Mg-5Li-xSn (x=0.15, 0.25 and 0.65, mass fraction) alloys were prepared. The microstructures of these alloys were investigated through optical microscope (OM), scanning electron microscope (SEM), X-ray diffractom...Mg-5Li-xSn (x=0.15, 0.25 and 0.65, mass fraction) alloys were prepared. The microstructures of these alloys were investigated through optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). The results indicate that Sn additions produce a strong grain refinement effect on Mg-5Li alloy. The mean grain size of as-cast Mg-Li alloys with Sn is reduced remarkably from 556 μm to 345 μm, and that of the as-extruded alloys is reduced from 33 μm to 23 μm when the Sn content increases from 0.15% to 0.65%. The near net-like Mg2Sn phase in the as-cast alloys is verified at the grain boundaries. After extrusion, the granular Mg2Sn phase mainly exists inside the grains and thus can act as nucleation sites of α-Mg grains during the dynamic recrystallization and make the microstructure finer.展开更多
The effects of Mn and Sn on the microstructure of Al?7Si?Mg alloy modified by Sr and Al?5Ti?B were studied. The results show that the columnar dendrites structure is observed with high content of Sr, indicating a pois...The effects of Mn and Sn on the microstructure of Al?7Si?Mg alloy modified by Sr and Al?5Ti?B were studied. The results show that the columnar dendrites structure is observed with high content of Sr, indicating a poisoning effect of the Al?5Ti?B grain refinement. In addition, Sr intermetallic compounds distribute on the TiB2 particles, which agglomerate inside the eutectic Si. The mechanism responsible for such poisoning was discussed. The addition of Mn changes the morphology of iron intermetallic compounds fromβ-Al5FeSi toα-Al(Mn,Fe)Si. Increasing the amount of Mn changes the morphology ofα-Al(Mn,Fe)Si from branched shape to rod-like shape with branched distribution, and finally convertsα-Al(Mn,Fe)Si to Chinese script shape. The microstructure observed by transmission electron microscopy (TEM) shows that Mg is more likely to interact with Sn in contrast with Si under the effect of Sn. Mg2Sn compound preferentially precipitates between the Si/Si interfaces and Al/Si interfaces.展开更多
The corrosion and electrochemical behaviors of 7A09 Al?Zn?Mg?Cu alloy were investigated in 3.5% NaCl (mass fraction) solution using complementary techniques such as scanning electron microscopy (SEM), metallogr...The corrosion and electrochemical behaviors of 7A09 Al?Zn?Mg?Cu alloy were investigated in 3.5% NaCl (mass fraction) solution using complementary techniques such as scanning electron microscopy (SEM), metallographic microscopy and electrochemical measurements. The results show that both pitting corrosion from or around the intermetallic particles and intergranular corrosion are observed after the immersion test due to the inhomogeneous nature of the microstructure of the 7A09 alloy. The preferential dissolution of the anodic Cu-depleted zone along grain boundaries is believed to be the possible cause of intergranular corrosion. The passivation and depassivation of this alloy show significant dependence of immersion time, owing to the formation and dissolution of various passive films on the sample surfaces. Furthermore, the corrosion process and corrosion mechanism were also analyzed.展开更多
Al-5C master alloy was prepared by powder in situ synthesis process, and its effects on grain refinement of AZ31 alloy and refining mechanism were investigated. The results indicate that the AI 5C master alloy consist...Al-5C master alloy was prepared by powder in situ synthesis process, and its effects on grain refinement of AZ31 alloy and refining mechanism were investigated. The results indicate that the AI 5C master alloy consists of a(Al) and A14C3 phases, and the size distribution of Al4C3 particles is controlled by sintering time. The AI 5C master alloy can remarkably reduce the grain size of AZ31 alloy, which decreases with the increasing addition amount of AI-SC master alloy when the addition amount is below 2%. The refining mechanism is attributed to the formation of new compounds of Al-C-Mnparticles by Al4C3 and Mn, which might act as nucleating substrates for a-Mg grain.展开更多
The as-cast and as-extruded Mg-9Li, Mg-9Li-0.3Ce alloys were respectively prepared through a simple alloying process and hot extrusion. The microstructures of these alloys were investigated by optical microscope (OM...The as-cast and as-extruded Mg-9Li, Mg-9Li-0.3Ce alloys were respectively prepared through a simple alloying process and hot extrusion. The microstructures of these alloys were investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). The results indicate that Ce addition produces a strong grain refining effect in Mg-9Li alloy. The grain size of the as-extruded alloy reduces abruptly from 88.2 μm to 10.5 μm when the addition of Ce is 0.36%. Mg12Ce is verified and exists inside the grains or at the grain boundaries, thus possibly pins up grain boundaries and restrains the grain growth.展开更多
The microstructure evolution of Al–Sr master alloy during continuous extrusion was investigated using X-ray diffractometer, scanning electron microscope and transmission electron microscope. Results indicate that t...The microstructure evolution of Al–Sr master alloy during continuous extrusion was investigated using X-ray diffractometer, scanning electron microscope and transmission electron microscope. Results indicate that the continuous extrusion process could change the Al4Sr particles of the alloy significantly in size and morphology. The as-cast needle-like Al4Sr particles are broken into small blocks in upsetting zone and crushed heavily in adhesion zone. Plenty of dislocations get tangled up in right-angle bending zone. Al4Sr particles grow in the extending zone. Finally, Al4Sr particles in products are approximately 28 μm in length. Al2Sr particles precipitate during the process. Compared with products by horizontal extrusion, Al4Sr particles by continuous extrusion are finer and distribute more evenly.展开更多
The electrochemical behaviors and coupling behaviors of the Mg2Si and Si phases with α(Al) were investigated, the corrosion morphologies of Al alloys containing Mg2Si and Si particles were observed, and the corrosi...The electrochemical behaviors and coupling behaviors of the Mg2Si and Si phases with α(Al) were investigated, the corrosion morphologies of Al alloys containing Mg2Si and Si particles were observed, and the corrosion mechanism associated with them in Al-Mg-Si alloys was advanced. The results show that Si particle is always cathodic to the alloy base, Mg2Si is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Mg and the enrichment of Si make Mg2Si transform to cathode from anode, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery at a later stage. As the mole ratio of Mg to Si in an Al-Mg-Si alloy is less than 1.73, it contains Mg2Si and Si particles simultaneously in the grain boundary area, and corrosion initiates on the Mg2Si surface and the precipitate-free zone (PFZ) at the adjacent periphery of Si particle. As corrosion time is extended, Si particle leads to severe anodic dissolution and corrosion of the PFZ at its adjacent periphery, expedites the polarity transformation between Mg2Si and the PFZ and accelerates the corrosion of PFZ at the adjacent periphery of Mg2Si particle.展开更多
A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed cry...A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed crystal with a diameter of (110-a:17) ~tm. The results indicate that A14C3 and TiC particle cluster, rather than a single particle, plays an important role in the refining process. Compared with the simplex smooth nucleating substrate, concave regions on the particle cluster provide easier route for the transformation from liquid Mg atoms to stable nucleus. Nucleus with a small size can also reach the critical nucleation radius when they attach on the concave regions of the substrate. A14C3 and TiC particle clusters thus become more favorable nucleating substrate for a-Mg grains.展开更多
The crystal structures,compositions and phase relations of the intermetallics of Mg-Zn-Ce system in the Mg-rich corner at 400 ℃ were identified through equilibrium alloy method.For Mg-Zn-Ce system,there is a linear t...The crystal structures,compositions and phase relations of the intermetallics of Mg-Zn-Ce system in the Mg-rich corner at 400 ℃ were identified through equilibrium alloy method.For Mg-Zn-Ce system,there is a linear ternary compound(T phase),whose chemical formula is(Mg1-xZnx)11Ce.The range of Zn content in T phase is from 9.6% to 43.6%(molar fraction).The crystal structure of T phase is C-centered orthorhombic lattice with lattice parameters of a=0.96-1.029 nm,b=1.115-1.204 nm,c=0.940-1.015 nm.And the lattice parameters of T phase are decreasing a little with increasing Zn content.According to the results of composition and crystal structure,the maximal solubility of Zn in Mg12Ce is about 7.8%(molar fraction),and the chemical formula of the solid solution can be identified as(Mg1-xZnx)12Ce.The isothermal section of Mg-Zn-Ce system in Mg-rich corner at 400 ℃ was constructed.展开更多
Ni-45.5Al-9Mo (mole fraction,%) alloy was directionally solidified with a constant temperature gradient (GL=334 K/cm) and growth rates ranging from 2 to 300 μm/s using a Bridgman type crystal growing facility wit...Ni-45.5Al-9Mo (mole fraction,%) alloy was directionally solidified with a constant temperature gradient (GL=334 K/cm) and growth rates ranging from 2 to 300 μm/s using a Bridgman type crystal growing facility with liquid metal cooling (LMC) technique. The effect of growth rate (v) on the solidified microstructures such as rod spacing (λ), rod size (d) and rod volume fraction was experimentally investigated. Two types of the solidified interfaces, planar and cellular, were identified. On the condition of both planar and cellular eutectic microstructures, the relationships between λ, d and v were given as: λv1/2=5.90 μm·μm1/2·s1/2 and dv1/2=2.18μm·μm1/2·s1/2, respectively. It was observed that the volume fraction of Mo phase could be adjusted in a certain range. The variation of phase volume fraction was attributed to undercooling increase and the growth characteristics of the individual constituent phases during the eutectic growth.展开更多
Mo5Si3-20%Al2O3 (mass fraction) nanocomposite was synthesized by mechanical alloying (MA) of mixture of MoO3,Mo,Si and Al powders.The structural evolutions of powder particles during mechanical alloying were studi...Mo5Si3-20%Al2O3 (mass fraction) nanocomposite was synthesized by mechanical alloying (MA) of mixture of MoO3,Mo,Si and Al powders.The structural evolutions of powder particles during mechanical alloying were studied by X-ray diffractometry (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM) and differential thermal analysis (DTA).Results show that Mo5Si3-20%Al2O3 was obtained after 10 h of milling.The spontaneous reaction of powders takes place in an explosive mode.The crystallite sizes of Mo5Si3 and Al2O3 after milling for 30 h were 36.3 nm and 21.9 nm,respectively.With longer milling time,the intensities of Mo5Si3 and Al2O3 peaks decreased and became broad due to the decrease in crystallite size.Thermal analysis results and XRD analysis results show that the Mo5Si3-Al2O3 nanocomposite powders are very stable during milling (up to 30 h) and heating (up to 1 000℃) and no transformation takes place.展开更多
The objective of the current study was to investigate the use of ultrasonic melt treatment technology in the production of grain-refined billets of the AC7 A alloy, which was intended for subsequent use as a feedstock...The objective of the current study was to investigate the use of ultrasonic melt treatment technology in the production of grain-refined billets of the AC7 A alloy, which was intended for subsequent use as a feedstock in forming operations. The experiments included the application of ultrasonic vibrations to the molten alloys via direct and indirect techniques. Several process parameters such as pouring temperatures(several temperatures between 740 and 660℃), and treatment time(from 12 min down to 2 min) were investigated. The experiment included continuous ultrasonic treatment from the liquid to the semisolid states. The results showed that both treatment techniques were viable for producing billets with the desirable microstructural characteristics. The optimum treatment conditions were the short treatment time(2 to 3 min), from about 660℃ down to 615℃ for the indirect treatment technique, and from 660℃ to 635℃ for the direct treatment technique. The resulting microstructures, at three positions along the height of the ingot, were characterized by fine, non-dendritic α(Al) grains in the order of a hundred microns, as compared to few thousands of microns for the conventional cast ingots. The intermetallic particles were also refined in size and modified in morphology by the ultrasonic treatment. The operating mechanisms by which the ultrasonic vibrations altered the ingot microstructures were discussed and analyzed.展开更多
Aluminum-10% TiB master alloy was added in various proportions in 7178 Al alloy in order to examine the effect of TiB on grain refinement, wear and compressive deformation of the later one. Microstructural characteriz...Aluminum-10% TiB master alloy was added in various proportions in 7178 Al alloy in order to examine the effect of TiB on grain refinement, wear and compressive deformation of the later one. Microstructural characterization reveals that TiB particles act as grain refiners for primary base alloy and result in globular dendrites. It was observed that the wear resistance and strength of the alloy decreased when the master alloy addition increased beyond 20%, even though the dendrites become much finer and almost spherical in nature.展开更多
Hot compression was performed on a multilayered Au−20Sn eutectic alloy to investigate the deformation behavior and microstructure evolution.During hot compression,microstructural spheroidization was initiated from pla...Hot compression was performed on a multilayered Au−20Sn eutectic alloy to investigate the deformation behavior and microstructure evolution.During hot compression,microstructural spheroidization was initiated from plastic instability regions,and it was preferentially activated in vertical lamellae with a growth direction parallel to the compressive direction.Continuous dynamic recrystallization associated with lattice dislocations was the mechanism in both AuSn and Au5Sn multilayers.After spheroidization,strain accumulations were weakened in both of the equiaxed phases,and the deformation mechanism was substantially replaced by grain boundary sliding and migration.Based on these findings,hot rolling was conducted on an as-cast Au−20Sn alloy and a foil with a thickness of~50μm was successfully prepared.The present study can promote the development of Au−20Sn foils,and provide insights into the deformation behavior and microstructure evolution of multilayered eutectic alloys.展开更多
The structure of the quaternary Al?(2?4)wt.%Ca?Ni?La system near the aluminum corner has been studied using computational analysis in the Thermo-Calc program and experimental studies(electron microscopy,microprobe ana...The structure of the quaternary Al?(2?4)wt.%Ca?Ni?La system near the aluminum corner has been studied using computational analysis in the Thermo-Calc program and experimental studies(electron microscopy,microprobe analysis and X-ray diffraction).Based on the phase equilibria data obtained,the experimental projection of the liquidus surface and solid state phase-field distribution of the Al?Ca?Ni?La system have been proposed.Microstructure studies reveal that the alloys with the 2?4 wt.%Ca,2?4 wt.%Ni and 1?3 wt.%La ranges have an ultra-fine hypoeutectic structure with 30%volume fraction of eutectic intermetallics,which allows one to classify these alloys as natural Al-matrix composites.The ultra-fine eutectic structure produces significant strengthening,the magnitude of which can be well described using the modified Orowan looping mechanism model.Small additives of Zr and Sc(0.2 and 0.1 wt.%,respectively)lead to significant strengthening(by^25%)due to the formation of L12 type phase(Al3(Zr,Sc))nanoparticles during annealing of the alloy at 350?400℃.Due to the high volume fraction of eutectic intermetallics,the new alloys have low coefficients of thermal expansion and high thermal stability of the structure and mechanical properties.展开更多
基金Projects (51171212, 50725413) supported by the National Natural Science Foundation of ChinaProject (2007CB613706) supported by the National Basic Research Program of China+1 种基金Project (2009AA03Z507) supported by the National High-tech Research Program of ChinaProjects (2010CSTC-BJLKR, CSTC2010AA4048) supported by Chongqing Science and Technology Commission, China
文摘Mg-5Li-xSn (x=0.15, 0.25 and 0.65, mass fraction) alloys were prepared. The microstructures of these alloys were investigated through optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). The results indicate that Sn additions produce a strong grain refinement effect on Mg-5Li alloy. The mean grain size of as-cast Mg-Li alloys with Sn is reduced remarkably from 556 μm to 345 μm, and that of the as-extruded alloys is reduced from 33 μm to 23 μm when the Sn content increases from 0.15% to 0.65%. The near net-like Mg2Sn phase in the as-cast alloys is verified at the grain boundaries. After extrusion, the granular Mg2Sn phase mainly exists inside the grains and thus can act as nucleation sites of α-Mg grains during the dynamic recrystallization and make the microstructure finer.
文摘The effects of Mn and Sn on the microstructure of Al?7Si?Mg alloy modified by Sr and Al?5Ti?B were studied. The results show that the columnar dendrites structure is observed with high content of Sr, indicating a poisoning effect of the Al?5Ti?B grain refinement. In addition, Sr intermetallic compounds distribute on the TiB2 particles, which agglomerate inside the eutectic Si. The mechanism responsible for such poisoning was discussed. The addition of Mn changes the morphology of iron intermetallic compounds fromβ-Al5FeSi toα-Al(Mn,Fe)Si. Increasing the amount of Mn changes the morphology ofα-Al(Mn,Fe)Si from branched shape to rod-like shape with branched distribution, and finally convertsα-Al(Mn,Fe)Si to Chinese script shape. The microstructure observed by transmission electron microscopy (TEM) shows that Mg is more likely to interact with Sn in contrast with Si under the effect of Sn. Mg2Sn compound preferentially precipitates between the Si/Si interfaces and Al/Si interfaces.
基金Project(JSJC2013209B057)supported by the National Defense Technology Foundation of China
文摘The corrosion and electrochemical behaviors of 7A09 Al?Zn?Mg?Cu alloy were investigated in 3.5% NaCl (mass fraction) solution using complementary techniques such as scanning electron microscopy (SEM), metallographic microscopy and electrochemical measurements. The results show that both pitting corrosion from or around the intermetallic particles and intergranular corrosion are observed after the immersion test due to the inhomogeneous nature of the microstructure of the 7A09 alloy. The preferential dissolution of the anodic Cu-depleted zone along grain boundaries is believed to be the possible cause of intergranular corrosion. The passivation and depassivation of this alloy show significant dependence of immersion time, owing to the formation and dissolution of various passive films on the sample surfaces. Furthermore, the corrosion process and corrosion mechanism were also analyzed.
基金Project(2011921065)supported by Liaoning BaiQianWan Talents Program,ChinaProject(DUT11ZD115)supported by the Fundamental Research Funds for the Central Universities,China
文摘Al-5C master alloy was prepared by powder in situ synthesis process, and its effects on grain refinement of AZ31 alloy and refining mechanism were investigated. The results indicate that the AI 5C master alloy consists of a(Al) and A14C3 phases, and the size distribution of Al4C3 particles is controlled by sintering time. The AI 5C master alloy can remarkably reduce the grain size of AZ31 alloy, which decreases with the increasing addition amount of AI-SC master alloy when the addition amount is below 2%. The refining mechanism is attributed to the formation of new compounds of Al-C-Mnparticles by Al4C3 and Mn, which might act as nucleating substrates for a-Mg grain.
基金Project(2007CB613706)supported by the National Basic Research Program of ChinaProject(2009AA03Z507)supported by the National High-tech Program of ChinaProjects(2010CSTC-HDLS,CSTC2010AA4048)supported by Chongqing Science and Technology Commission,China
文摘The as-cast and as-extruded Mg-9Li, Mg-9Li-0.3Ce alloys were respectively prepared through a simple alloying process and hot extrusion. The microstructures of these alloys were investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). The results indicate that Ce addition produces a strong grain refining effect in Mg-9Li alloy. The grain size of the as-extruded alloy reduces abruptly from 88.2 μm to 10.5 μm when the addition of Ce is 0.36%. Mg12Ce is verified and exists inside the grains or at the grain boundaries, thus possibly pins up grain boundaries and restrains the grain growth.
基金Project(51175055)supported by the National Natural Science Foundation of ChinaProject(LR2015011)supported by Program for Liaoning Excellent Talents in University,China
文摘The microstructure evolution of Al–Sr master alloy during continuous extrusion was investigated using X-ray diffractometer, scanning electron microscope and transmission electron microscope. Results indicate that the continuous extrusion process could change the Al4Sr particles of the alloy significantly in size and morphology. The as-cast needle-like Al4Sr particles are broken into small blocks in upsetting zone and crushed heavily in adhesion zone. Plenty of dislocations get tangled up in right-angle bending zone. Al4Sr particles grow in the extending zone. Finally, Al4Sr particles in products are approximately 28 μm in length. Al2Sr particles precipitate during the process. Compared with products by horizontal extrusion, Al4Sr particles by continuous extrusion are finer and distribute more evenly.
基金Project (21073162) supported by the National Natural Science Foundation of ChinaProject (2008) supported by the Scientific and Technological Projects of Ningxia, China+1 种基金Project (08JC1421600) supported by the Science and Technology Commission of Shanghai Municipality, ChinaProject (2008AZ2018) supported by the Science and Technology Bureau of Jiaxing City, China
文摘The electrochemical behaviors and coupling behaviors of the Mg2Si and Si phases with α(Al) were investigated, the corrosion morphologies of Al alloys containing Mg2Si and Si particles were observed, and the corrosion mechanism associated with them in Al-Mg-Si alloys was advanced. The results show that Si particle is always cathodic to the alloy base, Mg2Si is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Mg and the enrichment of Si make Mg2Si transform to cathode from anode, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery at a later stage. As the mole ratio of Mg to Si in an Al-Mg-Si alloy is less than 1.73, it contains Mg2Si and Si particles simultaneously in the grain boundary area, and corrosion initiates on the Mg2Si surface and the precipitate-free zone (PFZ) at the adjacent periphery of Si particle. As corrosion time is extended, Si particle leads to severe anodic dissolution and corrosion of the PFZ at its adjacent periphery, expedites the polarity transformation between Mg2Si and the PFZ and accelerates the corrosion of PFZ at the adjacent periphery of Mg2Si particle.
基金Project(DUT15JJ(G)01) supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2009AA03Z525) supported by the National High-tech Research and Development Program of China
文摘A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed crystal with a diameter of (110-a:17) ~tm. The results indicate that A14C3 and TiC particle cluster, rather than a single particle, plays an important role in the refining process. Compared with the simplex smooth nucleating substrate, concave regions on the particle cluster provide easier route for the transformation from liquid Mg atoms to stable nucleus. Nucleus with a small size can also reach the critical nucleation radius when they attach on the concave regions of the substrate. A14C3 and TiC particle clusters thus become more favorable nucleating substrate for a-Mg grains.
基金Project(N110323017) supported by the Fundamental Research Funds for the Central Universities,ChinaProject(E2010001390) supported by the Natural Science Foundation of Hebei Province,China
文摘The crystal structures,compositions and phase relations of the intermetallics of Mg-Zn-Ce system in the Mg-rich corner at 400 ℃ were identified through equilibrium alloy method.For Mg-Zn-Ce system,there is a linear ternary compound(T phase),whose chemical formula is(Mg1-xZnx)11Ce.The range of Zn content in T phase is from 9.6% to 43.6%(molar fraction).The crystal structure of T phase is C-centered orthorhombic lattice with lattice parameters of a=0.96-1.029 nm,b=1.115-1.204 nm,c=0.940-1.015 nm.And the lattice parameters of T phase are decreasing a little with increasing Zn content.According to the results of composition and crystal structure,the maximal solubility of Zn in Mg12Ce is about 7.8%(molar fraction),and the chemical formula of the solid solution can be identified as(Mg1-xZnx)12Ce.The isothermal section of Mg-Zn-Ce system in Mg-rich corner at 400 ℃ was constructed.
基金Project (51074128) supported by the National Natural Science Foundation of ChinaProject (2007ZF53067) supported by the Aeronautical Science Foundation of China+1 种基金Project (2010JM6002) supported by the Natural Science Foundation of Shaanxi Province of ChinaProjec t(2012NCL004) supported by the Innovation Foundation of Inner Mongolia University of Science and Technology
文摘Ni-45.5Al-9Mo (mole fraction,%) alloy was directionally solidified with a constant temperature gradient (GL=334 K/cm) and growth rates ranging from 2 to 300 μm/s using a Bridgman type crystal growing facility with liquid metal cooling (LMC) technique. The effect of growth rate (v) on the solidified microstructures such as rod spacing (λ), rod size (d) and rod volume fraction was experimentally investigated. Two types of the solidified interfaces, planar and cellular, were identified. On the condition of both planar and cellular eutectic microstructures, the relationships between λ, d and v were given as: λv1/2=5.90 μm·μm1/2·s1/2 and dv1/2=2.18μm·μm1/2·s1/2, respectively. It was observed that the volume fraction of Mo phase could be adjusted in a certain range. The variation of phase volume fraction was attributed to undercooling increase and the growth characteristics of the individual constituent phases during the eutectic growth.
基金Project(3ZS061-A25-038) supported by the Natural Science Foundation of Gansu Province,China
文摘Mo5Si3-20%Al2O3 (mass fraction) nanocomposite was synthesized by mechanical alloying (MA) of mixture of MoO3,Mo,Si and Al powders.The structural evolutions of powder particles during mechanical alloying were studied by X-ray diffractometry (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM) and differential thermal analysis (DTA).Results show that Mo5Si3-20%Al2O3 was obtained after 10 h of milling.The spontaneous reaction of powders takes place in an explosive mode.The crystallite sizes of Mo5Si3 and Al2O3 after milling for 30 h were 36.3 nm and 21.9 nm,respectively.With longer milling time,the intensities of Mo5Si3 and Al2O3 peaks decreased and became broad due to the decrease in crystallite size.Thermal analysis results and XRD analysis results show that the Mo5Si3-Al2O3 nanocomposite powders are very stable during milling (up to 30 h) and heating (up to 1 000℃) and no transformation takes place.
文摘The objective of the current study was to investigate the use of ultrasonic melt treatment technology in the production of grain-refined billets of the AC7 A alloy, which was intended for subsequent use as a feedstock in forming operations. The experiments included the application of ultrasonic vibrations to the molten alloys via direct and indirect techniques. Several process parameters such as pouring temperatures(several temperatures between 740 and 660℃), and treatment time(from 12 min down to 2 min) were investigated. The experiment included continuous ultrasonic treatment from the liquid to the semisolid states. The results showed that both treatment techniques were viable for producing billets with the desirable microstructural characteristics. The optimum treatment conditions were the short treatment time(2 to 3 min), from about 660℃ down to 615℃ for the indirect treatment technique, and from 660℃ to 635℃ for the direct treatment technique. The resulting microstructures, at three positions along the height of the ingot, were characterized by fine, non-dendritic α(Al) grains in the order of a hundred microns, as compared to few thousands of microns for the conventional cast ingots. The intermetallic particles were also refined in size and modified in morphology by the ultrasonic treatment. The operating mechanisms by which the ultrasonic vibrations altered the ingot microstructures were discussed and analyzed.
文摘Aluminum-10% TiB master alloy was added in various proportions in 7178 Al alloy in order to examine the effect of TiB on grain refinement, wear and compressive deformation of the later one. Microstructural characterization reveals that TiB particles act as grain refiners for primary base alloy and result in globular dendrites. It was observed that the wear resistance and strength of the alloy decreased when the master alloy addition increased beyond 20%, even though the dendrites become much finer and almost spherical in nature.
基金financial supports from the National Natural Science Foundation of China(Nos.U1502272,51901204)the Precious Metal Materials Genome Engineering in Yunnan Province,China(Nos.2019ZE001,202002AB080001)。
文摘Hot compression was performed on a multilayered Au−20Sn eutectic alloy to investigate the deformation behavior and microstructure evolution.During hot compression,microstructural spheroidization was initiated from plastic instability regions,and it was preferentially activated in vertical lamellae with a growth direction parallel to the compressive direction.Continuous dynamic recrystallization associated with lattice dislocations was the mechanism in both AuSn and Au5Sn multilayers.After spheroidization,strain accumulations were weakened in both of the equiaxed phases,and the deformation mechanism was substantially replaced by grain boundary sliding and migration.Based on these findings,hot rolling was conducted on an as-cast Au−20Sn alloy and a foil with a thickness of~50μm was successfully prepared.The present study can promote the development of Au−20Sn foils,and provide insights into the deformation behavior and microstructure evolution of multilayered eutectic alloys.
基金financial support of the grant of the Russian Science Foundation(Project No.18-79-00345)(preparation of alloys,electron microscopy(SEM,EMPA,TEM),tensile tests)Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of MISiS(No.P02-2017-2-10)(thermodynamic calculations,dilatometry,DSC and XRD).
文摘The structure of the quaternary Al?(2?4)wt.%Ca?Ni?La system near the aluminum corner has been studied using computational analysis in the Thermo-Calc program and experimental studies(electron microscopy,microprobe analysis and X-ray diffraction).Based on the phase equilibria data obtained,the experimental projection of the liquidus surface and solid state phase-field distribution of the Al?Ca?Ni?La system have been proposed.Microstructure studies reveal that the alloys with the 2?4 wt.%Ca,2?4 wt.%Ni and 1?3 wt.%La ranges have an ultra-fine hypoeutectic structure with 30%volume fraction of eutectic intermetallics,which allows one to classify these alloys as natural Al-matrix composites.The ultra-fine eutectic structure produces significant strengthening,the magnitude of which can be well described using the modified Orowan looping mechanism model.Small additives of Zr and Sc(0.2 and 0.1 wt.%,respectively)lead to significant strengthening(by^25%)due to the formation of L12 type phase(Al3(Zr,Sc))nanoparticles during annealing of the alloy at 350?400℃.Due to the high volume fraction of eutectic intermetallics,the new alloys have low coefficients of thermal expansion and high thermal stability of the structure and mechanical properties.