The present study aims to clarify the influence of Mo addition onα-dispersoids precipitation,associ-ated recrystallization resistance and mechanical performance of Mn-containing Al-Mg-Si-Cu alloys.Re-sults reveal tha...The present study aims to clarify the influence of Mo addition onα-dispersoids precipitation,associ-ated recrystallization resistance and mechanical performance of Mn-containing Al-Mg-Si-Cu alloys.Re-sults reveal that joint addition of Mn and Mo as dispersoid-forming elements dramatically enhancesα-dispersoids precipitation,achieving a fivefold increment in number density and a 26.5%reduction in size compared to the alloy containing only Mn addition.Additionally,the width of dispersoid-free zones is reduced from appropriately 5μm to<1μm.A portion of theα-Al(Mn,Mo,Fe)Si dispersoids exhibits the quasicrystal characteristics,forming coherent interfaces with the aluminum matrix.In compassion,α-Al(Mn,Fe)Si dispersoids transformed entirely into a simple cubic structure,being partially coherent with the matrix.The improvements inα-dispersoids precipitation contribute to higher pinning force on moving boundaries,resulting in superior resistance to recrystallization of the alloy.Consequently,an ideal fibrous microstructure is retained in alloy co-alloyed with Mn and Mo after solution treatment.Whereas,alloys containing only Mn or Mo show complete recrystallization.A superior balance between strength and ductility is achieved for 0.7Mn0.3Mo alloy,attributed to the increased work hardening capacity and suppression of dynamic recovery.展开更多
Semi-quantitative electron probe microanalysis （EPMA） mapping, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） were employed to study the effect of one-step and two-step treatments ...Semi-quantitative electron probe microanalysis （EPMA） mapping, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） were employed to study the effect of one-step and two-step treatments on the Zr distribution and Al3Zr dispersoid characteristics in as-cast commercial AA7150 aluminum alloy. It is shown that the Zr concentration in the dendrite centre regions is higher than that near the dendrite edges in the as-cast condition, and that homogenization at 460 °C for 20 h is insufficient to remove these concentration gradients. After homogenizing at 460-480 °C, a high number density of larger dispersoids can be observed in dendrite centre regions but not near dendrite edges. Furthermore, the dispersoid size increases with increasing the temperature during both one-step and two-step homogenization treatments.展开更多
The microstructural evolution of AA6061 and Mn-bearing Al-Mg-Si-Cu alloys was studied by compression tests that were carried out between 300 and 500 °C with a wide range of strain rates. Compared to the AA6061 al...The microstructural evolution of AA6061 and Mn-bearing Al-Mg-Si-Cu alloys was studied by compression tests that were carried out between 300 and 500 °C with a wide range of strain rates. Compared to the AA6061 alloy, the large amount of α-Al(MnFeCr)Si dispersoids in the Mn-bearing alloy yielded a significant increase in the flow stress under all deformation conditions. The effects of the deformation parameters on the evolution of the microstructure were studied using electronic backscatter diffraction measurements. The predominant softening mechanism of both alloys was dynamic recovery. The presence of α dispersoids in Mn-bearing alloys effectively refined the size of substructures with misorientation angles in the range of 2°-5°, which retarded the dynamic recovery. To predict the subgrain size under various deformation conditions, the threshold stresses that were caused by α dispersoids were calculated by the modified Orowan equation and incorporated into a conventional constitutive equation. The subgrain size that was predicted by the modified constitutive equation showed satisfactory agreement with the experimental measurements.展开更多
A NiAI-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAI-HfC during milling can be attributed to two chemical reacti...A NiAI-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAI-HfC during milling can be attributed to two chemical reactions: Ni+AI→NiAI+△H; Hf+C→HfC+△H, induced by mechanical collision in a certain period of time, which results in an abrupt exothemic reaction. Hot pressing (HP) and hot isostatic pressing (HIP) have been used to make the NiAI-10HfC compacts near fully dense. Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAI-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAI-10TiB2 composite. In the meantime, yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.展开更多
The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mecha...The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.展开更多
Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys(ODS-HEAs)were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-s...Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys(ODS-HEAs)were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties.Systematic micro structural analysis was carried out by X-ray diffraction(XRD),electron backscattered diffraction(EBSD),high-resolution transmission electron microscopy(HRTEM),atom probe tomography(APT),and small-angle neutron scattering(SANS).Cryo-milled powder analysis,grain structure evolution after spark plasma sintering,dispersoid characteristics,and matrix/dispersoid interface structure analysis of the insitu and ex-situ dispersoids within the high-entropy alloy(HEA)matrix were performed.The in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical composition,leading to an increase in the Zener pinning forces on the grain boundary movement.ODS-HEA with in-situ oxide dispersoids enhanced the formation of ultrafine-grained structures with an average diameter of 330 nm at a sintering temperature of 1173 K.This study shows that the Y pre-alloying method is efficient in achieving fine coherent dispersoids with an ultra fine-grained structure,resulting in an enhancement of the tensile strength of the CoCrFeMnNi HEA.展开更多
The dynamic recrystallization behavior of 7085 aluminum alloy during hot compression at various temperatures （573？723 K） and strain rates （0.01-10 s^-1） was studied by electron back scattered diffraction （EBSD...The dynamic recrystallization behavior of 7085 aluminum alloy during hot compression at various temperatures （573？723 K） and strain rates （0.01-10 s^-1） was studied by electron back scattered diffraction （EBSD）, electro-probe microanalyzer （EPMA） and transmission electron microscopy （TEM）. It is shown that dynamic recovery is the dominant softening mechanism at high Zener？Hollomon （Z） values, and dynamic recrystallization tends to appear at low Z values. Hot compression with ln Z=24.01 （723 K, 0.01 s？1） gives rise to the highest fraction of recrystallization of 10.2%. EBSD results show that the recrystallized grains are present near the original grain boundaries and exhibit similar orientation to the deformed grain. Strain-induced boundary migration is likely the mechanism for dynamic recrystallization. The low density of Al3Zr dispersoids near grain boundaries can make contribution to strain-induced boundary migration.展开更多
The effect of homogenization time on quench sensitivity of a cast 7085 aluminum alloy was investigated by means of end-quenching test, optical microscope （OM）, scanning electron microscope （SEM） and transmission e...The effect of homogenization time on quench sensitivity of a cast 7085 aluminum alloy was investigated by means of end-quenching test, optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscope （TEM）. The results show that with the increase of homogenization time from 48 h to 384 h, quench sensitivity increased slightly as the largest difference in the hardness was increased from 5.2% to 6.9% in the end-quenched and aged specimens. Prolonging homogenization had little effect on the grain structure, but improved the dissolution of soluble T phase and resulted in larger Al3Zr dispersoids with a low number density. Some small quench-induced η phase particles on Al3Zr dispersoids were observed inside grains during slow quenching, which decreased hardness after subsequent aging. The change in the character of Al3Zr dispersoids exerted slight influence on quench sensitivity.展开更多
The effect of grain structure on quench sensitivity of an Al-Zn-Mg-Cu-Cr alloy was investigated by hardness testing, optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscop...The effect of grain structure on quench sensitivity of an Al-Zn-Mg-Cu-Cr alloy was investigated by hardness testing, optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The results show that with the decrease of quenching rate from 960 ℃/s to 2 ℃/s, the hardness after aging is decreased by about 33% for the homogenized and solution heat treated alloy（H-alloy） with large equiaxed grains and about 43% for the extruded and solution heat treated alloy（E-alloy） with elongated grains and subgrains. Cr-containing dispersoids make contribution to about 33% decrement in hardness of the H-alloy due to slow quenching; while in the E-alloy, the amount of（sub） grain boundaries is increased by about one order of magnitude, which leads to a further 10% decrement in hardness due to slow quenching and therefore higher quench sensitivity.展开更多
Introducing trace rare earth elements(REEs)into L12 dispersoids(Al_(3)(Sc,Zr))can markedly enhance the mechanical properties of aluminum alloys,However,excessive amounts may cause adverse impacts.This study explores T...Introducing trace rare earth elements(REEs)into L12 dispersoids(Al_(3)(Sc,Zr))can markedly enhance the mechanical properties of aluminum alloys,However,excessive amounts may cause adverse impacts.This study explores Ti and Cu as transition metal candidates for Al-Zn-Mg-X alloys,aiming to enhance mechanical properties,elucidate microstructure evolution,and identify optimization mechanisms.The addition of Ti to the Al-6.8Zn-2.2Mg-0.2Sc-0.1Zr(AS)alloy results in a notable refinement of the grain size,reducing it from 170μm to 47μm.This refinement of Ti can be attributed to its role as a nucleating agent during solidification,its promotion of dynamic recrystallization during hot-rolling,and its inhibi-tion of static recrystallization during solid solution treatment stage.The formation of a new Ti-containing layer,which substitutes Al sites adjacent to Al_(3)Zr dispersoids,leads to an increase in the phase size from 16 nm to 25 nm.In addition,Cu significantly decreases the aging activation energy of the GP zone andη'precipitate,thereby facilitating their nucleation and growth,which enhances the mechanical proper-ties of the alloy.Ti markedly improves the hardness and strength of the alloy through grain refinement strengthening,Orowan strengthening and solid solution strengthening,while Cu predominantly enhances solid solution strengthening.Our findings suggest that Ti and Cu microalloying profoundly influences the properties and the microstructures of Al-Zn-Mg-X alloys across various scales offering a promising ap-proach for the advancement of high-performance aluminum alloys.展开更多
The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscop...The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were employed to elucidate the microstructural parameters of these two strengthening phases.The results show that the microstructural heterogeneity can be triggered by the absence of homogenization,resulting in the presence of dispersoid-free zones(DFZs)and dispersoid zones(DZs),in conjunction with bimodalβ″precipitates.Further analytical calculations,from the strengthening model,clarify that the strategically dispersedα-Al(Fe,Mn)Si andβ″particles create“soft”and“hard”domains within the alloy,resultantly improving the mechanical properties.展开更多
Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BC...Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3μm,and small amounts(<4 vol.%)of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27%and 87%at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm^(3),while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50%of the yield strength of the AlxCrNbVMo RHEAs.展开更多
In this paper,a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process.The dissolution of the second...In this paper,a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process.The dissolution of the secondary particles and the diffusion of solute were studied based on microstructure characterization and kinetics analysis.The precipitation behavior of Al3Zr dispersoids and its influence on recrystallization were investigated by using TEM and EBSD characterization.It was found that the large-size particles at triangular grain boundaries dissolve slower than the intragranular phases and other grain boundary phases.The required homogenization time depends on the dissolution processes of the large-size phases at grain boundaries.The size of grain boundary phases in the spray deposited alloy is much smaller than that in the as-cast alloy,so the homogenization time required for the spray deposited alloy is significantly shorter.Two-stage and ramp heating homogenization processes can promote the precipitation of Al3Zr dispersoids in the two alloys.In the spray deposited alloy,the dispersoids tend to precipitate at the positions of the T1 plates dissolved,which causes a non-uniform distribution and decreases the recrystallization resistance of the alloy.However,the distribution of the dispersoids in the as-cast alloy is more uniform after the homogenization,which brings a stronger inhibition on the recrystallization.According to the microstructural characterization and kinetics analysis results,it can be concluded that the homogenization with a slow ramp heating is suitable for the two 2195 alloys,and a shorter holding time can be used for spray deposited alloy,e.g.12 h at 500℃,while the holding time for the as-cast alloy is no less than 35 h at 500℃.展开更多
The nucleation and precipitation of Mn-containing dispersoids in an Al-Mg-Si-Mn alloy （6082） have been studied by optical microscopy,EPMA （electron probe microanalysis） and TEM （transmission electron microscopy）...The nucleation and precipitation of Mn-containing dispersoids in an Al-Mg-Si-Mn alloy （6082） have been studied by optical microscopy,EPMA （electron probe microanalysis） and TEM （transmission electron microscopy）.The influence of Mn-containing dispersoids on the recrystallization behavior was also investigated.The size and distribution of dispersoids were strongly affected by both the homogenization process and the alloying element distribution formed in the direct chill cast procedure.The Mn-containing dispersoids were observed to nucleate preferentially on the β-Mg 2 Si phase and to be aligned along the 〈100〉 direction of the matrix.After cold deformation,the morphology of dispersoids greatly influences the recrystallization and grain growth behavior in the annealing process.展开更多
A significant size effect is found in the Al3 Sc dispersoid-mediated precipitation in an Al-Mg-Si-Sc alloy.When the Al3 Sc dispersoid size smaller than about 40 nm,β " precipitates nucleate directly on the coher...A significant size effect is found in the Al3 Sc dispersoid-mediated precipitation in an Al-Mg-Si-Sc alloy.When the Al3 Sc dispersoid size smaller than about 40 nm,β " precipitates nucleate directly on the coherent dispersoids and grow by sacrificing the latter.While the dispersoid size greater than^40 nm,Q' and U2 phases are additionally produced that nucleate on the dislocations induced by the semi-/incoherent dispersoids.Mechanical and electrical properties are highly sensitive to the Al3 Sc dispersoid-tuned precipitation.The co-precipitation of β",Q' and U2 phases leads to an obvious improvement in hardness and simultaneously in electrical conductivity.展开更多
The tensile and fatigue behavior of a dispersoid strengthened, powder metallurgy Al-Fe-V-Si alloy at ambient and elevated temperatures was investigated. The results show that the strength and ductility of the alloy de...The tensile and fatigue behavior of a dispersoid strengthened, powder metallurgy Al-Fe-V-Si alloy at ambient and elevated temperatures was investigated. The results show that the strength and ductility of the alloy decrease significantly with increasing temperature and decreasing strain rate. Micro-structural examinations reveal that this change in mechanical behavior with increasing temperature is related to the mode of deformation of the alloy. Further observations show that localized shear deformation is responsible for the losses in both strength and ductility of the alloy at elevated temperature.展开更多
Therecent developments in elevated temperature ( ET) aluminum alloys prepared by therapidsolidification / powder metallurgy ( RS P/ M) process were reviewed briefly. TheRS P/ METaluminum alloyscan beclassified as(a)...Therecent developments in elevated temperature ( ET) aluminum alloys prepared by therapidsolidification / powder metallurgy ( RS P/ M) process were reviewed briefly. TheRS P/ METaluminum alloyscan beclassified as(a) the aluminum transition metaltype, such as Al Fe, Al Cr, Al Ti, Al Zrsystem alloys,etc.,and (b) thealuminum rareearth elementtype,such as Al Y, Al Nd system alloys,etc. Among them ,the Al Fe and Al Ti system alloysarethe most attractive, which possessthe potentialto replacethetitanium alloy partson aircraft,engines,etc.,fortheuseattemperaturesrangingfrom 200 315℃. Theproblemsin applicationsfor RS P/ M ETaluminum alloys werealso discussed .展开更多
Al-Mg-Zn-based alloys are newly developed high-performance age-hardenable 5xxx series alloys.How-ever,they suffer from poor surface quality due to the Lüders bands and the Portevin-Le-Chatelier(PLC)effect during ...Al-Mg-Zn-based alloys are newly developed high-performance age-hardenable 5xxx series alloys.How-ever,they suffer from poor surface quality due to the Lüders bands and the Portevin-Le-Chatelier(PLC)effect during plastic deformation,and the elongation(EL)is impaired by the large constituent particles.In this work,various homogenization regimes combined with minor addition of Zr were employed to manipulate the microstructural evolution of Al-7Mg-2Zn-0.15Zr alloy and thus the deformation character-istics.The results demonstrate that a two-step homogenization treatment of 400℃/12 h+465℃/12 h can sufficiently dissolve the constituent phase and eliminate the micro-segregation,as well as achieve a fine and uniform distribution of Al_(3)Zr dispersoids,which results in the enhanced yield strength(YS)of 201 MPa and ultimate strength(UTS)of 376 MPa after rolling and annealing.Most importantly,it has been revealed that the dispersed Al_(3)Zr formed via two-step homogenization is favorable to impede the movement of dislocations,which extends the waiting time,increases the stress amplitude,and thus di-minishes the number of PLC bands.Moreover,the dislocation network induced by dispersed Al_(3)Zr can further inhibit the movement of active dislocations,which inhibits the formation of Lüders bands.This study provides a simple and effective homogenization regime to optimize the mechanical response and surface quality of alloys with high-Mg contents.展开更多
The precipitation behavior of Mn-containing dispersoids in Al-Mg-Si 6082 alloys with different Mn contents(0,0.5 and 1.0 wt%)during various heat treatments(300–500℃)was investigated.The effects of dispersoids on ele...The precipitation behavior of Mn-containing dispersoids in Al-Mg-Si 6082 alloys with different Mn contents(0,0.5 and 1.0 wt%)during various heat treatments(300–500℃)was investigated.The effects of dispersoids on elevated-temperature strength and recrystallization resistance during hot-rolling and post-rolling annealing were evaluated.The results showed that the dispersoids in the Mn-containing alloys(0.5 and 1.0%)began to precipitate at 350℃and reached the optimum conditions after 2–4 h at 400℃.However,the dispersoids coarsened with increasing holding time at temperatures above450℃.After the peak precipitation treatment at 400℃for 2 h,the yield strength at 300℃increased from 28 MPa(base alloy free of Mn)to 55 MPa(alloy with 0.5%Mn)and 70 MPa(alloy with 1%Mn),respectively,demonstrating a significant dispersoid strengthening effect at elevated temperature.In addition,the dispersoids were thermally stable at 300℃for up to 1000 h holding owing to its relative high precipitation temperature(350–400℃),leading to the superior constant mechanical performance at elevated temperature during the long service life.During hot rolling and post-rolling annealing,the presence of a large amount of dispersoids results in the higher Zener drag PZcompared with base alloy and then significantly improved the recrystallization resistance.The alloy containing 0.5%Mn exhibited the highest recrystallization resistance among three experimental alloys studied during the post-rolling process,likely resulted from the lower coarsening rate of dispersoids and the lower dispersoids free zone.展开更多
The microstructural evolutions under as-homogenized and as-deformed conditions and after the postdeformation annealing of AA6082 aluminum alloys with different Mn content(0.05 wt.%-1 wt.%)were studied by optical,scann...The microstructural evolutions under as-homogenized and as-deformed conditions and after the postdeformation annealing of AA6082 aluminum alloys with different Mn content(0.05 wt.%-1 wt.%)were studied by optical,scanning electron,and transmission electron microscopies.The results showed that the presence of a large amount ofα-Al(Mn,Fe)Si dispersoids induced by Mn addition significantly improved the recrystallization resistance.In the base alloy free of Mn,static recrystallization occurred after 2 h of annealing,and grain growth commenced after 4 h of annealing,whereas in Mn-containing alloys,the recovered grain structure was well-retained after even 8 h of annealing.The alloy with 0.5%Mn exhibited the best recrystallization resistance,and a further increase of the Mn levels to 1%resulted in a gradual reduction of the recrystallization resistance,the reason for which was that recrystallization occurred only in the dispersoid-free zones(DFZs)and the increased DFZ fraction with Mn content led to an increase in the recrystallization fraction.The variation in the dispersoid number density and a coarsening of dispersoids during annealing have a limited influence on the static recrystallization in Mn-containing alloys.展开更多
基金financially supported by the National Natu-ral Science Foundation of China(No.52204395)the Key Tech-nology Research and Development Program of Shandong Province(No.2021SFGC1001)the Science and Technology Program of Suzhou(Nos.SYG202313 and SYG202324).
文摘The present study aims to clarify the influence of Mo addition onα-dispersoids precipitation,associ-ated recrystallization resistance and mechanical performance of Mn-containing Al-Mg-Si-Cu alloys.Re-sults reveal that joint addition of Mn and Mo as dispersoid-forming elements dramatically enhancesα-dispersoids precipitation,achieving a fivefold increment in number density and a 26.5%reduction in size compared to the alloy containing only Mn addition.Additionally,the width of dispersoid-free zones is reduced from appropriately 5μm to<1μm.A portion of theα-Al(Mn,Mo,Fe)Si dispersoids exhibits the quasicrystal characteristics,forming coherent interfaces with the aluminum matrix.In compassion,α-Al(Mn,Fe)Si dispersoids transformed entirely into a simple cubic structure,being partially coherent with the matrix.The improvements inα-dispersoids precipitation contribute to higher pinning force on moving boundaries,resulting in superior resistance to recrystallization of the alloy.Consequently,an ideal fibrous microstructure is retained in alloy co-alloyed with Mn and Mo after solution treatment.Whereas,alloys containing only Mn or Mo show complete recrystallization.A superior balance between strength and ductility is achieved for 0.7Mn0.3Mo alloy,attributed to the increased work hardening capacity and suppression of dynamic recovery.
文摘Semi-quantitative electron probe microanalysis （EPMA） mapping, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） were employed to study the effect of one-step and two-step treatments on the Zr distribution and Al3Zr dispersoid characteristics in as-cast commercial AA7150 aluminum alloy. It is shown that the Zr concentration in the dendrite centre regions is higher than that near the dendrite edges in the as-cast condition, and that homogenization at 460 °C for 20 h is insufficient to remove these concentration gradients. After homogenizing at 460-480 °C, a high number density of larger dispersoids can be observed in dendrite centre regions but not near dendrite edges. Furthermore, the dispersoid size increases with increasing the temperature during both one-step and two-step homogenization treatments.
基金the financial supports from the National Natural Science Foundation of China (No. U1864209)Jincheng Science and Technology Plan Project of Shanxi Province, China (No. 201702014)。
文摘The microstructural evolution of AA6061 and Mn-bearing Al-Mg-Si-Cu alloys was studied by compression tests that were carried out between 300 and 500 °C with a wide range of strain rates. Compared to the AA6061 alloy, the large amount of α-Al(MnFeCr)Si dispersoids in the Mn-bearing alloy yielded a significant increase in the flow stress under all deformation conditions. The effects of the deformation parameters on the evolution of the microstructure were studied using electronic backscatter diffraction measurements. The predominant softening mechanism of both alloys was dynamic recovery. The presence of α dispersoids in Mn-bearing alloys effectively refined the size of substructures with misorientation angles in the range of 2°-5°, which retarded the dynamic recovery. To predict the subgrain size under various deformation conditions, the threshold stresses that were caused by α dispersoids were calculated by the modified Orowan equation and incorporated into a conventional constitutive equation. The subgrain size that was predicted by the modified constitutive equation showed satisfactory agreement with the experimental measurements.
基金This research was supported by the National Natural Science Foundation of China(59895152)the National High Technology Committee of China(863-715-005-0030).
文摘A NiAI-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAI-HfC during milling can be attributed to two chemical reactions: Ni+AI→NiAI+△H; Hf+C→HfC+△H, induced by mechanical collision in a certain period of time, which results in an abrupt exothemic reaction. Hot pressing (HP) and hot isostatic pressing (HIP) have been used to make the NiAI-10HfC compacts near fully dense. Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAI-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAI-10TiB2 composite. In the meantime, yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.
基金financially supported by the National Natural Science Foundation of China(No.51871043)Fundamental Research Funds for the Central Universities of China(No.N180212010)Liaoning Natural Science Foundation of China(No.2019-MS-113)。
文摘The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.
基金supported by the Civil-Military Technology Cooperation Program under the Agency for Defence Development(ADD)of the Republic of Korea(No.1415156504)the National Research Foundation grant funded by the Korean government(Nos.NRF-2020R1A5A6017701 and 2017K1A3A7A09016308)。
文摘Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys(ODS-HEAs)were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties.Systematic micro structural analysis was carried out by X-ray diffraction(XRD),electron backscattered diffraction(EBSD),high-resolution transmission electron microscopy(HRTEM),atom probe tomography(APT),and small-angle neutron scattering(SANS).Cryo-milled powder analysis,grain structure evolution after spark plasma sintering,dispersoid characteristics,and matrix/dispersoid interface structure analysis of the insitu and ex-situ dispersoids within the high-entropy alloy(HEA)matrix were performed.The in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical composition,leading to an increase in the Zener pinning forces on the grain boundary movement.ODS-HEA with in-situ oxide dispersoids enhanced the formation of ultrafine-grained structures with an average diameter of 330 nm at a sintering temperature of 1173 K.This study shows that the Y pre-alloying method is efficient in achieving fine coherent dispersoids with an ultra fine-grained structure,resulting in an enhancement of the tensile strength of the CoCrFeMnNi HEA.
基金Project(2012CB619500)supported by the National Basic Research Program of China
文摘The dynamic recrystallization behavior of 7085 aluminum alloy during hot compression at various temperatures （573？723 K） and strain rates （0.01-10 s^-1） was studied by electron back scattered diffraction （EBSD）, electro-probe microanalyzer （EPMA） and transmission electron microscopy （TEM）. It is shown that dynamic recovery is the dominant softening mechanism at high Zener？Hollomon （Z） values, and dynamic recrystallization tends to appear at low Z values. Hot compression with ln Z=24.01 （723 K, 0.01 s？1） gives rise to the highest fraction of recrystallization of 10.2%. EBSD results show that the recrystallized grains are present near the original grain boundaries and exhibit similar orientation to the deformed grain. Strain-induced boundary migration is likely the mechanism for dynamic recrystallization. The low density of Al3Zr dispersoids near grain boundaries can make contribution to strain-induced boundary migration.
基金Project(2012CB619500)supported by the National Basic Research Program of ChinaProject supported by Yuying Project of Central South University
文摘The effect of homogenization time on quench sensitivity of a cast 7085 aluminum alloy was investigated by means of end-quenching test, optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscope （TEM）. The results show that with the increase of homogenization time from 48 h to 384 h, quench sensitivity increased slightly as the largest difference in the hardness was increased from 5.2% to 6.9% in the end-quenched and aged specimens. Prolonging homogenization had little effect on the grain structure, but improved the dissolution of soluble T phase and resulted in larger Al3Zr dispersoids with a low number density. Some small quench-induced η phase particles on Al3Zr dispersoids were observed inside grains during slow quenching, which decreased hardness after subsequent aging. The change in the character of Al3Zr dispersoids exerted slight influence on quench sensitivity.
基金Project(2012CB619500)supported by the National Basic Research Program of ChinaProject supported by Shenghua Yuying Project of Central South University,China
文摘The effect of grain structure on quench sensitivity of an Al-Zn-Mg-Cu-Cr alloy was investigated by hardness testing, optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The results show that with the decrease of quenching rate from 960 ℃/s to 2 ℃/s, the hardness after aging is decreased by about 33% for the homogenized and solution heat treated alloy（H-alloy） with large equiaxed grains and about 43% for the extruded and solution heat treated alloy（E-alloy） with elongated grains and subgrains. Cr-containing dispersoids make contribution to about 33% decrement in hardness of the H-alloy due to slow quenching; while in the E-alloy, the amount of（sub） grain boundaries is increased by about one order of magnitude, which leads to a further 10% decrement in hardness due to slow quenching and therefore higher quench sensitivity.
基金supported by the National Key Research and Development Program of China(No.2023YFB3711900 and 2022YFB3404700)the National Natural Science Foundation of China(Nos.51971077,52205341 and 52201071).
文摘Introducing trace rare earth elements(REEs)into L12 dispersoids(Al_(3)(Sc,Zr))can markedly enhance the mechanical properties of aluminum alloys,However,excessive amounts may cause adverse impacts.This study explores Ti and Cu as transition metal candidates for Al-Zn-Mg-X alloys,aiming to enhance mechanical properties,elucidate microstructure evolution,and identify optimization mechanisms.The addition of Ti to the Al-6.8Zn-2.2Mg-0.2Sc-0.1Zr(AS)alloy results in a notable refinement of the grain size,reducing it from 170μm to 47μm.This refinement of Ti can be attributed to its role as a nucleating agent during solidification,its promotion of dynamic recrystallization during hot-rolling,and its inhibi-tion of static recrystallization during solid solution treatment stage.The formation of a new Ti-containing layer,which substitutes Al sites adjacent to Al_(3)Zr dispersoids,leads to an increase in the phase size from 16 nm to 25 nm.In addition,Cu significantly decreases the aging activation energy of the GP zone andη'precipitate,thereby facilitating their nucleation and growth,which enhances the mechanical proper-ties of the alloy.Ti markedly improves the hardness and strength of the alloy through grain refinement strengthening,Orowan strengthening and solid solution strengthening,while Cu predominantly enhances solid solution strengthening.Our findings suggest that Ti and Cu microalloying profoundly influences the properties and the microstructures of Al-Zn-Mg-X alloys across various scales offering a promising ap-proach for the advancement of high-performance aluminum alloys.
基金supported by the National Natural Science Foundation of China(Nos.52301025,52371065,52301179)the Fundamental Research Program of Shanxi Province,China(Nos.202203021222039,202203021212124)。
文摘The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were employed to elucidate the microstructural parameters of these two strengthening phases.The results show that the microstructural heterogeneity can be triggered by the absence of homogenization,resulting in the presence of dispersoid-free zones(DFZs)and dispersoid zones(DZs),in conjunction with bimodalβ″precipitates.Further analytical calculations,from the strengthening model,clarify that the strategically dispersedα-Al(Fe,Mn)Si andβ″particles create“soft”and“hard”domains within the alloy,resultantly improving the mechanical properties.
基金the National Research Foundation(NRF)grant funded by the Ministry of Science and ICT of Korea through contracts NRF-2018K2A9A1A06069970,NRF2020R1A5A6017701the Asian Office of Aerospace Research and Development(AOARD)grant funded by the Air Force Office of Scientific Research(AFOSR)through a grant FA2386-19-1-4009。
文摘Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3μm,and small amounts(<4 vol.%)of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27%and 87%at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm^(3),while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50%of the yield strength of the AlxCrNbVMo RHEAs.
基金financially supported by the National Science Foundation of China(No.51735008)the Science Fund for Distinguished Young Scholars of Shandong Province(No.JQ201810)。
文摘In this paper,a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process.The dissolution of the secondary particles and the diffusion of solute were studied based on microstructure characterization and kinetics analysis.The precipitation behavior of Al3Zr dispersoids and its influence on recrystallization were investigated by using TEM and EBSD characterization.It was found that the large-size particles at triangular grain boundaries dissolve slower than the intragranular phases and other grain boundary phases.The required homogenization time depends on the dissolution processes of the large-size phases at grain boundaries.The size of grain boundary phases in the spray deposited alloy is much smaller than that in the as-cast alloy,so the homogenization time required for the spray deposited alloy is significantly shorter.Two-stage and ramp heating homogenization processes can promote the precipitation of Al3Zr dispersoids in the two alloys.In the spray deposited alloy,the dispersoids tend to precipitate at the positions of the T1 plates dissolved,which causes a non-uniform distribution and decreases the recrystallization resistance of the alloy.However,the distribution of the dispersoids in the as-cast alloy is more uniform after the homogenization,which brings a stronger inhibition on the recrystallization.According to the microstructural characterization and kinetics analysis results,it can be concluded that the homogenization with a slow ramp heating is suitable for the two 2195 alloys,and a shorter holding time can be used for spray deposited alloy,e.g.12 h at 500℃,while the holding time for the as-cast alloy is no less than 35 h at 500℃.
文摘The nucleation and precipitation of Mn-containing dispersoids in an Al-Mg-Si-Mn alloy （6082） have been studied by optical microscopy,EPMA （electron probe microanalysis） and TEM （transmission electron microscopy）.The influence of Mn-containing dispersoids on the recrystallization behavior was also investigated.The size and distribution of dispersoids were strongly affected by both the homogenization process and the alloying element distribution formed in the direct chill cast procedure.The Mn-containing dispersoids were observed to nucleate preferentially on the β-Mg 2 Si phase and to be aligned along the 〈100〉 direction of the matrix.After cold deformation,the morphology of dispersoids greatly influences the recrystallization and grain growth behavior in the annealing process.
基金the financial support of the project from the National Natural Science Foundation of China (No. 51771147)。
文摘A significant size effect is found in the Al3 Sc dispersoid-mediated precipitation in an Al-Mg-Si-Sc alloy.When the Al3 Sc dispersoid size smaller than about 40 nm,β " precipitates nucleate directly on the coherent dispersoids and grow by sacrificing the latter.While the dispersoid size greater than^40 nm,Q' and U2 phases are additionally produced that nucleate on the dislocations induced by the semi-/incoherent dispersoids.Mechanical and electrical properties are highly sensitive to the Al3 Sc dispersoid-tuned precipitation.The co-precipitation of β",Q' and U2 phases leads to an obvious improvement in hardness and simultaneously in electrical conductivity.
基金This research was supported by the National Natural Science Foundation of China （No. 59371039）；Professors E.A.Starke,Jr and R.P. Gangloff of University of Virginia is greatly appreciated.
文摘The tensile and fatigue behavior of a dispersoid strengthened, powder metallurgy Al-Fe-V-Si alloy at ambient and elevated temperatures was investigated. The results show that the strength and ductility of the alloy decrease significantly with increasing temperature and decreasing strain rate. Micro-structural examinations reveal that this change in mechanical behavior with increasing temperature is related to the mode of deformation of the alloy. Further observations show that localized shear deformation is responsible for the losses in both strength and ductility of the alloy at elevated temperature.
文摘Therecent developments in elevated temperature ( ET) aluminum alloys prepared by therapidsolidification / powder metallurgy ( RS P/ M) process were reviewed briefly. TheRS P/ METaluminum alloyscan beclassified as(a) the aluminum transition metaltype, such as Al Fe, Al Cr, Al Ti, Al Zrsystem alloys,etc.,and (b) thealuminum rareearth elementtype,such as Al Y, Al Nd system alloys,etc. Among them ,the Al Fe and Al Ti system alloysarethe most attractive, which possessthe potentialto replacethetitanium alloy partson aircraft,engines,etc.,fortheuseattemperaturesrangingfrom 200 315℃. Theproblemsin applicationsfor RS P/ M ETaluminum alloys werealso discussed .
基金support from the National Natural Science Foundation of China(No.52201004)the Beijing Natural Science Foundation(No.2222095)+1 种基金S.W.Pan would acknowledge the support from the China Postdoctoral Science Foundation(No.2023M730234)the National Natural Science Foundation of China(No.52301005).
文摘Al-Mg-Zn-based alloys are newly developed high-performance age-hardenable 5xxx series alloys.How-ever,they suffer from poor surface quality due to the Lüders bands and the Portevin-Le-Chatelier(PLC)effect during plastic deformation,and the elongation(EL)is impaired by the large constituent particles.In this work,various homogenization regimes combined with minor addition of Zr were employed to manipulate the microstructural evolution of Al-7Mg-2Zn-0.15Zr alloy and thus the deformation character-istics.The results demonstrate that a two-step homogenization treatment of 400℃/12 h+465℃/12 h can sufficiently dissolve the constituent phase and eliminate the micro-segregation,as well as achieve a fine and uniform distribution of Al_(3)Zr dispersoids,which results in the enhanced yield strength(YS)of 201 MPa and ultimate strength(UTS)of 376 MPa after rolling and annealing.Most importantly,it has been revealed that the dispersed Al_(3)Zr formed via two-step homogenization is favorable to impede the movement of dislocations,which extends the waiting time,increases the stress amplitude,and thus di-minishes the number of PLC bands.Moreover,the dislocation network induced by dispersed Al_(3)Zr can further inhibit the movement of active dislocations,which inhibits the formation of Lüders bands.This study provides a simple and effective homogenization regime to optimize the mechanical response and surface quality of alloys with high-Mg contents.
基金the financial support of the Natural Sciences and Engineering Research Council of Canada(NSERC)Rio Tinto Aluminum through the NSERC Industry Research Chair in the Metallurgy of Aluminum Transformation at the University of Quebec at Chicoutimi.
文摘The precipitation behavior of Mn-containing dispersoids in Al-Mg-Si 6082 alloys with different Mn contents(0,0.5 and 1.0 wt%)during various heat treatments(300–500℃)was investigated.The effects of dispersoids on elevated-temperature strength and recrystallization resistance during hot-rolling and post-rolling annealing were evaluated.The results showed that the dispersoids in the Mn-containing alloys(0.5 and 1.0%)began to precipitate at 350℃and reached the optimum conditions after 2–4 h at 400℃.However,the dispersoids coarsened with increasing holding time at temperatures above450℃.After the peak precipitation treatment at 400℃for 2 h,the yield strength at 300℃increased from 28 MPa(base alloy free of Mn)to 55 MPa(alloy with 0.5%Mn)and 70 MPa(alloy with 1%Mn),respectively,demonstrating a significant dispersoid strengthening effect at elevated temperature.In addition,the dispersoids were thermally stable at 300℃for up to 1000 h holding owing to its relative high precipitation temperature(350–400℃),leading to the superior constant mechanical performance at elevated temperature during the long service life.During hot rolling and post-rolling annealing,the presence of a large amount of dispersoids results in the higher Zener drag PZcompared with base alloy and then significantly improved the recrystallization resistance.The alloy containing 0.5%Mn exhibited the highest recrystallization resistance among three experimental alloys studied during the post-rolling process,likely resulted from the lower coarsening rate of dispersoids and the lower dispersoids free zone.
基金financially supported by the Natural Sciences and Engineering Research Council of Canada(No.CRDPJ 51465117)Rio Tinto Aluminum through the Research Chair in the Metallurgy of Aluminum Transformation at University of Quebec at Chicoutimi。
文摘The microstructural evolutions under as-homogenized and as-deformed conditions and after the postdeformation annealing of AA6082 aluminum alloys with different Mn content(0.05 wt.%-1 wt.%)were studied by optical,scanning electron,and transmission electron microscopies.The results showed that the presence of a large amount ofα-Al(Mn,Fe)Si dispersoids induced by Mn addition significantly improved the recrystallization resistance.In the base alloy free of Mn,static recrystallization occurred after 2 h of annealing,and grain growth commenced after 4 h of annealing,whereas in Mn-containing alloys,the recovered grain structure was well-retained after even 8 h of annealing.The alloy with 0.5%Mn exhibited the best recrystallization resistance,and a further increase of the Mn levels to 1%resulted in a gradual reduction of the recrystallization resistance,the reason for which was that recrystallization occurred only in the dispersoid-free zones(DFZs)and the increased DFZ fraction with Mn content led to an increase in the recrystallization fraction.The variation in the dispersoid number density and a coarsening of dispersoids during annealing have a limited influence on the static recrystallization in Mn-containing alloys.
