An ultrafine-grained（UFG） Mg-13Zn-1.55 Y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;Y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） ...An ultrafine-grained（UFG） Mg-13Zn-1.55 Y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;Y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） on the cast microstructure following homogenization. The alloy exhibited excellent superplasticity at low temperatures(tensile elongations of 455% and 1021% 473 K-10;s;and 523 K-10;s;,respectively). Compared with UFG Mg-9.25Zn-1.66 Y alloy（ZW92） with a lower volume fraction of I-phase particles（4.1%）, which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond523 K, leading to a loss of superplasticity. The high-temperature deformation behavior of the HRDSRprocessed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K.展开更多
The superplastic behavior has been found in Fe 3Al and FeAl alloys with grain sizes of 100～600 μm. The large grained Fe 3Al and FeAl alloys exhibit all deformation characteristics of conventional fine grain size sup...The superplastic behavior has been found in Fe 3Al and FeAl alloys with grain sizes of 100～600 μm. The large grained Fe 3Al and FeAl alloys exhibit all deformation characteristics of conventional fine grain size superplastic alloys. However, superplastic behavior was found in large grained iron aluminides without the usual prerequisites for the superplasticity of a fine grain size and grain boundary sliding. The metallographic examinations have shown that average grain size of large grained iron aluminides decreased during superplastic deformation. Transmission electron microscopy (TEM) observations have shown that there were a great number of subgrain boundaries which formed a network and among which the proportion of low and high angle boundaries increased with the increase of strain. The observed superplastic phenomenon is explained by continuous recovery and recrystallization. During superplastic deformation, an unstable subgrain network forms and these subboundaries absorb gliding dislocations and transform into low and high angle grain boundaries. A dislocation gliding and climb process accommodated by subboundary sliding, migration and rotation, allows the superplastic flow to proceed.展开更多
The formability of light-weight alloy, such as aluminum alloy, magnesium alloy, can be improved significantly when formed at elevated temperature. Superplastic forming (SPF) is a well-known manufacturing method to for...The formability of light-weight alloy, such as aluminum alloy, magnesium alloy, can be improved significantly when formed at elevated temperature. Superplastic forming (SPF) is a well-known manufacturing method to form complex part of these materials. In order to realize mass production of SPF in industry, forming at high strain rate should be realized. In this study, the mechanical properties of 5A06 sheet were tested by uniaxial tensile test at high strain rate and elevated temperatures up to 550 ℃. Free bulging test and forming of round cup were carried out to evaluate the formability of the 5A06 sheet. Results show that the total elongation of the 5A06 sheet began to increase rapidly after 200 ℃, and reached the maximum value at 450 ℃. At higher temperature, early brittle fracture occurred. In free bulging test, the bulging height remained almost constant about 27.0 mm, which means the formability of the sheet is not sensitive to forming temperature at elevated temperature. In the forming of round cup part, temperature has direct effect on the corner filling ability of the sheet, especially at temperature lower than 400 ℃.展开更多
An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process ...An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process and to establish optimum forming parameters.Formability was assessed using elevated temperature tensile testing and hot gas bulging,across a range of strain rates(1×10^(−1)−1×10^(−3)s^(−1))and temperatures(350−450℃).Circle grid analysis with GOM Aramis cameras was used to understand peak strains and material thinning in relation to industrial forming processes.Post forming EBSD and STEM analysis was conducted to understand the mechanisms responsible for the materials formability,with dynamic recrystallization being clearly evident.Peak elongation of 520%was achieved at 450℃ and 1×10^(−3)s^(−1);industrially relevant elongation was achieved at 1×10^(−2) s^(−1) at both 450℃(195%)and 400℃(170%).展开更多
The superplastic forming is an advanced processing technique and has been used in manufacturing some dies, especially extrusion die and forging die. In heavy load condition, the superplastic formed dies often exhibit ...The superplastic forming is an advanced processing technique and has been used in manufacturing some dies, especially extrusion die and forging die. In heavy load condition, the superplastic formed dies often exhibit low service life owing to the low surface strength and poor wear resistance. A commercial cold working die steel GCr15 pre treated into ultra fine grain sizes was chosen as the substrate material, on which the surface was thermal sprayed with the powders of a wear resistant alloy. At some appropriate temperatures and strain rates, the accommodated superplastic deformation of the substrate and coating occurred and the good cohesion was well performed. The coated layer shows high microhardness values and fairly smooth transition in hardness from substrate to the surface. The wear resistance of superplastically formed specimen has also been improved, compared with the GCr15 steel coated with the same alloy powder and treated by flame remelting. [展开更多
The superplastic deformation diffusion bonding of 00Cr25Ni7Mo3N duplex stainless steel was performed on a hot simulator. The microstructure of the bonding interface was characterized by scanning electron microscopy （...The superplastic deformation diffusion bonding of 00Cr25Ni7Mo3N duplex stainless steel was performed on a hot simulator. The microstructure of the bonding interface was characterized by scanning electron microscopy （SEM） and electron backscatter diffraction （EBSD）. The mechanical properties of the specimen were investigated by a shear strength test. The results indicated that the shear strength was improved with the increase of superplastic deformation reduction. When the deformation reduction was up to 50%, the shear strength of the specimen achieved 417 Mpa, approaching to that of the base metal. In addtion, the superplastic diffusion bonding technique was not very sensitive to surface roughness levels. When the surface roughness of the bonding specimen surpassed 0.416 pan （level G2）, the shear strength achieved at least 381 MPa.展开更多
基金supported financially by the Mid-Career Researcher Program through the National Research Foundation of Korea(2016) funded by the Ministry of Education, Science and Technology (2016R1A2B4015481)
文摘An ultrafine-grained（UFG） Mg-13Zn-1.55 Y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;Y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） on the cast microstructure following homogenization. The alloy exhibited excellent superplasticity at low temperatures(tensile elongations of 455% and 1021% 473 K-10;s;and 523 K-10;s;,respectively). Compared with UFG Mg-9.25Zn-1.66 Y alloy（ZW92） with a lower volume fraction of I-phase particles（4.1%）, which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond523 K, leading to a loss of superplasticity. The high-temperature deformation behavior of the HRDSRprocessed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K.
文摘The superplastic behavior has been found in Fe 3Al and FeAl alloys with grain sizes of 100～600 μm. The large grained Fe 3Al and FeAl alloys exhibit all deformation characteristics of conventional fine grain size superplastic alloys. However, superplastic behavior was found in large grained iron aluminides without the usual prerequisites for the superplasticity of a fine grain size and grain boundary sliding. The metallographic examinations have shown that average grain size of large grained iron aluminides decreased during superplastic deformation. Transmission electron microscopy (TEM) observations have shown that there were a great number of subgrain boundaries which formed a network and among which the proportion of low and high angle boundaries increased with the increase of strain. The observed superplastic phenomenon is explained by continuous recovery and recrystallization. During superplastic deformation, an unstable subgrain network forms and these subboundaries absorb gliding dislocations and transform into low and high angle grain boundaries. A dislocation gliding and climb process accommodated by subboundary sliding, migration and rotation, allows the superplastic flow to proceed.
基金National Nature Science Foundation of China (50805033)Natural Science Foundation of Heilongjiang Province of China (E200804)
文摘The formability of light-weight alloy, such as aluminum alloy, magnesium alloy, can be improved significantly when formed at elevated temperature. Superplastic forming (SPF) is a well-known manufacturing method to form complex part of these materials. In order to realize mass production of SPF in industry, forming at high strain rate should be realized. In this study, the mechanical properties of 5A06 sheet were tested by uniaxial tensile test at high strain rate and elevated temperatures up to 550 ℃. Free bulging test and forming of round cup were carried out to evaluate the formability of the 5A06 sheet. Results show that the total elongation of the 5A06 sheet began to increase rapidly after 200 ℃, and reached the maximum value at 450 ℃. At higher temperature, early brittle fracture occurred. In free bulging test, the bulging height remained almost constant about 27.0 mm, which means the formability of the sheet is not sensitive to forming temperature at elevated temperature. In the forming of round cup part, temperature has direct effect on the corner filling ability of the sheet, especially at temperature lower than 400 ℃.
基金The authors would like to thank the WMG High Value Manufacturing Catapult Centre for funding this work.In addition,the characterisation facility is supported from the Higher Education Funding Council for England(HEFCE).
文摘An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process and to establish optimum forming parameters.Formability was assessed using elevated temperature tensile testing and hot gas bulging,across a range of strain rates(1×10^(−1)−1×10^(−3)s^(−1))and temperatures(350−450℃).Circle grid analysis with GOM Aramis cameras was used to understand peak strains and material thinning in relation to industrial forming processes.Post forming EBSD and STEM analysis was conducted to understand the mechanisms responsible for the materials formability,with dynamic recrystallization being clearly evident.Peak elongation of 520%was achieved at 450℃ and 1×10^(−3)s^(−1);industrially relevant elongation was achieved at 1×10^(−2) s^(−1) at both 450℃(195%)and 400℃(170%).
基金Project (1997-0 4)supportedbytheScienceFoundationofHenanProvince P .R .China
文摘The superplastic forming is an advanced processing technique and has been used in manufacturing some dies, especially extrusion die and forging die. In heavy load condition, the superplastic formed dies often exhibit low service life owing to the low surface strength and poor wear resistance. A commercial cold working die steel GCr15 pre treated into ultra fine grain sizes was chosen as the substrate material, on which the surface was thermal sprayed with the powders of a wear resistant alloy. At some appropriate temperatures and strain rates, the accommodated superplastic deformation of the substrate and coating occurred and the good cohesion was well performed. The coated layer shows high microhardness values and fairly smooth transition in hardness from substrate to the surface. The wear resistance of superplastically formed specimen has also been improved, compared with the GCr15 steel coated with the same alloy powder and treated by flame remelting. [
文摘The superplastic deformation diffusion bonding of 00Cr25Ni7Mo3N duplex stainless steel was performed on a hot simulator. The microstructure of the bonding interface was characterized by scanning electron microscopy （SEM） and electron backscatter diffraction （EBSD）. The mechanical properties of the specimen were investigated by a shear strength test. The results indicated that the shear strength was improved with the increase of superplastic deformation reduction. When the deformation reduction was up to 50%, the shear strength of the specimen achieved 417 Mpa, approaching to that of the base metal. In addtion, the superplastic diffusion bonding technique was not very sensitive to surface roughness levels. When the surface roughness of the bonding specimen surpassed 0.416 pan （level G2）, the shear strength achieved at least 381 MPa.
