Mg-14Li-1Al （LA141）, LA141-0.3Y, LA141-0.3Sr, and LA141-0.3Y-0.3Sr alloys were prepared in an induction furnace in the argon atmosphere. The microstructures of these alloys were investigated through scanning electro...Mg-14Li-1Al （LA141）, LA141-0.3Y, LA141-0.3Sr, and LA141-0.3Y-0.3Sr alloys were prepared in an induction furnace in the argon atmosphere. The microstructures of these alloys were investigated through scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA141 alloy. The mean grain sizes of the alloys with addition of Y and/or Sr are reduced remarkably from 600 to 500, 260, 230 μm, respectively. Al 2 Y, Al 4 Sr and Mg 17 Sr 2 phases with different morphologies are verified and exist inside the grain or at the grain boundaries, thus possibly act as heterogeneous nucleation sites and pin up grain boundaries, which restrain the grain growth.展开更多
The refining effect of Al3Ti1B1RE master alloy on Al sheets used for pressure can manufacture and the behavior of mixed rare earths in master alloy were investigated with XRD, OM, SEM and EDAX. It is found that the r...The refining effect of Al3Ti1B1RE master alloy on Al sheets used for pressure can manufacture and the behavior of mixed rare earths in master alloy were investigated with XRD, OM, SEM and EDAX. It is found that the refining effect of the refiner on the material has superiority over foreign or domestic Al5Ti1B refiner, and the refiner still retains its refining ability for 6 h after adding it to molten Al, thus improving the strength and plasticity of the material remarkably. The excellent refining effect and stability of AlTiBRE refiner result from that RE can lower the surface energy of molten Al and improve the wetting characteristics of molten Al on refinement nuclei such as TiAl 3, TiB 2, etc., thus giving full play to the effect of heterogeneous nucleation and impeding the congregating tendency of TiB 2 phase in molten Al. At the same time, RE gathering in front of solid/liquid interface are also easy to cause composition supercooling in molten Al, thus impeding the growth of α Al grains and promoting α Al nucleation on refinement nuclei. In addition, RE also play certain role in purification and grain refinement, or modification, especially their effect of purification can improve the metallurgical quality of AlTiBRE master alloy.展开更多
To clarify the corrosion mechanism associated with the precipitate of T1(Al2CuLi)in Al-Li alloys,the simulated bulk precipitate of T1 was fabricated through melting and casting.Its electrochemical behavior and couplin...To clarify the corrosion mechanism associated with the precipitate of T1(Al2CuLi)in Al-Li alloys,the simulated bulk precipitate of T1 was fabricated through melting and casting.Its electrochemical behavior and coupling behavior with α(Al)in 3.5% NaCl solution were investigated.Meanwhile,the simulated Al alloy containing T1 particle was prepared and its corrosion morphology was observed.The results show that there exists a dynamic conversion corrosion mechanism associated with the precipitate of T1.At the beginning,the precipitate of T1 is anodic to the alloy base and corrosion occurs on its surface.However,during its corrosion process,its potential moves to a positive direction with immersion time increasing,due to the preferential dissolution of Li and the enrichment of Cu.As a result,the corroded T1 becomes cathodic to the alloy base at a later stage,leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery.It is suggested that the localized corrosion associated with the precipitate of T1 in Al-Li alloys is caused by the alternate anodic dissolution of the T1 precipitate and the alloy base at its adjacent periphery.展开更多
Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case,the fatigue crack growth sensitivity and fracture features with various tailoredαphase morphologies were thoroughly investigated using fatigue crack growth rate(...Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case,the fatigue crack growth sensitivity and fracture features with various tailoredαphase morphologies were thoroughly investigated using fatigue crack growth rate(FCGR)test,optical microscopy(OM)and scanning electron microscopy(SEM).The tailored microstructures by heat treatments include the fine and coarse secondaryαphase,as well as the widmanstatten and basket weave features.The sample with coarse secondaryαphase exhibits better comprehensive properties of good crack propagation resistance(with long Paris regime ranging from 15 to 60 MPa·m1/2),high yield strength(1113 MPa)and ultimate strength(1150 MPa),and good elongation(11.6%).The good crack propagation resistance can be attributed to crack deflection,long secondary crack,and tortuous crack path induced by coarse secondaryαphase.展开更多
The mechanical properties of castings depend on the grain size.There is evidence that titanium and boron(Al-5Ti-1B master alloy)affect the grain size of magnesium alloys.Here,the influence of the addition of 0-1 wt.%o...The mechanical properties of castings depend on the grain size.There is evidence that titanium and boron(Al-5Ti-1B master alloy)affect the grain size of magnesium alloys.Here,the influence of the addition of 0-1 wt.%of Al-5Ti-1B master alloy on the grain size of AZ91 magnesium alloy was investigated.Melting of the alloy was performed in steel and corundum crucibles.To study the effect of cooling rate on grain size,cylindrical samples were cast in steel and fireclay molds.The Al-5Ti-1B master alloy addition did not change the phase composition of the AZ91 alloy.This study demonstrates that the addition of Al-5Ti-1B did not contribute to the grain refinement of the AZ91 alloy,but rather led to its coarsening for samples cast in both the steel and fireclay molds.Increasing the holding time after the addition of the Al-5Ti-1B master alloy from 15 to 110 minutes also did not lead to significant grain coarsening.The mechanical properties of the AZ91 alloy samples slightly improved after Al-5Ti-1B addition.展开更多
The as-cast and as-extruded Mg–9Li–1Al–xCa alloys(x=0,0.2;wt%)were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2.The microstructures of the as-cast and as-extruded...The as-cast and as-extruded Mg–9Li–1Al–xCa alloys(x=0,0.2;wt%)were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2.The microstructures of the as-cast and as-extruded Mg–9Li–1Al–xCa alloys were observed to investigate the effect of calcium(Ca)element on the Mg–9Li–1Al(LA91)alloy,and the crystallographic calculations between Al_(2)Ca and the matrix(α-Mg andβ-Li phases)were examined on the basis of the edge-to-edge matching model.The experimental results indicate that the addition of 0.2 wt%Ca into LA91 alloy reduce the size of theα-Mg phases in the as-cast alloy and that ofβ-Li phases in the as-extruded alloy due to the Al_(2)Ca particles distributed inside the matrix.Crystallographic calculation results suggested that there is a good crystallographic matching between the matrix and Al_(2)Ca,which confirmed that Al_(2)Ca particles can act as a heterogeneous nucleation site for bothα-Mg andβ-Li phases and were effective grain refiners for LA91 alloy.展开更多
A near eutectic Al−12.6Si alloy was developed with 0.0wt%,2.0wt%,4.0wt%,and 6.0wt%Al−5Ti−1B master alloy.The micro-structural morphology,hardness,tensile strength,elongation,and fracture behaviour of the alloys were s...A near eutectic Al−12.6Si alloy was developed with 0.0wt%,2.0wt%,4.0wt%,and 6.0wt%Al−5Ti−1B master alloy.The micro-structural morphology,hardness,tensile strength,elongation,and fracture behaviour of the alloys were studied.The unmodified Al−12.6Si al-loy has an irregular needle and plate-like eutectic silicon(ESi)and coarse polygonal primary silicon(PSi)particles in the matrix-likeα-Al phase.The P_(Si),E_(Si),andα-Al morphology and volume fraction were changed due to the addition of the Al−5Ti−1B master alloy.The hardness,UTS,and elongation improved due to the microstructural modification.Nano-sized in-situ Al3Ti particles and ex-situ TiB_(2)particles caused the mi-crostructural modification.The fracture images of the developed alloys exhibit a ductile and brittle mode of fracture at the same time.The Al−5Ti−1B modified alloys have a more ductile mode of fracture and more dimples compared to the unmodified alloy.展开更多
The microstructure characteristics in early stage shear localization of near-αTi−6Al−2Zr−1Mo−1V titanium alloy were investigated by split Hopkinson pressure bar(SHPB)tests using hat-shaped specimens.The microstructur...The microstructure characteristics in early stage shear localization of near-αTi−6Al−2Zr−1Mo−1V titanium alloy were investigated by split Hopkinson pressure bar(SHPB)tests using hat-shaped specimens.The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction(EBSD)method.It is found that the nucleation and expansion of adiabatic shear band(ASB)are affected by both geometric and structural factors.The increase of dislocation density,structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions.In addition to the dislocation slips,the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect.Interestingly,the sandwich structure imposes a crucial influence on ASB,which finally becomes a mature wide ASB in the dynamic deformation.However,due to much larger width,the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation.展开更多
Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidati...Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3＋Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the AI content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.展开更多
Al-5Ti-1B master alloy was added into Mg-14Li-1Al(LA141)alloy and then LA141 sheets were prepared by extrusion and cold rolling.The effect of the addition level of Al-5Ti-1B master alloy on the grain size of LA141 all...Al-5Ti-1B master alloy was added into Mg-14Li-1Al(LA141)alloy and then LA141 sheets were prepared by extrusion and cold rolling.The effect of the addition level of Al-5Ti-1B master alloy on the grain size of LA141 alloy was investigated as well as the effects of the total reduction of cold rolling and the annealing temperature on microstructure,mechanical properties and plastic formability of the LA141 sheets.The results show that the optimal addition level of Al-5Ti-1B master alloy into LA141 alloy is 1.25%(mass fraction)and LA141 alloy has the finest grains.With the increase of the total reduction of cold rolling,the grains of the as-rolled LA141 sheets were flattened gradually.A proper anneal temperature of 200℃ is obtained for the cold rolled LA141 sheets. Under this condition,microstructure of the LA141 sheets consists of fine and uniform equiaxed grains and has higher Erichsen cupping index(IE).展开更多
AZ61 alloys with different levels of Al5Ti1B master alloy additions were prepared by conventional casting method.The effects of Al5Ti1B contents and holding time on microstructures and microhardness of AZ61 alloys wer...AZ61 alloys with different levels of Al5Ti1B master alloy additions were prepared by conventional casting method.The effects of Al5Ti1B contents and holding time on microstructures and microhardness of AZ61 alloys were studied by XRD,OM and microhardness testing techniques.The results show that when the addition level of Al5Ti1B master alloy is less than 0.5%(mass fraction),the average grain size of the alloys decreases with the increase of Al5Ti1B content at the same holding time.But the grain size increases somewhat with further addition of Al5Ti1B.The average grain size of the alloys decreases with the increase of the holding time as it is less than 30 min at the same addition level of Al5Ti1B.It is considered that TiB2 particles can serve as the heterogeneous nucleation sites ofα-Mg during solidification,and heterogeneous nucleation is the main reason for the grain refinement of AZ61 alloys.The microhardness of the refined AZ61 alloys with 1.0%Al5Ti1B addition is increased by about 8%.展开更多
The behavior of growth and coarsening of T-1(Al2CuLi) precipitates was comparatively studied by means of TEM technique in two Al-Li alloys 2090 and 2090+Ce (with cerium content less than 0.1% in mass fraction). Statis...The behavior of growth and coarsening of T-1(Al2CuLi) precipitates was comparatively studied by means of TEM technique in two Al-Li alloys 2090 and 2090+Ce (with cerium content less than 0.1% in mass fraction). Statistical analysis results show that T-1 precipitates in alloy 2090+Ce have smaller aspect ratio, which is connected with the more intersections between different T-1 variants in this alloy. It is also found that the variation of maximum length of T-1 precipitates with aging time can be obviously divided into two stages of growth and coarsening. The diffusion coefficients of solute atoms of Cu and Li are calculated via growth kinetics curves of T-1 precipitates. The results show that the diffusion of atom Cu plays a more important role in the formation of T-1 precipitates.展开更多
Al5Ti1B master alloy was produced by two-step method. Experimental results show that the structure of Al5TilB master alloy depends on that of AlTi and AlB master alloys, the morphologies of TiAl3 depend on AlTi master...Al5Ti1B master alloy was produced by two-step method. Experimental results show that the structure of Al5TilB master alloy depends on that of AlTi and AlB master alloys, the morphologies of TiAl3 depend on AlTi master alloy and the boride phases depend on AlB master alloy. There are remarkable structure heredity between Al5Ti1B master alloy and AlTi, AlB master alloys. Theoretical analyses show that AlTi and Al-B master alloys can change the melt structure of Al5Ti1B master alloy, then affect the solid structure of the master alloy.展开更多
Rotating electromagnetic field is applied to the centrifugal casting, the macrostructure of centrifugal casting Al-1%Cu alloy stirred with driving or backing magnetic field are both examined. It is shown that both kin...Rotating electromagnetic field is applied to the centrifugal casting, the macrostructure of centrifugal casting Al-1%Cu alloy stirred with driving or backing magnetic field are both examined. It is shown that both kinds of electromagnetic filed can enforce the columnar-equiaxed transition, the driving one decrease the tendency of porosity occurring due to the increase in the bulk liquid pressure. Stirring with braking electromagnetic field produces the mixture of outer fine grains and inner coarse grains in the casting, this is analyzed to be contributed to the differences both in electric conductivity and density between the crystal and the melt, as well as skin effects.展开更多
Grain refinement can offer significant benefits to both continuous casting and cast to shape products, and Al5Ti1B master alloy containing mainly TiAl 3 and TiB 2 particles in Al matrix has been proven to perform well...Grain refinement can offer significant benefits to both continuous casting and cast to shape products, and Al5Ti1B master alloy containing mainly TiAl 3 and TiB 2 particles in Al matrix has been proven to perform well for giving the best refinement, but the working method of adding Al5Ti1B rod to the furnace during casting are often related to solid deformation, and melt vibration may help to reduce the size of TiAl 3 and improve the distribution of TiB 2. Therefore the effects of solid deformation and melt vibration on the structures and refinement performance of Al5Ti1B master alloys were studied. The experimental results show that both solid deformation and melt vibration can improve the distribution of TiB 2 in Al5Ti1B master alloys, increase the interface energy and nucleation activity of TiB 2 particles. In the meantime, solid deformation can store deformation energy and melt vibration can break fragile plate like TiAl 3 compounds. So both methods can improve the refinement effectiveness of Al5Ti1B master alloys.展开更多
基金Project(50725413)supported by the National Natural Science Foundation of ChinaProject(2010CSTC-BJLKR)supported by Chongqing Science and Technology Commission, ChinaProject(CDJXS10132203)supported by the Fundamental Research Funds for the Central Universities,China
文摘Mg-14Li-1Al （LA141）, LA141-0.3Y, LA141-0.3Sr, and LA141-0.3Y-0.3Sr alloys were prepared in an induction furnace in the argon atmosphere. The microstructures of these alloys were investigated through scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA141 alloy. The mean grain sizes of the alloys with addition of Y and/or Sr are reduced remarkably from 600 to 500, 260, 230 μm, respectively. Al 2 Y, Al 4 Sr and Mg 17 Sr 2 phases with different morphologies are verified and exist inside the grain or at the grain boundaries, thus possibly act as heterogeneous nucleation sites and pin up grain boundaries, which restrain the grain growth.
文摘The refining effect of Al3Ti1B1RE master alloy on Al sheets used for pressure can manufacture and the behavior of mixed rare earths in master alloy were investigated with XRD, OM, SEM and EDAX. It is found that the refining effect of the refiner on the material has superiority over foreign or domestic Al5Ti1B refiner, and the refiner still retains its refining ability for 6 h after adding it to molten Al, thus improving the strength and plasticity of the material remarkably. The excellent refining effect and stability of AlTiBRE refiner result from that RE can lower the surface energy of molten Al and improve the wetting characteristics of molten Al on refinement nuclei such as TiAl 3, TiB 2, etc., thus giving full play to the effect of heterogeneous nucleation and impeding the congregating tendency of TiB 2 phase in molten Al. At the same time, RE gathering in front of solid/liquid interface are also easy to cause composition supercooling in molten Al, thus impeding the growth of α Al grains and promoting α Al nucleation on refinement nuclei. In addition, RE also play certain role in purification and grain refinement, or modification, especially their effect of purification can improve the metallurgical quality of AlTiBRE master alloy.
基金Project(50401012) supported by the National Natural Science Foundation of China
文摘To clarify the corrosion mechanism associated with the precipitate of T1(Al2CuLi)in Al-Li alloys,the simulated bulk precipitate of T1 was fabricated through melting and casting.Its electrochemical behavior and coupling behavior with α(Al)in 3.5% NaCl solution were investigated.Meanwhile,the simulated Al alloy containing T1 particle was prepared and its corrosion morphology was observed.The results show that there exists a dynamic conversion corrosion mechanism associated with the precipitate of T1.At the beginning,the precipitate of T1 is anodic to the alloy base and corrosion occurs on its surface.However,during its corrosion process,its potential moves to a positive direction with immersion time increasing,due to the preferential dissolution of Li and the enrichment of Cu.As a result,the corroded T1 becomes cathodic to the alloy base at a later stage,leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery.It is suggested that the localized corrosion associated with the precipitate of T1 in Al-Li alloys is caused by the alternate anodic dissolution of the T1 precipitate and the alloy base at its adjacent periphery.
基金Project(U1867201)supported by the National Natural Science Foundation of ChinaProject supported by State Key Laboratory of Powder Metallurgy,Central South University,China。
文摘Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case,the fatigue crack growth sensitivity and fracture features with various tailoredαphase morphologies were thoroughly investigated using fatigue crack growth rate(FCGR)test,optical microscopy(OM)and scanning electron microscopy(SEM).The tailored microstructures by heat treatments include the fine and coarse secondaryαphase,as well as the widmanstatten and basket weave features.The sample with coarse secondaryαphase exhibits better comprehensive properties of good crack propagation resistance(with long Paris regime ranging from 15 to 60 MPa·m1/2),high yield strength(1113 MPa)and ultimate strength(1150 MPa),and good elongation(11.6%).The good crack propagation resistance can be attributed to crack deflection,long secondary crack,and tortuous crack path induced by coarse secondaryαphase.
文摘The mechanical properties of castings depend on the grain size.There is evidence that titanium and boron(Al-5Ti-1B master alloy)affect the grain size of magnesium alloys.Here,the influence of the addition of 0-1 wt.%of Al-5Ti-1B master alloy on the grain size of AZ91 magnesium alloy was investigated.Melting of the alloy was performed in steel and corundum crucibles.To study the effect of cooling rate on grain size,cylindrical samples were cast in steel and fireclay molds.The Al-5Ti-1B master alloy addition did not change the phase composition of the AZ91 alloy.This study demonstrates that the addition of Al-5Ti-1B did not contribute to the grain refinement of the AZ91 alloy,but rather led to its coarsening for samples cast in both the steel and fireclay molds.Increasing the holding time after the addition of the Al-5Ti-1B master alloy from 15 to 110 minutes also did not lead to significant grain coarsening.The mechanical properties of the AZ91 alloy samples slightly improved after Al-5Ti-1B addition.
基金The authors are grateful for the financial supports from National Natural Science Foundation of China(51171212)Chongqing Science and Technology Commission(CSTC2012JJJQ50001,CSTC2013jcyjC60001,cstc2012ggB 50003)+1 种基金The National Science and Technology Program of China(2013DFA71070)the Fundamental Research Funds for the Central Universities(CDJZR13138801).
文摘The as-cast and as-extruded Mg–9Li–1Al–xCa alloys(x=0,0.2;wt%)were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2.The microstructures of the as-cast and as-extruded Mg–9Li–1Al–xCa alloys were observed to investigate the effect of calcium(Ca)element on the Mg–9Li–1Al(LA91)alloy,and the crystallographic calculations between Al_(2)Ca and the matrix(α-Mg andβ-Li phases)were examined on the basis of the edge-to-edge matching model.The experimental results indicate that the addition of 0.2 wt%Ca into LA91 alloy reduce the size of theα-Mg phases in the as-cast alloy and that ofβ-Li phases in the as-extruded alloy due to the Al_(2)Ca particles distributed inside the matrix.Crystallographic calculation results suggested that there is a good crystallographic matching between the matrix and Al_(2)Ca,which confirmed that Al_(2)Ca particles can act as a heterogeneous nucleation site for bothα-Mg andβ-Li phases and were effective grain refiners for LA91 alloy.
基金The authors would also like to thank NIT,Durgapur RIG#2 project for financial support and the Director of National In-stitute of Technology Durgapur,India,for his continuous en-couragement.
文摘A near eutectic Al−12.6Si alloy was developed with 0.0wt%,2.0wt%,4.0wt%,and 6.0wt%Al−5Ti−1B master alloy.The micro-structural morphology,hardness,tensile strength,elongation,and fracture behaviour of the alloys were studied.The unmodified Al−12.6Si al-loy has an irregular needle and plate-like eutectic silicon(ESi)and coarse polygonal primary silicon(PSi)particles in the matrix-likeα-Al phase.The P_(Si),E_(Si),andα-Al morphology and volume fraction were changed due to the addition of the Al−5Ti−1B master alloy.The hardness,UTS,and elongation improved due to the microstructural modification.Nano-sized in-situ Al3Ti particles and ex-situ TiB_(2)particles caused the mi-crostructural modification.The fracture images of the developed alloys exhibit a ductile and brittle mode of fracture at the same time.The Al−5Ti−1B modified alloys have a more ductile mode of fracture and more dimples compared to the unmodified alloy.
基金financial support from Pre-research Project of Equipment Development Department of China(No.41422010505)the Technology Innovation Leading Program of Shanxi Province,China(No.2019CGHJ-21)。
文摘The microstructure characteristics in early stage shear localization of near-αTi−6Al−2Zr−1Mo−1V titanium alloy were investigated by split Hopkinson pressure bar(SHPB)tests using hat-shaped specimens.The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction(EBSD)method.It is found that the nucleation and expansion of adiabatic shear band(ASB)are affected by both geometric and structural factors.The increase of dislocation density,structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions.In addition to the dislocation slips,the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect.Interestingly,the sandwich structure imposes a crucial influence on ASB,which finally becomes a mature wide ASB in the dynamic deformation.However,due to much larger width,the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation.
基金the National Natural Science Foundation of China under grant Nos. 50371095 , 50571106.
文摘Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3＋Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the AI content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.
基金Project(50604020)supported by the National Natural Science Foundation of ChinaProject(2007CB613706)supported by the National Basic Research Program of ChinaProject(2009AA03Z507)supported by the National High-tech Research and Development Program of China
文摘Al-5Ti-1B master alloy was added into Mg-14Li-1Al(LA141)alloy and then LA141 sheets were prepared by extrusion and cold rolling.The effect of the addition level of Al-5Ti-1B master alloy on the grain size of LA141 alloy was investigated as well as the effects of the total reduction of cold rolling and the annealing temperature on microstructure,mechanical properties and plastic formability of the LA141 sheets.The results show that the optimal addition level of Al-5Ti-1B master alloy into LA141 alloy is 1.25%(mass fraction)and LA141 alloy has the finest grains.With the increase of the total reduction of cold rolling,the grains of the as-rolled LA141 sheets were flattened gradually.A proper anneal temperature of 200℃ is obtained for the cold rolled LA141 sheets. Under this condition,microstructure of the LA141 sheets consists of fine and uniform equiaxed grains and has higher Erichsen cupping index(IE).
基金Project(2010RFQXG117)supported by the Special Fund for Technological Innovation Program of Harbin,China
文摘AZ61 alloys with different levels of Al5Ti1B master alloy additions were prepared by conventional casting method.The effects of Al5Ti1B contents and holding time on microstructures and microhardness of AZ61 alloys were studied by XRD,OM and microhardness testing techniques.The results show that when the addition level of Al5Ti1B master alloy is less than 0.5%(mass fraction),the average grain size of the alloys decreases with the increase of Al5Ti1B content at the same holding time.But the grain size increases somewhat with further addition of Al5Ti1B.The average grain size of the alloys decreases with the increase of the holding time as it is less than 30 min at the same addition level of Al5Ti1B.It is considered that TiB2 particles can serve as the heterogeneous nucleation sites ofα-Mg during solidification,and heterogeneous nucleation is the main reason for the grain refinement of AZ61 alloys.The microhardness of the refined AZ61 alloys with 1.0%Al5Ti1B addition is increased by about 8%.
文摘The behavior of growth and coarsening of T-1(Al2CuLi) precipitates was comparatively studied by means of TEM technique in two Al-Li alloys 2090 and 2090+Ce (with cerium content less than 0.1% in mass fraction). Statistical analysis results show that T-1 precipitates in alloy 2090+Ce have smaller aspect ratio, which is connected with the more intersections between different T-1 variants in this alloy. It is also found that the variation of maximum length of T-1 precipitates with aging time can be obviously divided into two stages of growth and coarsening. The diffusion coefficients of solute atoms of Cu and Li are calculated via growth kinetics curves of T-1 precipitates. The results show that the diffusion of atom Cu plays a more important role in the formation of T-1 precipitates.
文摘Al5Ti1B master alloy was produced by two-step method. Experimental results show that the structure of Al5TilB master alloy depends on that of AlTi and AlB master alloys, the morphologies of TiAl3 depend on AlTi master alloy and the boride phases depend on AlB master alloy. There are remarkable structure heredity between Al5Ti1B master alloy and AlTi, AlB master alloys. Theoretical analyses show that AlTi and Al-B master alloys can change the melt structure of Al5Ti1B master alloy, then affect the solid structure of the master alloy.
文摘Rotating electromagnetic field is applied to the centrifugal casting, the macrostructure of centrifugal casting Al-1%Cu alloy stirred with driving or backing magnetic field are both examined. It is shown that both kinds of electromagnetic filed can enforce the columnar-equiaxed transition, the driving one decrease the tendency of porosity occurring due to the increase in the bulk liquid pressure. Stirring with braking electromagnetic field produces the mixture of outer fine grains and inner coarse grains in the casting, this is analyzed to be contributed to the differences both in electric conductivity and density between the crystal and the melt, as well as skin effects.
文摘Grain refinement can offer significant benefits to both continuous casting and cast to shape products, and Al5Ti1B master alloy containing mainly TiAl 3 and TiB 2 particles in Al matrix has been proven to perform well for giving the best refinement, but the working method of adding Al5Ti1B rod to the furnace during casting are often related to solid deformation, and melt vibration may help to reduce the size of TiAl 3 and improve the distribution of TiB 2. Therefore the effects of solid deformation and melt vibration on the structures and refinement performance of Al5Ti1B master alloys were studied. The experimental results show that both solid deformation and melt vibration can improve the distribution of TiB 2 in Al5Ti1B master alloys, increase the interface energy and nucleation activity of TiB 2 particles. In the meantime, solid deformation can store deformation energy and melt vibration can break fragile plate like TiAl 3 compounds. So both methods can improve the refinement effectiveness of Al5Ti1B master alloys.
