Obtaining an appropriate grain size is crucial for Al alloys or Al matrix composites prior to processing,as it significantly influences the mechanical properties of components and workability during the manufacturing ...Obtaining an appropriate grain size is crucial for Al alloys or Al matrix composites prior to processing,as it significantly influences the mechanical properties of components and workability during the manufacturing process.TiB_(2)particles are exceptional grain refiners in Al and serve as excellent reinforcement particles for particulate-reinforced aluminum matrix composites.However,the optimal particle content for achieving excellent refinement and strengthening effects depends on the matrix composition and requires further investigation.Additionally,homogenization is essential for mitigating the element segregation in the ingot.Although it is anticipated that adding suitable particles can effectively inhibit undesired grain growth during homogenization,comprehensive investigations on this aspect are currently lacking.Therefore,TiB_(2)/2219Al matrix composites with varying reinforcement contents(0,1,3,5 wt%)were fabricated through traditional casting followed by homogenization treatment to address these research gaps.The effects of reinforcement content and homogenization treatment on the microstructure and mechanical properties of in-situ TiB_(2)/2219Al composites were investigated.The results demonstrate a gradual strengthening of the refining effect with increasing particle concentration.Moreover,composites containing 3 wt%TiB_(2)particles exhibit superior comprehensive mechanical properties in both as-cast and homogenized state.Additionally,potential orientation relationships are observed and calculated between undissolved Al_(2)Cu eutectic phase and submicron or nanometer-sized TiB_(2)particles,resulting in a mixture structure with enhanced bonding strength.This mixture structure is continuously distributed along grain boundaries during solidification,forming a three-dimensional cellular network that acts as primary retarding forces for grain growth during homogenization.Furthermore,the established homogenization kinetic equations were further utilized to analyze the correlation between homogenization time and grain size,as well as the influence of homogenization temperature.展开更多
Mge3Lie0.4Zr alloys containing RE elements(Gd,La,Nd)(Mge3LieREe0.4Zr alloys)are investigated to reveal the influence of homogenization treatment on microstructures and distributions of RE,Zr elements.It is found that...Mge3Lie0.4Zr alloys containing RE elements(Gd,La,Nd)(Mge3LieREe0.4Zr alloys)are investigated to reveal the influence of homogenization treatment on microstructures and distributions of RE,Zr elements.It is found that 300C24 h homogenization treatment shows better improvement on the microstructure including the refinement of grain size,the dispersion of cellular dendrite and low melting point particles.Before treatment,La and Nd segregate effectively at grain boundary and Zr segregates in the form of precipitates.Homogenization treatment induces the reduction of RE segregation.However,the segregation of Zr in precipitates cannot be abated due to the relatively low diffusion rate compared with RE elements.展开更多
Microstructural improvement of Al-Cu-Li alloys with high Li content plays a critical role for the acquisition of excellent mechanical properties and ultra-low density.In this regard,the Al-Cu-Li alloy castings with hi...Microstructural improvement of Al-Cu-Li alloys with high Li content plays a critical role for the acquisition of excellent mechanical properties and ultra-low density.In this regard,the Al-Cu-Li alloy castings with high Li content from 1.5 wt.%to 4.5 wt.%were prepared by near-rapid solidification,followed by two-stage homogenization treatment(490℃/16 h and 530℃/16 h).The microstructural evolution and solidification behavior of the as-cast and homogenized alloys with different Li contents were systematically studied by combining experiments with calculations by Pandat software.The results indicate that with the increase of Li content,the grain sizes decrease,the solution ability of Cu in the matrixα-Al phase increases,while the content of secondary dendrites increases and the precipitated phases change from low melting point phases to high melting point phases under the near-rapid solidification.Additionally,by the coupling of near-rapid solidification and two-stage homogenization,the metastable precipitated phases(Al7Cu4Li and AlCu3)can be dissolved effectively in the alloys with Li content of 1.5 wt.%-2.5 wt.%;moreover,the stable precipitated phases(Al6CuLi3 and Al2CuLi)uniformly distribute at the grain boundaries in the alloys with Li content of 3.5 wt.%-4.5 wt.%.As a result,the refined and homogenized microstructure can be obtained.展开更多
A new point of view on the homogenization treatment has been proposed.It is supposed that a little liquid in the alloy may promote the homogenization process in some aspects and reduce the time for eliminating the Lav...A new point of view on the homogenization treatment has been proposed.It is supposed that a little liquid in the alloy may promote the homogenization process in some aspects and reduce the time for eliminating the Laves-phase in alloy GH169.The microprocess of the elimination of Laves-phase in the case of a little liquid existing in the alloy has also been described.展开更多
In comparison with the homogenization treatment without an electric field prior to the same solid solution and aging treatment, the homogenization treatment in an electric field increases the hardness and strength of ...In comparison with the homogenization treatment without an electric field prior to the same solid solution and aging treatment, the homogenization treatment in an electric field increases the hardness and strength of 1420 Al Li alloy, but somewhat decreases the elongation of the alloy. Moreover, the elongation of the alloy increases with the homogenization temperature in an electric field increasing. TEM observation showed that the homogenization treatment in an electric field can accelerate the dissolution of the coarse particles of second phase on the grain boundary as well as make δ′phase precipitated in subsequent aging process finer and more numerous.展开更多
Abstract The microstructure evolution and composition distribution of as-cast and homogenized 2099 aluminumlithium （Al-Li） alloy were studied by optical microscopy （OM）, differential thermal analysis （DTA）, scan...Abstract The microstructure evolution and composition distribution of as-cast and homogenized 2099 aluminumlithium （Al-Li） alloy were studied by optical microscopy （OM）, differential thermal analysis （DTA）, scanning electron microscopy （SEM）, energy dispersive spectrometry （EDS）, area and line scanning, X-ray diffraction （XRD）, and Vickers microhardness test methods. The results show that severe dendrite exists in the as-cast alloy. Cu, Zn, Mn, and Mg distribute unevenly from the grain boundary to inside. The low-melting point nonequilibrium eutectic phases dis- solve into the matrix during the first-step homogenization, whereas the melting point of residual eutectic phases is elevated. After the second-step homogenization, most of the remaining eutectic phases dissolve into the matrix, except a small amount of A1-Cu-Fe phases. An optimized homogenization process of the 2099 A1-Li alloy is developed （515℃ - 18 h ＋ 525℃ - 16 h）, which shows a good agreement with the homogenization kinetic analysis results.展开更多
For 2091 Al-Li alloy, the volume fraction of second phase particles is greatly determined by the homogenization temperature and homogenization time under an electric field and the ductility of the alloy is determined ...For 2091 Al-Li alloy, the volume fraction of second phase particles is greatly determined by the homogenization temperature and homogenization time under an electric field and the ductility of the alloy is determined by the fraciton of second phase particles. The combined homogenization treatment shortens the homogenization time, reduces the loss ofLi content and increases the ductity of the alloy.展开更多
Homogenization treatment under an electric field increases the distributive homogeneity of the T1 precipitation and improves the yield strength of 2091 Al-Li alloy.
Both of chromium and zinc could appear as either minor impurities or alloying elements in recycled and commercial aluminum alloys, and they could have detrimental effects on the final product properties if not control...Both of chromium and zinc could appear as either minor impurities or alloying elements in recycled and commercial aluminum alloys, and they could have detrimental effects on the final product properties if not controlled in an appropriate way. A Kampmann-Wagner numerical modeling approach, built on the basis of computational thermodynamics and diffusion kinetics, is employed to investigate the effect of these two minor impurities on dispersoids precipitation during homogenization heat treatment of AA3xxx alloys. The simulation results obtained from different simulation set-ups were compared. The aim is to demonstrate that the modeling approach has the potential to guide the design or optimization of the chemical compositions and heat treatment parameters of aluminum alloys.展开更多
A precipitation-hardening high-entropy alloy(HEA),(FeCoNi)_(86)Al_(7) Ti_(7),was successfully fabricated using selective laser melting(SLM).Severe segregation of Ti occurred at the boundaries of dislocation cells.Ther...A precipitation-hardening high-entropy alloy(HEA),(FeCoNi)_(86)Al_(7) Ti_(7),was successfully fabricated using selective laser melting(SLM).Severe segregation of Ti occurred at the boundaries of dislocation cells.Therefore,homogenization heat treatment at 1150℃for 0.5 h was performed to alleviate the microsegregation.After homogenization,almost no dislocation cells were left in the grains,and recrystallization occurred as the average grain size increased from 37 to 54μm.Compared with the initial as-built HEA,the ductility of the HEA increases significantly from 29%to 40%,and the strength decreases slightly from 710 to 606 MPa.For further aging,pre-homogenization can decrease the precipitation of ordered L2_(1) phases.Because void has a high propensity to initiate from the matrix/L2_(1) incoherent interface,pre-homogenization reduced the number of weak points,thus considerably improving the plastic deformation ability of the aged HEA by 36%.In addition,the strengthening mechanism has also been analyzed for the aged HEA.It was revealed that the coherent L1_(2)precipitate contributed the most to the increased strength.展开更多
The microstructural evolution of a DC cast 7085 alloy during homogenization treatment was investigated by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry (EDS), differential scan...The microstructural evolution of a DC cast 7085 alloy during homogenization treatment was investigated by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry (EDS), differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The results showed that serious dendritic segregation existed in the as-cast 7085 alloy. Numerous eutectic microstructures and phases were observed at the grain boundary. During homogenization process, eutecticα(Al)+T(AlZnMgCu) microstructure gradually was dissolved into matrix. IntermetallicS(Al2CuMg) phase formed and grew along the eutectic microstructure and disappeared into the matrix completely when it was homogenized at 460 °C for 24 h. It could be found that the evolution of primary eutectic structure of 7085 alloy consisted of three processes, dissolution of eutecticα+T microstructure, phase transformation fromT phase toS phase and the dissolution ofS phase. The optimum homogenization parameter was at 470 °C for 24 h.展开更多
To investigate the effects of homogenizing and aging treatments on the microstructure of an Nb-Ti-Cr-Si based ultrahigh temperature alloy,coupons were homogenized at 1 200-1 500 °C for 24 h,and then aged at 1 000...To investigate the effects of homogenizing and aging treatments on the microstructure of an Nb-Ti-Cr-Si based ultrahigh temperature alloy,coupons were homogenized at 1 200-1 500 °C for 24 h,and then aged at 1 000 °C for 24 h.The results show that the heat-treated alloy is composed of Nb solid solution（Nbss）,（Nb,X）5Si3 and Cr2Nb phases.With the increase of heat-treatment temperature,previous Nbss dendrites transformed into equiaxed grains,and petal-like Nbss/（Nb,X）5Si3 eutectic colonies gradually changed into small（Nb,X）5Si3 particles distributed in Nbss matrix.A drastic change occurred in the morphology of the Laves phase after homogenizing treatment.Previously coarse Cr2Nb blocks dissolved during homogenizing at temperature above 1 300 °C,and then much finer and crowded Cr2Nb flakes precipitated in the Nbss matrix in cooling.Aging treatment at 1 000 °C for 24 h led to further precipitation of fine particles of Laves phase in Nbss matrix and made the difference in concentrations of Ti,Hf and Al in Nbss,（Nb,X）5Si3 and Cr2Nb phases reduced.展开更多
Optical microscopy （OM）, scanning electronic microscopy （SEM） and X-ray diffraction （XRD） were performed to inves- tigate the influence of homogenization on the microstructures of the Mg-7Gd-5Y-1MM （Ce-rich RE...Optical microscopy （OM）, scanning electronic microscopy （SEM） and X-ray diffraction （XRD） were performed to inves- tigate the influence of homogenization on the microstructures of the Mg-7Gd-5Y-1MM （Ce-rich RE）-0.5Zr magnesium alloy. The results indicated that α-Mg, Mg24（GdY）5 phase, Mg5（GdY） phase and Mg12MM phase coexisted together in as-cast alloy; the micro- structures were largely characterized by α-Mg matrix and gray globular or elliptic ball Mg12MM phase, in addition to those with cubic block Mg24（GdY）5 phase after homogenization; the reasonable homogenization regime was maintained at 530 ℃ for 32 h.展开更多
Microstructure evolution during the homogenization heat treatment of an Al?Mg?Si?Fe?Mn(AA6xxx)alloy wasinvestigated using a combination of modelling and experimental studies.The model is based on the CALPHAD-coupledho...Microstructure evolution during the homogenization heat treatment of an Al?Mg?Si?Fe?Mn(AA6xxx)alloy wasinvestigated using a combination of modelling and experimental studies.The model is based on the CALPHAD-coupledhomogenization heat treatment model originally developed for AA3xxx alloys(i.e.,Al?Mn?Fe?Si).In this work,the model wasadapted to the more complex AA6xxx system(Al?Mg?Si?Mn?Fe)to predict the evolution of critical microstructural features suchas the spatial distribution of solute,the type and fraction of constituent particles and dispersoid number density and size distribution.Experiments were also conducted using three direct chill(DC)cast AA6xxx alloys with different Mn levels subjected to varioushomogenization treatments.The resulting microstructures were characterized using a range of techniques including scanning electronmicroscopy,electron microprobe analysis(EPMA),XRD,and electrical resistivity measurements.The model predictions werecompared with the experimental measurements,and reasonable agreement was found.展开更多
To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)stru...To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)structures in the Mg-Gd-Y-Zn-Zr alloy annealed at 300℃~500℃.Various types of metastable LPSO building block clusters were found to exist in alloy structures at different temperatures,which precipitate during the solidification and homogenization process.The stability of Zn/Y clusters is explained by the first principles of density functional theory.The LPSO structure is distinguished by the arrangement of its different Zn/Y enriched LPSO structural units,which comprises local fcc stacking sequences upon a tightly packed plane.The presence of solute atoms causes local lattice distortion,thereby enabling the rearrangement of Mg atoms in the different configurations in the local lattice,and local HCP-FCC transitions occur between Mg and Zn atoms occupying the nearest neighbor positions.This finding indicates that LPSO structures can generate necessary Schockley partial dislocations on specific slip surfaces,providing direct evidence of the transition from 18R to 14H.Growth of the LPSO,devoid of any defects and non-coherent interfaces,was observed separately from other precipitated phases.As a result,the precipitation sequence of LPSO in the solidification stage was as follows:Zn/Ycluster+Mg layers→various metastable LPSO building block clusters→18R/24R LPSO;whereas the precipitation sequence of LPSO during homogenization treatment was observed to be as follows:18R LPSO→various metastable LPSO building block clusters→14H LPSO.Of these,14H LPSO was found to be the most thermodynamically stable structure.展开更多
Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the mic...Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the microstructures become uniform, the long and big primary （Nb,X）sSi3 （X represents Ti and Hf elements） plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the （Nb,X）sSi3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution （Nbss） in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 μm/s and then heat-treated at （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, which is 72.8 % higher than that under DS condition.展开更多
The influence of Mo content on the microstructure and mechanical properties of the Ti?45Al?5Nb?xMo?0.3Y(x=0.6,0.8,1.0,1.2)alloys was studied using small ingots produced by non-consumable electrode argon arc melting.Th...The influence of Mo content on the microstructure and mechanical properties of the Ti?45Al?5Nb?xMo?0.3Y(x=0.6,0.8,1.0,1.2)alloys was studied using small ingots produced by non-consumable electrode argon arc melting.The results show that smallquantities ofβphase are distributed alongγ/α2lamellar colony boundaries as discontinuous network in the TiAl alloys owing to thesegregation of Mo element.Theγphase forms in the interdentritic microsegregation area when the Mo addition exceeds0.8%.Theβandγphases can be eliminated effectively by subsequent homogenization heat treatment at the temperature above Tα.The evolutionof the strength,microhardness and ductility at different Mo contents under as-cast and as-homogenization treated conditions wasanalyzed,indicating that excessive Mo addition is prone to cause the microsegregation,thus decreasing the strength andmicrohardness obviously,which can be improved effectively by subsequent homogenization heat treatment.展开更多
An Al-Mn-Fe-Si model alloy was subjected to two homogenization treatments, to achieve materials with different levels of Mn in solid solution and dispersoid densities, followed by cold rolling and back-annealing. Char...An Al-Mn-Fe-Si model alloy was subjected to two homogenization treatments, to achieve materials with different levels of Mn in solid solution and dispersoid densities, followed by cold rolling and back-annealing. Characterization of homogenization and deformation structures with respect to the effect of different microchemistries and strains on the structures was performed. Time-temperature-transformation （TTT） diagram with respect to precipitation and recrystallisation as a basis for analysis of the degree of concurrent precipitation was established. The TTT-diagram shows a strong effect of Mn concentration in solid solution and dispersoid density on the softening behavior. Recrystallization which finishes without the effect of concurrent precipitation results in an even, fine and equiaxed grain structure. Precipitation prior to or during recrystallization （concurrent） does retard the softening kinetics and leads to a coarse grain structure. However, the effect also depends on the duration of recrystallization and amount of precipitation. Recrystallization proceeding over a long time combined with a large amount of concurrent precipitation has a strong effect, otherwise the effect will be limited. Pre-existing fine and dense dispersoids （mean size 0.1 μm） before back-annealing do also lead to a coarse grain structure after recrystallization no matter whether additional concurrent precipitation occurs.展开更多
Stress relaxation resistance is one of the most significant properties that are critical to the service life of the fasteners.In this study,the stress relaxation behavior of a Nb-stabilized austenitic stainless steel ...Stress relaxation resistance is one of the most significant properties that are critical to the service life of the fasteners.In this study,the stress relaxation behavior of a Nb-stabilized austenitic stainless steel was investigated.It was revealed that the homogenization treatment at 1250℃could make more primary NbC particles dissolved back into the matrix and consequently get a great number of nano-sized secondary NbC carbides.Therefore,the stress relaxation resistance will be enhanced due to the effective pinning of such higher density of nano-sized secondary NbC carbides on the dislocation movement.展开更多
The microstructure and tensile properties of the as-cast and solution treatment Mg-4.5Zn-1Y-xNd-0.5Zr （x=0, 1 wt.%, 2 wt.%, 3 wt.%） alloys were investigated. The results showed that the microstructure of Mg-4.5Zn-1Y...The microstructure and tensile properties of the as-cast and solution treatment Mg-4.5Zn-1Y-xNd-0.5Zr （x=0, 1 wt.%, 2 wt.%, 3 wt.%） alloys were investigated. The results showed that the microstructure of Mg-4.5Zn-1Y-0.5Zr alloy consisted of α-Mg, Zn-Zr, W （Mg3Y2Zn3） and I （Mg3YZn6） phases. With the addition of Nd, I-phase disappeared and Mg3Y2Zn3 phase changed into Mg3（Nd,Y）2Zn3 phase. When the content of Nd reached 3 wt.%, T phase, i.e., ternary Mg-Zn-Nd phase, formed. In addition, with the increase of Nd content in the alloys, the secondary dendritic arm spacing decreased, while the amount of intermetallic phases increased. For as-cast Mg-4.5Zn-1Y-xNd-0.5Zr alloys, after solution treatment, microsegregation was eliminated and the shape of eutectic structure of α-Mg＋W transformed from lamellar into spherical. The tensile strength and elongation of Mg-4.5Zn-1Y- 3Nd-0.5Zr alloy were increased from 219.2 MPa and 11.0% to 247.5 MPa and 20.0%, respectively.展开更多
基金supported by the National Key Research and Development Program of China(No.2022YFB3400142)the National Natural Science Foundation of China(Nos.52174356,52022017,51927801,51971051,51901034 and U22A20174)+3 种基金the Science and Technology Plan Project of Liaoning Province(Nos.2022010005-JH6/1001 and 2022JH2/1013)the Innovation Foundation of Science and Technology of Dalian(Nos.2020JJ25CY002 and 2020J12GX037)the Major Science and Technology Projects of Longmen Laboratory(No.231100220400)the Fundamental Research Funds for the Central Universities.
文摘Obtaining an appropriate grain size is crucial for Al alloys or Al matrix composites prior to processing,as it significantly influences the mechanical properties of components and workability during the manufacturing process.TiB_(2)particles are exceptional grain refiners in Al and serve as excellent reinforcement particles for particulate-reinforced aluminum matrix composites.However,the optimal particle content for achieving excellent refinement and strengthening effects depends on the matrix composition and requires further investigation.Additionally,homogenization is essential for mitigating the element segregation in the ingot.Although it is anticipated that adding suitable particles can effectively inhibit undesired grain growth during homogenization,comprehensive investigations on this aspect are currently lacking.Therefore,TiB_(2)/2219Al matrix composites with varying reinforcement contents(0,1,3,5 wt%)were fabricated through traditional casting followed by homogenization treatment to address these research gaps.The effects of reinforcement content and homogenization treatment on the microstructure and mechanical properties of in-situ TiB_(2)/2219Al composites were investigated.The results demonstrate a gradual strengthening of the refining effect with increasing particle concentration.Moreover,composites containing 3 wt%TiB_(2)particles exhibit superior comprehensive mechanical properties in both as-cast and homogenized state.Additionally,potential orientation relationships are observed and calculated between undissolved Al_(2)Cu eutectic phase and submicron or nanometer-sized TiB_(2)particles,resulting in a mixture structure with enhanced bonding strength.This mixture structure is continuously distributed along grain boundaries during solidification,forming a three-dimensional cellular network that acts as primary retarding forces for grain growth during homogenization.Furthermore,the established homogenization kinetic equations were further utilized to analyze the correlation between homogenization time and grain size,as well as the influence of homogenization temperature.
基金This work was supported by the Major State Basic Research Development Program of China(No.2013CB632203)National Key Technology R&D Program of China(2011BAE22B03)+3 种基金(2012BAF09B01)National Natural Science Foundation of China(51074207)Chinese Postdoctoral Science Foundation(2012M520634)the Fundamental Research Foundation of Central Universities(Grant Nos.N120509002 and N120309003).
文摘Mge3Lie0.4Zr alloys containing RE elements(Gd,La,Nd)(Mge3LieREe0.4Zr alloys)are investigated to reveal the influence of homogenization treatment on microstructures and distributions of RE,Zr elements.It is found that 300C24 h homogenization treatment shows better improvement on the microstructure including the refinement of grain size,the dispersion of cellular dendrite and low melting point particles.Before treatment,La and Nd segregate effectively at grain boundary and Zr segregates in the form of precipitates.Homogenization treatment induces the reduction of RE segregation.However,the segregation of Zr in precipitates cannot be abated due to the relatively low diffusion rate compared with RE elements.
基金the National Key Research and Development Program of China(Grant No.2017YFA0403804)the National Natural Science Foundation of China(Grant No.51425402)。
文摘Microstructural improvement of Al-Cu-Li alloys with high Li content plays a critical role for the acquisition of excellent mechanical properties and ultra-low density.In this regard,the Al-Cu-Li alloy castings with high Li content from 1.5 wt.%to 4.5 wt.%were prepared by near-rapid solidification,followed by two-stage homogenization treatment(490℃/16 h and 530℃/16 h).The microstructural evolution and solidification behavior of the as-cast and homogenized alloys with different Li contents were systematically studied by combining experiments with calculations by Pandat software.The results indicate that with the increase of Li content,the grain sizes decrease,the solution ability of Cu in the matrixα-Al phase increases,while the content of secondary dendrites increases and the precipitated phases change from low melting point phases to high melting point phases under the near-rapid solidification.Additionally,by the coupling of near-rapid solidification and two-stage homogenization,the metastable precipitated phases(Al7Cu4Li and AlCu3)can be dissolved effectively in the alloys with Li content of 1.5 wt.%-2.5 wt.%;moreover,the stable precipitated phases(Al6CuLi3 and Al2CuLi)uniformly distribute at the grain boundaries in the alloys with Li content of 3.5 wt.%-4.5 wt.%.As a result,the refined and homogenized microstructure can be obtained.
文摘A new point of view on the homogenization treatment has been proposed.It is supposed that a little liquid in the alloy may promote the homogenization process in some aspects and reduce the time for eliminating the Laves-phase in alloy GH169.The microprocess of the elimination of Laves-phase in the case of a little liquid existing in the alloy has also been described.
文摘In comparison with the homogenization treatment without an electric field prior to the same solid solution and aging treatment, the homogenization treatment in an electric field increases the hardness and strength of 1420 Al Li alloy, but somewhat decreases the elongation of the alloy. Moreover, the elongation of the alloy increases with the homogenization temperature in an electric field increasing. TEM observation showed that the homogenization treatment in an electric field can accelerate the dissolution of the coarse particles of second phase on the grain boundary as well as make δ′phase precipitated in subsequent aging process finer and more numerous.
基金financially supported by the National Key Basic Research Development Program of China(No.2012CB619504)
文摘Abstract The microstructure evolution and composition distribution of as-cast and homogenized 2099 aluminumlithium （Al-Li） alloy were studied by optical microscopy （OM）, differential thermal analysis （DTA）, scanning electron microscopy （SEM）, energy dispersive spectrometry （EDS）, area and line scanning, X-ray diffraction （XRD）, and Vickers microhardness test methods. The results show that severe dendrite exists in the as-cast alloy. Cu, Zn, Mn, and Mg distribute unevenly from the grain boundary to inside. The low-melting point nonequilibrium eutectic phases dis- solve into the matrix during the first-step homogenization, whereas the melting point of residual eutectic phases is elevated. After the second-step homogenization, most of the remaining eutectic phases dissolve into the matrix, except a small amount of A1-Cu-Fe phases. An optimized homogenization process of the 2099 A1-Li alloy is developed （515℃ - 18 h ＋ 525℃ - 16 h）, which shows a good agreement with the homogenization kinetic analysis results.
文摘For 2091 Al-Li alloy, the volume fraction of second phase particles is greatly determined by the homogenization temperature and homogenization time under an electric field and the ductility of the alloy is determined by the fraciton of second phase particles. The combined homogenization treatment shortens the homogenization time, reduces the loss ofLi content and increases the ductity of the alloy.
文摘Homogenization treatment under an electric field increases the distributive homogeneity of the T1 precipitation and improves the yield strength of 2091 Al-Li alloy.
文摘Both of chromium and zinc could appear as either minor impurities or alloying elements in recycled and commercial aluminum alloys, and they could have detrimental effects on the final product properties if not controlled in an appropriate way. A Kampmann-Wagner numerical modeling approach, built on the basis of computational thermodynamics and diffusion kinetics, is employed to investigate the effect of these two minor impurities on dispersoids precipitation during homogenization heat treatment of AA3xxx alloys. The simulation results obtained from different simulation set-ups were compared. The aim is to demonstrate that the modeling approach has the potential to guide the design or optimization of the chemical compositions and heat treatment parameters of aluminum alloys.
基金financially supported by the National Natural Science Foundation of China (No.51971149)the Science and Technology Innovation Commission of Shenzhen (No.KQJSCX20180328095612712)
文摘A precipitation-hardening high-entropy alloy(HEA),(FeCoNi)_(86)Al_(7) Ti_(7),was successfully fabricated using selective laser melting(SLM).Severe segregation of Ti occurred at the boundaries of dislocation cells.Therefore,homogenization heat treatment at 1150℃for 0.5 h was performed to alleviate the microsegregation.After homogenization,almost no dislocation cells were left in the grains,and recrystallization occurred as the average grain size increased from 37 to 54μm.Compared with the initial as-built HEA,the ductility of the HEA increases significantly from 29%to 40%,and the strength decreases slightly from 710 to 606 MPa.For further aging,pre-homogenization can decrease the precipitation of ordered L2_(1) phases.Because void has a high propensity to initiate from the matrix/L2_(1) incoherent interface,pre-homogenization reduced the number of weak points,thus considerably improving the plastic deformation ability of the aged HEA by 36%.In addition,the strengthening mechanism has also been analyzed for the aged HEA.It was revealed that the coherent L1_(2)precipitate contributed the most to the increased strength.
基金Project(2012CB619503)supported by the National Basic Research Program of ChinaProject(2013AH100055)supported by the Special Foundation for Science and Technology Innovation of Foshan,China
文摘The microstructural evolution of a DC cast 7085 alloy during homogenization treatment was investigated by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry (EDS), differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The results showed that serious dendritic segregation existed in the as-cast 7085 alloy. Numerous eutectic microstructures and phases were observed at the grain boundary. During homogenization process, eutecticα(Al)+T(AlZnMgCu) microstructure gradually was dissolved into matrix. IntermetallicS(Al2CuMg) phase formed and grew along the eutectic microstructure and disappeared into the matrix completely when it was homogenized at 460 °C for 24 h. It could be found that the evolution of primary eutectic structure of 7085 alloy consisted of three processes, dissolution of eutecticα+T microstructure, phase transformation fromT phase toS phase and the dissolution ofS phase. The optimum homogenization parameter was at 470 °C for 24 h.
基金Project (51071124) supported by the National Natural Science Foundation of ChinaProject (20096102110012) supported by the Ministry of Education, China Project (07-TP-2008) supported by the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,China
文摘To investigate the effects of homogenizing and aging treatments on the microstructure of an Nb-Ti-Cr-Si based ultrahigh temperature alloy,coupons were homogenized at 1 200-1 500 °C for 24 h,and then aged at 1 000 °C for 24 h.The results show that the heat-treated alloy is composed of Nb solid solution（Nbss）,（Nb,X）5Si3 and Cr2Nb phases.With the increase of heat-treatment temperature,previous Nbss dendrites transformed into equiaxed grains,and petal-like Nbss/（Nb,X）5Si3 eutectic colonies gradually changed into small（Nb,X）5Si3 particles distributed in Nbss matrix.A drastic change occurred in the morphology of the Laves phase after homogenizing treatment.Previously coarse Cr2Nb blocks dissolved during homogenizing at temperature above 1 300 °C,and then much finer and crowded Cr2Nb flakes precipitated in the Nbss matrix in cooling.Aging treatment at 1 000 °C for 24 h led to further precipitation of fine particles of Laves phase in Nbss matrix and made the difference in concentrations of Ti,Hf and Al in Nbss,（Nb,X）5Si3 and Cr2Nb phases reduced.
基金Project supported by National Natural Science Foundation of China(51204020)National Basic Research Program of China(2013CB632202,2013CB632205)
文摘Optical microscopy （OM）, scanning electronic microscopy （SEM） and X-ray diffraction （XRD） were performed to inves- tigate the influence of homogenization on the microstructures of the Mg-7Gd-5Y-1MM （Ce-rich RE）-0.5Zr magnesium alloy. The results indicated that α-Mg, Mg24（GdY）5 phase, Mg5（GdY） phase and Mg12MM phase coexisted together in as-cast alloy; the micro- structures were largely characterized by α-Mg matrix and gray globular or elliptic ball Mg12MM phase, in addition to those with cubic block Mg24（GdY）5 phase after homogenization; the reasonable homogenization regime was maintained at 530 ℃ for 32 h.
基金support from Rio Tinto AluminiumNSERC are gratefully acknowledged
文摘Microstructure evolution during the homogenization heat treatment of an Al?Mg?Si?Fe?Mn(AA6xxx)alloy wasinvestigated using a combination of modelling and experimental studies.The model is based on the CALPHAD-coupledhomogenization heat treatment model originally developed for AA3xxx alloys(i.e.,Al?Mn?Fe?Si).In this work,the model wasadapted to the more complex AA6xxx system(Al?Mg?Si?Mn?Fe)to predict the evolution of critical microstructural features suchas the spatial distribution of solute,the type and fraction of constituent particles and dispersoid number density and size distribution.Experiments were also conducted using three direct chill(DC)cast AA6xxx alloys with different Mn levels subjected to varioushomogenization treatments.The resulting microstructures were characterized using a range of techniques including scanning electronmicroscopy,electron microprobe analysis(EPMA),XRD,and electrical resistivity measurements.The model predictions werecompared with the experimental measurements,and reasonable agreement was found.
基金financially funded by Natural Science Basic Research Program of Shaanxi(grant number 2022JM-239)Key Research and Development Project of Shaanxi Provincial(grant number 2021LLRH-05–08)。
文摘To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)structures in the Mg-Gd-Y-Zn-Zr alloy annealed at 300℃~500℃.Various types of metastable LPSO building block clusters were found to exist in alloy structures at different temperatures,which precipitate during the solidification and homogenization process.The stability of Zn/Y clusters is explained by the first principles of density functional theory.The LPSO structure is distinguished by the arrangement of its different Zn/Y enriched LPSO structural units,which comprises local fcc stacking sequences upon a tightly packed plane.The presence of solute atoms causes local lattice distortion,thereby enabling the rearrangement of Mg atoms in the different configurations in the local lattice,and local HCP-FCC transitions occur between Mg and Zn atoms occupying the nearest neighbor positions.This finding indicates that LPSO structures can generate necessary Schockley partial dislocations on specific slip surfaces,providing direct evidence of the transition from 18R to 14H.Growth of the LPSO,devoid of any defects and non-coherent interfaces,was observed separately from other precipitated phases.As a result,the precipitation sequence of LPSO in the solidification stage was as follows:Zn/Ycluster+Mg layers→various metastable LPSO building block clusters→18R/24R LPSO;whereas the precipitation sequence of LPSO during homogenization treatment was observed to be as follows:18R LPSO→various metastable LPSO building block clusters→14H LPSO.Of these,14H LPSO was found to be the most thermodynamically stable structure.
基金Project(51071124)supported by the National Natural Science Foundation of ChinaProject(CX200605)supported by the Doctorate Foundation of Northwestern Polytechnical University,ChinaProject(20096102110012)supported by a Special Research Fund for Doctoral Disciplines in Colleges and Universities of the Ministry of Education,China
文摘Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the microstructures become uniform, the long and big primary （Nb,X）sSi3 （X represents Ti and Hf elements） plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the （Nb,X）sSi3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution （Nbss） in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 μm/s and then heat-treated at （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, which is 72.8 % higher than that under DS condition.
基金Project(51275132)supported by the National Natural Science Foundation of ChinaProject(2008RFQXG040)supported by the Youth Science and Technology Project of Harbin,China
文摘The influence of Mo content on the microstructure and mechanical properties of the Ti?45Al?5Nb?xMo?0.3Y(x=0.6,0.8,1.0,1.2)alloys was studied using small ingots produced by non-consumable electrode argon arc melting.The results show that smallquantities ofβphase are distributed alongγ/α2lamellar colony boundaries as discontinuous network in the TiAl alloys owing to thesegregation of Mo element.Theγphase forms in the interdentritic microsegregation area when the Mo addition exceeds0.8%.Theβandγphases can be eliminated effectively by subsequent homogenization heat treatment at the temperature above Tα.The evolutionof the strength,microhardness and ductility at different Mo contents under as-cast and as-homogenization treated conditions wasanalyzed,indicating that excessive Mo addition is prone to cause the microsegregation,thus decreasing the strength andmicrohardness obviously,which can be improved effectively by subsequent homogenization heat treatment.
基金Project (KMB:193179/I40) supported by the Research Council of Norway
文摘An Al-Mn-Fe-Si model alloy was subjected to two homogenization treatments, to achieve materials with different levels of Mn in solid solution and dispersoid densities, followed by cold rolling and back-annealing. Characterization of homogenization and deformation structures with respect to the effect of different microchemistries and strains on the structures was performed. Time-temperature-transformation （TTT） diagram with respect to precipitation and recrystallisation as a basis for analysis of the degree of concurrent precipitation was established. The TTT-diagram shows a strong effect of Mn concentration in solid solution and dispersoid density on the softening behavior. Recrystallization which finishes without the effect of concurrent precipitation results in an even, fine and equiaxed grain structure. Precipitation prior to or during recrystallization （concurrent） does retard the softening kinetics and leads to a coarse grain structure. However, the effect also depends on the duration of recrystallization and amount of precipitation. Recrystallization proceeding over a long time combined with a large amount of concurrent precipitation has a strong effect, otherwise the effect will be limited. Pre-existing fine and dense dispersoids （mean size 0.1 μm） before back-annealing do also lead to a coarse grain structure after recrystallization no matter whether additional concurrent precipitation occurs.
基金supported by the LingChuang Research Project of China National Nuclear Corporation,the Natural Science Foundation of Liaoning Province(2023-MS-019)the project of"Novel corrosion-resistant low-active 1000 MPa Grade high strength steel for water resources and electric engineering"from Guangdong Polytechnic of Water Resources and Electric Engineering.
文摘Stress relaxation resistance is one of the most significant properties that are critical to the service life of the fasteners.In this study,the stress relaxation behavior of a Nb-stabilized austenitic stainless steel was investigated.It was revealed that the homogenization treatment at 1250℃could make more primary NbC particles dissolved back into the matrix and consequently get a great number of nano-sized secondary NbC carbides.Therefore,the stress relaxation resistance will be enhanced due to the effective pinning of such higher density of nano-sized secondary NbC carbides on the dislocation movement.
基金supported by National Key Technology R&D Program(2011BAE22B01-1)the National Basic Research Program of China(2013CB632205)
文摘The microstructure and tensile properties of the as-cast and solution treatment Mg-4.5Zn-1Y-xNd-0.5Zr （x=0, 1 wt.%, 2 wt.%, 3 wt.%） alloys were investigated. The results showed that the microstructure of Mg-4.5Zn-1Y-0.5Zr alloy consisted of α-Mg, Zn-Zr, W （Mg3Y2Zn3） and I （Mg3YZn6） phases. With the addition of Nd, I-phase disappeared and Mg3Y2Zn3 phase changed into Mg3（Nd,Y）2Zn3 phase. When the content of Nd reached 3 wt.%, T phase, i.e., ternary Mg-Zn-Nd phase, formed. In addition, with the increase of Nd content in the alloys, the secondary dendritic arm spacing decreased, while the amount of intermetallic phases increased. For as-cast Mg-4.5Zn-1Y-xNd-0.5Zr alloys, after solution treatment, microsegregation was eliminated and the shape of eutectic structure of α-Mg＋W transformed from lamellar into spherical. The tensile strength and elongation of Mg-4.5Zn-1Y- 3Nd-0.5Zr alloy were increased from 219.2 MPa and 11.0% to 247.5 MPa and 20.0%, respectively.
