Magnesium(Mg) alloys, as the lightest metal engineering materials, have broad application prospects.However, the strength and ductility of traditional Mg alloys are still relativity low and difficult to improve simult...Magnesium(Mg) alloys, as the lightest metal engineering materials, have broad application prospects.However, the strength and ductility of traditional Mg alloys are still relativity low and difficult to improve simultaneously.Refining grain size via the deformation process based on the grain boundary strengthening and the transition of deformation mechanisms is one of the feasible strategies to prepare Mg alloys with high strength and high ductility.In this review, the effects of grain size on the strength and ductility of Mg alloys are summarized, and fine-grained Mg alloys with high strength and high ductility developed by various severe plastic deformation technologies and improved traditional deformation technologies are introduced.Although some achievements have been made, the effects of grain size on various Mg alloys are rarely discussed systematically and some key mechanisms are unclear or lack direct microscopic evidence.This review can be used as a reference for further development of high-performance fine-grained Mg alloys.展开更多
The grain refining process of an AZ91D Mg alloy by Sr addition was studied and the heterogeneous nucleating particles of α-Mg were investigated by electron probe microanalysis （EPMA）. With 0.6 wt% Sr addition, the ...The grain refining process of an AZ91D Mg alloy by Sr addition was studied and the heterogeneous nucleating particles of α-Mg were investigated by electron probe microanalysis （EPMA）. With 0.6 wt% Sr addition, the mean grain size of AZ91D alloy was refined from 235.4μm to 52.5 μm at the one-half radius of the ingot. The morphology of primary crystal changed from a sixford symmetrical shape to a petallike shape, Mg-Sr-Al-Fe-Mn heterogeneous nucleating particles were observed at the grain centers and Sr solute atoms presented segregation along the grain boundaries. Grain refinement was facilitated by both the Mg-Sr-Al- Fe-Mn nucleating particles and the Sr solute atoms, and the former played a dominate role in the process.展开更多
The effect of trace addition of 0.1wt%Y on the grain refinement and mechanical properties of Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys at as-cast and heat-treated states was investigated.Results show that the additi...The effect of trace addition of 0.1wt%Y on the grain refinement and mechanical properties of Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys at as-cast and heat-treated states was investigated.Results show that the addition of 0.1wt%Y into the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys can elevate the nucleation temperature of the Al_(3)(Sc,Zr)phase,leading to the preferential precipitation of the Al_(3)(Sc,Zr)phase and increasing the amount of Al_(3)(Sc,Zr)phase in the matrix.Al_(3)(Sc,Zr)phase can also act as a heterogeneous nucleation site in theα-Al matrix to promote nucleation and refine grains.The addition of element Y changes the precipitation phase characteristics at the grain boundaries in the as-cast alloy,which changes the distribution characteristics of secondary phases from initially continuous and coarse strip-like distribution at grain boundaries into the discontinuous dot-like and rod-like distribution.Besides,the size of secondary phases becomes smaller and their amount increases.Under the combined effects of grain refinement strengthening and precipitation strengthening,the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc-0.1Y alloy after 175℃/10 h aging treatment achieves an ultimate tensile strength of 412 MPa and an elongation of 6.3%.Compared with those of the alloy without Y addition,the ultimate tensile strength and elongation of the added alloy increase by 16.1%and 53.7%,respectively.展开更多
Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of...Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.展开更多
Al-7.5Si-4Cu cast alloy melt modified by Al-5Ti-B, RE and Al-10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners a...Al-7.5Si-4Cu cast alloy melt modified by Al-5Ti-B, RE and Al-10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners and modifiers on the mechanical properties, microstructures, grain refining and modification, and intermetallic compounds of the alloy. The results show that the mechanical properties and the microstructures of Al-7.5Si-4Cu cast alloys are improved immensely by combining addition of 0.8%Al-5Ti-B, 0.1%RE and 0.1%Al-10Sr grain refiners and modifiers compared with the individual addition and cast conditions. For individual addition condition, addition of 0.8%Al-5Ti-B master alloy can obtain superior tensile strength, Brinell hardness and finer equiaxedα（Al） dendrites. The alloy with 0.1%RE master alloy shows the highest improvement in ductility because the rare earth can purify the molten metal and change the shape of intermetallic compounds. While the alloy with 0.1%Al-10Sr modifier shows only good improvement in yield strength, and the improvement of other performance is unsatisfactory. The Al-10Sr modifier has a significant metamorphism for the eutectic silicon, but will make the gas content in the aluminum alloy melt increase to form serious columnar grain structures. The effects of grain refining and modification on mean area and aspect ratio have the same conclusions obtained in the mechanical properties and the microstructures analyses.展开更多
A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed cry...A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed crystal with a diameter of （110-a：17） ~tm. The results indicate that A14C3 and TiC particle cluster, rather than a single particle, plays an important role in the refining process. Compared with the simplex smooth nucleating substrate, concave regions on the particle cluster provide easier route for the transformation from liquid Mg atoms to stable nucleus. Nucleus with a small size can also reach the critical nucleation radius when they attach on the concave regions of the substrate. A14C3 and TiC particle clusters thus become more favorable nucleating substrate for a-Mg grains.展开更多
Al-Ti-B-Er refiner was successfully prepared by CR （contact reaction process）, a process based on SHS （self propagating high-temperature synthesis）. The microstructure of the alloy was studied by optical microscop...Al-Ti-B-Er refiner was successfully prepared by CR （contact reaction process）, a process based on SHS （self propagating high-temperature synthesis）. The microstructure of the alloy was studied by optical microscopy, X-ray diffraction （XRD）, scanning electron microscopy （SEM） equipped with energy-dispersive spectrometry. The results showed that Al-Ti-B-Er alloy was composed of α-Al, block-like TiAl3 and flocked TiB2. Compared with Al-Ti-B refiner, formation of TiAlEr compounds, Er modified the morphology of TiAl3 phase, and dispersed the TiB2 and TiAl3. An excellent grain refining performance was obtained when adding 1 wt.% Al-Ti-B-Er in Al-10Zn-1.9Mg-1.6Cu-0.12Zr alloy, the average grain size was about 40 μm. The refinement mechanism of Al-Ti-B-Er was also discussed. Er changed the morphology of TiAl3, TiB2 phase, the refiner would be more efficient. The decomposition of TiAlEr compounds which released Er refrained the growth of TiAl3 and made TiB2 difficult to aggregate or deposit, therefore resulted in more particles being efficient nucleation substrate.展开更多
Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing propertie...Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing properties of existing Mg alloys and introducing new alloy systems to industrial producers.An important way to improve properties of metallic materials is to decrease grain size that results almost in increasing all kind of properties of the material.This review paper aims to summarize the literature about grain refining of magnesium alloys.The text is consisting of three sections,which focused on the(1)grain refining methods used in the past,which are not used today,(2)grain refining methods currently being used in the industry and(3)novel and newly developed methods that may find usage in the industry in future.Before explaining grain refining methods of magnesium alloys a general summary about grain refinement of metals is also provided.展开更多
The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatmen...The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate someδphases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT temperature is 980℃.The phenomenon attributes to the uneven distribution ofδphase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number ofδphases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with fewδphases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prerequisite to precipitate even-distributedδphase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation aroundδphase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).展开更多
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners...Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB_(2)provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB_(2)and(1-100)NbB_(2)surface can be substituted by Al to form(Al,Nb)B_(2)intermedia layers.In addition,a layer of NbAl_(3)-like compound(NbAl_(3)')can cover the surface of NbB_(2)with the orientation relation of(1-100)[11-20]NbB_(2/)/(110)[110]NbAl_(3)'.Both of the(Al,Nb)B_(2)and NbAl_(3)'intermedia layers contribute to enhancing the nucleation potency of NbB_(2)particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys.展开更多
Grain refinement is critical to surpassing the bottlenecks of inherent hot tearing of high-strength aluminum alloys fabricated by additive manufacturing(AM).In this study,a synergistic grain-refining strategy includin...Grain refinement is critical to surpassing the bottlenecks of inherent hot tearing of high-strength aluminum alloys fabricated by additive manufacturing(AM).In this study,a synergistic grain-refining strategy including heterogeneous nucleation,solute-driven growth restriction and nanoparticle-induced growth restriction was introduced to control the microstructure of Al-Zn-Mg-Cu alloys during the laser powder bed fusion(LPBF)process.Crack-free Al-Zn-Mg-Cu alloys with significantly refined grains were safely fabricated via LPBF by coincorporation of Ti C and TiHparticles.In-situ L1-AlTi particles were produced to promote the heterogeneous nucleation.The grain growth was restricted by adding Ti solute,while introduced TiC nanoparticles(NPs)improved the density of heterogeneous nucleation sites and blocked grain growth physically.The resultant elimination of columnar grains and hot cracks in the(1 wt.%)TiC-and(0.8 wt.%)TiH-modified Al-Zn-Mg-Cu alloy resulted in excellent ultimate tensile strength(UTS)of 593±24 MPa,yield strength(YS)of 485±41 MPa and elongation(EL)of 10.0%±2.5%under the T6 condition.This study provides new insights into improving the grain microstructure and mechanical properties of high-strength aluminum alloys during LPBF.展开更多
An Al 50wt%TiC composite was directly synthesized by self propagating high temperature synthesis (SHS) technology,and then was used as a grain refining master alloy for commercially pure aluminum.The microstructure...An Al 50wt%TiC composite was directly synthesized by self propagating high temperature synthesis (SHS) technology,and then was used as a grain refining master alloy for commercially pure aluminum.The microstructure and grain refining performance of the synthesized master alloy were emphatically investigated.The SHS master alloy only contained submicron TiC particles except for Al matrix.Moreover,TiC particles were relatively free of agglomeration. Grain refining tests show that adding only 0.1 wt% of the master alloys to the aluminum melt could transform the structure of the solidified samples from coarse columnar grains to fine equiaxed grains (average grain size 120μm),and that this grain refining effectiveness could be maintained for almost 1.5h at 1003K. Therefore,it is concluded that the SHS master alloy is an effective grain refiner for aluminum and its alloys, and that it is highly resistant to the grain refining fading encountered with most grain refiners.展开更多
The Al-5Ti-0.2C-based grain refiners with different contents of rare earth （RE） were successfully prepared via powder metallurgy and vacuum casting. The microstructural evolution has been studied by X-ray diffracti...The Al-5Ti-0.2C-based grain refiners with different contents of rare earth （RE） were successfully prepared via powder metallurgy and vacuum casting. The microstructural evolution has been studied by X-ray diffraction （XRD）, differential scanning calorimetry （DSC）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results showed that the RE addition resulted in the formation of TiAl3/Ti2Al20RE core-shell structured primary particles, and the size of TiAl3 core decreased, while the thickness of Ti2Al20RE increased with increase of RE contents. As compared to Al-5Ti-0.2C grain refiner, the grain refining efficiency was gradually improved with increase of RE contents, which was mainly attributed to the TiAl3/Ti2Al20RE core-shell structured primary particles and insoluble TiC nuclei formed inα-Al matrix. The formation mechanism of core-shell structure was further investigated based on Ginstling-Brounstein model.展开更多
AM30 was inoculated by MgCO_(3) powder with different holding time.The influence of MgO decomposed by MgCO_(3)on the grain refinement effect was mainly discussed in the present study.Three sets of comparative samples ...AM30 was inoculated by MgCO_(3) powder with different holding time.The influence of MgO decomposed by MgCO_(3)on the grain refinement effect was mainly discussed in the present study.Three sets of comparative samples were prepared.They were AM30 alloy inoculated by MgO and pure Mg inoculated by MgO and MgCO_(3).The possible nucleating particles were observed and analyzed by EPMA and SEM.AM30 alloy could be effectively refined by either MgCO_(3)or MgO inoculation.Grain refining efficiency and fading effect of MgO inoculation were better than those of MgCO_(3) inoculation.However,pure Mg could not be refined by these two inoculants.Al is an indispensable element to determine the grain refinement of Mg alloys inoculated by either MgCO_(3)or MgO.MgO should not be the effective substrates forα-Mg phase.A novel grain refining mechanism of MgCO_(3) inoculation on AM30 alloy was proposed by combining experimental results with theoretical calculation,i.e.,MgAl_(2)O_(4) should be the potent nuclei ofα-Mg grain for the AM30 alloy in addition to Al_(4)C_(3).展开更多
Al-Ti-C grain refiner was prepared by SHS （self-propagating high-temperature synthesis ）-melting technique. The effect of La on the microstructures of grain refiner was studied by OM, TEM, SEM, XRD, and EDS. The exp...Al-Ti-C grain refiner was prepared by SHS （self-propagating high-temperature synthesis ）-melting technique. The effect of La on the microstructures of grain refiner was studied by OM, TEM, SEM, XRD, and EDS. The experimental results indicate that La can improve the wettability between liquid aluminum and graphite ; the addition of La results in dispersive distribution of TiAl3 and TiC particles in the matrix. An excellent grain refining performance of Al-Ti-C grain refiner on commercially pure Al was obtained.展开更多
In the conventional melt preparation of magnesium rare-earth(Mg-RE)alloys,the repeated heating/cooling process involved in grain refinement and flux refining usually prolongs the preparation period and aggravates melt...In the conventional melt preparation of magnesium rare-earth(Mg-RE)alloys,the repeated heating/cooling process involved in grain refinement and flux refining usually prolongs the preparation period and aggravates melt oxidation.In this work,the purification and grain refinement of Mg-9Gd-3Y(GW93)alloy was simultaneously realized by one-step refining at 740℃ by using a self-developed compound flux.The results show that,only after holding for 10 min,the inclusion content of the alloy is reduced by 81%to 0.29%,while the grain size is reduced by 84%to 119μm.A physical model depicting the interactions between compound flux and alloy melt was proposed based on thermodynamic calculation and microstructure observation.The grain refinement mechanism has been analyzed by considering the presence of Zr particle(Zr_(p))and Zr solute(Zr_(s)).In addition,the generated RECl_(3) was found to be readily absorbed by the flux,decreasing the surface tension and promoting the purification efficacy of the flux,which plays an important role in the promoted elongation of the as-cast Mg-9Gd-3Y-0.5Zr(GW93K)alloy.This work presents a unique prospect in simplifying the melt preparation of Mg-RE alloy with a promoted quality.展开更多
As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low...As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.展开更多
The differences of grain-refining effect between Sc and Ti additions in aluminum,which cannot be substantially explained by traditional theories,were carefully studied.The empirical electron theory(EET) of solids and ...The differences of grain-refining effect between Sc and Ti additions in aluminum,which cannot be substantially explained by traditional theories,were carefully studied.The empirical electron theory(EET) of solids and molecules was employed to calculate the valence electron structures(VES) of Al3Ti and Al3Sc.The conclusions can be drawn that,in the two alloys Al-Ti and Al-Sc,the different valence electron structures of Al3Ti and Al3Sc and the consequent differences of growth habit of the two particles,and the different interfacial electron density between particles and matrix fundamentally lead to the differences of grain-refining effect between Sc and Ti additions on aluminum and make Sr the better grain-refiner of aluminum.展开更多
The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO_(3)were investigated and then a refining technique was developed.Simultaneously,the corresponding mechanisms were discussed...The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO_(3)were investigated and then a refining technique was developed.Simultaneously,the corresponding mechanisms were discussed.The results indicate that increasing addition temperature of MgCO_(3)or pouring temperature is beneficial for obtaining fine grains.There is an optimal addition amount of 1.2%at the addition temperature of 790°C.Prolonging holding time at 790°C will increase grain size.The grain refining technique that 1.2%MgCO_(3)is added at 790°C followed by holding for 10 min and pouring can decrease the grain size from 348μm of the un-refined alloy to 69μm.The nucleation substrates are actually the Al4C3 particles formed from reactions between the MgCO_(3)and alloying elements in the melt.Besides the heterogeneous nucleation regime,growth restriction of the Al4C3 particles agglomerated at growing front is the other mechanism.展开更多
Hot rolling of AZ31 Mg alloy was performed by using as-cast alloy ingot as the starting material.The microstructures and mechanical properties of the as-rolled alloy subjected to various rolling passes were investigat...Hot rolling of AZ31 Mg alloy was performed by using as-cast alloy ingot as the starting material.The microstructures and mechanical properties of the as-rolled alloy subjected to various rolling passes were investigated.The results show that the grain size of the alloy can be refined steadily with increasing rolling passes by dynamic recrystallization.With the steady refining of the grain size,both the mechanical strength and the plasticity of the alloy are improved correspondingly.In particular,when the grain size is reduced to about 5μm after 5 rolling passes,the yield strength,ultimate tensile strength and tensile fracture strain of the alloy are 211 MPa,280 MPa and 0.28 in the transverse direction,they are 200 MPa,268 MPa and 0.32 in the rolling direction,respectively.展开更多
基金supported by the National Natural Science Foundation of China (Nos.51871069 and 52071093)the Fundamental Research Funds for the Central Universities (No.3072020CF1009)+2 种基金the Science and Technology Innovation Major Project of Ningbo City, China (No.2019B10103)the Domain Foundation of Equipment Advance Research of 13th Five-year Plan (No.61409220118)the Open Funds of the State Key Laboratory of Rare Earth Resource Utilization (No.RERU2020008)。
文摘Magnesium(Mg) alloys, as the lightest metal engineering materials, have broad application prospects.However, the strength and ductility of traditional Mg alloys are still relativity low and difficult to improve simultaneously.Refining grain size via the deformation process based on the grain boundary strengthening and the transition of deformation mechanisms is one of the feasible strategies to prepare Mg alloys with high strength and high ductility.In this review, the effects of grain size on the strength and ductility of Mg alloys are summarized, and fine-grained Mg alloys with high strength and high ductility developed by various severe plastic deformation technologies and improved traditional deformation technologies are introduced.Although some achievements have been made, the effects of grain size on various Mg alloys are rarely discussed systematically and some key mechanisms are unclear or lack direct microscopic evidence.This review can be used as a reference for further development of high-performance fine-grained Mg alloys.
基金Funded by the National Natural Science Foundation of China (No. 50171037) Key Project of Science and Technology Research of Ministry of Education of China (No. 01105)
文摘The grain refining process of an AZ91D Mg alloy by Sr addition was studied and the heterogeneous nucleating particles of α-Mg were investigated by electron probe microanalysis （EPMA）. With 0.6 wt% Sr addition, the mean grain size of AZ91D alloy was refined from 235.4μm to 52.5 μm at the one-half radius of the ingot. The morphology of primary crystal changed from a sixford symmetrical shape to a petallike shape, Mg-Sr-Al-Fe-Mn heterogeneous nucleating particles were observed at the grain centers and Sr solute atoms presented segregation along the grain boundaries. Grain refinement was facilitated by both the Mg-Sr-Al- Fe-Mn nucleating particles and the Sr solute atoms, and the former played a dominate role in the process.
基金National Natural Science Foundation of China(52071065)Fundamental Research Funds for the Central Universities(N2007007)+2 种基金Joint Fund of Henan Province Science and Technology R&D Program(N225200810040)High-Level Talent Research Start-Up Project Funding of Henan Academy of Sciences(N242017003)Liaoning Provincial Department of Education Basic Research Projects for Colleges and Universities(LJ212410142093)。
文摘The effect of trace addition of 0.1wt%Y on the grain refinement and mechanical properties of Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys at as-cast and heat-treated states was investigated.Results show that the addition of 0.1wt%Y into the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys can elevate the nucleation temperature of the Al_(3)(Sc,Zr)phase,leading to the preferential precipitation of the Al_(3)(Sc,Zr)phase and increasing the amount of Al_(3)(Sc,Zr)phase in the matrix.Al_(3)(Sc,Zr)phase can also act as a heterogeneous nucleation site in theα-Al matrix to promote nucleation and refine grains.The addition of element Y changes the precipitation phase characteristics at the grain boundaries in the as-cast alloy,which changes the distribution characteristics of secondary phases from initially continuous and coarse strip-like distribution at grain boundaries into the discontinuous dot-like and rod-like distribution.Besides,the size of secondary phases becomes smaller and their amount increases.Under the combined effects of grain refinement strengthening and precipitation strengthening,the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc-0.1Y alloy after 175℃/10 h aging treatment achieves an ultimate tensile strength of 412 MPa and an elongation of 6.3%.Compared with those of the alloy without Y addition,the ultimate tensile strength and elongation of the added alloy increase by 16.1%and 53.7%,respectively.
基金Project supported by Tsinghua-Wuxi Science Foundation, China
文摘Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.
基金Project (09C26279200863) supported by Technology Innovation Fund Project of High-tech Small and Medium Enterprises,Ministry of Science and Technology of ChinaProject (BA2011084) supported by Special Fund Project on Science and Technology Achievement Transformation of Jiangsu Province,China
文摘Al-7.5Si-4Cu cast alloy melt modified by Al-5Ti-B, RE and Al-10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners and modifiers on the mechanical properties, microstructures, grain refining and modification, and intermetallic compounds of the alloy. The results show that the mechanical properties and the microstructures of Al-7.5Si-4Cu cast alloys are improved immensely by combining addition of 0.8%Al-5Ti-B, 0.1%RE and 0.1%Al-10Sr grain refiners and modifiers compared with the individual addition and cast conditions. For individual addition condition, addition of 0.8%Al-5Ti-B master alloy can obtain superior tensile strength, Brinell hardness and finer equiaxedα（Al） dendrites. The alloy with 0.1%RE master alloy shows the highest improvement in ductility because the rare earth can purify the molten metal and change the shape of intermetallic compounds. While the alloy with 0.1%Al-10Sr modifier shows only good improvement in yield strength, and the improvement of other performance is unsatisfactory. The Al-10Sr modifier has a significant metamorphism for the eutectic silicon, but will make the gas content in the aluminum alloy melt increase to form serious columnar grain structures. The effects of grain refining and modification on mean area and aspect ratio have the same conclusions obtained in the mechanical properties and the microstructures analyses.
基金Project(DUT15JJ(G)01) supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2009AA03Z525) supported by the National High-tech Research and Development Program of China
文摘A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed crystal with a diameter of （110-a：17） ~tm. The results indicate that A14C3 and TiC particle cluster, rather than a single particle, plays an important role in the refining process. Compared with the simplex smooth nucleating substrate, concave regions on the particle cluster provide easier route for the transformation from liquid Mg atoms to stable nucleus. Nucleus with a small size can also reach the critical nucleation radius when they attach on the concave regions of the substrate. A14C3 and TiC particle clusters thus become more favorable nucleating substrate for a-Mg grains.
基金supported by Beijing Municipal Natural Science Foundation(KZ20122100050008)National Basic Research Program of China(2012CB6198503)
文摘Al-Ti-B-Er refiner was successfully prepared by CR （contact reaction process）, a process based on SHS （self propagating high-temperature synthesis）. The microstructure of the alloy was studied by optical microscopy, X-ray diffraction （XRD）, scanning electron microscopy （SEM） equipped with energy-dispersive spectrometry. The results showed that Al-Ti-B-Er alloy was composed of α-Al, block-like TiAl3 and flocked TiB2. Compared with Al-Ti-B refiner, formation of TiAlEr compounds, Er modified the morphology of TiAl3 phase, and dispersed the TiB2 and TiAl3. An excellent grain refining performance was obtained when adding 1 wt.% Al-Ti-B-Er in Al-10Zn-1.9Mg-1.6Cu-0.12Zr alloy, the average grain size was about 40 μm. The refinement mechanism of Al-Ti-B-Er was also discussed. Er changed the morphology of TiAl3, TiB2 phase, the refiner would be more efficient. The decomposition of TiAlEr compounds which released Er refrained the growth of TiAl3 and made TiB2 difficult to aggregate or deposit, therefore resulted in more particles being efficient nucleation substrate.
文摘Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing properties of existing Mg alloys and introducing new alloy systems to industrial producers.An important way to improve properties of metallic materials is to decrease grain size that results almost in increasing all kind of properties of the material.This review paper aims to summarize the literature about grain refining of magnesium alloys.The text is consisting of three sections,which focused on the(1)grain refining methods used in the past,which are not used today,(2)grain refining methods currently being used in the industry and(3)novel and newly developed methods that may find usage in the industry in future.Before explaining grain refining methods of magnesium alloys a general summary about grain refinement of metals is also provided.
基金the National Natural Science Foundation of China(No.51975593)the Hunan Provincial Natural Science Foundation of China(No.2020JJ4113)the Science and Technology Innovation Planning Project of Hunan Province(No.2019XK2301)。
文摘The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate someδphases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT temperature is 980℃.The phenomenon attributes to the uneven distribution ofδphase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number ofδphases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with fewδphases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prerequisite to precipitate even-distributedδphase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation aroundδphase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).
基金supported by the National Natural Science Foundation of China(51871138)Science and Technology Commission of Shanghai Municipality(19010500400)the 111 project(No.D16002)。
文摘Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB_(2)provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB_(2)and(1-100)NbB_(2)surface can be substituted by Al to form(Al,Nb)B_(2)intermedia layers.In addition,a layer of NbAl_(3)-like compound(NbAl_(3)')can cover the surface of NbB_(2)with the orientation relation of(1-100)[11-20]NbB_(2/)/(110)[110]NbAl_(3)'.Both of the(Al,Nb)B_(2)and NbAl_(3)'intermedia layers contribute to enhancing the nucleation potency of NbB_(2)particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys.
基金the Research and Development Program Project in Key Areas of Guangdong Province,China(No.2019B090907001)the Major Special Project for Science and Technology Program of Guangdong Province,China(No.2014B010129002)。
文摘Grain refinement is critical to surpassing the bottlenecks of inherent hot tearing of high-strength aluminum alloys fabricated by additive manufacturing(AM).In this study,a synergistic grain-refining strategy including heterogeneous nucleation,solute-driven growth restriction and nanoparticle-induced growth restriction was introduced to control the microstructure of Al-Zn-Mg-Cu alloys during the laser powder bed fusion(LPBF)process.Crack-free Al-Zn-Mg-Cu alloys with significantly refined grains were safely fabricated via LPBF by coincorporation of Ti C and TiHparticles.In-situ L1-AlTi particles were produced to promote the heterogeneous nucleation.The grain growth was restricted by adding Ti solute,while introduced TiC nanoparticles(NPs)improved the density of heterogeneous nucleation sites and blocked grain growth physically.The resultant elimination of columnar grains and hot cracks in the(1 wt.%)TiC-and(0.8 wt.%)TiH-modified Al-Zn-Mg-Cu alloy resulted in excellent ultimate tensile strength(UTS)of 593±24 MPa,yield strength(YS)of 485±41 MPa and elongation(EL)of 10.0%±2.5%under the T6 condition.This study provides new insights into improving the grain microstructure and mechanical properties of high-strength aluminum alloys during LPBF.
文摘An Al 50wt%TiC composite was directly synthesized by self propagating high temperature synthesis (SHS) technology,and then was used as a grain refining master alloy for commercially pure aluminum.The microstructure and grain refining performance of the synthesized master alloy were emphatically investigated.The SHS master alloy only contained submicron TiC particles except for Al matrix.Moreover,TiC particles were relatively free of agglomeration. Grain refining tests show that adding only 0.1 wt% of the master alloys to the aluminum melt could transform the structure of the solidified samples from coarse columnar grains to fine equiaxed grains (average grain size 120μm),and that this grain refining effectiveness could be maintained for almost 1.5h at 1003K. Therefore,it is concluded that the SHS master alloy is an effective grain refiner for aluminum and its alloys, and that it is highly resistant to the grain refining fading encountered with most grain refiners.
基金Project supported by National High Technology Research and Development Program of China(2013AA031001)the National Basic Research Program of China(2012CB619503)International Science&Technology Cooperation Program of China(2012DFA50630)
文摘The Al-5Ti-0.2C-based grain refiners with different contents of rare earth （RE） were successfully prepared via powder metallurgy and vacuum casting. The microstructural evolution has been studied by X-ray diffraction （XRD）, differential scanning calorimetry （DSC）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results showed that the RE addition resulted in the formation of TiAl3/Ti2Al20RE core-shell structured primary particles, and the size of TiAl3 core decreased, while the thickness of Ti2Al20RE increased with increase of RE contents. As compared to Al-5Ti-0.2C grain refiner, the grain refining efficiency was gradually improved with increase of RE contents, which was mainly attributed to the TiAl3/Ti2Al20RE core-shell structured primary particles and insoluble TiC nuclei formed inα-Al matrix. The formation mechanism of core-shell structure was further investigated based on Ginstling-Brounstein model.
基金the National Natural Science Foundation of China(51574127)Natural Science Foundation of Guangdong Province(2014A030313221).
文摘AM30 was inoculated by MgCO_(3) powder with different holding time.The influence of MgO decomposed by MgCO_(3)on the grain refinement effect was mainly discussed in the present study.Three sets of comparative samples were prepared.They were AM30 alloy inoculated by MgO and pure Mg inoculated by MgO and MgCO_(3).The possible nucleating particles were observed and analyzed by EPMA and SEM.AM30 alloy could be effectively refined by either MgCO_(3)or MgO inoculation.Grain refining efficiency and fading effect of MgO inoculation were better than those of MgCO_(3) inoculation.However,pure Mg could not be refined by these two inoculants.Al is an indispensable element to determine the grain refinement of Mg alloys inoculated by either MgCO_(3)or MgO.MgO should not be the effective substrates forα-Mg phase.A novel grain refining mechanism of MgCO_(3) inoculation on AM30 alloy was proposed by combining experimental results with theoretical calculation,i.e.,MgAl_(2)O_(4) should be the potent nuclei ofα-Mg grain for the AM30 alloy in addition to Al_(4)C_(3).
基金Project supported by the Natural Science Foundation of Shanxi Province (20011047)Patent Generalization Project ofShanxi Province (051025)
文摘Al-Ti-C grain refiner was prepared by SHS （self-propagating high-temperature synthesis ）-melting technique. The effect of La on the microstructures of grain refiner was studied by OM, TEM, SEM, XRD, and EDS. The experimental results indicate that La can improve the wettability between liquid aluminum and graphite ; the addition of La results in dispersive distribution of TiAl3 and TiC particles in the matrix. An excellent grain refining performance of Al-Ti-C grain refiner on commercially pure Al was obtained.
基金supported by the National Natural Science Foundation of China(Nos.U2037601 and 51821001)the Research Program of Joint Research Center of Advanced Spaceflight Technologies(No.USCAST2020-31).
文摘In the conventional melt preparation of magnesium rare-earth(Mg-RE)alloys,the repeated heating/cooling process involved in grain refinement and flux refining usually prolongs the preparation period and aggravates melt oxidation.In this work,the purification and grain refinement of Mg-9Gd-3Y(GW93)alloy was simultaneously realized by one-step refining at 740℃ by using a self-developed compound flux.The results show that,only after holding for 10 min,the inclusion content of the alloy is reduced by 81%to 0.29%,while the grain size is reduced by 84%to 119μm.A physical model depicting the interactions between compound flux and alloy melt was proposed based on thermodynamic calculation and microstructure observation.The grain refinement mechanism has been analyzed by considering the presence of Zr particle(Zr_(p))and Zr solute(Zr_(s)).In addition,the generated RECl_(3) was found to be readily absorbed by the flux,decreasing the surface tension and promoting the purification efficacy of the flux,which plays an important role in the promoted elongation of the as-cast Mg-9Gd-3Y-0.5Zr(GW93K)alloy.This work presents a unique prospect in simplifying the melt preparation of Mg-RE alloy with a promoted quality.
基金financially supported by the National Natu-ral Science Foundation of China(nos.92163208,51902233,and 51972243)the National Key Research and Development Plan of China(no.2021YFB3701400)the Independent Innovation Projects of the Hubei Longzhong Laboratory(no.2022ZZ-11).
文摘As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.
基金Project(20050003042) supported by Research Fund for the Doctoral Program of Higher Education of China
文摘The differences of grain-refining effect between Sc and Ti additions in aluminum,which cannot be substantially explained by traditional theories,were carefully studied.The empirical electron theory(EET) of solids and molecules was employed to calculate the valence electron structures(VES) of Al3Ti and Al3Sc.The conclusions can be drawn that,in the two alloys Al-Ti and Al-Sc,the different valence electron structures of Al3Ti and Al3Sc and the consequent differences of growth habit of the two particles,and the different interfacial electron density between particles and matrix fundamentally lead to the differences of grain-refining effect between Sc and Ti additions on aluminum and make Sr the better grain-refiner of aluminum.
基金Project(G2010CB635106)supported by the National Basic Research Program of China+1 种基金Project(NCET-10-0023)supported by the Program for New Century Excellent Talents in University of China
文摘The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO_(3)were investigated and then a refining technique was developed.Simultaneously,the corresponding mechanisms were discussed.The results indicate that increasing addition temperature of MgCO_(3)or pouring temperature is beneficial for obtaining fine grains.There is an optimal addition amount of 1.2%at the addition temperature of 790°C.Prolonging holding time at 790°C will increase grain size.The grain refining technique that 1.2%MgCO_(3)is added at 790°C followed by holding for 10 min and pouring can decrease the grain size from 348μm of the un-refined alloy to 69μm.The nucleation substrates are actually the Al4C3 particles formed from reactions between the MgCO_(3)and alloying elements in the melt.Besides the heterogeneous nucleation regime,growth restriction of the Al4C3 particles agglomerated at growing front is the other mechanism.
文摘Hot rolling of AZ31 Mg alloy was performed by using as-cast alloy ingot as the starting material.The microstructures and mechanical properties of the as-rolled alloy subjected to various rolling passes were investigated.The results show that the grain size of the alloy can be refined steadily with increasing rolling passes by dynamic recrystallization.With the steady refining of the grain size,both the mechanical strength and the plasticity of the alloy are improved correspondingly.In particular,when the grain size is reduced to about 5μm after 5 rolling passes,the yield strength,ultimate tensile strength and tensile fracture strain of the alloy are 211 MPa,280 MPa and 0.28 in the transverse direction,they are 200 MPa,268 MPa and 0.32 in the rolling direction,respectively.
