A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of ...A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of pretreatment were optimized by orthogonal experiment design and proper precursor was prepared.The evolution of microstructure of semi-solid slurry during isothermal treatment was analyzed and the mechanism of microstructure refining was discussed.The result of orthogonal experiment design shows that the optimum parameters are 462 ℃for solution temperature,40min for solution time,132 ℃for aging temperature and 14 h for aging time.Microstructure of isothermal treatment is fine,homogenous,with globular solid grains and a solid fraction between 50%and 70%,which is qualified for later semi-solid forming process.Mechanism of microstructure evolution includes the agglomeration ofα-phase and Ostwald ripening.Precipitations prepared by solution and aging treatment prevent the grains from coarsening and promote the grain ripening to globular shape.展开更多
Zn-Al eutectoid alloy(ZA22)has ultra-high damping property,but its mechanical properties are still relatively low.In order to simultaneously improve the tensile strength and plasticity,a novel Al matrix composite inoc...Zn-Al eutectoid alloy(ZA22)has ultra-high damping property,but its mechanical properties are still relatively low.In order to simultaneously improve the tensile strength and plasticity,a novel Al matrix composite inoculant containing in-situ formed Al_(2)O_(3) and Al3Zr particles was designed and used to reinforce the ZA22 alloy.The microstructure of the ZA22 alloy was significantly refined.Fine Al_(2)O_(3) particles were uniformly distributed in theαphase and the lamellar eutectoid structure,whereas Al3Zr particles were distributed in theαphase and at theα/ηinterface.Property tests showed that the tensile mechanical properties of the reinforced ZA22 alloys were significantly improved.The maximum tensile strength and elongation reached 355 MPa and 7.62%,which were 1.50 and 1.89 times those of the original ZA22 alloy,respectively.The increase in mechanical properties is attributed to the multiple strengthening and toughening factors constructed in the refined microstructure.展开更多
The influence of processing parameters ofrelaxation-precipitation-controlling phase transformation (RPC) technique, finish rollingtemperature, reduction ratio and relaxing time on the microstructure was studied byther...The influence of processing parameters ofrelaxation-precipitation-controlling phase transformation (RPC) technique, finish rollingtemperature, reduction ratio and relaxing time on the microstructure was studied bythermo-simulation for a low carbon Nb and Ti containing micro-alloyed steel. The microstructure wasinvestigated by optical microscope, transmission electron microscope and electron back scatterdiffraction (EBSD). The statistical results of the packet size were calculated. It shows that, afterRPC process, the steel is a composite microstructure of bainite and matensite. The bestthermo-simulation process for refinement in this experiment is deformation for 30 percent at 850 degC, and then relaxing at this temperature for 60 s to 200 s. Increasing the reduction ratio from 30percent to 60 or decreasing the deformation temperature to 800 deg C would cause the best relaxationtime to become shorter, increasing the deformation temperature to 900 deg C would cause therefinement effect to be weak.展开更多
Very high cycle fatigue behaviors of two bainite/martensite dual-phase steels were investigated.One of the steels was cyclic rapid heat treated and its microstructures were refined. Fatigue strength of the steel is 22...Very high cycle fatigue behaviors of two bainite/martensite dual-phase steels were investigated.One of the steels was cyclic rapid heat treated and its microstructures were refined. Fatigue strength of the steel is 225 MPa higher than that without refining.Observation of fracture surfaces show that the fatigue cracks initiate at bainites for non-refined steel and at non-metallic inclusions for the refined steel.The size of inclusions is much smaller than that of bainites which results in the improvement of fatigue strength.展开更多
The effects of on-line solution, off-line solution and aging heat treatment on the microstructure and hardness of the die-cast AZ91D alloys were investigated. Brinell hardness of die-cast AZ91D alloy increases through...The effects of on-line solution, off-line solution and aging heat treatment on the microstructure and hardness of the die-cast AZ91D alloys were investigated. Brinell hardness of die-cast AZ91D alloy increases through on-line solution and off-line aging treatment but decreases after off-line solution treatment. By X-ray diffractometry, optical microscopy, differential thermal analysis, scanning electron microscopy and X-ray energy dispersive spectroscopy, it is found that the microstructures of the die-cast AZ91D magnesium alloy before and after on-line solution and off-line aging are similar, consisting of α-Mg and β-Al12Mg17. The precipitation of Al element is prevented by on-line solution so that the effect of solid solution strengthening is enhanced. The β-Al12Mg17 phases precipitate from supersaturated Mg solid solution after off-line aging treatment, and lead to microstructure refinement of AZ91D alloy, so the effect of precipitation hardening is enhanced. The β-Al12Mg17 phases dissolve in the substructure after off-line solution treatment, which leads to that the grain boundary strengthening phase is reduced significantly and the hardness of die cast AZ91D is reduced.展开更多
This study investigates zinc’s(Zn)key role in enhancing the precipitation kinetics and refinement of Mg_(17)Al_(12)and Mg_(2)Sn phases in magnesium alloys through trace sodium(Na)additions.Magnesium alloys with varyi...This study investigates zinc’s(Zn)key role in enhancing the precipitation kinetics and refinement of Mg_(17)Al_(12)and Mg_(2)Sn phases in magnesium alloys through trace sodium(Na)additions.Magnesium alloys with varying compositions of aluminum(Al),tin(Sn),Zn,and Na were prepared and aged at 453 K.Microstructural analyses were conducted using transmission electron microscopy(TEM),scanning transmission electron microscopy(STEM),and atom probe tomography(APT).Trace additions of Na significantly enhanced the precipitation responses of both Mg_(17)Al_(12)and Mg_(2)Sn phases.When Zn was co-added with Na,as in the ATZ641N3 alloy(Mg–6Al–4Sn–1Zn–0.3Na),there was a pronounced refinement in precipitate morphology and acceleration of precipitation kinetics.The ATZ641N3 alloy achieved a peak hardness of 103 Hv at 36 hours,compared to 91 Hv at 72 hours for the ATZ641 alloy without Na.The simultaneous addition of Zn and Na led to the formation of Sn–Na–Zn particles that acted as effective nucleation sites for Mg_(2)Sn,promoting aluminum partitioning and accelerating the precipitation of Mg_(17)Al_(12)through Al-rich regions.Additionally,Zn and Na co-segregated within the Mg_(17)Al_(12)phase,reducing misfit strain caused by Zn substitution and improving precipitate stability and refinement.These findings highlight Zn’s critical role,alongside trace Na additions,in refining and accelerating the precipitation of Mg_(17)Al_(12)and Mg_(2)Sn phases,thereby enhancing the age-hardening response of magnesium alloys.展开更多
The microstructures and tensile properties of Mg-6.0 Zn-0.6 Zr(ZK60) and ZK60 + 1.8 Gd(ZEK620(RE = Gd)) alloys extruded at 290, 305, 320, 340 and360 ℃ were investigated. The results indicate that Gd addition can refi...The microstructures and tensile properties of Mg-6.0 Zn-0.6 Zr(ZK60) and ZK60 + 1.8 Gd(ZEK620(RE = Gd)) alloys extruded at 290, 305, 320, 340 and360 ℃ were investigated. The results indicate that Gd addition can refine the microstructures of ZK60 alloy and the extrusion parameters such as the extrusion temperature will influence the tensile properties of both as-extruded ZK60 and ZEK620 alloys, although it is much slighter for ZK60 alloy. And the sensitivity is closely related to the textures developed during extrusion. In addition, Gd addition will also clearly improve the tensile strength at room temperature(24 ℃) and particularly at high temperatures(150 and 200 ℃), due to the much finer grains and smaller intermetallic particles. The highest strength is achieved in the as-extruded ZEK620 alloy with extrusion temperature of 320 ℃, with ultimate tensile strength(UTS) and tensile yield strength(TYS) of 405 and375 MPa, respectively, which are improved by approximately 9% and 11% than those of the as-extruded ZK60 alloy which owns the highest strength at extrusion temperature of 290 ℃.展开更多
Additive manufacturing(AM)has the potential to transform manufacturing by enabling previously un-thinkable products,digital inventory and delivery,and distributed manufacturing.Here we presented an extrusion-based met...Additive manufacturing(AM)has the potential to transform manufacturing by enabling previously un-thinkable products,digital inventory and delivery,and distributed manufacturing.Here we presented an extrusion-based metal AM method(refer to“SoftTouch”depositionin thefiledpatent)thatis suitablefor making the metal feedstock flowable prior to the deposition through dynamic recrystallization induced grain refinement at elevated temperatures.The flowable metal was extruded out of the printer head like a paste for building dense metal parts with fine equiaxed grains and wrought mechanical properties.Off-the-shelf metal rods were used as feedstock and the printing process was completed in an open-air environment,avoiding pricy powders and costly inert or vacuum conditions.The resulting multi-layer de-posited 6061 aluminum alloys yield strength and ductility comparable to wrought 6061 aluminum alloys after the same T6 heat treatment.The extrusion-based metal AM method can also be advanced as green manufacturing technologies for fabricating novel alloys and composites,adding novel features to existing parts,repairing damaged metal parts,and welding advanced metals for supporting sustainable manufac-turing,in addition to being developed into a cost-effective manufacturing process for the fabrication of dense metal of complex structural forms.展开更多
Effect of electromagnetic stirring on microstructure of AZ91-0.8%Ce magnesium alloy was investigated. The results show that electromagnetic stirring causes a change of morphology of α-Mg phase from coarse dendrites t...Effect of electromagnetic stirring on microstructure of AZ91-0.8%Ce magnesium alloy was investigated. The results show that electromagnetic stirring causes a change of morphology of α-Mg phase from coarse dendrites to fine rosette-like or spherical shape. Grain size is significantly refined within the range of input voltage 75?125 V, moreover, the optimum input voltage corresponded to the minimum value (64 μm) of grain size is 125 V. Compared to the non-stirred condition, the amount of β-Mg17Al12 precipitate under the stirred condition obviously increases. The grain refinement of AZ91-0.8%Ce alloy is mainly attributed to multiplication of existing grains in the melt caused by forced fluid flow under electromagnetic stirring condition. Addition of 0.8% Ce results in the formation of ‘necking’ at secondary dendrite arm roots of α-Mg crystals, and consequently, it is helpful to increase the number of heterogeneous nucleation.展开更多
The effect of relaxation treatment after finish rolling on microstructure and mechanical properties has been investigated for a vanadium and nitrogen microalloyed low carbon bainitic steel.Finer lath bainite microstru...The effect of relaxation treatment after finish rolling on microstructure and mechanical properties has been investigated for a vanadium and nitrogen microalloyed low carbon bainitic steel.Finer lath bainite microstructure can be obtained in the plate with relaxation.The results of quantitative statistics show that in the plate without relaxation,80% of the total bainite lath bundles are in the range 5-15μm in length and 3-13μm in width,while in the plate with relaxation 80% of the total bundles are in the range 3-9μm in length and 1-7μm in width.The mechanical properties show that the plate with relaxation has higher impact energy,yield strength and hardness than the plate without relaxation,also the comprehensive performance after tempered at 650℃ is superior to the plate without relaxation.展开更多
Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）...Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）.The results showed that the dendrites sizes of α phase were decreased by the Nd addition.When the amount of addition Nd was 1.6 wt.%,the alloy with the smallest α phase was obtained.The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front.Furthermore,the compound Al 2 Nd generated by the reaction of Al and Nd,which distributed at the phase boundary and inside β phase,could also restrain the growth of α phase.Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy,however,excessive Al 2 Nd might also become crack source and decrease the elongation.展开更多
In order to examine the effect of extrusion ratio on the microstructure and mechanical behavior in Al-Cu-Mg-Ag alloy, the Al-6.3 Cu-0.48 Mg-0.4 Ag alloy was subjected to extruding with different extrusion ratios of 17...In order to examine the effect of extrusion ratio on the microstructure and mechanical behavior in Al-Cu-Mg-Ag alloy, the Al-6.3 Cu-0.48 Mg-0.4 Ag alloy was subjected to extruding with different extrusion ratios of 17, 30 and 67. The results indicate that the grains are refined and the strength is improved effectively with increasing extrusion ratio. However, further investigation shows that the extrusion ratio of 30 is more effective than the lower extrusion ratio（17） and the higher extrusion ratio（67） to refine the grains in the T6-temper alloy. Moreover, the sample with an extrusion ratio of 30 obtains more precipitates and superior mechanical properties after T6 treatment. This study supports the idea that there exists a critical extrusion ratio for grain refinement and improvement of mechanical properties for the T6-temper alloy. Recrystallization and precipitation during T6 treatment were introduced to explain the effects of extrusion ratio on the microstructure and mechanical properties of the Al-Cu-Mg-Ag alloys.展开更多
Previous Particle Boundary(PPB),as the detrimental structure in Powder Metallurgy(PM)components,should be eliminated by subsequent hot process to improve the mechanical properties.The objective is to investigate the D...Previous Particle Boundary(PPB),as the detrimental structure in Powder Metallurgy(PM)components,should be eliminated by subsequent hot process to improve the mechanical properties.The objective is to investigate the Dynamic Recrystallization(DRX)nucleation mechanisms and grain growth behavior of the 3rd-generation PM superalloy with PPB structure.Microstructure observation reveals that PPB decorated with(Ti,Ta,Nb)C carbides belongs to the discontinuous chain-like structure.The elimination of PPB networks can be achieved effectively via hot deformation due to the occurrence of DRX.Four different DRX nucleation mechanisms were proposed and discussed in detail according to the special microstructure characteristics of the PM superalloy.Firstly,local lattice rotations can be detected in the vicinity of(Ti,Ta,Nb)C carbides during hot deformation and thus PPB structure serves as the preferential nucleation sites for DRX grains via Particle-Stimulated Nucleation(PSN).Then,Discontinuous-DRX(DDRX)characterized by grain boundary bulging dominates the microstructure refinement and Continuous-DRX(CDRX)operated by subgrain rotation can be regarded as an important assistant mechanism.At last,the initial Σ3 boundaries would lose their twin characteristics owing to the crystal rotation and then transform into the general High Angle Grain Boundaries(HAGBs).The distorted twins provide additional DRX nucleation sites,viz.,twin-assisted nucleation.Particular attention was focused on the grain growth behavior of the PM superalloy in subsequent annealing process.The recrystallization temperature was determined to be about 1110.C and 1140.C can be considered as the critical temperature for grain growth.The findings would provide theoretical support for microstructure refinement of the 3rd-generation PM superalloy,which is of pivotal significance for improving the mechanical properties of aviation components.展开更多
In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti 49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1?...In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti 49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1?100 ℃ with strain rates of 10 -3 10 -1 s -1 . Within this range, the deformation behavior obeys the power law relationship, which can be described using the kinetic rate equation. The stress exponent, n , has a value of about 5.0, and the apparent activation energy is about 320 J/mol, which fits well with the value estimated in previous investigations. The results show that, the dependence of flow stress on the recrystallized grain size can be expressed by the equation: σ=K 1d rex -0 56 . The relationship between the deformed microstructure and the process control parameter can be expressed by the formula: lg d rex =-0 281?1gZ +3 908?1.展开更多
TIG surface remelting was performed to strengthen the surface of ZL109G alloy piston.The macrostructure indicates that surface remelting leads to the production of a remelted zone(RZ).The diameter of the primary Si de...TIG surface remelting was performed to strengthen the surface of ZL109G alloy piston.The macrostructure indicates that surface remelting leads to the production of a remelted zone(RZ).The diameter of the primary Si decreases from 65.8μm in the base metal(BM)to 7.1μm in RZ.The grain size of the RZ is refined to be approximately one-seventh that of the BM.The cellular microstructure in the RZ is characterised by theα(Al)in the centre and intermetallics preferentially located at the cellular boundaries.The results of the mechanical properties demonstrate that the average hardness value of RZ increases by 39%compared to that of BM.For the transverse samples,the ultimate tensile strength increases by~24.5%,which can be attributed to the solution strengthening of Si inα(Al).The average fracture toughness values are 15.0 and 12.7 MPa·m^(1/2)forα(Al)in BM and RZ,respectively.展开更多
It is well-known that grain refiners can tailor the microstructure and enhance the mechanical properties of titanium alloys fabricated by additive manufacturing(AM). However, the intrinsic mechanisms of Ni addition on...It is well-known that grain refiners can tailor the microstructure and enhance the mechanical properties of titanium alloys fabricated by additive manufacturing(AM). However, the intrinsic mechanisms of Ni addition on AM-built Ti–6Al–4V alloy is not well established. This limits its industrial applications. This work systematically investigated the influence of Ni additive on Ti–6Al–4V alloy fabricated by laser aided additive manufacturing(LAAM). The results showed that Ni addition yields three key effects on the microstructural evolution of LAAM-built Ti–6Al–4V alloy.(a) Ni additive remarkably refines the prior-β grains, which is due to the widened solidification range. As the Ni addition increased from 0 to 2.5 wt. %, the major-axis length and aspect ratio of the prior-β grains reduced from over 1500 μm and 7 to 97.7 μm and1.46, respectively.(b) Ni additive can discernibly induce the formation of globular α phase,which is attributed to the enhanced concentration gradient between the β and α phases. This is the driving force of globularization according to the termination mass transfer theory. The aspect ratio of the α laths decreased from 4.14 to 2.79 as the Ni addition increased from 0 to2.5 wt. %.(c) Ni as a well-known β-stabilizer and it can remarkably increase the volume fraction of β phase. Room-temperature tensile results demonstrated an increase in mechanical strength and an almost linearly decreasing elongation with increasing Ni addition. A modified mathematical model was used to quantitatively analyze the strengthening mechanism. It was evident from the results that the α lath phase and the solid solutes contribute the most to the overall yield strength of the LAAM-built Ti–6Al–4V–x Ni alloys in this work. Furthermore, the decrease in elongation with increasing Ni addition is due to the deterioration in deformability of the β phase caused by a large amount of solid-solution Ni atoms. These findings can accelerate the development of additively manufactured titanium alloys.展开更多
A new serve plastic deformation(SPD) including initial forward extrusion and subsequent shearing process(ES) was proposed.The influence of the ES forming on the grain refinement of the microstructure was researched.Th...A new serve plastic deformation(SPD) including initial forward extrusion and subsequent shearing process(ES) was proposed.The influence of the ES forming on the grain refinement of the microstructure was researched.The components of ES forming die were manufactured and installed to Gleeble1500D thermo-mechanical simulator.The microstructure observations were carried out on the as-extruded rods(as-received) and ES formed rods.From the simulation results,ES forming can increase the cumulative strain enormously and the volume fraction of dynamic recrystallization.From the physical modeling results,the microstructures can be refined.展开更多
A new process to refine the microstructure of α+βtvpe Ti alloys was developed by using hydrogen as a temporary alloying element.It involves hydrogenating the alloys below the hydrogenated β transus temperature abou...A new process to refine the microstructure of α+βtvpe Ti alloys was developed by using hydrogen as a temporary alloying element.It involves hydrogenating the alloys below the hydrogenated β transus temperature about 0-40 K,air cooling to room temperature and then dehydrogenating at 948 K.Ti-6AI-4V and Ti-5AI-2.5Fe alloys treated hy this new process show much refined microstructures,and the yield strength,ultimate strength as well as the elongation increase 8—15,5—13 and 7—14% respectively展开更多
The microstructure evolution during deformation enhanced transformation of undercooled austenite of a plain low carbon steel has been investigated by means of hot compression simulation experiment under various condit...The microstructure evolution during deformation enhanced transformation of undercooled austenite of a plain low carbon steel has been investigated by means of hot compression simulation experiment under various conditions of strain rate, deformation temperature and strain. The effect of austenite grain size on the strain enhanced ferrite transformation has been studied. The ferrite dynamic recrystallization involved in successive hot deformation has been explored.展开更多
Effects of calcium addition and electromagnetic stirring on the microstructure of AZ91 magnesium alloy and refinement mechanism were investigated. The results show that calcium addition ranging from 0.1wt% to 0.3 wt% ...Effects of calcium addition and electromagnetic stirring on the microstructure of AZ91 magnesium alloy and refinement mechanism were investigated. The results show that calcium addition ranging from 0.1wt% to 0.3 wt% does not lead to formation of any new phases but cause the refinement of ascast microstructure.However, combined calcium alloying and electromagnetic stirring significantly decrease the grain size, change the morphologies of the β-Mg17Al12 phases,and reduce their volume percentage. The minimum grain size of AZ91 alloy is obtained in the case of the addition of 0.2 wt%Ca with exciting voltage of 100 V. The microstructural refinement is attributed to the increase of the degree of undercooling and nucleation temperature of primary α-Mg phases on the basis of DTA analysis results.展开更多
基金Project(2007-83)supported by Science and Technology Development Projects of Weihai,Shandong Province。
文摘A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of pretreatment were optimized by orthogonal experiment design and proper precursor was prepared.The evolution of microstructure of semi-solid slurry during isothermal treatment was analyzed and the mechanism of microstructure refining was discussed.The result of orthogonal experiment design shows that the optimum parameters are 462 ℃for solution temperature,40min for solution time,132 ℃for aging temperature and 14 h for aging time.Microstructure of isothermal treatment is fine,homogenous,with globular solid grains and a solid fraction between 50%and 70%,which is qualified for later semi-solid forming process.Mechanism of microstructure evolution includes the agglomeration ofα-phase and Ostwald ripening.Precipitations prepared by solution and aging treatment prevent the grains from coarsening and promote the grain ripening to globular shape.
基金supported by the Foundation Strengthening Program of China(No.2019-JCJQ-ZD-142-00)the Natural Science Foundation of Hebei Province,China(No.E2021202017)the Foundation of Guangdong Academy of Sciences,China(No.2021GDASYL-20210102002)。
文摘Zn-Al eutectoid alloy(ZA22)has ultra-high damping property,but its mechanical properties are still relatively low.In order to simultaneously improve the tensile strength and plasticity,a novel Al matrix composite inoculant containing in-situ formed Al_(2)O_(3) and Al3Zr particles was designed and used to reinforce the ZA22 alloy.The microstructure of the ZA22 alloy was significantly refined.Fine Al_(2)O_(3) particles were uniformly distributed in theαphase and the lamellar eutectoid structure,whereas Al3Zr particles were distributed in theαphase and at theα/ηinterface.Property tests showed that the tensile mechanical properties of the reinforced ZA22 alloys were significantly improved.The maximum tensile strength and elongation reached 355 MPa and 7.62%,which were 1.50 and 1.89 times those of the original ZA22 alloy,respectively.The increase in mechanical properties is attributed to the multiple strengthening and toughening factors constructed in the refined microstructure.
文摘The influence of processing parameters ofrelaxation-precipitation-controlling phase transformation (RPC) technique, finish rollingtemperature, reduction ratio and relaxing time on the microstructure was studied bythermo-simulation for a low carbon Nb and Ti containing micro-alloyed steel. The microstructure wasinvestigated by optical microscope, transmission electron microscope and electron back scatterdiffraction (EBSD). The statistical results of the packet size were calculated. It shows that, afterRPC process, the steel is a composite microstructure of bainite and matensite. The bestthermo-simulation process for refinement in this experiment is deformation for 30 percent at 850 degC, and then relaxing at this temperature for 60 s to 200 s. Increasing the reduction ratio from 30percent to 60 or decreasing the deformation temperature to 800 deg C would cause the best relaxationtime to become shorter, increasing the deformation temperature to 900 deg C would cause therefinement effect to be weak.
文摘Very high cycle fatigue behaviors of two bainite/martensite dual-phase steels were investigated.One of the steels was cyclic rapid heat treated and its microstructures were refined. Fatigue strength of the steel is 225 MPa higher than that without refining.Observation of fracture surfaces show that the fatigue cracks initiate at bainites for non-refined steel and at non-metallic inclusions for the refined steel.The size of inclusions is much smaller than that of bainites which results in the improvement of fatigue strength.
基金Projects (2011BAE22B01, 2011BAE22B06) supported by the National Key Technologies R&D Program During the 12th Five-Year Plan Period of ChinaProject (2010NC018) supported by the Innovation Fund of Inner Mongolia University of Science and Technology, China
文摘The effects of on-line solution, off-line solution and aging heat treatment on the microstructure and hardness of the die-cast AZ91D alloys were investigated. Brinell hardness of die-cast AZ91D alloy increases through on-line solution and off-line aging treatment but decreases after off-line solution treatment. By X-ray diffractometry, optical microscopy, differential thermal analysis, scanning electron microscopy and X-ray energy dispersive spectroscopy, it is found that the microstructures of the die-cast AZ91D magnesium alloy before and after on-line solution and off-line aging are similar, consisting of α-Mg and β-Al12Mg17. The precipitation of Al element is prevented by on-line solution so that the effect of solid solution strengthening is enhanced. The β-Al12Mg17 phases precipitate from supersaturated Mg solid solution after off-line aging treatment, and lead to microstructure refinement of AZ91D alloy, so the effect of precipitation hardening is enhanced. The β-Al12Mg17 phases dissolve in the substructure after off-line solution treatment, which leads to that the grain boundary strengthening phase is reduced significantly and the hardness of die cast AZ91D is reduced.
基金supported by the Fundamental Research Program(PNKA130)of the Korea Institute of Materials Science,Republic of Korea。
文摘This study investigates zinc’s(Zn)key role in enhancing the precipitation kinetics and refinement of Mg_(17)Al_(12)and Mg_(2)Sn phases in magnesium alloys through trace sodium(Na)additions.Magnesium alloys with varying compositions of aluminum(Al),tin(Sn),Zn,and Na were prepared and aged at 453 K.Microstructural analyses were conducted using transmission electron microscopy(TEM),scanning transmission electron microscopy(STEM),and atom probe tomography(APT).Trace additions of Na significantly enhanced the precipitation responses of both Mg_(17)Al_(12)and Mg_(2)Sn phases.When Zn was co-added with Na,as in the ATZ641N3 alloy(Mg–6Al–4Sn–1Zn–0.3Na),there was a pronounced refinement in precipitate morphology and acceleration of precipitation kinetics.The ATZ641N3 alloy achieved a peak hardness of 103 Hv at 36 hours,compared to 91 Hv at 72 hours for the ATZ641 alloy without Na.The simultaneous addition of Zn and Na led to the formation of Sn–Na–Zn particles that acted as effective nucleation sites for Mg_(2)Sn,promoting aluminum partitioning and accelerating the precipitation of Mg_(17)Al_(12)through Al-rich regions.Additionally,Zn and Na co-segregated within the Mg_(17)Al_(12)phase,reducing misfit strain caused by Zn substitution and improving precipitate stability and refinement.These findings highlight Zn’s critical role,alongside trace Na additions,in refining and accelerating the precipitation of Mg_(17)Al_(12)and Mg_(2)Sn phases,thereby enhancing the age-hardening response of magnesium alloys.
基金financially supported by the National Natural Science Foundation of China (No. 21521092)the National Science and Technology Project (No. 2015DFH50210)the Project of Science and Technology Department of Jilin Province (Nos.20140306003GX,201602011004GX, 2016SYHZ0006 and 20170414001GH)
文摘The microstructures and tensile properties of Mg-6.0 Zn-0.6 Zr(ZK60) and ZK60 + 1.8 Gd(ZEK620(RE = Gd)) alloys extruded at 290, 305, 320, 340 and360 ℃ were investigated. The results indicate that Gd addition can refine the microstructures of ZK60 alloy and the extrusion parameters such as the extrusion temperature will influence the tensile properties of both as-extruded ZK60 and ZEK620 alloys, although it is much slighter for ZK60 alloy. And the sensitivity is closely related to the textures developed during extrusion. In addition, Gd addition will also clearly improve the tensile strength at room temperature(24 ℃) and particularly at high temperatures(150 and 200 ℃), due to the much finer grains and smaller intermetallic particles. The highest strength is achieved in the as-extruded ZEK620 alloy with extrusion temperature of 320 ℃, with ultimate tensile strength(UTS) and tensile yield strength(TYS) of 405 and375 MPa, respectively, which are improved by approximately 9% and 11% than those of the as-extruded ZK60 alloy which owns the highest strength at extrusion temperature of 290 ℃.
基金This work was financially supported by the University of Michi-gan College of Engineering startup grant and FL and PD acknowl-edge the technical support from the Michigan Center for Materials Characterization(MC^(2)).
文摘Additive manufacturing(AM)has the potential to transform manufacturing by enabling previously un-thinkable products,digital inventory and delivery,and distributed manufacturing.Here we presented an extrusion-based metal AM method(refer to“SoftTouch”depositionin thefiledpatent)thatis suitablefor making the metal feedstock flowable prior to the deposition through dynamic recrystallization induced grain refinement at elevated temperatures.The flowable metal was extruded out of the printer head like a paste for building dense metal parts with fine equiaxed grains and wrought mechanical properties.Off-the-shelf metal rods were used as feedstock and the printing process was completed in an open-air environment,avoiding pricy powders and costly inert or vacuum conditions.The resulting multi-layer de-posited 6061 aluminum alloys yield strength and ductility comparable to wrought 6061 aluminum alloys after the same T6 heat treatment.The extrusion-based metal AM method can also be advanced as green manufacturing technologies for fabricating novel alloys and composites,adding novel features to existing parts,repairing damaged metal parts,and welding advanced metals for supporting sustainable manufac-turing,in addition to being developed into a cost-effective manufacturing process for the fabrication of dense metal of complex structural forms.
基金Project(2004ABA110) supported by the Natural Science Foundation of Hubei Province project(471-38300843) supported by the Research Foundation for the Doctoral Program of Wuhan University of Technology
文摘Effect of electromagnetic stirring on microstructure of AZ91-0.8%Ce magnesium alloy was investigated. The results show that electromagnetic stirring causes a change of morphology of α-Mg phase from coarse dendrites to fine rosette-like or spherical shape. Grain size is significantly refined within the range of input voltage 75?125 V, moreover, the optimum input voltage corresponded to the minimum value (64 μm) of grain size is 125 V. Compared to the non-stirred condition, the amount of β-Mg17Al12 precipitate under the stirred condition obviously increases. The grain refinement of AZ91-0.8%Ce alloy is mainly attributed to multiplication of existing grains in the melt caused by forced fluid flow under electromagnetic stirring condition. Addition of 0.8% Ce results in the formation of ‘necking’ at secondary dendrite arm roots of α-Mg crystals, and consequently, it is helpful to increase the number of heterogeneous nucleation.
文摘The effect of relaxation treatment after finish rolling on microstructure and mechanical properties has been investigated for a vanadium and nitrogen microalloyed low carbon bainitic steel.Finer lath bainite microstructure can be obtained in the plate with relaxation.The results of quantitative statistics show that in the plate without relaxation,80% of the total bainite lath bundles are in the range 5-15μm in length and 3-13μm in width,while in the plate with relaxation 80% of the total bundles are in the range 3-9μm in length and 1-7μm in width.The mechanical properties show that the plate with relaxation has higher impact energy,yield strength and hardness than the plate without relaxation,also the comprehensive performance after tempered at 650℃ is superior to the plate without relaxation.
基金supported by the National High Technology Research and Development Program ("863" Program) of China (2009AA03Z525)the Program of New Century Excellent Talents of the Ministry of Education of China (NCET-08-0080)+1 种基金the Science and Technology Fund of Dalian City (2009J21DW003)the Fundamental Research Funds for the Central Universities (DUT11ZD115)
文摘Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）.The results showed that the dendrites sizes of α phase were decreased by the Nd addition.When the amount of addition Nd was 1.6 wt.%,the alloy with the smallest α phase was obtained.The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front.Furthermore,the compound Al 2 Nd generated by the reaction of Al and Nd,which distributed at the phase boundary and inside β phase,could also restrain the growth of α phase.Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy,however,excessive Al 2 Nd might also become crack source and decrease the elongation.
基金Funded by the National Natural Science Foundation of China(No.51071075)the Deep Continental Scientific Drilling Equipment Development(Sino Probe-09-05)by the 985 Project-Automotive Engineering of Jilin University
文摘In order to examine the effect of extrusion ratio on the microstructure and mechanical behavior in Al-Cu-Mg-Ag alloy, the Al-6.3 Cu-0.48 Mg-0.4 Ag alloy was subjected to extruding with different extrusion ratios of 17, 30 and 67. The results indicate that the grains are refined and the strength is improved effectively with increasing extrusion ratio. However, further investigation shows that the extrusion ratio of 30 is more effective than the lower extrusion ratio（17） and the higher extrusion ratio（67） to refine the grains in the T6-temper alloy. Moreover, the sample with an extrusion ratio of 30 obtains more precipitates and superior mechanical properties after T6 treatment. This study supports the idea that there exists a critical extrusion ratio for grain refinement and improvement of mechanical properties for the T6-temper alloy. Recrystallization and precipitation during T6 treatment were introduced to explain the effects of extrusion ratio on the microstructure and mechanical properties of the Al-Cu-Mg-Ag alloys.
基金supported by the National Natural Science Foundation of China(No.52175363)the National Key Research and Development Program,China(Nos.XXXXKF2019-8-1,XX-XX-0015-0087)。
文摘Previous Particle Boundary(PPB),as the detrimental structure in Powder Metallurgy(PM)components,should be eliminated by subsequent hot process to improve the mechanical properties.The objective is to investigate the Dynamic Recrystallization(DRX)nucleation mechanisms and grain growth behavior of the 3rd-generation PM superalloy with PPB structure.Microstructure observation reveals that PPB decorated with(Ti,Ta,Nb)C carbides belongs to the discontinuous chain-like structure.The elimination of PPB networks can be achieved effectively via hot deformation due to the occurrence of DRX.Four different DRX nucleation mechanisms were proposed and discussed in detail according to the special microstructure characteristics of the PM superalloy.Firstly,local lattice rotations can be detected in the vicinity of(Ti,Ta,Nb)C carbides during hot deformation and thus PPB structure serves as the preferential nucleation sites for DRX grains via Particle-Stimulated Nucleation(PSN).Then,Discontinuous-DRX(DDRX)characterized by grain boundary bulging dominates the microstructure refinement and Continuous-DRX(CDRX)operated by subgrain rotation can be regarded as an important assistant mechanism.At last,the initial Σ3 boundaries would lose their twin characteristics owing to the crystal rotation and then transform into the general High Angle Grain Boundaries(HAGBs).The distorted twins provide additional DRX nucleation sites,viz.,twin-assisted nucleation.Particular attention was focused on the grain growth behavior of the PM superalloy in subsequent annealing process.The recrystallization temperature was determined to be about 1110.C and 1140.C can be considered as the critical temperature for grain growth.The findings would provide theoretical support for microstructure refinement of the 3rd-generation PM superalloy,which is of pivotal significance for improving the mechanical properties of aviation components.
文摘In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti 49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1?100 ℃ with strain rates of 10 -3 10 -1 s -1 . Within this range, the deformation behavior obeys the power law relationship, which can be described using the kinetic rate equation. The stress exponent, n , has a value of about 5.0, and the apparent activation energy is about 320 J/mol, which fits well with the value estimated in previous investigations. The results show that, the dependence of flow stress on the recrystallized grain size can be expressed by the equation: σ=K 1d rex -0 56 . The relationship between the deformed microstructure and the process control parameter can be expressed by the formula: lg d rex =-0 281?1gZ +3 908?1.
基金the financial support of the National Natural Science Foundation of China(Nos.52205394,12202251,52305432),ChinaPostdoctoral Science Foundation(No.2021M702024)+3 种基金Ministry of Education Industry-School Cooperative Education Project,China(No.220606517023742)Natural Science Foundation of Shandong Province,China(No.ZR2022QE122)the Open Projects Fund of State Key Laboratory of Mechanical System and Vibration,China(No.MSV202215)Shanghai Key Laboratory of Digital Manufacture of Thin-walled Structure,China(No.202302).
文摘TIG surface remelting was performed to strengthen the surface of ZL109G alloy piston.The macrostructure indicates that surface remelting leads to the production of a remelted zone(RZ).The diameter of the primary Si decreases from 65.8μm in the base metal(BM)to 7.1μm in RZ.The grain size of the RZ is refined to be approximately one-seventh that of the BM.The cellular microstructure in the RZ is characterised by theα(Al)in the centre and intermetallics preferentially located at the cellular boundaries.The results of the mechanical properties demonstrate that the average hardness value of RZ increases by 39%compared to that of BM.For the transverse samples,the ultimate tensile strength increases by~24.5%,which can be attributed to the solution strengthening of Si inα(Al).The average fracture toughness values are 15.0 and 12.7 MPa·m^(1/2)forα(Al)in BM and RZ,respectively.
基金supported by the Agency for Science,Technology and Research(A*Star),Republic of Singapore under the IAF-PP program‘Integrated large format hybrid manufacturing using wire-fed and powder-blown technology for LAAM process’,Grant No.A1893a0031the Academy of Sciences Project of Guangdong Province,Grant No.2016GDASRC-0105。
文摘It is well-known that grain refiners can tailor the microstructure and enhance the mechanical properties of titanium alloys fabricated by additive manufacturing(AM). However, the intrinsic mechanisms of Ni addition on AM-built Ti–6Al–4V alloy is not well established. This limits its industrial applications. This work systematically investigated the influence of Ni additive on Ti–6Al–4V alloy fabricated by laser aided additive manufacturing(LAAM). The results showed that Ni addition yields three key effects on the microstructural evolution of LAAM-built Ti–6Al–4V alloy.(a) Ni additive remarkably refines the prior-β grains, which is due to the widened solidification range. As the Ni addition increased from 0 to 2.5 wt. %, the major-axis length and aspect ratio of the prior-β grains reduced from over 1500 μm and 7 to 97.7 μm and1.46, respectively.(b) Ni additive can discernibly induce the formation of globular α phase,which is attributed to the enhanced concentration gradient between the β and α phases. This is the driving force of globularization according to the termination mass transfer theory. The aspect ratio of the α laths decreased from 4.14 to 2.79 as the Ni addition increased from 0 to2.5 wt. %.(c) Ni as a well-known β-stabilizer and it can remarkably increase the volume fraction of β phase. Room-temperature tensile results demonstrated an increase in mechanical strength and an almost linearly decreasing elongation with increasing Ni addition. A modified mathematical model was used to quantitatively analyze the strengthening mechanism. It was evident from the results that the α lath phase and the solid solutes contribute the most to the overall yield strength of the LAAM-built Ti–6Al–4V–x Ni alloys in this work. Furthermore, the decrease in elongation with increasing Ni addition is due to the deterioration in deformability of the β phase caused by a large amount of solid-solution Ni atoms. These findings can accelerate the development of additively manufactured titanium alloys.
基金Project(2007CB613700) supported by the National Basic Research Program of ChinaProject(2007BAG06B04) supported by the National Science and Technology Pillar Program during the 11th Five-Year Plan Period+1 种基金Project(50725413) supported by the National Natural Science Foundation of ChinaProject(CSTC2009AB4008) supported by Chongqing Science and Technology Development Program,China
文摘A new serve plastic deformation(SPD) including initial forward extrusion and subsequent shearing process(ES) was proposed.The influence of the ES forming on the grain refinement of the microstructure was researched.The components of ES forming die were manufactured and installed to Gleeble1500D thermo-mechanical simulator.The microstructure observations were carried out on the as-extruded rods(as-received) and ES formed rods.From the simulation results,ES forming can increase the cumulative strain enormously and the volume fraction of dynamic recrystallization.From the physical modeling results,the microstructures can be refined.
文摘A new process to refine the microstructure of α+βtvpe Ti alloys was developed by using hydrogen as a temporary alloying element.It involves hydrogenating the alloys below the hydrogenated β transus temperature about 0-40 K,air cooling to room temperature and then dehydrogenating at 948 K.Ti-6AI-4V and Ti-5AI-2.5Fe alloys treated hy this new process show much refined microstructures,and the yield strength,ultimate strength as well as the elongation increase 8—15,5—13 and 7—14% respectively
基金Acknowledgements-Financial support of National Science and Technology Ministry to the research projectfundamental research of
文摘The microstructure evolution during deformation enhanced transformation of undercooled austenite of a plain low carbon steel has been investigated by means of hot compression simulation experiment under various conditions of strain rate, deformation temperature and strain. The effect of austenite grain size on the strain enhanced ferrite transformation has been studied. The ferrite dynamic recrystallization involved in successive hot deformation has been explored.
基金the Natural Science Foundation of Hubei Province(No.2004ABA110)the Research Foundation for the Doctoral Program of Wuhan University of Technology(No.471-38300843)
文摘Effects of calcium addition and electromagnetic stirring on the microstructure of AZ91 magnesium alloy and refinement mechanism were investigated. The results show that calcium addition ranging from 0.1wt% to 0.3 wt% does not lead to formation of any new phases but cause the refinement of ascast microstructure.However, combined calcium alloying and electromagnetic stirring significantly decrease the grain size, change the morphologies of the β-Mg17Al12 phases,and reduce their volume percentage. The minimum grain size of AZ91 alloy is obtained in the case of the addition of 0.2 wt%Ca with exciting voltage of 100 V. The microstructural refinement is attributed to the increase of the degree of undercooling and nucleation temperature of primary α-Mg phases on the basis of DTA analysis results.
