 80%of all kinds of aluminum alloys,which are the most widely utilized nonferrous alloys.Although most Al-Si alloys consist of multiple componen...Being used more and more widely in engineering,AlSi alloys comprise about 80%of all kinds of aluminum alloys,which are the most widely utilized nonferrous alloys.Although most Al-Si alloys consist of multiple components,the eutectics in the structure accounts for 50%-90%of the sum volume of such alloys.Therefore,understanding the modification mechanism and function rules of the AlSi eutectic solidification is the technical key in controlling the structures and properties of such casting alloys.The present paper chiefly reviews recent investigation developments and important conclusions along the lines of the functions of modification elements and their modification mechanism in the eutectic solidification of Al-Si alloys.展开更多
The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) cast iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason ...The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) cast iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason should be the difference in their graphitization during the eutectic solidification. In this paper, we discuss the difference in the solidification mechanism of both cast irons for solving these problems using unidirectional solidification and the cooling curves of the spheroidal graphite cast iron. The eutectic solidification rate of the SG cast iron is controlled by the diffusion of carbon through the austenite shell, and the final thickness is 1.4 times the radius of the SG, therefore, the reduction of the SG size, namely, the increase in the number, is the main solution of these problems.展开更多
As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidi...As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidification and microstructure of the Al-13%Si alloy, an investigation has been undertaken by means of thermal analysis and micro/macro-structure observation. Results indicate that addition of phosphor in near eutectic Al-Si alloy promotes the nucleation of eutectic but has little refinement impact on primary Si particles as expected. Conversely, both primary Si particles and eutectic Si flakes become slightly coarser in P-rich alloys. The coarsening of eutectic Si flakes ties closely to the increased eutectic growth temperature with phosphor addition. The eutectic solidification of the alloy proceeds from the near mold zone towards the center, and it is also found that a few independent nucleation regions emerge in liquid at the solidification front due to the addition of phosphor.展开更多
An electromagnetic vibration was generated by simultaneously imposing a strong static magnetic field （up to 10 T） and an alternative electricity current to the metal. Its effects on the solidification structure of e...An electromagnetic vibration was generated by simultaneously imposing a strong static magnetic field （up to 10 T） and an alternative electricity current to the metal. Its effects on the solidification structure of eutectic Al-Si alloy have been investigated experimentally. It is found that the eutectic structure has been refined by solely imposing high magnetic field while it is coarsened under the electromagnetic vibration. Furthermore, polyhedral Si grains and non-dendritic α-Al appeared when the electromagnetic vibration strength was strong enough. The refining of eutectic structure is attributed to the decrease of diffusion coefficient caused by the strong magnetic field. The coarseness of eutectic structure may be attributed to the convection caused by electromagnetic vibration. Strong convection may break co-operative growth of eutectic phases to form polyhedral Si grains and non-dendritic α-Al.展开更多
In situ eutectic Al_(11)La_3/Al composite material with regular arrangement was prepared by zone melt liquid metal cooling directionally solidification under conditions of high temperature gradient G=700K/cm and growt...In situ eutectic Al_(11)La_3/Al composite material with regular arrangement was prepared by zone melt liquid metal cooling directionally solidification under conditions of high temperature gradient G=700K/cm and growth rate R=6.0-20.0μm/s.Superpose diffraction pat- tern of Al_(11)La_3/Al composite shows that the preferred growth direction is[100]Al// [33]Al_(11)La_3,and the habit plane is(002)Al//(116)Al_(11)La_3.A low density(103)twin is ob- served in Al_(11)La_3 and the growth of(103)twin induces to branching to change the interlamellar spacing.展开更多
Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates （5.32-250.0μm/s） at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus.The values of eutectic spac...Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates （5.32-250.0μm/s） at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus.The values of eutectic spacing were measured from transverse sections of the samples.The dependences of the eutectic spacing and undercooling on growth rate are determined as λ=9.21V-0.53 and ΔT=0.0245V0.53,respectively.The results obtained in this work were compared with the Jackson-Hunt eutectic theory and the similar experimental results in the literature.Microhardness of directionally solidified samples was also measured by using a microhardness test device.The dependency of the microhardness on growth rate is found as Hv=115.64V0.13.Afterwards,the electrical resistivity （r） of the casting alloy changes from 40×10-9 to 108×10-9 Ω·m with the temperature rising in the range of 300-630 K.The enthalpy of fusion （ΔH） and specific heat （Cp） for the Zn-Al eutectic alloy are calculated to be 113.37 J/g and 0.309 J/（g·K）,respectively by means of differential scanning calorimetry （DSC） from heating trace during the transformation from liquid to solid.展开更多
Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the ...Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.展开更多
Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inher...Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inherent heterogeneous nuclei. The recalcscence phenomenon and its dependence on undercooling and on crystal nuclcation and growth, as well as its relationship to solidification microstructures are studied. The crystalli/ation fraction during recalcsccnce is also calculated. Experiments reveal that recalcscence degree increases with undercooling when the latter is below a certain critical value∧Te, but it decreases as undercooling increases above A 7'( (under present conditions∧Te= 245K, i. c. 0.17TE). The greater the recalescencc degree, the larger the proportion of anomalous eutectic in solidified structures. It is inferred that anomalous eutectic is the product of rapid solidification while lamellar eutectic forms at much slower nuclcation rate and growth velocity.展开更多
The modification of eutectic silicon is of general interest since fine eutectic silicon along with fine primary aluminum grains improves mechanical properties and ductilities. In this study, high intensity ultrasonic ...The modification of eutectic silicon is of general interest since fine eutectic silicon along with fine primary aluminum grains improves mechanical properties and ductilities. In this study, high intensity ultrasonic vibration was used to modify the complex microstructure of aluminum hypoeutectic alloys. The ultrasonic vibrator was placed at the bottom of a copper mold with molten aluminum. Hypoeutectic AI-Si alloy specimens with a unique in-depth profile of microstructure distribution were obtained. Polyhedral silicon particles, which should form in a hypereutectic alloy, were obtained in a hypoeutectic AI-Si alloy near the ultrasonic radiator where the silicon concentration was higher than the eutectic composition. The formation of hypereutectic silicon near the radiator surface indicates that high-intensity ultrasonic vibration can be used to influence the phase transformation process of metals and alloys. The size and morphology of both the silicon phase and the aluminum phase varies with increasing distance from the ultrasonic probe/radiator. Silicon morphology develops into three zones. Polyhedral primary silicon particles present in zone I, within 15 mm from the ultrasonic probe/radiator. Transition from hypereutectic silicon to eutectic silicon occurs in zone II about 15 to 20 pm from the ultrasonic probe/radiator. The bulk of the ingot is in zone III and is hypoeutectic AI-Si alloy containing fine lamellar and fibrous eutectic silicon. The grain size is about 15 to 25 IJm in zone I, 25 to 35 IJm in zone II, and 25 to 55 pm in zone II1. The morphology of the primary a-AI phase is also changed from dendritic （in untreated samples） to globular. Phase evolution during the solidification process of the alloy subjected to ultrasonic vibration is described.展开更多
The effects of bismuth and the combination of bismuth and strontium on the eutectic silicon structure in Al-7Si-0.4Mg alloys were investigated under different solidification conditions.The results show that bismuth ha...The effects of bismuth and the combination of bismuth and strontium on the eutectic silicon structure in Al-7Si-0.4Mg alloys were investigated under different solidification conditions.The results show that bismuth has a refining effect on the eutectic silicon and its refinement behavior increases with increasing Bi content up to 0.5% （mass fraction）.When bismuth is added into the molten alloy modified with strontium,a higher Sr/Bi mass ratio of at least 0.45 is required to attain full modification of the eutectic silicon.展开更多
By comparisons of interface growth temperatures of different phases in eutectic systems, competitive growth between the primary phase, halo structure and coupled eutectic has been discussed. The compositions for the f...By comparisons of interface growth temperatures of different phases in eutectic systems, competitive growth between the primary phase, halo structure and coupled eutectic has been discussed. The compositions for the formation of coupled eutectic have been discussed at the coexisting with the primary phase in eutectic under directional solidification. Solidification conditions, such as growth rate and composition required for the formation of the primary phase, halo structure and coupled eutectic have been proposed. Numerical calculation results show that no halo structure formed in directionally solidified Sn-Pb eutectic, but in Al-Si eutectic, competitive growth structures of the primary β-Si phase, α-Al halo structure and coupled eutectic (α+β) may exist at the hypereutectic composition between 12.6% and 25% Si. The calculated results of Al-Si eutectic fit in with the reported experiment results.展开更多
In this study NieN i3 Si eutectic in situ composites are obtained by Bridgman directional solidification technique when the solidification rate varies from 6.0 mm/s to 40.0 mm/s. At the low solidification rates the la...In this study NieN i3 Si eutectic in situ composites are obtained by Bridgman directional solidification technique when the solidification rate varies from 6.0 mm/s to 40.0 mm/s. At the low solidification rates the lamellar spacing is decreased with increasing the solidification rate. When the solidification rate is higher than 25 mm/s, the lamellar spacing tends to be increased, because the higher undercooling makes the mass transport less effective. The adjustments of lamellar spacing are also observed during the directional solidification process, which is consistent with the minimum undercooling criterion. Moreover, the transitions from planar interface to cellular, then to dendritic interface, and finally to cellular interface morphologies with increasing velocity are observed by sudden quenching when the crystal growth tends to be stable.展开更多
Directionally solidified eutectic ceramics such as Al2O3/ZrO2 are promising structural materials for ap- plications in harsh environment with an ultrahigh temperature. In this work, through adopting assistant heating ...Directionally solidified eutectic ceramics such as Al2O3/ZrO2 are promising structural materials for ap- plications in harsh environment with an ultrahigh temperature. In this work, through adopting assistant heating laser 3D printing, Al2O3/ZrO2 eutectic samples were manufactured with suppressing the forma- tion of cracks. The dependence of the average rod spacing （λav） on the scanning rate （V） follows a relation with λavV0.5 = 1 μm1.5 s^-0.5. Typical eutectic microstructures, so-called complex regular, were analyzed with respect to its evolution with modulating the growth conditions. Formation mechanism of the solidifi- cation defect, shrinkage porosity, was discussed and the defect is found to be significantly suppressed by optimizing the solidification parameters. The maximum hardness and fracture toughness are mea- sured to he 16.7 GPa and 4.5 MPa m1/2, respectively. The interplay between the propagation of cracks and the Al2O3/ZrO2 interface is discussed.展开更多
文摘Being used more and more widely in engineering,AlSi alloys comprise about 80%of all kinds of aluminum alloys,which are the most widely utilized nonferrous alloys.Although most Al-Si alloys consist of multiple components,the eutectics in the structure accounts for 50%-90%of the sum volume of such alloys.Therefore,understanding the modification mechanism and function rules of the AlSi eutectic solidification is the technical key in controlling the structures and properties of such casting alloys.The present paper chiefly reviews recent investigation developments and important conclusions along the lines of the functions of modification elements and their modification mechanism in the eutectic solidification of Al-Si alloys.
文摘The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) cast iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason should be the difference in their graphitization during the eutectic solidification. In this paper, we discuss the difference in the solidification mechanism of both cast irons for solving these problems using unidirectional solidification and the cooling curves of the spheroidal graphite cast iron. The eutectic solidification rate of the SG cast iron is controlled by the diffusion of carbon through the austenite shell, and the final thickness is 1.4 times the radius of the SG, therefore, the reduction of the SG size, namely, the increase in the number, is the main solution of these problems.
基金financially supported by the National Natural Science Foundation of China under grant No. 50771031
文摘As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidification and microstructure of the Al-13%Si alloy, an investigation has been undertaken by means of thermal analysis and micro/macro-structure observation. Results indicate that addition of phosphor in near eutectic Al-Si alloy promotes the nucleation of eutectic but has little refinement impact on primary Si particles as expected. Conversely, both primary Si particles and eutectic Si flakes become slightly coarser in P-rich alloys. The coarsening of eutectic Si flakes ties closely to the increased eutectic growth temperature with phosphor addition. The eutectic solidification of the alloy proceeds from the near mold zone towards the center, and it is also found that a few independent nucleation regions emerge in liquid at the solidification front due to the addition of phosphor.
基金supported by the National Natural Science Foundation of China(No.59871026)
文摘An electromagnetic vibration was generated by simultaneously imposing a strong static magnetic field （up to 10 T） and an alternative electricity current to the metal. Its effects on the solidification structure of eutectic Al-Si alloy have been investigated experimentally. It is found that the eutectic structure has been refined by solely imposing high magnetic field while it is coarsened under the electromagnetic vibration. Furthermore, polyhedral Si grains and non-dendritic α-Al appeared when the electromagnetic vibration strength was strong enough. The refining of eutectic structure is attributed to the decrease of diffusion coefficient caused by the strong magnetic field. The coarseness of eutectic structure may be attributed to the convection caused by electromagnetic vibration. Strong convection may break co-operative growth of eutectic phases to form polyhedral Si grains and non-dendritic α-Al.
文摘In situ eutectic Al_(11)La_3/Al composite material with regular arrangement was prepared by zone melt liquid metal cooling directionally solidification under conditions of high temperature gradient G=700K/cm and growth rate R=6.0-20.0μm/s.Superpose diffraction pat- tern of Al_(11)La_3/Al composite shows that the preferred growth direction is[100]Al// [33]Al_(11)La_3,and the habit plane is(002)Al//(116)Al_(11)La_3.A low density(103)twin is ob- served in Al_(11)La_3 and the growth of(103)twin induces to branching to change the interlamellar spacing.
基金supported by Erciyes University Scientific Research Project Unit (No.FBA-10-3376)
文摘Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates （5.32-250.0μm/s） at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus.The values of eutectic spacing were measured from transverse sections of the samples.The dependences of the eutectic spacing and undercooling on growth rate are determined as λ=9.21V-0.53 and ΔT=0.0245V0.53,respectively.The results obtained in this work were compared with the Jackson-Hunt eutectic theory and the similar experimental results in the literature.Microhardness of directionally solidified samples was also measured by using a microhardness test device.The dependency of the microhardness on growth rate is found as Hv=115.64V0.13.Afterwards,the electrical resistivity （r） of the casting alloy changes from 40×10-9 to 108×10-9 Ω·m with the temperature rising in the range of 300-630 K.The enthalpy of fusion （ΔH） and specific heat （Cp） for the Zn-Al eutectic alloy are calculated to be 113.37 J/g and 0.309 J/（g·K）,respectively by means of differential scanning calorimetry （DSC） from heating trace during the transformation from liquid to solid.
文摘Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.
文摘Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inherent heterogeneous nuclei. The recalcscence phenomenon and its dependence on undercooling and on crystal nuclcation and growth, as well as its relationship to solidification microstructures are studied. The crystalli/ation fraction during recalcsccnce is also calculated. Experiments reveal that recalcscence degree increases with undercooling when the latter is below a certain critical value∧Te, but it decreases as undercooling increases above A 7'( (under present conditions∧Te= 245K, i. c. 0.17TE). The greater the recalescencc degree, the larger the proportion of anomalous eutectic in solidified structures. It is inferred that anomalous eutectic is the product of rapid solidification while lamellar eutectic forms at much slower nuclcation rate and growth velocity.
基金supported by the US Department of Energy,Office of Energy Efficiency and Renewable Energy,Industrial Technologies Program,Industrial Materials for the Future(IMF),under Contractor No.DE-PS07-02ID14270 with UT-Battelle,LLC
文摘The modification of eutectic silicon is of general interest since fine eutectic silicon along with fine primary aluminum grains improves mechanical properties and ductilities. In this study, high intensity ultrasonic vibration was used to modify the complex microstructure of aluminum hypoeutectic alloys. The ultrasonic vibrator was placed at the bottom of a copper mold with molten aluminum. Hypoeutectic AI-Si alloy specimens with a unique in-depth profile of microstructure distribution were obtained. Polyhedral silicon particles, which should form in a hypereutectic alloy, were obtained in a hypoeutectic AI-Si alloy near the ultrasonic radiator where the silicon concentration was higher than the eutectic composition. The formation of hypereutectic silicon near the radiator surface indicates that high-intensity ultrasonic vibration can be used to influence the phase transformation process of metals and alloys. The size and morphology of both the silicon phase and the aluminum phase varies with increasing distance from the ultrasonic probe/radiator. Silicon morphology develops into three zones. Polyhedral primary silicon particles present in zone I, within 15 mm from the ultrasonic probe/radiator. Transition from hypereutectic silicon to eutectic silicon occurs in zone II about 15 to 20 pm from the ultrasonic probe/radiator. The bulk of the ingot is in zone III and is hypoeutectic AI-Si alloy containing fine lamellar and fibrous eutectic silicon. The grain size is about 15 to 25 IJm in zone I, 25 to 35 IJm in zone II, and 25 to 55 pm in zone II1. The morphology of the primary a-AI phase is also changed from dendritic （in untreated samples） to globular. Phase evolution during the solidification process of the alloy subjected to ultrasonic vibration is described.
基金Universiti Teknologi Malaysia for providing research facilitiesthe Ministry of Science and Technology of Malaysia for financial support under the vote 79352
文摘The effects of bismuth and the combination of bismuth and strontium on the eutectic silicon structure in Al-7Si-0.4Mg alloys were investigated under different solidification conditions.The results show that bismuth has a refining effect on the eutectic silicon and its refinement behavior increases with increasing Bi content up to 0.5% （mass fraction）.When bismuth is added into the molten alloy modified with strontium,a higher Sr/Bi mass ratio of at least 0.45 is required to attain full modification of the eutectic silicon.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.50395102,50401014)the Aeronautical Science Foundation of China(Grant No.01G53038) DPOP Project in NWPU.
文摘By comparisons of interface growth temperatures of different phases in eutectic systems, competitive growth between the primary phase, halo structure and coupled eutectic has been discussed. The compositions for the formation of coupled eutectic have been discussed at the coexisting with the primary phase in eutectic under directional solidification. Solidification conditions, such as growth rate and composition required for the formation of the primary phase, halo structure and coupled eutectic have been proposed. Numerical calculation results show that no halo structure formed in directionally solidified Sn-Pb eutectic, but in Al-Si eutectic, competitive growth structures of the primary β-Si phase, α-Al halo structure and coupled eutectic (α+β) may exist at the hypereutectic composition between 12.6% and 25% Si. The calculated results of Al-Si eutectic fit in with the reported experiment results.
基金the National Natural Science Foundation of China (No. 51201121)the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20096120120017)+2 种基金the Fund of the State Key Laboratory of Solidification Processing in NWPU (No. SKLSP200904)the Natural Science Foundation of Shaanxi Province of China (No. 2012JQ6004)the Specialized Research Fund of Education Commission of Shaanxi Province of China (No. 12JK0425)
文摘In this study NieN i3 Si eutectic in situ composites are obtained by Bridgman directional solidification technique when the solidification rate varies from 6.0 mm/s to 40.0 mm/s. At the low solidification rates the lamellar spacing is decreased with increasing the solidification rate. When the solidification rate is higher than 25 mm/s, the lamellar spacing tends to be increased, because the higher undercooling makes the mass transport less effective. The adjustments of lamellar spacing are also observed during the directional solidification process, which is consistent with the minimum undercooling criterion. Moreover, the transitions from planar interface to cellular, then to dendritic interface, and finally to cellular interface morphologies with increasing velocity are observed by sudden quenching when the crystal growth tends to be stable.
基金the National Natural Science Foundation of China (No. 81170983) China Postdoctoral Science Foundation (No. 2015M572597)
文摘Directionally solidified eutectic ceramics such as Al2O3/ZrO2 are promising structural materials for ap- plications in harsh environment with an ultrahigh temperature. In this work, through adopting assistant heating laser 3D printing, Al2O3/ZrO2 eutectic samples were manufactured with suppressing the forma- tion of cracks. The dependence of the average rod spacing （λav） on the scanning rate （V） follows a relation with λavV0.5 = 1 μm1.5 s^-0.5. Typical eutectic microstructures, so-called complex regular, were analyzed with respect to its evolution with modulating the growth conditions. Formation mechanism of the solidifi- cation defect, shrinkage porosity, was discussed and the defect is found to be significantly suppressed by optimizing the solidification parameters. The maximum hardness and fracture toughness are mea- sured to he 16.7 GPa and 4.5 MPa m1/2, respectively. The interplay between the propagation of cracks and the Al2O3/ZrO2 interface is discussed.
