Volume 44,Issue 10,2015 Table of Contents
2015, 44(10):2353-2357.
Abstract:
Undercooling solidification experiments were carried out to analyze the precipitation and evolution behavior of different phases of Co-Ru peritectic alloy. The maximum undercooling of this alloy up to 217 K (0.12TL) was obtained by applying glass fluxing combined with cyclic superheating method. According to the calculation results of the classical nucleation theory, the nucleation of stable phase (ξ) is favored in the whole temperature range. Results show that typical peritectic microstructures are observed if the initial undercooling (ΔT) was lower than critical value (ΔT* ≈ 180 K). In this condition, the precipitation of peritectic phase (α) depends on the different morphologies of ξ phase. When ΔT >ΔT*, α phase precipitates from the undercooled melt directly and grows competitively with ξ phase, although ξ phase is still the primary one in the undercooled melt. With increasing ΔT, the relative content of peritectic phase goes through a course of increasing, then decreasing and finally increasing again
Undercooling solidification experiments were carried out to analyze the precipitation and evolution behavior of different phases of Co-Ru peritectic alloy. The maximum undercooling of this alloy up to 217 K (0.12TL) was obtained by applying glass fluxing combined with cyclic superheating method. According to the calculation results of the classical nucleation theory, the nucleation of stable phase (ξ) is favored in the whole temperature range. Results show that typical peritectic microstructures are observed if the initial undercooling (ΔT) was lower than critical value (ΔT* ≈ 180 K). In this condition, the precipitation of peritectic phase (α) depends on the different morphologies of ξ phase. When ΔT >ΔT*, α phase precipitates from the undercooled melt directly and grows competitively with ξ phase, although ξ phase is still the primary one in the undercooled melt. With increasing ΔT, the relative content of peritectic phase goes through a course of increasing, then decreasing and finally increasing again
2015, 44(10):2358-2362.
Abstract:
The cold expansion method was proposed to improve the high cycle fatigue (HCF) property of 7A85 aluminum alloy straight lugs. The microstructure, the microhardness and the residual stress near the hole wall of cold expanded lugs were investigated. The results indicate that a plastic deformation layer with about 150 μm in thickness is formed on the surface of the hole wall. Within the plastic deformation layer, the microhardness and the compressive residual stress are high, and the grains are stretched along the moving direction of the mandrel and compressed perpendicular to it. The fatigue life and fatigue strength were found to be improved significantly by cold expansion (CE). The fatigue crack initiation and propagation of cold expansion specimens were analyzed compared with those of the specimens without cold expansion (WCE). The mechanism of the improved fatigue property for cold expanded 7A85 aluminum alloy straight lugs was discussed
The cold expansion method was proposed to improve the high cycle fatigue (HCF) property of 7A85 aluminum alloy straight lugs. The microstructure, the microhardness and the residual stress near the hole wall of cold expanded lugs were investigated. The results indicate that a plastic deformation layer with about 150 μm in thickness is formed on the surface of the hole wall. Within the plastic deformation layer, the microhardness and the compressive residual stress are high, and the grains are stretched along the moving direction of the mandrel and compressed perpendicular to it. The fatigue life and fatigue strength were found to be improved significantly by cold expansion (CE). The fatigue crack initiation and propagation of cold expansion specimens were analyzed compared with those of the specimens without cold expansion (WCE). The mechanism of the improved fatigue property for cold expanded 7A85 aluminum alloy straight lugs was discussed
2015, 44(10):2363-2367.
Abstract:
Due to the high melting point, excellent high temperature strength and anticorrosive property, iridium is the unique material which can be used under extremely hostile environments. However, iridium exhibits an anomalous brittle fracture behavior, a mixed brittle intergranular fracture (BIF) and brittle transgranular fracture (BTF), even though it is of face-centred cubic (fcc) crystal structure. A great deal of efforts have been made to explore the embrittlement mechanisms since the anomalous fracture behavior was recognized in 1960 s, up to now, there has not been a reasonable conclusion yet. This paper emphatically reviewed the possible embrittlement mechanism of iridium, including impurity-induced brittleness, intrinsic brittleness and special defect structure induced embrittlement, discussed the research status quo about the deformation and failure mechanisms of iridium. Finally, the research direction and research method of the embrittlement mechanism of iridium were forecasted
Due to the high melting point, excellent high temperature strength and anticorrosive property, iridium is the unique material which can be used under extremely hostile environments. However, iridium exhibits an anomalous brittle fracture behavior, a mixed brittle intergranular fracture (BIF) and brittle transgranular fracture (BTF), even though it is of face-centred cubic (fcc) crystal structure. A great deal of efforts have been made to explore the embrittlement mechanisms since the anomalous fracture behavior was recognized in 1960 s, up to now, there has not been a reasonable conclusion yet. This paper emphatically reviewed the possible embrittlement mechanism of iridium, including impurity-induced brittleness, intrinsic brittleness and special defect structure induced embrittlement, discussed the research status quo about the deformation and failure mechanisms of iridium. Finally, the research direction and research method of the embrittlement mechanism of iridium were forecasted
2015, 44(10):2373-2375.
Abstract:
High silicon steel has been prepared by physical vapor deposition, i. e. multi-arc ion coating and diffusion. Subsequent annealing in vacuum at 1180 and 1200 oC result in penetration of silicon into the substrate. X-ray diffraction (XRD) reveals that the surface layers of all samples remain α-Fe bcc structure after high temperature-diffusion treatment. Once Fe3Si is formed in the surface layer, a further heat treatment will make the composition of the sample homogenizations. The silicon concentration distribution along the cross-section is 4.6 wt%~5.1 wt% after annealing at 1200 oC for 1 h which was tested by field emission scanning election microscopy (FE-SEM) equipped with energy dispersive spectroscope (EDS), and was further confirmed by micro Vickers-hardness, where the average cross-section micro Vickers-hardness is 2800 MPa
High silicon steel has been prepared by physical vapor deposition, i. e. multi-arc ion coating and diffusion. Subsequent annealing in vacuum at 1180 and 1200 oC result in penetration of silicon into the substrate. X-ray diffraction (XRD) reveals that the surface layers of all samples remain α-Fe bcc structure after high temperature-diffusion treatment. Once Fe3Si is formed in the surface layer, a further heat treatment will make the composition of the sample homogenizations. The silicon concentration distribution along the cross-section is 4.6 wt%~5.1 wt% after annealing at 1200 oC for 1 h which was tested by field emission scanning election microscopy (FE-SEM) equipped with energy dispersive spectroscope (EDS), and was further confirmed by micro Vickers-hardness, where the average cross-section micro Vickers-hardness is 2800 MPa
2015, 44(10):2387-2390.
Abstract:
The preparation of TiAl-based alloys with ultrafine crystal/nanocrystalline by in situ sintering was investigated. TiH2, Al, Si and Nb powders were firstly refined to the nanoscale level by ball milling; then, the milled powders were pressed into green compacts, which were sintered into bulks by spark plasma sintering (SPS). The functional characteristics of milled powders and sintered bulk were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron?microscope (TEM). High temperature?oxidation resistance was examined by differential scanning calorimeter (DSC). The results reveal that amorphous products,?Ti3Al nanocrystalline?and decomposition?products of TiH2 are formed during milling. When milled powders are sintered at high temperature, these fine powders rapidly transform into TiAl and Ti3Al phase. The grain sizes of TiAl and Ti3Al are 500 nm~1 μm and a few nanometers, respectively. This sintered bulk ultrafine microstructure is?quite stable?below?1000 oC, and has excellent oxidation resistance
The preparation of TiAl-based alloys with ultrafine crystal/nanocrystalline by in situ sintering was investigated. TiH2, Al, Si and Nb powders were firstly refined to the nanoscale level by ball milling; then, the milled powders were pressed into green compacts, which were sintered into bulks by spark plasma sintering (SPS). The functional characteristics of milled powders and sintered bulk were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron?microscope (TEM). High temperature?oxidation resistance was examined by differential scanning calorimeter (DSC). The results reveal that amorphous products,?Ti3Al nanocrystalline?and decomposition?products of TiH2 are formed during milling. When milled powders are sintered at high temperature, these fine powders rapidly transform into TiAl and Ti3Al phase. The grain sizes of TiAl and Ti3Al are 500 nm~1 μm and a few nanometers, respectively. This sintered bulk ultrafine microstructure is?quite stable?below?1000 oC, and has excellent oxidation resistance
6 Preparation of Al/SiC Composite Coatings on Surface of Aluminum Alloy by Atmospheric Plasma Spraying
2015, 44(10):2396-2400.
Abstract:
Al/SiC composite coatings were deposited on the surface of aluminum alloy by atmospheric plasma spraying. The effects of SiC volume in Al/SiC composite powders on the deposition behavior and the properties of the Al/SiC coatings were investigated. It is found that the decarburization and oxidation of pure SiC powder occur in the plasma flame. With the increase of SiC content, the deposition of the Al/SiC composite powder becomes more difficult through plasma spraying. There exist cracks between the bond coat and the aluminum alloy substrate resulting in poor adhesion between them. The hardness of the composite coating becomes higher with the increase of SiC content. The Al/SiC (50:50) deposit with a thickness of 70 μm and a hardness of 3690 MPa can strengthen the surface of aluminum alloy
Al/SiC composite coatings were deposited on the surface of aluminum alloy by atmospheric plasma spraying. The effects of SiC volume in Al/SiC composite powders on the deposition behavior and the properties of the Al/SiC coatings were investigated. It is found that the decarburization and oxidation of pure SiC powder occur in the plasma flame. With the increase of SiC content, the deposition of the Al/SiC composite powder becomes more difficult through plasma spraying. There exist cracks between the bond coat and the aluminum alloy substrate resulting in poor adhesion between them. The hardness of the composite coating becomes higher with the increase of SiC content. The Al/SiC (50:50) deposit with a thickness of 70 μm and a hardness of 3690 MPa can strengthen the surface of aluminum alloy
2015, 44(10):2401-2404.
Abstract:
The effects of Cd on the microstructure and the mechanical properties of Mg-Cd magnesium alloy were investigated. The Mg-Cd binary magnesium alloy was analyzed by metallograph, XRD, SEM and EDS examinations. The results show that the microstructure of the Mg-Cd magnesium alloy is refined obviously by adding a little amount of Cd. When Cd addition(wt%) is from 0% to 0.7%, the alloy is composed of α-Mg matrix. Cd dissolves in the matrix to form a solid solution, and there is no new phase formed, which contributes to the increase of the impact toughness, Brinell hardness of the experimental alloy by 52.9%, 11.9%, respectively. With the Cd content increasing, the mechanical properties of Mg-Cd magnesium alloy are improved accordingly
The effects of Cd on the microstructure and the mechanical properties of Mg-Cd magnesium alloy were investigated. The Mg-Cd binary magnesium alloy was analyzed by metallograph, XRD, SEM and EDS examinations. The results show that the microstructure of the Mg-Cd magnesium alloy is refined obviously by adding a little amount of Cd. When Cd addition(wt%) is from 0% to 0.7%, the alloy is composed of α-Mg matrix. Cd dissolves in the matrix to form a solid solution, and there is no new phase formed, which contributes to the increase of the impact toughness, Brinell hardness of the experimental alloy by 52.9%, 11.9%, respectively. With the Cd content increasing, the mechanical properties of Mg-Cd magnesium alloy are improved accordingly
2015, 44(10):2419-2428.
Abstract:
Short time stress rupture properties (10 min~3 h) of GH4098 alloy have been investigated at different temperatures (800~1000 °C) and stresses (90~680 MPa) after solution and aging treatment, combined with the characterization of microstructures and fracture features. The results show that fracture features of GH4098 alloy are ductile and intergranular in all temperature range. Short time stress rupture properties of the alloy degrade gradually with increasing the testing temperature, but they are significantly worse at 1000 °C. Microstructural characterization indicates that there is little change in grain size with increasing the temperature. The deterioration of short time stress rupture properties at higher temperature is ascribed to the reduction of γ’ volume fraction as well as the coarsening of γ’ precipitates and grain boundary carbides. In addition, the influence of cooling rate on microstructures as well as the differences between short time creep and traditional creep was also discussed
Short time stress rupture properties (10 min~3 h) of GH4098 alloy have been investigated at different temperatures (800~1000 °C) and stresses (90~680 MPa) after solution and aging treatment, combined with the characterization of microstructures and fracture features. The results show that fracture features of GH4098 alloy are ductile and intergranular in all temperature range. Short time stress rupture properties of the alloy degrade gradually with increasing the testing temperature, but they are significantly worse at 1000 °C. Microstructural characterization indicates that there is little change in grain size with increasing the temperature. The deterioration of short time stress rupture properties at higher temperature is ascribed to the reduction of γ’ volume fraction as well as the coarsening of γ’ precipitates and grain boundary carbides. In addition, the influence of cooling rate on microstructures as well as the differences between short time creep and traditional creep was also discussed
2015, 44(10):2429-2434.
Abstract:
The effect of Zn additions on the microstructure and mechanical properties of Mg-11Gd-(1, 1.5, 2)Zn alloys was investigated by OM, SEM, TEM and electronic universal testing machine. The results show that the microstructure of as-cast Mg-11Gd-(1, 1.5, 2)Zn alloys are composed of a-Mg matrix, (Mg, Zn)3Gd eutectic phase and lamellar 14H-LPSO structure. With the increase of Zn additions, both the volume fractions of (Mg, Zn)3Gd eutectic phase and LPSO phase increase, and the thermal stability of the (Mg, Zn)3Gd phase is improved as well. Tensile tests at room temperature indicate that the strength of as-extruded Mg-11Gd-(1, 1.5, 2)Zn alloys decreases with the increasing Zn content. The Mg-11Gd-1Zn alloy, which contains the lowest Zn among all the alloys studied, exhibits the highest tensile strength with good ductility after T6 treatment. However, the tensile strengths of the Mg-11Gd-1.5Zn and Mg-11Gd-2Zn alloys after T6 treatment are lower than that after T5 treatment. The creep tests at 200 °C/80 MPa reveal that all of the alloys studied have higher creep resistance than the WE54 alloy, and the creep resistance of the alloys decreases gradually with the increase of Zn addition
The effect of Zn additions on the microstructure and mechanical properties of Mg-11Gd-(1, 1.5, 2)Zn alloys was investigated by OM, SEM, TEM and electronic universal testing machine. The results show that the microstructure of as-cast Mg-11Gd-(1, 1.5, 2)Zn alloys are composed of a-Mg matrix, (Mg, Zn)3Gd eutectic phase and lamellar 14H-LPSO structure. With the increase of Zn additions, both the volume fractions of (Mg, Zn)3Gd eutectic phase and LPSO phase increase, and the thermal stability of the (Mg, Zn)3Gd phase is improved as well. Tensile tests at room temperature indicate that the strength of as-extruded Mg-11Gd-(1, 1.5, 2)Zn alloys decreases with the increasing Zn content. The Mg-11Gd-1Zn alloy, which contains the lowest Zn among all the alloys studied, exhibits the highest tensile strength with good ductility after T6 treatment. However, the tensile strengths of the Mg-11Gd-1.5Zn and Mg-11Gd-2Zn alloys after T6 treatment are lower than that after T5 treatment. The creep tests at 200 °C/80 MPa reveal that all of the alloys studied have higher creep resistance than the WE54 alloy, and the creep resistance of the alloys decreases gradually with the increase of Zn addition
2015, 44(10):2435-2439.
Abstract:
The formation of the oxidation coatings on the AZ91D magnesium alloy under different processing conditions was studied by optical microscope and the scanning electron microscope. The growth mechanism of coatings was also discussed. The results show that under the test voltages, the process of arcing could be divided to three stages: the first stage is the competing stage between partly corrosion and oxidation, the corrosion begins at the defects of the surfaces firstly, loose oxidation coatings are forming, and at the same time electrolysis of water happens; the second stage is the microcell discharging stage, the surfaces are oxidized integrally and compact oxidation coatings with a few pores are formed, and the electrolysis of water is aggravated; the third stage is the arcing discharging stage, the oxidation process becomes more drastic, the formed coatings are punctured by arcing to form connected pores, and the size and number of pores are increased
The formation of the oxidation coatings on the AZ91D magnesium alloy under different processing conditions was studied by optical microscope and the scanning electron microscope. The growth mechanism of coatings was also discussed. The results show that under the test voltages, the process of arcing could be divided to three stages: the first stage is the competing stage between partly corrosion and oxidation, the corrosion begins at the defects of the surfaces firstly, loose oxidation coatings are forming, and at the same time electrolysis of water happens; the second stage is the microcell discharging stage, the surfaces are oxidized integrally and compact oxidation coatings with a few pores are formed, and the electrolysis of water is aggravated; the third stage is the arcing discharging stage, the oxidation process becomes more drastic, the formed coatings are punctured by arcing to form connected pores, and the size and number of pores are increased
2015, 44(10):2440-2444.
Abstract:
The laser welding test was carried out on the AZ91 magnesium alloy with thickness of 1.8 mm and the 6016 aluminum alloy with thickness of 1.2 mm. By optical microscopy, horizontal microscope, scanning electron microscopy, X-ray diffraction, electron micro-hardness and tensile test, the weld surface morphology, microstructure, interface element distribution, fracture morphology, main phase, hardness and mechanical properties of joints were studied. The results indicate that the morphology of welding surface can be improved, the heat affected zone is narrow and grain size is fine when the welding power is 1900 W, welding speed is 50 mm/s, the defocus distance is 0 mm, and Ar gas acts as the protection gas with flow rate 15 L/min. The average tensile and shear strength of the welding sample reaches 13.99 MPa and 12.79 MPa, respectively. The hardness in magnesium and aluminum side is both higher than that of the based material, shear fracture is relatively flat and smooth, and parallel fatigue cracks appear. Tensile fracture has many cleavage steps with brittle fracture characteristics. The main phase, such as Mg17Al12 and Mg2Al3, can be found in magnesium and aluminum weld interface, and Mg17Al12 brittle phase is more stable than Mg2Al3 with ductility at high temperatures, which lead to the brittle welded joints and thus it is difficult to realize the welding between magnesium and aluminum
The laser welding test was carried out on the AZ91 magnesium alloy with thickness of 1.8 mm and the 6016 aluminum alloy with thickness of 1.2 mm. By optical microscopy, horizontal microscope, scanning electron microscopy, X-ray diffraction, electron micro-hardness and tensile test, the weld surface morphology, microstructure, interface element distribution, fracture morphology, main phase, hardness and mechanical properties of joints were studied. The results indicate that the morphology of welding surface can be improved, the heat affected zone is narrow and grain size is fine when the welding power is 1900 W, welding speed is 50 mm/s, the defocus distance is 0 mm, and Ar gas acts as the protection gas with flow rate 15 L/min. The average tensile and shear strength of the welding sample reaches 13.99 MPa and 12.79 MPa, respectively. The hardness in magnesium and aluminum side is both higher than that of the based material, shear fracture is relatively flat and smooth, and parallel fatigue cracks appear. Tensile fracture has many cleavage steps with brittle fracture characteristics. The main phase, such as Mg17Al12 and Mg2Al3, can be found in magnesium and aluminum weld interface, and Mg17Al12 brittle phase is more stable than Mg2Al3 with ductility at high temperatures, which lead to the brittle welded joints and thus it is difficult to realize the welding between magnesium and aluminum
2015, 44(10):2440-2444.
Abstract:
The laser welding test was carried out on AZ91 magnesium alloy with thickness 1.8 mm and 6016 aluminum alloy with thickness 1.2 mm. By using optical microscopy, horizontal microscope, scanning electron microscopy, X-ray diffraction, electron micro-hardness and tensile test, the weld surface morphology, microstructure, interface element distribution,fracture morphology, main phase,hardness and mechanical properties of joints were studied. The results indicate that the morphology of welding surface can be improved, heat affected zone is narrow and grain size is fine when the welding power is 1900 W, welding speed is 50 mm/s, the defocus distance is 0 mm, and Ar gas acts as the protection gas with flow rate 15 L/min. The average tensile and shear strength of the welding sample reaches 13.99 MPa, 12.79MPa, respectively.The hardness in magnesium and aluminum side is both higher than that of the based material, shear fracture is relatively flat and smooth, parallel fatigue crack appears.Tensile fracture has more cleavage step with brittle fracture characteristics. The main phase,such as Mg17Al12, Mg2Al3, can be found in magnesium and aluminum weld interface, Mg17Al12 brittle phase is stable than that of Mg2Al3 with ductility at high temperatures, which lead to the welded joints brittle and is difficult to realize the welding between magnesium and aluminum.
The laser welding test was carried out on AZ91 magnesium alloy with thickness 1.8 mm and 6016 aluminum alloy with thickness 1.2 mm. By using optical microscopy, horizontal microscope, scanning electron microscopy, X-ray diffraction, electron micro-hardness and tensile test, the weld surface morphology, microstructure, interface element distribution,fracture morphology, main phase,hardness and mechanical properties of joints were studied. The results indicate that the morphology of welding surface can be improved, heat affected zone is narrow and grain size is fine when the welding power is 1900 W, welding speed is 50 mm/s, the defocus distance is 0 mm, and Ar gas acts as the protection gas with flow rate 15 L/min. The average tensile and shear strength of the welding sample reaches 13.99 MPa, 12.79MPa, respectively.The hardness in magnesium and aluminum side is both higher than that of the based material, shear fracture is relatively flat and smooth, parallel fatigue crack appears.Tensile fracture has more cleavage step with brittle fracture characteristics. The main phase,such as Mg17Al12, Mg2Al3, can be found in magnesium and aluminum weld interface, Mg17Al12 brittle phase is stable than that of Mg2Al3 with ductility at high temperatures, which lead to the welded joints brittle and is difficult to realize the welding between magnesium and aluminum.
2015, 44(10):2445-2448.
Abstract:
The microstructure and isothermal oxidation kinetics of Zr-Nb-Cu alloy under water vapor environment in the temperature range 700°C to 1000°C were studied, and the evolution laws of oxide film macro-morphologies and microstructures were also analyzed. The results show that the weight gain curves of water vapor oxidation of the alloy between 700°C and 900°C are in accordance with parabolic law, and the curve deviates from the parabolic law at 1000°C. According to the oxidation weight gain curves, the oxidation activation energy Q, the expressions of the parabolic rate constant Kp and the weight gain W were calculated respectively. The oxide film structure analysis results indicate that the oxidation temperature is higher, the crack and bulge of oxide film is more obvious.
The microstructure and isothermal oxidation kinetics of Zr-Nb-Cu alloy under water vapor environment in the temperature range 700°C to 1000°C were studied, and the evolution laws of oxide film macro-morphologies and microstructures were also analyzed. The results show that the weight gain curves of water vapor oxidation of the alloy between 700°C and 900°C are in accordance with parabolic law, and the curve deviates from the parabolic law at 1000°C. According to the oxidation weight gain curves, the oxidation activation energy Q, the expressions of the parabolic rate constant Kp and the weight gain W were calculated respectively. The oxide film structure analysis results indicate that the oxidation temperature is higher, the crack and bulge of oxide film is more obvious.
2015, 44(10):2449-2453.
Abstract:
The MnAl alloy powder was prepared by high-energy ball milling and heat treatment process. Effect of Al content on the microstructure and microwave absorbing properties of MnAl powder were investigated with the help of scanning electron microscope (SEM), X-ray diffraction (XRD) and network vector analyzer. The results show that with the increase of Al content, Al0.89Mn1.11, β-Mn and Al2Mn3 contents in MnAl alloy powder decrease while the Al8Mn5 content increases; as a result, the powder magnetic loss and dielectric loss increase, resonance frequency moves to the low frequency, and more absorption peaks appear. When absorbing layer thickness is 2.0 mm, the Mn40Al60 sample has a maximum absorption peak at 12.2 GHz frequency, the reflectivity minimum is –26.5 dB, showing a better bandwidth effect. MnAl powder absorbing mechanism of electromagnetic wave includes the electromagnetic loss in the inner of the absorber and the interference loss between the reflection waves from the back interface and the front interface
The MnAl alloy powder was prepared by high-energy ball milling and heat treatment process. Effect of Al content on the microstructure and microwave absorbing properties of MnAl powder were investigated with the help of scanning electron microscope (SEM), X-ray diffraction (XRD) and network vector analyzer. The results show that with the increase of Al content, Al0.89Mn1.11, β-Mn and Al2Mn3 contents in MnAl alloy powder decrease while the Al8Mn5 content increases; as a result, the powder magnetic loss and dielectric loss increase, resonance frequency moves to the low frequency, and more absorption peaks appear. When absorbing layer thickness is 2.0 mm, the Mn40Al60 sample has a maximum absorption peak at 12.2 GHz frequency, the reflectivity minimum is –26.5 dB, showing a better bandwidth effect. MnAl powder absorbing mechanism of electromagnetic wave includes the electromagnetic loss in the inner of the absorber and the interference loss between the reflection waves from the back interface and the front interface
2015, 44(10):2454-2458.
Abstract:
Ultra-narrow-gap welding experiment of 1Cr18Ni9Ti austenitic stainless steel has been carried out by the method of constricting arc with ultra-fine granular flux, and microstructures and mechanical property of ultra-narrow-gap welding joint have been measured and analyzed. The results indicate that ultra-narrow-gap welding joint of 1Cr18Ni9Ti austenitic stainless steel takes on equiaxed grains in the backing weld zone and coarse columnar grains in the weld zone of filling bead and cover pass. Equiaxed grain and columnar grain mainly are made of austenite, but there is a small quantity of lath ferrite in the equiaxed grain and columnar grain. Backing weld and filling bead of ultra-narrow-gap welding joint have the similar hardness as base metal, but the hardness of cover pass is lower than that of base metal. The properties of ultra-narrow-gap welding joint are higher than the minimum of corresponding properties of base metal including the tensile strength, yield strength and elongation ratio except reduction of area and impact energy. Besides, corrosion rate of ultra-narrow-gap welding joint is 0.417 g/(m2.h), which is obviously lower than that of base metal
Ultra-narrow-gap welding experiment of 1Cr18Ni9Ti austenitic stainless steel has been carried out by the method of constricting arc with ultra-fine granular flux, and microstructures and mechanical property of ultra-narrow-gap welding joint have been measured and analyzed. The results indicate that ultra-narrow-gap welding joint of 1Cr18Ni9Ti austenitic stainless steel takes on equiaxed grains in the backing weld zone and coarse columnar grains in the weld zone of filling bead and cover pass. Equiaxed grain and columnar grain mainly are made of austenite, but there is a small quantity of lath ferrite in the equiaxed grain and columnar grain. Backing weld and filling bead of ultra-narrow-gap welding joint have the similar hardness as base metal, but the hardness of cover pass is lower than that of base metal. The properties of ultra-narrow-gap welding joint are higher than the minimum of corresponding properties of base metal including the tensile strength, yield strength and elongation ratio except reduction of area and impact energy. Besides, corrosion rate of ultra-narrow-gap welding joint is 0.417 g/(m2.h), which is obviously lower than that of base metal
16 Crystallization Behavior and Electrochemical Corrosion Characteristics of Amorphous Ni-Fe-W-B Alloy
2015, 44(10):2459-2464.
Abstract:
57.5Ni-24.5Fe-14.5W-3.5B (wt%) amorphous ribbons were prepared by a melt spinning method, and then annealed at different temperatures. The crystallization process and evolution of phases were identified by differential scanning calorimeter and X-ray diffraction. A comparative study of the electrochemical corrosion behaviors of the samples was performed by the linear polarization method and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution. The morphologies and components of the samples after potentiodynamic polarization were analyzed by SEM and EDS, respectively. The results show that the crystallization process of the amorphous ribbons could be divided into three steps, and their crystallization temperature are about 430 °C, 470 °C and 700 °C. Compared with the completely amorphous alloy, the corrosion properties of the annealed amorphous sample increase obviously. A stable passive film is formed on the surface of the amorphous ribbon annealed at 500 °C, which contributes to its excellent corrosion resistance. However, the passive films on the surfaces of completely amorphous and amorphous samples annealed at 720 °C are not stable, which are susceptible to be attacked by pitting corrosion and localized corrosion.
57.5Ni-24.5Fe-14.5W-3.5B (wt%) amorphous ribbons were prepared by a melt spinning method, and then annealed at different temperatures. The crystallization process and evolution of phases were identified by differential scanning calorimeter and X-ray diffraction. A comparative study of the electrochemical corrosion behaviors of the samples was performed by the linear polarization method and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution. The morphologies and components of the samples after potentiodynamic polarization were analyzed by SEM and EDS, respectively. The results show that the crystallization process of the amorphous ribbons could be divided into three steps, and their crystallization temperature are about 430 °C, 470 °C and 700 °C. Compared with the completely amorphous alloy, the corrosion properties of the annealed amorphous sample increase obviously. A stable passive film is formed on the surface of the amorphous ribbon annealed at 500 °C, which contributes to its excellent corrosion resistance. However, the passive films on the surfaces of completely amorphous and amorphous samples annealed at 720 °C are not stable, which are susceptible to be attacked by pitting corrosion and localized corrosion.
2015, 44(10):2471-2475.
Abstract:
The extrusion process of AZ31 magnesium alloy has been simulated. An actual experiment was also carried out and simulated by DEFORM-2D. The result shows that the simulated temperature-time curve agrees well with the measured one, indicating the good accuracy of the simulation parameters. And then a series of simulations of AZ31 extrusion were analyzed. The temperature distributions, stress distributions and extrusion loads were obtained. Matlab were used to describe the relationship among them in four-dimensional space
The extrusion process of AZ31 magnesium alloy has been simulated. An actual experiment was also carried out and simulated by DEFORM-2D. The result shows that the simulated temperature-time curve agrees well with the measured one, indicating the good accuracy of the simulation parameters. And then a series of simulations of AZ31 extrusion were analyzed. The temperature distributions, stress distributions and extrusion loads were obtained. Matlab were used to describe the relationship among them in four-dimensional space
2015, 44(10):2476-2480.
Abstract:
Red emitting phosphors KLa0.7-x(MoO4)2:0.3Eu3+, xSm3+ were synthesized by a solid-state reaction. Analysis on XRD patterns confirms that all the obtained phosphors exhibit pure phase. The luminescence properties and energy transfer behavior were studied via fluorescence spectral measurements. When the Sm3+ concentration is lower, the emission intensities under 277 and 394 nm excitations almost do not change with Sm3+ concentration, but effective luminescent enhancement is discovered in the samples with lower Sm3+ concentrations by 404 nm. However, Sm3+ doping quenches the emission of Eu3+ when the Sm3+ doping concentration is higher. The electric multipole interaction and exchange interaction models were adopted to explore physical nature for the energy transfer mechanism, and the exchange interaction between Sm3+ and Eu3+ is confirmed to be the right mechanism. It is found from the fluorescence decays that Sm3+ is the donor when the Sm3+ concentration is lower, but the Sm3+ doping quenches the luminescence of Eu3+ when the Sm3+ concentration is higher
Red emitting phosphors KLa0.7-x(MoO4)2:0.3Eu3+, xSm3+ were synthesized by a solid-state reaction. Analysis on XRD patterns confirms that all the obtained phosphors exhibit pure phase. The luminescence properties and energy transfer behavior were studied via fluorescence spectral measurements. When the Sm3+ concentration is lower, the emission intensities under 277 and 394 nm excitations almost do not change with Sm3+ concentration, but effective luminescent enhancement is discovered in the samples with lower Sm3+ concentrations by 404 nm. However, Sm3+ doping quenches the emission of Eu3+ when the Sm3+ doping concentration is higher. The electric multipole interaction and exchange interaction models were adopted to explore physical nature for the energy transfer mechanism, and the exchange interaction between Sm3+ and Eu3+ is confirmed to be the right mechanism. It is found from the fluorescence decays that Sm3+ is the donor when the Sm3+ concentration is lower, but the Sm3+ doping quenches the luminescence of Eu3+ when the Sm3+ concentration is higher
2015, 44(10):2486-2490.
Abstract:
Based on the instability mechanism of wave formation at the interface in explosive welding and fluid-elastic-plastic model, the conditions for Rayleigh-Taylor and Kelvin-Helmholtz instability were found between fly plate back and air. Therefore, the instability between metal fluid foil and air was proposed. It can be deduced from the ratio of amplitude and wavelength that linear relationship is proper. Then we established double layer fluid flow instability linear control equations, and gained expression of instability development exponent. Results show that at the competition between metal fluid elastic-viscosity and Helmholtz-Taylor synthesized instability, disturbances of special wavelength are prior developed, while others are attenuation or have no time to develop. Consequently, the wavelength and amplitude of welding interface along detonation direction is uniform. In addition, experiments also validate this conclusion
Based on the instability mechanism of wave formation at the interface in explosive welding and fluid-elastic-plastic model, the conditions for Rayleigh-Taylor and Kelvin-Helmholtz instability were found between fly plate back and air. Therefore, the instability between metal fluid foil and air was proposed. It can be deduced from the ratio of amplitude and wavelength that linear relationship is proper. Then we established double layer fluid flow instability linear control equations, and gained expression of instability development exponent. Results show that at the competition between metal fluid elastic-viscosity and Helmholtz-Taylor synthesized instability, disturbances of special wavelength are prior developed, while others are attenuation or have no time to develop. Consequently, the wavelength and amplitude of welding interface along detonation direction is uniform. In addition, experiments also validate this conclusion
2015, 44(10):2501-2508.
Abstract:
The evolution law of precipitated phase in 028 alloy was studied at different aging temperatures and for different aging time by scanning electron microscope, X-ray diffraction and hardness test. The chemical compositions, structure and hardness of the precipitated phase was analyzed, and the transformation kinetics and the growth of precipitated phase was analyzed as well. The results show that with the aging temperature increasing and the extension of time, the amount and size of precipitated phase of 028 alloy increase, and the hardness rises. Precipitate phase in grain boundaries and intragranular is mainly σ phase containing Cr, Mo, Fe and Ni elements. The transformation kinetics equation of 028 alloy at different temperatures was deduced using Avrami equation, the kinetics curve was drawn and one-dimensional growing up situation of precipitated phase was calculated, and finally the one-dimensional growth equation was obtained.
The evolution law of precipitated phase in 028 alloy was studied at different aging temperatures and for different aging time by scanning electron microscope, X-ray diffraction and hardness test. The chemical compositions, structure and hardness of the precipitated phase was analyzed, and the transformation kinetics and the growth of precipitated phase was analyzed as well. The results show that with the aging temperature increasing and the extension of time, the amount and size of precipitated phase of 028 alloy increase, and the hardness rises. Precipitate phase in grain boundaries and intragranular is mainly σ phase containing Cr, Mo, Fe and Ni elements. The transformation kinetics equation of 028 alloy at different temperatures was deduced using Avrami equation, the kinetics curve was drawn and one-dimensional growing up situation of precipitated phase was calculated, and finally the one-dimensional growth equation was obtained.
Xiao Jingkun
,
Song Chengwen
,
Zhang Xiaoni
,
Chu Xuan
,
Wu Shuaihua
,
Cheng Murong
,
Song Mingyan
,
Yu Yingtao
2015, 44(10):2509-2512.
Abstract:
Ni-doped SnO2 powders were prepared by the solvethermal method. The morphology, structure and elemental composition of Ni-doped SnO2 were characterized by TEM, EDAX, XRD, Raman and XPS. Gas sensing properties of Ni-doped SnO2 were also investigated by sensitivity measurements. The results show that Ni doping inhibits the grain growth of SnO2 and decreases the grain size, thus enhancing the gas sensitivity of SnO2. Oxygen vacancies formed by the substitution of Ni2+ for Sn4+ in the SnO2 matrix improves the gas sensing performance at low level of Ni doping. However, when Ni concentration reaches 30 wt%, the addition of Ni to SnO2 decreases gas sensitivity, which is attributed to the counteraction of the n- and p-type sensors
Ni-doped SnO2 powders were prepared by the solvethermal method. The morphology, structure and elemental composition of Ni-doped SnO2 were characterized by TEM, EDAX, XRD, Raman and XPS. Gas sensing properties of Ni-doped SnO2 were also investigated by sensitivity measurements. The results show that Ni doping inhibits the grain growth of SnO2 and decreases the grain size, thus enhancing the gas sensitivity of SnO2. Oxygen vacancies formed by the substitution of Ni2+ for Sn4+ in the SnO2 matrix improves the gas sensing performance at low level of Ni doping. However, when Ni concentration reaches 30 wt%, the addition of Ni to SnO2 decreases gas sensitivity, which is attributed to the counteraction of the n- and p-type sensors
2015, 44(10):2513-2518.
Abstract:
The commercial pure zirconium samples were processed by surface mechanical attrition treatment (SMAT) to realize the surface nanocrystallization, and the compressive residual stress was induced at the same time. The microstructure was studied by PM and TEM after SMAT. The macroscopic residual stress at different depths from surface was evaluated by XRD after different cycles. The distribution characteristics of FWHM were investigated. Fitting the peaks from XRD by Voigt function, microstrain and dislocation density at different depths from top surface after different cycles were obtained. The results indicate that the biggest relaxation rate (about 25%) is found at initial stage, and the more cycles, the less residual stress relaxation. Under different cycles, with the increase of the depth from the top surface, the FWHM decreases rapidly, and then reaches to a steady state. The distribution characteristics of the microstrain and dislocation density at different depths from surface are similar to FWHM after different cycles. Along with the decrease of dislocation density, the residual stress increases gradually. The depth where the dislocation density value is about 2×1010 cm-2 is similar to that of the maximum compressive residual stress. The residual stress relaxation is achieved by the accumulation of plastic deformation in the process of dislocation motion under cyclic loading
The commercial pure zirconium samples were processed by surface mechanical attrition treatment (SMAT) to realize the surface nanocrystallization, and the compressive residual stress was induced at the same time. The microstructure was studied by PM and TEM after SMAT. The macroscopic residual stress at different depths from surface was evaluated by XRD after different cycles. The distribution characteristics of FWHM were investigated. Fitting the peaks from XRD by Voigt function, microstrain and dislocation density at different depths from top surface after different cycles were obtained. The results indicate that the biggest relaxation rate (about 25%) is found at initial stage, and the more cycles, the less residual stress relaxation. Under different cycles, with the increase of the depth from the top surface, the FWHM decreases rapidly, and then reaches to a steady state. The distribution characteristics of the microstrain and dislocation density at different depths from surface are similar to FWHM after different cycles. Along with the decrease of dislocation density, the residual stress increases gradually. The depth where the dislocation density value is about 2×1010 cm-2 is similar to that of the maximum compressive residual stress. The residual stress relaxation is achieved by the accumulation of plastic deformation in the process of dislocation motion under cyclic loading
2015, 44(10):2519-2522.
Abstract:
The deformation behavior of Ti-1300 alloy has been investigated using optical microscope (OM) and transmission electron microscope (TEM) at ambient temperature. The results show that the tensile stress-strain curves of Ti-1300 alloys solution treated at different temperatures don’t present a double yield effect. The Ti-1300 alloy contains a great deal of β stable elements, thus increasing the stability of β phase of this alloy for restraining stress/strain induced transformation. Therefore, the deformation mechanism of Ti-1300 alloy is mainly dislocation slip and twinning at room temperature. With the increase of the plastic deformation of 10%, the micro-hardness of Ti-1300 alloy increases by about 210 MPa. It can be attributed to the dislocation glide, dislocation tangles and their interaction in the plastic deformation process of Ti-1300 alloys
The deformation behavior of Ti-1300 alloy has been investigated using optical microscope (OM) and transmission electron microscope (TEM) at ambient temperature. The results show that the tensile stress-strain curves of Ti-1300 alloys solution treated at different temperatures don’t present a double yield effect. The Ti-1300 alloy contains a great deal of β stable elements, thus increasing the stability of β phase of this alloy for restraining stress/strain induced transformation. Therefore, the deformation mechanism of Ti-1300 alloy is mainly dislocation slip and twinning at room temperature. With the increase of the plastic deformation of 10%, the micro-hardness of Ti-1300 alloy increases by about 210 MPa. It can be attributed to the dislocation glide, dislocation tangles and their interaction in the plastic deformation process of Ti-1300 alloys
24 Solvent Thermal-Sol Gel Synthesis and Luminescence Properties of (Y,Gd)(P,V)O4:Eu3+,Bi3+ Phosphors
2015, 44(10):2529-2533.
Abstract:
A series of (Y1-z,Gdz)1-x-y(Pz,V1-z)O4: xEu3+,yBi3+ red phosphors have been synthesized by a solvent thermal-sol gel method. The crystal structure, surface morphology and spectral characteristics of the samples were investigated by X-ray diffraction (XRD), SEM and fluorescence spectrophotometer, respectively. It is found that the synthesized crystalline powders are of tetragonal system. The doped ions have little impact on the matrix crystal structure. The sample grains show short rods or elliptical and the structure is uniform and loose. The excitation spectrum is composed of the broadband in 250~400 nm (O2--V5+ band and Eu3+-O2- band). The strongest emission peak locates at 619 nm(Eu3+: 5D0→7F2). The best doping amount of Eu3+ is 5 mol% and the excess concentration will lead to concentration quenching. The co-doping of Bi3+, Gd3+ and P5+ can improve the luminous intensity of the samples significantly. The doping of Bi3+ can make the excitation band move to near 400 nm, indicating samples can match with the N-UV chips and then be used in white-LEDs
A series of (Y1-z,Gdz)1-x-y(Pz,V1-z)O4: xEu3+,yBi3+ red phosphors have been synthesized by a solvent thermal-sol gel method. The crystal structure, surface morphology and spectral characteristics of the samples were investigated by X-ray diffraction (XRD), SEM and fluorescence spectrophotometer, respectively. It is found that the synthesized crystalline powders are of tetragonal system. The doped ions have little impact on the matrix crystal structure. The sample grains show short rods or elliptical and the structure is uniform and loose. The excitation spectrum is composed of the broadband in 250~400 nm (O2--V5+ band and Eu3+-O2- band). The strongest emission peak locates at 619 nm(Eu3+: 5D0→7F2). The best doping amount of Eu3+ is 5 mol% and the excess concentration will lead to concentration quenching. The co-doping of Bi3+, Gd3+ and P5+ can improve the luminous intensity of the samples significantly. The doping of Bi3+ can make the excitation band move to near 400 nm, indicating samples can match with the N-UV chips and then be used in white-LEDs
2015, 44(10):2539-2543.
Abstract:
The Cu-SiO2 nano-composite thin films with different Cu target powers and substrate temperatures were prepared by DC and RF magnetron sputtering in an alternating deposition method. The phase structure and optical absorption properties of Cu-SiO2 nano-composite films were studied. The results indicate that with the increase of the Cu target power, the size of the Cu nanoparticles increases, and the peak in the optical absorption spectra presents a red-shift. Due to the re-evaporation effect, the size of Cu nanoparticles decreases and the peak exhibits a blue-shift with increasing of the substrate temperature. Compared with the films deposited at RT, the films at different substrate temperatures display a clear surface plasmon resonance absorption peak in the visible band. Therefore, the Cu target power and the substrate temperature significantly influence the crystallization states and optical absorption properties of the Cu-SiO2 nano-composite films
The Cu-SiO2 nano-composite thin films with different Cu target powers and substrate temperatures were prepared by DC and RF magnetron sputtering in an alternating deposition method. The phase structure and optical absorption properties of Cu-SiO2 nano-composite films were studied. The results indicate that with the increase of the Cu target power, the size of the Cu nanoparticles increases, and the peak in the optical absorption spectra presents a red-shift. Due to the re-evaporation effect, the size of Cu nanoparticles decreases and the peak exhibits a blue-shift with increasing of the substrate temperature. Compared with the films deposited at RT, the films at different substrate temperatures display a clear surface plasmon resonance absorption peak in the visible band. Therefore, the Cu target power and the substrate temperature significantly influence the crystallization states and optical absorption properties of the Cu-SiO2 nano-composite films
2015, 44(10):2553-2556.
Abstract:
In order to improve the edge quality of horizontal continuous casting phosphor bronze slab, three methods including applying silicon steel at ends of the traveling magnetic field stirrer, changing the length of traveling magnetic field stirrer, and reducing the ends current intensity of traveling magnetic field stirrer were proposed, and a numerical simulation method was used to study the flow and solidification process of continuous casting phosphor bronze slab. The results show that compared to the other two methods, the method of placing the silicon steel sheet on the edge of the traveling electromagnet stirrer is more beneficial to improve the melt flow. When the length of the silicon steel sheet is 150 mm, the strong flow at the melt ends disappears and the ends melt solidification process is more uniform, which is helpful to prevent the crack and segregation defect and improve the edge quality of continuous casting phosphor bronze slab.
In order to improve the edge quality of horizontal continuous casting phosphor bronze slab, three methods including applying silicon steel at ends of the traveling magnetic field stirrer, changing the length of traveling magnetic field stirrer, and reducing the ends current intensity of traveling magnetic field stirrer were proposed, and a numerical simulation method was used to study the flow and solidification process of continuous casting phosphor bronze slab. The results show that compared to the other two methods, the method of placing the silicon steel sheet on the edge of the traveling electromagnet stirrer is more beneficial to improve the melt flow. When the length of the silicon steel sheet is 150 mm, the strong flow at the melt ends disappears and the ends melt solidification process is more uniform, which is helpful to prevent the crack and segregation defect and improve the edge quality of continuous casting phosphor bronze slab.
2015, 44(10):2566-2570.
Abstract:
The?degradation?property of biomedical magnesium alloy is the key to determine its application on cardiovascular stents and bone replacement material, etc. In this paper, we discussed the effect of degradation on magnesium alloy with various cations. AZ31B magnesium alloy samples were immersed into NaCl aq., KCl aq., MgCl2 aq. and CaCl2 aq. with the same concentration of Cl- used as body fluid. The potentiodynamic polarization curve (PPC) and electrochemical impedance spectroscopy (EIS) of these magnesium samples were analyzed. Results show that the corrosion potential and impedance have the similar tendency with the pH values and gravimetric curve. Namely, the metal cations affect the degradation property of magnesium alloy directly and the order is NaCl > KCl > CaCl2 > MgCl2. Na+ is superior to other cations in magnesium alloy degradation
The?degradation?property of biomedical magnesium alloy is the key to determine its application on cardiovascular stents and bone replacement material, etc. In this paper, we discussed the effect of degradation on magnesium alloy with various cations. AZ31B magnesium alloy samples were immersed into NaCl aq., KCl aq., MgCl2 aq. and CaCl2 aq. with the same concentration of Cl- used as body fluid. The potentiodynamic polarization curve (PPC) and electrochemical impedance spectroscopy (EIS) of these magnesium samples were analyzed. Results show that the corrosion potential and impedance have the similar tendency with the pH values and gravimetric curve. Namely, the metal cations affect the degradation property of magnesium alloy directly and the order is NaCl > KCl > CaCl2 > MgCl2. Na+ is superior to other cations in magnesium alloy degradation
2015, 44(10):2571-2575.
Abstract:
The paper studied the change rule of the forepart of initial solidified shell, cross-section structure and elements distribution of horizontal continuous casting Zn-Cu alloy billets under electromagnetic field. The results show that the forepart position changes with the casting speed, pouring temperature and current intensity. Among these parameters, casting speed plays the most important role. It is only adjusting the corresponding casting speed according to the current strength and the pouring temperature that can improve the structure and reduce segregation. The forepart moves backwards by enhancing the current and the casting speeds. When the liquid-solid interface locates in the interspace between the cooling water jacket and the electromagnetic stirrer, the inverse segregation of Cu can be effectively suppressed. Electromagnetic field removes the nonuniform cross-section structures and the difference between the final solidification area and billet geometric center, and refines the dendrite structure. Stirring does not completely eliminate the deep gray dendritic copper rich phases in the edge or center of the billets, instead of slightly larger dendrite sizes and the small edge-center structure difference. When casting speed and current intensity is 3 m/h and 100 A, respectively, the most uniform and refined structure is obtained, while no obvious change can be seen for other currents and frequencies. The addition of Ti cannot refine the billet structure or eliminate the inverse segregation, but make the melt sticky with poor fluidity
The paper studied the change rule of the forepart of initial solidified shell, cross-section structure and elements distribution of horizontal continuous casting Zn-Cu alloy billets under electromagnetic field. The results show that the forepart position changes with the casting speed, pouring temperature and current intensity. Among these parameters, casting speed plays the most important role. It is only adjusting the corresponding casting speed according to the current strength and the pouring temperature that can improve the structure and reduce segregation. The forepart moves backwards by enhancing the current and the casting speeds. When the liquid-solid interface locates in the interspace between the cooling water jacket and the electromagnetic stirrer, the inverse segregation of Cu can be effectively suppressed. Electromagnetic field removes the nonuniform cross-section structures and the difference between the final solidification area and billet geometric center, and refines the dendrite structure. Stirring does not completely eliminate the deep gray dendritic copper rich phases in the edge or center of the billets, instead of slightly larger dendrite sizes and the small edge-center structure difference. When casting speed and current intensity is 3 m/h and 100 A, respectively, the most uniform and refined structure is obtained, while no obvious change can be seen for other currents and frequencies. The addition of Ti cannot refine the billet structure or eliminate the inverse segregation, but make the melt sticky with poor fluidity
2015, 44(10):2576-2582.
Abstract:
Micro-arc oxidation was conducted on AZ31 Mg alloy under CC mode by single variable experiments to improve its corrosion resistance and bio-activity. The microstructure, Ca/P ratio and corrosion rate were studied to investigate the influence of the Ca- or P-containing compositions on the coating. Furthermore, the properties of the optimized coating were studied. The results reveal that Ca/P ratio depends on the concentration of Ca(Ac)2, (Na2PO3)6 and NaH2PO4. With the increase of Ca(Ac)2, the coating thickness decreases, but it becomes more uniform; while (Na2PO3)6 has little effects on surface morphology or coating thickness. The content of P increases with (Na2PO3)6. The more NaH2PO4, the bigger the pore size and the smaller Ca/P ratio. The optimized coating possesses a flat and compact surface covered by micropores with diameters of about 10.7 μm and there are microcracks. And the coating phases are mainly MgO, Mg and a small amount of Ca2P2O7 and SiO2, which make the coating harder and more resistant to corrosion. The coating roughness Ra is 0.4482 μm and the wetting angle is 42.65°, which are good for cells to adhere to and grow on.
Micro-arc oxidation was conducted on AZ31 Mg alloy under CC mode by single variable experiments to improve its corrosion resistance and bio-activity. The microstructure, Ca/P ratio and corrosion rate were studied to investigate the influence of the Ca- or P-containing compositions on the coating. Furthermore, the properties of the optimized coating were studied. The results reveal that Ca/P ratio depends on the concentration of Ca(Ac)2, (Na2PO3)6 and NaH2PO4. With the increase of Ca(Ac)2, the coating thickness decreases, but it becomes more uniform; while (Na2PO3)6 has little effects on surface morphology or coating thickness. The content of P increases with (Na2PO3)6. The more NaH2PO4, the bigger the pore size and the smaller Ca/P ratio. The optimized coating possesses a flat and compact surface covered by micropores with diameters of about 10.7 μm and there are microcracks. And the coating phases are mainly MgO, Mg and a small amount of Ca2P2O7 and SiO2, which make the coating harder and more resistant to corrosion. The coating roughness Ra is 0.4482 μm and the wetting angle is 42.65°, which are good for cells to adhere to and grow on.
2015, 44(10):2596-2600.
Abstract:
Magnesium alloys, as heat-sink materials, have great potential for the application of electronics, communication and computer industries due to their low density, excellent electromagnetic shielding and damping capacity, high specific strength. Meanwhile, the thermal conductive ability of unit mass is better compared to aluminum alloy. State of research and development on high thermal conductivity magnesium alloy is reviewed in this paper, and Mg-Zn, Mg-RE, Mg-Th and Mg-Mn alloys with excellent thermal conductivities are analyzed. The problems existing in the study and the research direction of future are forecasted for high thermal conductivity of magnesium alloys
Magnesium alloys, as heat-sink materials, have great potential for the application of electronics, communication and computer industries due to their low density, excellent electromagnetic shielding and damping capacity, high specific strength. Meanwhile, the thermal conductive ability of unit mass is better compared to aluminum alloy. State of research and development on high thermal conductivity magnesium alloy is reviewed in this paper, and Mg-Zn, Mg-RE, Mg-Th and Mg-Mn alloys with excellent thermal conductivities are analyzed. The problems existing in the study and the research direction of future are forecasted for high thermal conductivity of magnesium alloys
