To improve the wettability of hypereutectic Al−60Si alloy and enhance the mechanical properties of the joints,Al−60Si alloy was joined by ultrasonic soldering with Sn-9Zn solder,and a sound joint with in-situ Si parti...To improve the wettability of hypereutectic Al−60Si alloy and enhance the mechanical properties of the joints,Al−60Si alloy was joined by ultrasonic soldering with Sn-9Zn solder,and a sound joint with in-situ Si particle reinforcement was obtained.The oxide film of Al−60Si alloy at the interface was identified by transmission electron microscopy(TEM)analysis as amorphous Al_(2)O_(3).The oxide of Si particles in the base metal was also alumina.The oxide film of Al−60Si alloy was observed to be removed by ultrasonic vibration instead of holding treatment.Si particle-reinforced joints(35.7 vol.%)were obtained by increasing the ultrasonication time.The maximum shear strength peaked at 99.5 MPa for soldering at 330℃with an ultrasonic vibration time of 50 s.A model of forming of Si particles reinforced joint under the ultrasound was proposed,and ultrasonic vibration was considered to promote the dissolution of Al and migration of Si particles.展开更多
In this study,the effects of Eu addition on the microstructures and mechanical properties of A390 alloy were investigated,along with the spheroidization mechanism of primary silicon with Eu.The results showed that whe...In this study,the effects of Eu addition on the microstructures and mechanical properties of A390 alloy were investigated,along with the spheroidization mechanism of primary silicon with Eu.The results showed that when the Eu addition reached 0.6 wt%,both refinement and spheroidization of primary silicon,alongside fibrous eutectic silicon can be obtained.Owing to such a microstructural modification,the ultimate tensile strength and elongation were increased by 24.9%and 101.2%,respectively.While in the unmodified alloy,the octahedral,plate-like,and five-star primary silicon particles exhibited fewΣ3 twin boundaries,whereas in the Eu-modified alloy,spheroidal primary silicon displayed curvedΣ3 twin boundaries,sub-grain boundaries,and specialΣ9 twin boundaries.Atom probe tomography analysis indicated that Al and Eu atoms were present in the spheroidal primary silicon as spheroidal,T-shaped,straight rod-like,and curved rod-like clusters,with the Al:Eu ratio of 2.92±0.46.The spheroidization mechanism of primary silicon was proposed through five aspects:(ⅰ)spheroidal clusters inducing parallel and intersectingΣ3 twins,(ⅱ)straight rod-like clusters causing poisoning of twin plane re-entrant edge,(ⅲ)T-shaped clusters leading to multithickness intersectingΣ3 twins,(ⅳ)curved rod-like clusters resulting in curvedΣ3 twins,and(ⅴ)curved rod-like clusters induce specialΣ9 twins.These mechanisms facilitate a transition from initially anisotropic to isotropic growth of primary silicon with Eu addition.The present work provides an important insight for the development of a novel way to achieve the primary Si spheroidization and the improvement of mechanical properties of hypereutectic Al-Si alloys.展开更多
Hypereutectic Al-Si alloy with variant Mg contents were fabricated by casting,and the effects of Mg content on the microstructure of primary Mg2Si particles in hypereutectic Al-Si alloys were investigated.The results ...Hypereutectic Al-Si alloy with variant Mg contents were fabricated by casting,and the effects of Mg content on the microstructure of primary Mg2Si particles in hypereutectic Al-Si alloys were investigated.The results show that the volume fraction of primary Mg2Si particles increases linearly with raising the Mg content,but the average size of Mg2Si particles does not exhibit a corresponding change.When the Mg content is 3%,á1 0 0？ directions have the fastest growth velocity,so that Mg2Si particles are likely to form octahedron shape.When gradually increasing the Mg content,the distributions of Mg and Si atoms on the solid-liquid interface become inhomogeneous,which results in the formation of irregular octahedron structures.Finally,when the Mg content is about 10%,the morphology of primary Mg2Si particles changes from the octahedron shape into various complex structures with a large size.展开更多
The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The r...The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The results indicate that the Cu-P master alloy possesses not only obvious modification effect,but also longevity effect with more than 8 h on the hypereutectic Al-Si alloy.It is shown from thermal calculation,scanning electron microscope（SEM）,and energy dispersive analysis of X-rays（EDAX） that the modification mechanism of Cu-P on primary silicon in the castings is heterogeneous nucleation around AlP particles.The Cu-P master alloy has no or little modifying effect on eutectic silicon,even though it has obvious modification on primary silicon in the castings.This may be because of the fast transformation of eutectic silicon at a very narrow temperature,which will notably weaken the role of AlP particles as heterogeneous nuclei for eutectic silicon.展开更多
Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and sp...Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and spray forming （SF） processes, were investigated by differential scanning calorimetry （DSC） and scanning electron microscopy （SEM） combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that A17Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K and 800-815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.展开更多
The effect of squeeze casting on microstructure and mechanical properties of hypereutectic Al-xS i alloys（x = 15, 17.5, 22 wt%） was investigated in this study. Results show that microstructure of the hypereutectic A...The effect of squeeze casting on microstructure and mechanical properties of hypereutectic Al-xS i alloys（x = 15, 17.5, 22 wt%） was investigated in this study. Results show that microstructure of the hypereutectic Al-x Si alloys was obviously improved by squeeze casting. The amount of coarse primary Si phase decreased, while that of fine primary α-Al dendrites increased with the increase of squeeze casting pressure. Due to the decrease of coarse primary Si particles, cracking of the matrix was reduced, whilst the fine microstructure, and mechanical properties of the squeeze casting alloys were improved. Compared with gravity casting alloys, mechanical properties of the hypereutectic Al-xS i alloys solidified at 600 MPa were improved significantly. Hardness of the squeeze casting hypereutectic Al-（15, 17.5, 22 wt%） Si alloys was improved by 15.91%, 12.23%, 17.48%, ultimate tensile strength was improved by 37.85%, 32.27%, 22.74%,and elongation was improved by 55.83%, 167.86%, 126.76%, respectively. Due to the uniform distribution of Si phases in squeeze casting Al-x Si alloys, their wear resistance was markedly enhanced.展开更多
The feasibility of semi solid processing of hypereutectic A390 alloys using a novel rheoforming process was investigated. A combination of the swirl enthalpy equilibration device （SEED） process, isothermal holding u...The feasibility of semi solid processing of hypereutectic A390 alloys using a novel rheoforming process was investigated. A combination of the swirl enthalpy equilibration device （SEED） process, isothermal holding using insulation and addition of solid alloy during swirling was introduced as a novel method to improve the processability of semi solid slurry. The effects of isothermal holding and the addition of solid alloy on the temperature gradient between the centre and the wall and on the formation of a（Al） particles were examined. In additional tests, phosphorus and strontium were added to the molten metal to refine the primary and eutectic silicon structure to facilitate semi solid processing. The results show that the combination of the SEED process with two additional processing steps can produce semi-solid A390 alloys that can be rheoprocessed. The microstructure reveals an adequate amount of non-dendritic a（Al） globules surrounded by liquid, which greatly improves the processability of semi-solid slurry.展开更多
The effects of pouring temperature,vibration frequency,and the number of curves in a serpentine channel,on themicrostructure and mechanical properties of Al-30%Si alloy processed by rheo-diecasting(RDC)were investigat...The effects of pouring temperature,vibration frequency,and the number of curves in a serpentine channel,on themicrostructure and mechanical properties of Al-30%Si alloy processed by rheo-diecasting(RDC)were investigated.The semisolidAl-30%Si alloy slurry was prepared by vibration serpentine channel pouring(VSCP)process in the RDC process.The results showthat the pouring temperature,the vibration frequency,and the number of the curves strongly affect the microstructure and mechanicalproperties of Al-30%Si alloy.Under experimental conditions of a pouring temperature of850°C,a twelve-curve copper channel anda vibration frequency of80Hz,the primary Si grains are refined into fine compact grains with average grain size of about24.6μm inthe RDC samples assisted with VSCP.Moreover,the ultimate tensile strength(UTS),elongation and hardness of the RDC sample are296MPa,0.87%and HB155,respectively.It is concluded that the VSCP process can effectively refine the primary Si grains.Therefinement of primary Si grains is the major cause for the improvement of the mechanical properties of the RDC sample.展开更多
The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase.So,optical microscopy(OM) and X-ray diffraction(XRD) were adopted to study affection of...The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase.So,optical microscopy(OM) and X-ray diffraction(XRD) were adopted to study affection of Nd on primary silicon of hypereutectic Al-15%Si alloy in this paper.The results of OM showed that pure Nd could effectively refine primary silicon of hypereutectic Al-15%Si alloy.When Nd addition was 0.3%,the average size of primary silicon reduced from 20-40 μm of initial sample to 10-20 μm of modified sample.XRD pattern showed that no new phase was formed after Nd modification.The results of mechanical properties test showed that whole properties of modified samples were significantly improved.Tensile strength increased about 32.6% from 147 MPa to 195 MPa.Elongation was increased about 160% from 1.0% to 2.6%.The improvement of mechanical properties should attribute to primary silicon refinement after modification.展开更多
The fracture behavior of high-pressure die-cast hypereutectic(HPDC) Al-Si alloys was investigated using a high-resolution laboratory CT and synchrotron X-ray tomography with a particular focus on the influence of HPDC...The fracture behavior of high-pressure die-cast hypereutectic(HPDC) Al-Si alloys was investigated using a high-resolution laboratory CT and synchrotron X-ray tomography with a particular focus on the influence of HPDC microstructure. Results showed that microstructure of the alloy was mainly comprised of primary silicon particles(PSPs), Al dendrites, Cu-rich phases and pores. Most of the coarse PSPs, Cu-rich phases and pores were located in the center of the specimen. The rapid solidification of HPDC led to a heterogeneous microstructural feature. Elemental Cu was enriched in the frontiers of solid-liquid interface, causing the formation of large size dendritic arms. The pores were formed in the interdendrites which endured high stress intensity under high applied stress. Microcracks were originated from pores and further connected Cu-rich phases causing intergranular fracture. PSPs worked as obstacles causing piling-up dislocations in the phase interface. In the regions where large size of PSPs enriched in, PSPs ruptured rather than debonded from matrix, indicating transgranular fractures of PSPs. Microcracks originated around pores and PSPs tended to converge on the main cracks to decrease the energy required for crack propagation.展开更多
Plastic deformation of sprayed alloy is an effective method to fabricate the hypereutectic aluminum-silicon alloy which combines good conductivity and toughness. In this study, Al-20Si-0.35 RE (wt%) alloy was synthesi...Plastic deformation of sprayed alloy is an effective method to fabricate the hypereutectic aluminum-silicon alloy which combines good conductivity and toughness. In this study, Al-20Si-0.35 RE (wt%) alloy was synthesized by spray atomization and deposition technique. The sprayed deposition and over-spray powder were hot-extruded and plastic deformed respectively. Microstructure and conductivity were systematically performed in order to understand the influence of deformation on microstructure and conductivity of the hypereutectic alloy. The Si particles are refining and uniformly distributed in the Al matrix due to the proper addition of rare earth metal and the rapid solidification preparation method. The microstructure of plastic deformed alloy has invariably indicated that severe plastic deformation lead to the even refinement of microstructure. Both the conductivity of over-spray powder extrusion and sprayed deposition extrusion were obviously improved after plastic deformation. Possible mechanisms of deformation on microstructure and conductivity of hypereutectic aluminum-silicon alloy are discussed.展开更多
Semisolid hypereutectic Al Si alloy billets were obtained by electromagnetic stirring, in which microstructure of primary silicon gets rounder and there are a large number of rosette α phases appearing. Compared with...Semisolid hypereutectic Al Si alloy billets were obtained by electromagnetic stirring, in which microstructure of primary silicon gets rounder and there are a large number of rosette α phases appearing. Compared with conventional gravity die casting alloys, the tensile strength and elongation of semisolid forming hypereutectic Al Si get obviously improved. Change of primary silicon morphology of semisolid hypereutectic Al Si alloy made by electromagnetic stirring is the main reason of better tensile strength, and a large number of rosette α phases precipitation is the main reason of better elongation.展开更多
Controlled Diffusion Solidification(CDS) is a promising process relied on mixing two liquid alloys of precisely controlled chemistry and temperature in order to produce a predetermined alloy composition. In this study...Controlled Diffusion Solidification(CDS) is a promising process relied on mixing two liquid alloys of precisely controlled chemistry and temperature in order to produce a predetermined alloy composition. In this study, the CDS was employed to prepare hypereutectic Al-20%Si(mass fraction) alloy using Al-30%Si and pure Al of different temperatures. The mixing rate was controlled using three small crucibles with a hole of different diameters in their bottom. The effect of mixing rate and temperature on the microstructure of the primary Si-phase during the mixing of molten Al and Al-30%Si was studied. The results showed that when the diameter of the small crucible bottom hole is 16 mm, a higher mass mixing rate 0.217 kg·s-1 would results in a lower stream velocity 0.414 m·s-1. Conversely a lower mass mixing rate 0.114 kg·s-1(the diameter of the small crucible bottom hole is 8 mm) would result in a higher fluid stream velocity 0.879 m·s-1. A lower mass mixing rate would be better to refine the primary Si than a higher mass mixing rate. Meanwhile, the morphology and distribution of primary Si could also be improved. Especially, when Al-30%Si alloy at 820 °C was mixed with pure Al at 670 °C in the case of a mass mixing rate of 0.114 kg·s-1 and a pouring temperature of 680 °C, the average size of the primary Si phase would be only 18.2 μm. Its morphology would mostly be octahedral and the primary Si would distribute uniformly in the matrix microstructure. The lower mass mixing rate(0.114 kg·s-1) will enhance the broken tendency of Al-30%Si steam and the mixing agitation of resultant melt, so the primary Si phase can be better refined.展开更多
The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y203 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase str...The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y203 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase structures of the coatings were determined by X-ray diffraction. The microstructures were observed by optical microscopy. The morphologies of the hypereutectic Fe-Cr-C hardfacing coatings were observed by a field emission scanning electron microscope equipped with an X-ray energy disper- sive spectrometer. The effectiveness ofY203 as heterogeneous nuclei of primary M7C3 was calculated with the misfit theory. The ex- periment results showed that, the microstructures of the hypereutectic Fe-Cr-C hardfacing coatings consisted of M7C3, ？-Fe and a-Fe phases. With the increase of nano-Y203 additives, primary M7C3 in hypereutectic Fe-Cr-C coatings could be refined gradually. The average size of the primary M7C3 was the minimum, which was 22 pro, when nano-Y203 additive was 2.54 wt.%. The calculated re- sults showed that, the two-dimensional lattice misfit between the face （001） of Y203 and face （100） of orthorhombic M7C3 was 4.911%, which indicated that Y203 as heterogeneous nuclei of M7C3 was middle effective to refine the primary M7C3.展开更多
This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them...This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness and abrasion wear resistance tests were conducted. Fracture and worn surfaces were studied. Results indicated that microstructural control during solidifciation is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in hypereutectic iron. Combined action of Nb addition and dynamic solidifciation improves impact toughness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness and abrasion resistance were increased after dynamic solidification compared to statically solidified one by 71.4% and 10%, respectively. This enhancement was increased to 114.3 % and 28.8 % by adding 2% Nb. Lower tempering temperature of 260°C exhibits better impact and abrasion resistance than the sub-critical tempering temperature of 500°C.展开更多
Eutectic high-entropy alloys,composed of FCC/B2 phases with a narrow solidification interval and excel-lent fluidity,have become a new hotspot in additive manufacturing.Nevertheless,their microstructures exhibit signi...Eutectic high-entropy alloys,composed of FCC/B2 phases with a narrow solidification interval and excel-lent fluidity,have become a new hotspot in additive manufacturing.Nevertheless,their microstructures exhibit significant sensitivity to processing parameters,feedstocks,and composition,ultimately limiting the alloys’engineering applications.Here,a hypereutectic Al_(0.7)CoCrFeNi_(2.4)alloy with a low cracking sus-ceptibility index was designed by Thermo-Calc calculation and fabricated by laser powder bed fusion.Results show that the as-printed Al_(0.7)CoCrFeNi_(2.4)alloy manifests a stable cellular structure,coupled with appreciable ultimate tensile strength(≥1200 MPa)and ductility(≥20%)over a wide range of process-ing parameters.After aging at 800℃for 30 min,outstanding strength(1500 MPa)and elongation(15%)were obtained.Considerable mechanical properties after aging stem from a triple strengthening mecha-nism,i.e.,L1_(2) nanoprecipitates and rod-shaped B2 particles within the FCC matrix,along with Cr-enriched spherical nanoparticles in the B2 phase.Meanwhile,hierarchical structure,i.e.,FCC dominated matrix,a discontinuous B2 phase,a precipitation-free zone in the B2 phase,and a K-S orientation relationship be-tween FCC and B2,facilitate to maintain excellent plasticity.These results guide designing HEAs by AM with controllable microstructures and outstanding mechanical properties for industrial applications.展开更多
In this paper, the ring-type ingot of hypereutectic high Cr cast iron was obtained by slope cooling bodycentrifugal casting method （SC-CCM）, and its microstructure and impact toughness were investigated, respectivel...In this paper, the ring-type ingot of hypereutectic high Cr cast iron was obtained by slope cooling bodycentrifugal casting method （SC-CCM）, and its microstructure and impact toughness were investigated, respectively. The results indicated that, first, the primary carbides in the microstructure are prominently finer than those in the hypereutectic high Cr cast iron prepared by conventional casting method. Second, in the ring-type ingot, the primary carbides near radial outer field are finer than those near radial inner field; furthermore, there is dividing field in the microstructure. Finally, the impact toughness values of the specimens impacted on the radial outer face and on the radial inner face are improved respectively about 36% and 138% more than that of the hypereutectic high Cr one prepared by conventional casting method.展开更多
The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that th...The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.展开更多
Large and segregated primary Si particles may drastically decrease the mechanical properties of AI-Si alloys. To solve this problem, a P-Cr complex modifier was added into the alloy, and the effects of P-Cr complex mo...Large and segregated primary Si particles may drastically decrease the mechanical properties of AI-Si alloys. To solve this problem, a P-Cr complex modifier was added into the alloy, and the effects of P-Cr complex modification and solidification conditions on the microstructure of hypereutectic Al-Si alloys casting produced in wedge-shaped copper mould were studied. The thermal analysis technique was applied to calculate the cooling rate during solidification. The microstructures were observed by means of optical and scanning electron microscopies. Results showed that the primary Si segregates in the as-cast hypereutectic AI-Si alloys. The segregation of primary Si can be inhibited by adding a P＋Cr complex modifier and increasing the cooling rate during solidification. The refinement of primary Si particles by P＋Cr complex modification is due to the formation of CrSi2 and AlP particles which act as the heterogeneous nuclei for the primary Si phase. The segregation of Si was also inhibited through the adherence of heavier CrSi2 particles to the primary Si particles.展开更多
In order to review the effect of partial remelting time on the morphology of initial carbides, semisolid ingots of hypereutectic high Cr17 cast iron were remelted at 1270℃ for four different times, and the changing c...In order to review the effect of partial remelting time on the morphology of initial carbides, semisolid ingots of hypereutectic high Cr17 cast iron were remelted at 1270℃ for four different times, and the changing characteristics of shape factor and the equivalent diameter of initial carbides were analyzed quantitatively using a Leica image analyzer. The results indicate that firstly, the evolution process of the initial carbides' morphology undergoes melting, spheroidization and refining during the partial remelting; secondly, the solute diffusion and interface tension take dominant roles at the primary and the middle-final stages respectively in the process of initial carbide evolution; finally, a perfect structure can be obtained by remelting semisolid ingots at 1270℃ for 15 min.展开更多
基金financial support from the National Natural Science Foundation of China(Nos.52275385,U2167216)Sichuan Province Science and Technology Support Program,China(No.2022YFG0086).
文摘To improve the wettability of hypereutectic Al−60Si alloy and enhance the mechanical properties of the joints,Al−60Si alloy was joined by ultrasonic soldering with Sn-9Zn solder,and a sound joint with in-situ Si particle reinforcement was obtained.The oxide film of Al−60Si alloy at the interface was identified by transmission electron microscopy(TEM)analysis as amorphous Al_(2)O_(3).The oxide of Si particles in the base metal was also alumina.The oxide film of Al−60Si alloy was observed to be removed by ultrasonic vibration instead of holding treatment.Si particle-reinforced joints(35.7 vol.%)were obtained by increasing the ultrasonication time.The maximum shear strength peaked at 99.5 MPa for soldering at 330℃with an ultrasonic vibration time of 50 s.A model of forming of Si particles reinforced joint under the ultrasound was proposed,and ultrasonic vibration was considered to promote the dissolution of Al and migration of Si particles.
基金financially supported by the National Natural Science Foundation of China(Nos.52301046,U24A2028 and U22A20174)the Program for Science&Technology Innovation Talents in Universities of Henan Province(25HASTIT007)+2 种基金the Frontier Exploration Projects of Longmen Laboratory(No.LMQYT-SKT005)the Central Plains Talents Planthe support of Provincial and Ministerial Co-construction of Collaborative Innovation Center for Non-ferrous Metal New Materials and Advanced Processing Technology
文摘In this study,the effects of Eu addition on the microstructures and mechanical properties of A390 alloy were investigated,along with the spheroidization mechanism of primary silicon with Eu.The results showed that when the Eu addition reached 0.6 wt%,both refinement and spheroidization of primary silicon,alongside fibrous eutectic silicon can be obtained.Owing to such a microstructural modification,the ultimate tensile strength and elongation were increased by 24.9%and 101.2%,respectively.While in the unmodified alloy,the octahedral,plate-like,and five-star primary silicon particles exhibited fewΣ3 twin boundaries,whereas in the Eu-modified alloy,spheroidal primary silicon displayed curvedΣ3 twin boundaries,sub-grain boundaries,and specialΣ9 twin boundaries.Atom probe tomography analysis indicated that Al and Eu atoms were present in the spheroidal primary silicon as spheroidal,T-shaped,straight rod-like,and curved rod-like clusters,with the Al:Eu ratio of 2.92±0.46.The spheroidization mechanism of primary silicon was proposed through five aspects:(ⅰ)spheroidal clusters inducing parallel and intersectingΣ3 twins,(ⅱ)straight rod-like clusters causing poisoning of twin plane re-entrant edge,(ⅲ)T-shaped clusters leading to multithickness intersectingΣ3 twins,(ⅳ)curved rod-like clusters resulting in curvedΣ3 twins,and(ⅴ)curved rod-like clusters induce specialΣ9 twins.These mechanisms facilitate a transition from initially anisotropic to isotropic growth of primary silicon with Eu addition.The present work provides an important insight for the development of a novel way to achieve the primary Si spheroidization and the improvement of mechanical properties of hypereutectic Al-Si alloys.
基金Project(CDJZR12240056)supported by the Fundamental Research Funds for Central Universities,ChinaProject(cstc2013jcyj A50014)supported by the Foundational and Cutting-edge Research Plan of Chongqing,China
文摘Hypereutectic Al-Si alloy with variant Mg contents were fabricated by casting,and the effects of Mg content on the microstructure of primary Mg2Si particles in hypereutectic Al-Si alloys were investigated.The results show that the volume fraction of primary Mg2Si particles increases linearly with raising the Mg content,but the average size of Mg2Si particles does not exhibit a corresponding change.When the Mg content is 3%,á1 0 0？ directions have the fastest growth velocity,so that Mg2Si particles are likely to form octahedron shape.When gradually increasing the Mg content,the distributions of Mg and Si atoms on the solid-liquid interface become inhomogeneous,which results in the formation of irregular octahedron structures.Finally,when the Mg content is about 10%,the morphology of primary Mg2Si particles changes from the octahedron shape into various complex structures with a large size.
文摘The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The results indicate that the Cu-P master alloy possesses not only obvious modification effect,but also longevity effect with more than 8 h on the hypereutectic Al-Si alloy.It is shown from thermal calculation,scanning electron microscope（SEM）,and energy dispersive analysis of X-rays（EDAX） that the modification mechanism of Cu-P on primary silicon in the castings is heterogeneous nucleation around AlP particles.The Cu-P master alloy has no or little modifying effect on eutectic silicon,even though it has obvious modification on primary silicon in the castings.This may be because of the fast transformation of eutectic silicon at a very narrow temperature,which will notably weaken the role of AlP particles as heterogeneous nuclei for eutectic silicon.
基金supported by the Major State Basic Research & Development Program of China (No2006CB605204)
文摘Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and spray forming （SF） processes, were investigated by differential scanning calorimetry （DSC） and scanning electron microscopy （SEM） combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that A17Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K and 800-815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.
基金support from the National Natural Science Foundation of China(Grant No.51674168)Shenyang Application Basic Research Fund(Grant No.F14-231-1-23)
文摘The effect of squeeze casting on microstructure and mechanical properties of hypereutectic Al-xS i alloys（x = 15, 17.5, 22 wt%） was investigated in this study. Results show that microstructure of the hypereutectic Al-x Si alloys was obviously improved by squeeze casting. The amount of coarse primary Si phase decreased, while that of fine primary α-Al dendrites increased with the increase of squeeze casting pressure. Due to the decrease of coarse primary Si particles, cracking of the matrix was reduced, whilst the fine microstructure, and mechanical properties of the squeeze casting alloys were improved. Compared with gravity casting alloys, mechanical properties of the hypereutectic Al-xS i alloys solidified at 600 MPa were improved significantly. Hardness of the squeeze casting hypereutectic Al-（15, 17.5, 22 wt%） Si alloys was improved by 15.91%, 12.23%, 17.48%, ultimate tensile strength was improved by 37.85%, 32.27%, 22.74%,and elongation was improved by 55.83%, 167.86%, 126.76%, respectively. Due to the uniform distribution of Si phases in squeeze casting Al-x Si alloys, their wear resistance was markedly enhanced.
基金the financial support provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Rio Tinto Alcan through the NSERC Industrial Research Chair in Metallurgy of Aluminum Transformation at Université du Québec à Chicoutimi
文摘The feasibility of semi solid processing of hypereutectic A390 alloys using a novel rheoforming process was investigated. A combination of the swirl enthalpy equilibration device （SEED） process, isothermal holding using insulation and addition of solid alloy during swirling was introduced as a novel method to improve the processability of semi solid slurry. The effects of isothermal holding and the addition of solid alloy on the temperature gradient between the centre and the wall and on the formation of a（Al） particles were examined. In additional tests, phosphorus and strontium were added to the molten metal to refine the primary and eutectic silicon structure to facilitate semi solid processing. The results show that the combination of the SEED process with two additional processing steps can produce semi-solid A390 alloys that can be rheoprocessed. The microstructure reveals an adequate amount of non-dendritic a（Al） globules surrounded by liquid, which greatly improves the processability of semi-solid slurry.
基金Project(5077400) supported by the National Natural Science Foundation of China
文摘The effects of pouring temperature,vibration frequency,and the number of curves in a serpentine channel,on themicrostructure and mechanical properties of Al-30%Si alloy processed by rheo-diecasting(RDC)were investigated.The semisolidAl-30%Si alloy slurry was prepared by vibration serpentine channel pouring(VSCP)process in the RDC process.The results showthat the pouring temperature,the vibration frequency,and the number of the curves strongly affect the microstructure and mechanicalproperties of Al-30%Si alloy.Under experimental conditions of a pouring temperature of850°C,a twelve-curve copper channel anda vibration frequency of80Hz,the primary Si grains are refined into fine compact grains with average grain size of about24.6μm inthe RDC samples assisted with VSCP.Moreover,the ultimate tensile strength(UTS),elongation and hardness of the RDC sample are296MPa,0.87%and HB155,respectively.It is concluded that the VSCP process can effectively refine the primary Si grains.Therefinement of primary Si grains is the major cause for the improvement of the mechanical properties of the RDC sample.
基金Project supported by Doctoral Fund of Ministry of Education of China (200801451082)National "Eleventh Five-Year" Scientific and Technological Project (2009BAE80B01 and 2009BAE85803)
文摘The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase.So,optical microscopy(OM) and X-ray diffraction(XRD) were adopted to study affection of Nd on primary silicon of hypereutectic Al-15%Si alloy in this paper.The results of OM showed that pure Nd could effectively refine primary silicon of hypereutectic Al-15%Si alloy.When Nd addition was 0.3%,the average size of primary silicon reduced from 20-40 μm of initial sample to 10-20 μm of modified sample.XRD pattern showed that no new phase was formed after Nd modification.The results of mechanical properties test showed that whole properties of modified samples were significantly improved.Tensile strength increased about 32.6% from 147 MPa to 195 MPa.Elongation was increased about 160% from 1.0% to 2.6%.The improvement of mechanical properties should attribute to primary silicon refinement after modification.
基金the National Natural Science Foundation of China (Grant No. 51775297)the National Science and the Tsinghua University Initiative Scientific Research Program (No. 20151080370)UK Royal Academy of Engineering/Royal Society through the Newton International Fellowship Scheme for financial support
文摘The fracture behavior of high-pressure die-cast hypereutectic(HPDC) Al-Si alloys was investigated using a high-resolution laboratory CT and synchrotron X-ray tomography with a particular focus on the influence of HPDC microstructure. Results showed that microstructure of the alloy was mainly comprised of primary silicon particles(PSPs), Al dendrites, Cu-rich phases and pores. Most of the coarse PSPs, Cu-rich phases and pores were located in the center of the specimen. The rapid solidification of HPDC led to a heterogeneous microstructural feature. Elemental Cu was enriched in the frontiers of solid-liquid interface, causing the formation of large size dendritic arms. The pores were formed in the interdendrites which endured high stress intensity under high applied stress. Microcracks were originated from pores and further connected Cu-rich phases causing intergranular fracture. PSPs worked as obstacles causing piling-up dislocations in the phase interface. In the regions where large size of PSPs enriched in, PSPs ruptured rather than debonded from matrix, indicating transgranular fractures of PSPs. Microcracks originated around pores and PSPs tended to converge on the main cracks to decrease the energy required for crack propagation.
基金Foundation item: Shanghai Science and Technology Expertise Program (10QB1400800)Shanghai Science and Technology Committee Foundation (08DZ2201300)National Natural Science Foundation of China (50901052)
文摘Plastic deformation of sprayed alloy is an effective method to fabricate the hypereutectic aluminum-silicon alloy which combines good conductivity and toughness. In this study, Al-20Si-0.35 RE (wt%) alloy was synthesized by spray atomization and deposition technique. The sprayed deposition and over-spray powder were hot-extruded and plastic deformed respectively. Microstructure and conductivity were systematically performed in order to understand the influence of deformation on microstructure and conductivity of the hypereutectic alloy. The Si particles are refining and uniformly distributed in the Al matrix due to the proper addition of rare earth metal and the rapid solidification preparation method. The microstructure of plastic deformed alloy has invariably indicated that severe plastic deformation lead to the even refinement of microstructure. Both the conductivity of over-spray powder extrusion and sprayed deposition extrusion were obviously improved after plastic deformation. Possible mechanisms of deformation on microstructure and conductivity of hypereutectic aluminum-silicon alloy are discussed.
文摘Semisolid hypereutectic Al Si alloy billets were obtained by electromagnetic stirring, in which microstructure of primary silicon gets rounder and there are a large number of rosette α phases appearing. Compared with conventional gravity die casting alloys, the tensile strength and elongation of semisolid forming hypereutectic Al Si get obviously improved. Change of primary silicon morphology of semisolid hypereutectic Al Si alloy made by electromagnetic stirring is the main reason of better tensile strength, and a large number of rosette α phases precipitation is the main reason of better elongation.
基金supported by the National Natural Science Foundation of China(Grant Nos.51064017 and 51464031)
文摘Controlled Diffusion Solidification(CDS) is a promising process relied on mixing two liquid alloys of precisely controlled chemistry and temperature in order to produce a predetermined alloy composition. In this study, the CDS was employed to prepare hypereutectic Al-20%Si(mass fraction) alloy using Al-30%Si and pure Al of different temperatures. The mixing rate was controlled using three small crucibles with a hole of different diameters in their bottom. The effect of mixing rate and temperature on the microstructure of the primary Si-phase during the mixing of molten Al and Al-30%Si was studied. The results showed that when the diameter of the small crucible bottom hole is 16 mm, a higher mass mixing rate 0.217 kg·s-1 would results in a lower stream velocity 0.414 m·s-1. Conversely a lower mass mixing rate 0.114 kg·s-1(the diameter of the small crucible bottom hole is 8 mm) would result in a higher fluid stream velocity 0.879 m·s-1. A lower mass mixing rate would be better to refine the primary Si than a higher mass mixing rate. Meanwhile, the morphology and distribution of primary Si could also be improved. Especially, when Al-30%Si alloy at 820 °C was mixed with pure Al at 670 °C in the case of a mass mixing rate of 0.114 kg·s-1 and a pouring temperature of 680 °C, the average size of the primary Si phase would be only 18.2 μm. Its morphology would mostly be octahedral and the primary Si would distribute uniformly in the matrix microstructure. The lower mass mixing rate(0.114 kg·s-1) will enhance the broken tendency of Al-30%Si steam and the mixing agitation of resultant melt, so the primary Si phase can be better refined.
基金supported by National Natural Science Foundation of China(51271163,51471148)
文摘The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y203 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase structures of the coatings were determined by X-ray diffraction. The microstructures were observed by optical microscopy. The morphologies of the hypereutectic Fe-Cr-C hardfacing coatings were observed by a field emission scanning electron microscope equipped with an X-ray energy disper- sive spectrometer. The effectiveness ofY203 as heterogeneous nuclei of primary M7C3 was calculated with the misfit theory. The ex- periment results showed that, the microstructures of the hypereutectic Fe-Cr-C hardfacing coatings consisted of M7C3, ？-Fe and a-Fe phases. With the increase of nano-Y203 additives, primary M7C3 in hypereutectic Fe-Cr-C coatings could be refined gradually. The average size of the primary M7C3 was the minimum, which was 22 pro, when nano-Y203 additive was 2.54 wt.%. The calculated re- sults showed that, the two-dimensional lattice misfit between the face （001） of Y203 and face （100） of orthorhombic M7C3 was 4.911%, which indicated that Y203 as heterogeneous nuclei of M7C3 was middle effective to refine the primary M7C3.
文摘This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness and abrasion wear resistance tests were conducted. Fracture and worn surfaces were studied. Results indicated that microstructural control during solidifciation is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in hypereutectic iron. Combined action of Nb addition and dynamic solidifciation improves impact toughness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness and abrasion resistance were increased after dynamic solidification compared to statically solidified one by 71.4% and 10%, respectively. This enhancement was increased to 114.3 % and 28.8 % by adding 2% Nb. Lower tempering temperature of 260°C exhibits better impact and abrasion resistance than the sub-critical tempering temperature of 500°C.
基金The authors would like to acknowledge experimental help and invaluable discussions from Shanzi Yu,Xianglong Li,Zhongliang Shu,Shichao Liu,Ruifeng Xu,Pengda Niu,Dan Li,Rou Ding,Min Liu,Haoyang Li,and Taomei Zhang.The authors would also like to acknowledge the financial support from the Natural science foundation of China(No.52271046,No.52171052)the Natural Science Foundation of Hunan Province,China(No.2022JJ20061,No.2023JJ30684)+4 种基金the Key R&D Program of Guangdong Province,China(No.2019B010943001)the Transformation and Industrializa-tion Plan of Scientific and Technological Achievements of Hunan Province,China(No.2020GK2031)the National Natural Science Foundation of China(No.52171052)the funding from State Key Laboratory of Powder Metallurgy,Central South Universitythe Fundamental Research Funds for the Central Universities of Central South University.
文摘Eutectic high-entropy alloys,composed of FCC/B2 phases with a narrow solidification interval and excel-lent fluidity,have become a new hotspot in additive manufacturing.Nevertheless,their microstructures exhibit significant sensitivity to processing parameters,feedstocks,and composition,ultimately limiting the alloys’engineering applications.Here,a hypereutectic Al_(0.7)CoCrFeNi_(2.4)alloy with a low cracking sus-ceptibility index was designed by Thermo-Calc calculation and fabricated by laser powder bed fusion.Results show that the as-printed Al_(0.7)CoCrFeNi_(2.4)alloy manifests a stable cellular structure,coupled with appreciable ultimate tensile strength(≥1200 MPa)and ductility(≥20%)over a wide range of process-ing parameters.After aging at 800℃for 30 min,outstanding strength(1500 MPa)and elongation(15%)were obtained.Considerable mechanical properties after aging stem from a triple strengthening mecha-nism,i.e.,L1_(2) nanoprecipitates and rod-shaped B2 particles within the FCC matrix,along with Cr-enriched spherical nanoparticles in the B2 phase.Meanwhile,hierarchical structure,i.e.,FCC dominated matrix,a discontinuous B2 phase,a precipitation-free zone in the B2 phase,and a K-S orientation relationship be-tween FCC and B2,facilitate to maintain excellent plasticity.These results guide designing HEAs by AM with controllable microstructures and outstanding mechanical properties for industrial applications.
基金This work was supported by the National Natural Science Foundation of China under grant No.50571079.
文摘In this paper, the ring-type ingot of hypereutectic high Cr cast iron was obtained by slope cooling bodycentrifugal casting method （SC-CCM）, and its microstructure and impact toughness were investigated, respectively. The results indicated that, first, the primary carbides in the microstructure are prominently finer than those in the hypereutectic high Cr cast iron prepared by conventional casting method. Second, in the ring-type ingot, the primary carbides near radial outer field are finer than those near radial inner field; furthermore, there is dividing field in the microstructure. Finally, the impact toughness values of the specimens impacted on the radial outer face and on the radial inner face are improved respectively about 36% and 138% more than that of the hypereutectic high Cr one prepared by conventional casting method.
基金supported by National Natural Science Foundation of China (Grant No. 50971092)Innovation Team Plan pf Liaoning Provincical Education Department (Grant no. 2007T132)
文摘The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.
基金financially supported by the National Basic Research Program of China(Grant No.:2012CB723307-03)the Fundamental Research Funds for the Central Universities(Grant No.:N130409003)the National Natural Science Foundation of China(Grant No.:51204046)of China
文摘Large and segregated primary Si particles may drastically decrease the mechanical properties of AI-Si alloys. To solve this problem, a P-Cr complex modifier was added into the alloy, and the effects of P-Cr complex modification and solidification conditions on the microstructure of hypereutectic Al-Si alloys casting produced in wedge-shaped copper mould were studied. The thermal analysis technique was applied to calculate the cooling rate during solidification. The microstructures were observed by means of optical and scanning electron microscopies. Results showed that the primary Si segregates in the as-cast hypereutectic AI-Si alloys. The segregation of primary Si can be inhibited by adding a P＋Cr complex modifier and increasing the cooling rate during solidification. The refinement of primary Si particles by P＋Cr complex modification is due to the formation of CrSi2 and AlP particles which act as the heterogeneous nuclei for the primary Si phase. The segregation of Si was also inhibited through the adherence of heavier CrSi2 particles to the primary Si particles.
文摘In order to review the effect of partial remelting time on the morphology of initial carbides, semisolid ingots of hypereutectic high Cr17 cast iron were remelted at 1270℃ for four different times, and the changing characteristics of shape factor and the equivalent diameter of initial carbides were analyzed quantitatively using a Leica image analyzer. The results indicate that firstly, the evolution process of the initial carbides' morphology undergoes melting, spheroidization and refining during the partial remelting; secondly, the solute diffusion and interface tension take dominant roles at the primary and the middle-final stages respectively in the process of initial carbide evolution; finally, a perfect structure can be obtained by remelting semisolid ingots at 1270℃ for 15 min.
