Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to a...Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to address leakage defects in die-cast Al alloys.In this study,the efficacy of the VPI technique in sealing alloy parts was investigated using a combination of nondestructive micro X-ray computed tomography(micro XCT)and a standard leak test.The results demonstrate that the commonly used water leak test is insufficient for determining the sealing performance.Instead,micro XCT shows distinct advantages by enabling more comprehensive analysis.It reveals the presence of a low atomic number impregnates sealant within casting defects,which has low grey contrast and allows for visualizing primary leakage paths in 3D.The effective atomic number of impregnated resin is 6.75 and that of Al alloy is 13.69 by dual-energy X-ray CT.This research findings will contribute to enhancing the standard VPI process parameters and the properties of impregnating sealants to improve quality assurance for impregnation in industrial metals.展开更多
Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace,automotive,and energy indus-tries owing to its extraordinary thermomechanical properties.The effects of different two-step s...Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace,automotive,and energy indus-tries owing to its extraordinary thermomechanical properties.The effects of different two-step solid solution treatments on microstructure andδphase precipitation of Inconel 718 alloy were studied,and the transformation mechanism fromγ″metastable phase toδphase was clarified.The precipitates were statistically analyzed by X-ray diffractometry.The results show that theδphase content firstly increased,and then decreased with the temperature of the second-step solid solution.The changes in microstructure andδphase were studied by scanning electron microscopy and transmission electron microscopy.An intragranularδphase formed in Inconel 718 alloy at the second-[100]_(δ)[011]γ step solid solution temperature of 925℃,and its orientation relationship withγmatrix was determined as//and(010)_(δ)//(111)γ.Furthermore,the Vickers hardness of different heat treatment samples was measured,and the sample treated by second-step solid solution at 1010℃ reached the maximum hardness of HV 446.84.展开更多
An extensive investigation was made on the effects of micro-alloying with small amounts of Sc and Mn on the microstructure and mechanical properties of the Al-Mg based alloys. It is found that the micro-alloying can s...An extensive investigation was made on the effects of micro-alloying with small amounts of Sc and Mn on the microstructure and mechanical properties of the Al-Mg based alloys. It is found that the micro-alloying can significantly enhance the tensile strength of the alloys, and eliminate the dendritic cast structure in it. Many fine, spherical and dispersive Al3Sc particles are found in the annealed Al-Mg-Mn-Sc alloys, which can strongly pin up dislocations and subgrain boundaries, thus strongly retarding the recrystallization of the alloys. The strengthening of the micro-alloyed Al-Mg alloys is attributed to the precipitation strengthening by the Al3Sc particles and to the substructure strengthening.展开更多
The strengthening effect of phosphorus and boron on wrought superalloys is reviewed and discussed. The addition of phosphorus and boron can prolong the rupture life of some wrought superalloys over 3 times, and lowers...The strengthening effect of phosphorus and boron on wrought superalloys is reviewed and discussed. The addition of phosphorus and boron can prolong the rupture life of some wrought superalloys over 3 times, and lowers the constant creep rate by an order of magnitude. By micro-alloying with phosphorus and boron,the alloys with extended rupture life are developed and the service temperature of IN718 alloy is enhanced, and the alloys which can be used for a long time at 700℃ with higher comprehensive properties can be developed.展开更多
A new low-cost corrosion-resistant rebar（HRB400 R） was designed and fabricated by chromium micro-alloying. The effects of Cr on the passivation and corrosion behavior of this rebar in the simulated concrete pore sol...A new low-cost corrosion-resistant rebar（HRB400 R） was designed and fabricated by chromium micro-alloying. The effects of Cr on the passivation and corrosion behavior of this rebar in the simulated concrete pore solutions were studied systematically, and its improved corrosion resistance was revealed. In the Cl--free saturated Ca（OH）_2 solution, the HRB400 R rebar presented nearly the same passive film and similar passivation ability compared to the common carbon steel rebar. In the long-term immersion corrosion test in the Cl--contained Ca（OH）_2 solution, the HRB400 R rebar presented improved corrosion resistance and obvious longer passivation-maintaining period. Micro-alloying of Cr element in the rebar matrix enhanced its corrosion resistance against Cl--attack and retarded the corrosion initiation in the matrix. In the alkaline Na Cl salt spraying test, the HRB400 R rebar also presented obviously lower mass-loss rate. The enrichment of Cr element in the rust layer improved its retardant effect to the penetration of aggressive medium, and decreased the corrosion propagation rate of the rebar.展开更多
The hot ductility of the V-containing micro-alloying steel CC (continuouscasting) slabs and precipitation of vanadium carbide in the tensile specimens were investigated. Theresults indicate that the precipitation rati...The hot ductility of the V-containing micro-alloying steel CC (continuouscasting) slabs and precipitation of vanadium carbide in the tensile specimens were investigated. Theresults indicate that the precipitation ratio and precipitation rate of vanadium in the specimensreach maximum respectively at 900, -825 and 825 deg C. There is still l0 percent-l7 percent ofvanadium precipitated when the deformation temperature decreases to 800-700 deg C. Vanadium largelyaffects the ductility of the steel in the low ductility temperature Region III. Embrittlement ofsteel with higher V content is severer in the region and the embrittlement extends to lowertemperature.展开更多
The optimization of micro milling electrical discharge machining（EDM） process parameters of Inconel 718 alloy to achieve multiple performance characteristics such as low electrode wear,high material removal rate and...The optimization of micro milling electrical discharge machining（EDM） process parameters of Inconel 718 alloy to achieve multiple performance characteristics such as low electrode wear,high material removal rate and low working gap was investigated by the Grey-Taguchi method.The influences of peak current,pulse on-time,pulse off-time and spark gap on electrode wear（EW）,material removal rate（MRR） and working gap（WG） in the micro milling electrical discharge machining of Inconel 718 were analyzed.The experimental results show that the electrode wear decreases from 5.6×10-9 to 5.2×10-9 mm3/min,the material removal rate increases from 0.47×10-8 to 1.68×10-8 mm3/min,and the working gap decreases from 1.27 to 1.19 μm under optimal micro milling electrical discharge machining process parameters.Hence,it is clearly shown that multiple performance characteristics can be improved by using the Grey-Taguchi method.展开更多
A novel process for manufacturing A1-0.70Fe-0.24Cu alloy conductor was proposed, which includes horizontal continuous casting and subsequent continuous extrusion forming （Conform）. The mechanical properties, electri...A novel process for manufacturing A1-0.70Fe-0.24Cu alloy conductor was proposed, which includes horizontal continuous casting and subsequent continuous extrusion forming （Conform）. The mechanical properties, electrical conductivity and the compressed creep behaviour of the alloy were studied. The results indicate that the Conform process induces obvious grain refinement, strain-induced precipitation of AI7CuzFe phase and the transformation of crystal orientation distribution. The processed alloy has good comprehensive mechanical properties and electrical conductivity. Moreover, a better creep resistance under the conditions of 90 ~C and 76 MPa is shown compared with pure A1 and annealed copper, and the relationship between primary creep strain and time may comply with the logarithmic law. The enhanced properties are attributed to the grain refinement as well as the fine and homogeneously distributed thermally stable A1Fe and A17Cu2Fe precipitation phases.展开更多
The effects of Zn content on the microstxucture and the mechanical and corrosion properties of as-cast low-alloyed Mg-xZn~.2Ca alloys （x = 0.6wt%, 2.0wt%, 2.5wt%, hereafter denoted as 0.6Zn, 2.0Zn, and 2.5Zn alloys, ...The effects of Zn content on the microstxucture and the mechanical and corrosion properties of as-cast low-alloyed Mg-xZn~.2Ca alloys （x = 0.6wt%, 2.0wt%, 2.5wt%, hereafter denoted as 0.6Zn, 2.0Zn, and 2.5Zn alloys, respectively） axe investigated. The results show that the Zn content not only influences grain refinement but also induces different phase precipitation behaviors. The as-cast microstxucture of the 0.6Zn alloy is composed of ct-Mg, Mg2Ca, and Ca2Mg6Zn3 phases, whereas 2.0Zn and 2.5Zn alloys only contain ct-Mg and Ca2Mg6Zn3 phases, as revealed by X-ray diffraction （XRD） and txonsmission electron microscopy （TEM） analyses. Moreover, with in- creasing Zn content, both the ultimate tensile strength （UTS） and the elongation to fracture first increase and then decrease. Among the three investigated alloys, the largest UTS （178 MPa） and the highest elongation to fracture （6.5%） are obtained for the 2.0Zn alloy. In addition, the corrosion rate increases with increasing Zn content. This paper provides on updated investigation of the alloy composi- tion-microstxucture-property relationships of different Zn-containing Mg-Zn-Ca alloys.展开更多
In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investig...In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investigated, then the reheating microstructures were investigated. Results show that: the difference of temperature between the outer and center is small and the difference of their microstructures are also small. During reheating at 576℃ the spheroidization of grains is significant after 5min and no rosettes are visible after 20min by optical microscopy. Similar observations were madeon materials reheated at 596℃, but the ripening process is faster. The grains growup to 30-60μm, fine enough for thixoforming.展开更多
In recent years,magnesium and its alloys are considered as biodegradable implants.However magnesium implants may rapidly corrode before the natural healing process of the tissue is completed.In this investigation,micr...In recent years,magnesium and its alloys are considered as biodegradable implants.However magnesium implants may rapidly corrode before the natural healing process of the tissue is completed.In this investigation,micro arc oxidation process has been studied for avoiding primary corrosion of the magnesium alloy in simulated body fluid.Anodized coating was formed on AZ31 alloy in nontoxic silicate-alkaline solution at constant current.The effects of silicate concentration and conductivity of electrolyte solution on microstructure and corrosion properties of coating were evaluated.Scanning electron microscopy showed that a thick and condensed coating is formed after enough anodizing period.Energy dispersive spectroscopy showed that Si,O and Mg are the main components of the coating.Corrosion resistance of the coated and uncoated samples was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy tests in SBF at 37℃ and pH of 7.4.Maximum corrosion resistance was achieved at 30 g/L concentration of sodium silicate in anodizing solution.It was observed that further increase in silicate concentration decreased the corrosion resistance.展开更多
A novel semisolid micro fused-casting(MFC) for preparing A356 alloy strips is proposed, and the effects of process parameters of pouring temperature on the microstructure and properties of A356 alloy strips are invest...A novel semisolid micro fused-casting(MFC) for preparing A356 alloy strips is proposed, and the effects of process parameters of pouring temperature on the microstructure and properties of A356 alloy strips are investigated. MFC means that the semisolid metal slurry was pressed out from the outlet of bottom of crucible to the movable plate, and directly solidified and formed layer by layer. The microstructure and properties of A356 semisolid alloy slurry were influenced by the cooling conditions. Results show that the aluminu alloy A356 strip samples fabricated by micro fused-casting had good performances and uniform structures with the pouring temperature at 595 ℃ and the substrate movement speed at 18 mm/s. The fine grains of the primary a-Al phase with average grain size of 53 μm and shape factor up to 0.72 was obtained, the ultimate tensile strength of the aluminum alloy A356 strip reaches 243.79±3.91 MPa, while the average vickers hardness is 82.65±1.86 HV.展开更多
In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)proce...In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)process on Ti6Al4V alloy in NaF electrolyte.The influence of NaF concentration(0.15-0.50 mol/L)on the PEO process,microstructure,phase composition,corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy,energy dispersive spectroscopy,atomic force microscopy,X-ray diffractometer,and potentiodynamic polarization.The results demonstrated that Ti6Al4V alloy had low PEO voltage(less than 200 V)in NaF electrolyte,which decreased further as the NaF concentration increased.A micro/nano-structured coating with 10-15μm pits and 200-800 nm pores was formed in NaF electrolyte;the morphology was different from the typical pancake structure obtained with other electrolytes.The coating formed in NaF electrolyte had low surface roughness and was thin(<4μm).The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase,but greatly affected the corrosion resistance.In general,as the NaF concentration increased,the surface roughness,phase(anatase and rutile)contents,corrosion resistance,and thickness of the coating first increased and then decreased,reaching the maximum values at 0.25 mol/L NaF.展开更多
Coating technologies are a commonly used way to protect metals against corrosion.However,with more and more severe service environments of materials,many protective coating systems often are not environmentally friend...Coating technologies are a commonly used way to protect metals against corrosion.However,with more and more severe service environments of materials,many protective coating systems often are not environmentally friendly or toxic as in the case of chromates.Based on the world’s abundant ideal magnesium(Mg)and its alloy,the smart self-healing anticorrosive coating can autonomously restore the damaged part of the coating according to the environmental changes,strengthen the corrosion protection ability,and prolong its service life.This paper reviews the research progress of smart self-healing coatings on Mg alloys.These coatings mostly contain suitable corrosion inhibitors encapsulated into micro/nano containers.Moreover,the different self-healing mechanisms and functionalities of micro/nano containers are discussed.The micro/nano containers range from inorganic nanocontainers such as mesoporous nanoparticles(silica(SiO_(2)),titanium dioxide(TiO_(2)),etc.),over inorganic clays(halloysite,hydrotalcite-like,zeolite),to organic nanocontainers such as polymer microcapsules,nanofibers,chitosan(CS)and cyclodextrin(CD),as well as,carbon materials such as graphene and carbon nanotubes and hybrids such as metal organic frameworks.The functioning of micro/nano containers can be divided in two principal groups:autonomous(based on defect filling and corrosion inhibition)and non-autonomous(based on dynamic bonds and shape memory polymers).Moreover,multi functionalities and composite applications of various micro/nano containers are summarized.At present,significant progress has been made in the preparation methods and technologies of micro/nano containers.Achieving long-term self-healing properties of coatings sensing of coating failure and early warning after self-healing function failure can be expected as the main development direction of self-healing corrosion protection coatings in the future.展开更多
A novel semisolid continuous Micro Fused-Casting additive manufacturing technology for producing a ZL101 alloy strip was developed, Micro Fused-Casting means that the semisolid metal slurry was pressed out from the ou...A novel semisolid continuous Micro Fused-Casting additive manufacturing technology for producing a ZL101 alloy strip was developed, Micro Fused-Casting means that the semisolid metal slurry was pressed out from the outlet of bottom of crucible to the movable plate. The degree of sub-cooling was easily provided by movement of substrate in the micro fused-casting area. Under the aid of 3 D manufacturing software, the ZL101 alloy strip was solidified and formed layer by layer. The microstructure and properties of ZL101 semisolid slurry were improved by the cooling conditions. The results showed that the ZL101 alloy strip samples fabricated by Micro Fused-Casting had uniform structures and good performances with the substrate movement speed at 20 mm/s and the temperature at 590 ℃, the ultimate tensile strength and elongation of the ZL101 alloy strip reached 242.59 MPa and 7.71%, while the average Vickers hardness was 82.55 HV.展开更多
文摘Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to address leakage defects in die-cast Al alloys.In this study,the efficacy of the VPI technique in sealing alloy parts was investigated using a combination of nondestructive micro X-ray computed tomography(micro XCT)and a standard leak test.The results demonstrate that the commonly used water leak test is insufficient for determining the sealing performance.Instead,micro XCT shows distinct advantages by enabling more comprehensive analysis.It reveals the presence of a low atomic number impregnates sealant within casting defects,which has low grey contrast and allows for visualizing primary leakage paths in 3D.The effective atomic number of impregnated resin is 6.75 and that of Al alloy is 13.69 by dual-energy X-ray CT.This research findings will contribute to enhancing the standard VPI process parameters and the properties of impregnating sealants to improve quality assurance for impregnation in industrial metals.
基金supported by the National Natural Science Foundation of China(Nos.52201203 and 52171107)the Hebei Provincial Natural Science Foundation,China(No.E2021501026)+1 种基金the National Natural Science Foundation of China-Joint Fund of Iron and Steel Research(No.U1960204)the“333”Talent Project of Hebei Province,China(No.B20221001).
文摘Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace,automotive,and energy indus-tries owing to its extraordinary thermomechanical properties.The effects of different two-step solid solution treatments on microstructure andδphase precipitation of Inconel 718 alloy were studied,and the transformation mechanism fromγ″metastable phase toδphase was clarified.The precipitates were statistically analyzed by X-ray diffractometry.The results show that theδphase content firstly increased,and then decreased with the temperature of the second-step solid solution.The changes in microstructure andδphase were studied by scanning electron microscopy and transmission electron microscopy.An intragranularδphase formed in Inconel 718 alloy at the second-[100]_(δ)[011]γ step solid solution temperature of 925℃,and its orientation relationship withγmatrix was determined as//and(010)_(δ)//(111)γ.Furthermore,the Vickers hardness of different heat treatment samples was measured,and the sample treated by second-step solid solution at 1010℃ reached the maximum hardness of HV 446.84.
文摘An extensive investigation was made on the effects of micro-alloying with small amounts of Sc and Mn on the microstructure and mechanical properties of the Al-Mg based alloys. It is found that the micro-alloying can significantly enhance the tensile strength of the alloys, and eliminate the dendritic cast structure in it. Many fine, spherical and dispersive Al3Sc particles are found in the annealed Al-Mg-Mn-Sc alloys, which can strongly pin up dislocations and subgrain boundaries, thus strongly retarding the recrystallization of the alloys. The strengthening of the micro-alloyed Al-Mg alloys is attributed to the precipitation strengthening by the Al3Sc particles and to the substructure strengthening.
文摘The strengthening effect of phosphorus and boron on wrought superalloys is reviewed and discussed. The addition of phosphorus and boron can prolong the rupture life of some wrought superalloys over 3 times, and lowers the constant creep rate by an order of magnitude. By micro-alloying with phosphorus and boron,the alloys with extended rupture life are developed and the service temperature of IN718 alloy is enhanced, and the alloys which can be used for a long time at 700℃ with higher comprehensive properties can be developed.
基金Funded by the National Basic Research Program of China(973 Program,2015CB655100)the Natural Science Foundation of China(Nos.51308111 and 51278098)+5 种基金the Industry-UniversityResearch Cooperative Innovation Fund of Jiangsu Province(No.BY2013091)the Research Project of Science and Technology Development of China Railway Corporation(No.2014G004-F)the“Six Talent Peak”Project of Jiangsu Province(No.2014-XCL-023 and 2016-XCL-196)the China Postdoctoral Science Foundation(No.2013M531249)the Postdoctoral Science Foundation of Jiangsu Province of China(1202008C)the Applied Research Foundation of Nantong City(No.BK2013001)
文摘A new low-cost corrosion-resistant rebar（HRB400 R） was designed and fabricated by chromium micro-alloying. The effects of Cr on the passivation and corrosion behavior of this rebar in the simulated concrete pore solutions were studied systematically, and its improved corrosion resistance was revealed. In the Cl--free saturated Ca（OH）_2 solution, the HRB400 R rebar presented nearly the same passive film and similar passivation ability compared to the common carbon steel rebar. In the long-term immersion corrosion test in the Cl--contained Ca（OH）_2 solution, the HRB400 R rebar presented improved corrosion resistance and obvious longer passivation-maintaining period. Micro-alloying of Cr element in the rebar matrix enhanced its corrosion resistance against Cl--attack and retarded the corrosion initiation in the matrix. In the alkaline Na Cl salt spraying test, the HRB400 R rebar also presented obviously lower mass-loss rate. The enrichment of Cr element in the rust layer improved its retardant effect to the penetration of aggressive medium, and decreased the corrosion propagation rate of the rebar.
文摘The hot ductility of the V-containing micro-alloying steel CC (continuouscasting) slabs and precipitation of vanadium carbide in the tensile specimens were investigated. Theresults indicate that the precipitation ratio and precipitation rate of vanadium in the specimensreach maximum respectively at 900, -825 and 825 deg C. There is still l0 percent-l7 percent ofvanadium precipitated when the deformation temperature decreases to 800-700 deg C. Vanadium largelyaffects the ductility of the steel in the low ductility temperature Region III. Embrittlement ofsteel with higher V content is severer in the region and the embrittlement extends to lowertemperature.
文摘The optimization of micro milling electrical discharge machining（EDM） process parameters of Inconel 718 alloy to achieve multiple performance characteristics such as low electrode wear,high material removal rate and low working gap was investigated by the Grey-Taguchi method.The influences of peak current,pulse on-time,pulse off-time and spark gap on electrode wear（EW）,material removal rate（MRR） and working gap（WG） in the micro milling electrical discharge machining of Inconel 718 were analyzed.The experimental results show that the electrode wear decreases from 5.6×10-9 to 5.2×10-9 mm3/min,the material removal rate increases from 0.47×10-8 to 1.68×10-8 mm3/min,and the working gap decreases from 1.27 to 1.19 μm under optimal micro milling electrical discharge machining process parameters.Hence,it is clearly shown that multiple performance characteristics can be improved by using the Grey-Taguchi method.
基金Project(20130161110007) supported by the Doctoral Program of Higher Education of China
文摘A novel process for manufacturing A1-0.70Fe-0.24Cu alloy conductor was proposed, which includes horizontal continuous casting and subsequent continuous extrusion forming （Conform）. The mechanical properties, electrical conductivity and the compressed creep behaviour of the alloy were studied. The results indicate that the Conform process induces obvious grain refinement, strain-induced precipitation of AI7CuzFe phase and the transformation of crystal orientation distribution. The processed alloy has good comprehensive mechanical properties and electrical conductivity. Moreover, a better creep resistance under the conditions of 90 ~C and 76 MPa is shown compared with pure A1 and annealed copper, and the relationship between primary creep strain and time may comply with the logarithmic law. The enhanced properties are attributed to the grain refinement as well as the fine and homogeneously distributed thermally stable A1Fe and A17Cu2Fe precipitation phases.
基金supported by the National Natural Science Foundation of China(No.51671017)Fundamental Research Funds for the Central Universities(No.FRF-GF-17-B3)+1 种基金Beijing Laboratory of Metallic Materials and Processing for Modern Transportation,the Opening Research Fund of State Key Laboratory for Advanced Metals and Materials(Nos.2016Z-11,2017Z-08)State's Key Project of Research and Development Plan(No.2016YFB0300801)
文摘The effects of Zn content on the microstxucture and the mechanical and corrosion properties of as-cast low-alloyed Mg-xZn~.2Ca alloys （x = 0.6wt%, 2.0wt%, 2.5wt%, hereafter denoted as 0.6Zn, 2.0Zn, and 2.5Zn alloys, respectively） axe investigated. The results show that the Zn content not only influences grain refinement but also induces different phase precipitation behaviors. The as-cast microstxucture of the 0.6Zn alloy is composed of ct-Mg, Mg2Ca, and Ca2Mg6Zn3 phases, whereas 2.0Zn and 2.5Zn alloys only contain ct-Mg and Ca2Mg6Zn3 phases, as revealed by X-ray diffraction （XRD） and txonsmission electron microscopy （TEM） analyses. Moreover, with in- creasing Zn content, both the ultimate tensile strength （UTS） and the elongation to fracture first increase and then decrease. Among the three investigated alloys, the largest UTS （178 MPa） and the highest elongation to fracture （6.5%） are obtained for the 2.0Zn alloy. In addition, the corrosion rate increases with increasing Zn content. This paper provides on updated investigation of the alloy composi- tion-microstxucture-property relationships of different Zn-containing Mg-Zn-Ca alloys.
基金The National Natural Science Foundation of China (Grants No. 59974009) is greatly acknowledged for their financial support.
文摘In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investigated, then the reheating microstructures were investigated. Results show that: the difference of temperature between the outer and center is small and the difference of their microstructures are also small. During reheating at 576℃ the spheroidization of grains is significant after 5min and no rosettes are visible after 20min by optical microscopy. Similar observations were madeon materials reheated at 596℃, but the ripening process is faster. The grains growup to 30-60μm, fine enough for thixoforming.
文摘In recent years,magnesium and its alloys are considered as biodegradable implants.However magnesium implants may rapidly corrode before the natural healing process of the tissue is completed.In this investigation,micro arc oxidation process has been studied for avoiding primary corrosion of the magnesium alloy in simulated body fluid.Anodized coating was formed on AZ31 alloy in nontoxic silicate-alkaline solution at constant current.The effects of silicate concentration and conductivity of electrolyte solution on microstructure and corrosion properties of coating were evaluated.Scanning electron microscopy showed that a thick and condensed coating is formed after enough anodizing period.Energy dispersive spectroscopy showed that Si,O and Mg are the main components of the coating.Corrosion resistance of the coated and uncoated samples was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy tests in SBF at 37℃ and pH of 7.4.Maximum corrosion resistance was achieved at 30 g/L concentration of sodium silicate in anodizing solution.It was observed that further increase in silicate concentration decreased the corrosion resistance.
文摘A novel semisolid micro fused-casting(MFC) for preparing A356 alloy strips is proposed, and the effects of process parameters of pouring temperature on the microstructure and properties of A356 alloy strips are investigated. MFC means that the semisolid metal slurry was pressed out from the outlet of bottom of crucible to the movable plate, and directly solidified and formed layer by layer. The microstructure and properties of A356 semisolid alloy slurry were influenced by the cooling conditions. Results show that the aluminu alloy A356 strip samples fabricated by micro fused-casting had good performances and uniform structures with the pouring temperature at 595 ℃ and the substrate movement speed at 18 mm/s. The fine grains of the primary a-Al phase with average grain size of 53 μm and shape factor up to 0.72 was obtained, the ultimate tensile strength of the aluminum alloy A356 strip reaches 243.79±3.91 MPa, while the average vickers hardness is 82.65±1.86 HV.
文摘In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)process on Ti6Al4V alloy in NaF electrolyte.The influence of NaF concentration(0.15-0.50 mol/L)on the PEO process,microstructure,phase composition,corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy,energy dispersive spectroscopy,atomic force microscopy,X-ray diffractometer,and potentiodynamic polarization.The results demonstrated that Ti6Al4V alloy had low PEO voltage(less than 200 V)in NaF electrolyte,which decreased further as the NaF concentration increased.A micro/nano-structured coating with 10-15μm pits and 200-800 nm pores was formed in NaF electrolyte;the morphology was different from the typical pancake structure obtained with other electrolytes.The coating formed in NaF electrolyte had low surface roughness and was thin(<4μm).The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase,but greatly affected the corrosion resistance.In general,as the NaF concentration increased,the surface roughness,phase(anatase and rutile)contents,corrosion resistance,and thickness of the coating first increased and then decreased,reaching the maximum values at 0.25 mol/L NaF.
基金supported by the National Natural Science Foundation of China(51971040,52171101)the Natural Science Foundation of Chongqing(cstc2021jcyj-msxmX0613)+1 种基金the National Natural Science Foundation of China(52001036,51971044)the Independent Research Project of State Key Laboratory of Mechanical Transmissions(SKLMT-ZZKT-2022M12).
文摘Coating technologies are a commonly used way to protect metals against corrosion.However,with more and more severe service environments of materials,many protective coating systems often are not environmentally friendly or toxic as in the case of chromates.Based on the world’s abundant ideal magnesium(Mg)and its alloy,the smart self-healing anticorrosive coating can autonomously restore the damaged part of the coating according to the environmental changes,strengthen the corrosion protection ability,and prolong its service life.This paper reviews the research progress of smart self-healing coatings on Mg alloys.These coatings mostly contain suitable corrosion inhibitors encapsulated into micro/nano containers.Moreover,the different self-healing mechanisms and functionalities of micro/nano containers are discussed.The micro/nano containers range from inorganic nanocontainers such as mesoporous nanoparticles(silica(SiO_(2)),titanium dioxide(TiO_(2)),etc.),over inorganic clays(halloysite,hydrotalcite-like,zeolite),to organic nanocontainers such as polymer microcapsules,nanofibers,chitosan(CS)and cyclodextrin(CD),as well as,carbon materials such as graphene and carbon nanotubes and hybrids such as metal organic frameworks.The functioning of micro/nano containers can be divided in two principal groups:autonomous(based on defect filling and corrosion inhibition)and non-autonomous(based on dynamic bonds and shape memory polymers).Moreover,multi functionalities and composite applications of various micro/nano containers are summarized.At present,significant progress has been made in the preparation methods and technologies of micro/nano containers.Achieving long-term self-healing properties of coatings sensing of coating failure and early warning after self-healing function failure can be expected as the main development direction of self-healing corrosion protection coatings in the future.
基金Funded by the National Natural Science Foundation of China(No.51341009)
文摘A novel semisolid continuous Micro Fused-Casting additive manufacturing technology for producing a ZL101 alloy strip was developed, Micro Fused-Casting means that the semisolid metal slurry was pressed out from the outlet of bottom of crucible to the movable plate. The degree of sub-cooling was easily provided by movement of substrate in the micro fused-casting area. Under the aid of 3 D manufacturing software, the ZL101 alloy strip was solidified and formed layer by layer. The microstructure and properties of ZL101 semisolid slurry were improved by the cooling conditions. The results showed that the ZL101 alloy strip samples fabricated by Micro Fused-Casting had uniform structures and good performances with the substrate movement speed at 20 mm/s and the temperature at 590 ℃, the ultimate tensile strength and elongation of the ZL101 alloy strip reached 242.59 MPa and 7.71%, while the average Vickers hardness was 82.55 HV.
