The effect of aging on the microstructure and mechanical properties of AZ80 and ZK60 wrought magnesium alloys was studied with optical microscope and mechanical testers. The results demonstrate that both the tensile s...The effect of aging on the microstructure and mechanical properties of AZ80 and ZK60 wrought magnesium alloys was studied with optical microscope and mechanical testers. The results demonstrate that both the tensile strength and elongation of AZ80 alloy increase firstly and then decrease as the aging temperature rises, the peak values appear when the aging temperature is 170 ℃ The hardness of ZK60 alloy increases firstly and then decreases as the aging temperature rises, and the hardness reaches its peak value at 170 ℃. However, the toughness of the alloy is just the opposite. Moreover, ZK60 alloy has good performances in both impact toughness and other mechanical properties at the aging temperature from 140 ℃ to 200 ℃.展开更多
Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process a...Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process and growth mechanism were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS),confocal laser scanning microscopy and X-ray diffraction(XRD).The results indicate that the growth process of MAO coating mainly goes through“forming→puncturing→rapid growth of micro-arc oxidation→large arc discharge→self-repairing”.The coating grows inward and outward at the same time in the initial stage,but outward growth of the coating is dominant later.Mg,Mg_(2)SiO_(4) and MgO are the main phases of ceramic coating.展开更多
In this study,the effect of Y addition(0,0.5,1 and 2 wt%)on microstructure and corrosion properties of Mg-6Zn-0.5Zr-1 Nd(wt%)alloy was investigated.The alloys were produced by low-pressure die casting method and extru...In this study,the effect of Y addition(0,0.5,1 and 2 wt%)on microstructure and corrosion properties of Mg-6Zn-0.5Zr-1 Nd(wt%)alloy was investigated.The alloys were produced by low-pressure die casting method and extruded at 300℃and 400℃after homogenization treatment at 400℃for 24 h.The results showed that the as-cast microstructure of the alloy with no Y addition consisted ofα-Mg,Mg-Zn binary and Mg-Zn-Nd ternary phases.With increasing Y additions,the average grain size showed a substantial decrease and two kinds of ternary Mg-Zn-Y ternary phases,designated as I-phase(Mg3Zn6Y)and W-phase(Mg3Zn3Y2)were formed.Homogenization treatment resulted in a partial dissolution of second phase particles.Extrusion process gave rise to a remarkable grain refinement due to the DRX mechanism.The extruded alloys with no Y addition exhibited poor corrosion resistance due to the strong micro galvanic coupling effect.Y additions up to 1 wt%improved the corrosion resistance due to the formation of finer grains,fine and uniform distribution of second phase particles and more stable oxide film.展开更多
Finite element method was used to study the strain distribution in ZK60 Mg alloy during multi-pass cyclic extrusion and compression （CEC）. In order to optimize the CEC processing, the effects of friction condition a...Finite element method was used to study the strain distribution in ZK60 Mg alloy during multi-pass cyclic extrusion and compression （CEC）. In order to optimize the CEC processing, the effects of friction condition and die geometry on the distribution of total equivalent plastic strain were investigated. The results show that the strain distributions in the workpieces are inhomogeneous after CEC deformation. The strains of the both ends of the workpieces are lower than that of the center region. The process parameters have significant effects on the strain distribution. The friction between die and workpiece is detrimental to strain homogeneity, thus the friction should be decreased. In order to improve the strain homogeneity, a large corner radius and a low extrusion angle should be used.展开更多
The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constituti...The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of -0.2 to -0.8. The alloy experienced complete dynamic recrystallization （DRX） and showed good workability in the temperature range of 300-400 ℃ and the strain rate range of 0.01-0.001 s-Z, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over -0.5, strain rates above 0.1 s-1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.展开更多
ZK60 magnesium alloy possess good mechanical properties and is a potential biodegradable material.But its high degradation rate is not desirable.In this study the effect of heat treatment on the biodegradable property...ZK60 magnesium alloy possess good mechanical properties and is a potential biodegradable material.But its high degradation rate is not desirable.In this study the effect of heat treatment on the biodegradable property of ZK60 alloy was investigated.T5 treated,T6 treated,as-cast and as-extruded ZK60 alloys were studied.Microstructure characterization,electrochemical measurement and immersion test were carried out.The results showed that both the mechanical properties and degradation behavior were improved after T5 treatment due to the formation of small and uniformly distributed MgZn phases.The as-cast alloys also exhibited good corrosion resistance.However,the as-extruded and T6 treated samples were severely corroded due to the formation of large amounts of second phases accelerating the corrosion rate owing to the galvanic corrosion.The corrosion resistance of ZK60 alloy was as following:T5 treated>as-cast>T6 treated>as-extruded.展开更多
Micro-arc oxidation （MAO） process was cartied out in an optimized dual electrolyte system to fabricate a compact, smooth, and corrosion resistant coating on ZK60 Mg alloy. The microstructural characteristics of coat...Micro-arc oxidation （MAO） process was cartied out in an optimized dual electrolyte system to fabricate a compact, smooth, and corrosion resistant coating on ZK60 Mg alloy. The microstructural characteristics of coating were investigated by scanning electron microscopy （SEM） coupled with an energy dispersive spectrometer （EDS） and X-ray diffraction （XRD）. Test of mass loss was conducted at a 3.5 % NaCl solution to assess the resistance to corrosion. The bonding strength between the coating and ZK60 substrate was evaluated using scratch experiment. The results reveal that MgA1204 and MgO are the main phases of ceramic coating obtained in the dual electrolyte system. The corrosion rate of coating prepared in the optimized dual electrolyte is only 0.0061 g.m-2.h-1, which demonstrates excellent corrosion resistance. This is mainly due to the compact, uniform coating with high bonding strength.展开更多
The dissimilar joints of AZ61 and ZK60 magnesium alloys were obtained by tungsten inert gas arc(TIG)welding and activating tungsten inert gas arc(A-TIG)welding processes.Microstructure characterization shows that,the ...The dissimilar joints of AZ61 and ZK60 magnesium alloys were obtained by tungsten inert gas arc(TIG)welding and activating tungsten inert gas arc(A-TIG)welding processes.Microstructure characterization shows that,the fineα-Mg equiaxed dendrite crystals contained Mg17Al12 and MgZn2 particles in the fusion zone.The average size of theα-Mg grains in the fusion zone was refined to 19μm at welding current of 80 A,which resulted in the largest tensile strength of 207 MPa.The tensile strength and the width of the beam of the A-TIG welded AZ61/ZK60 joints showed strong dependence on the amount of TiO2.However,the inhomogeneity of the heat-affected zone near different base metals presented no significant effect on the mechanical properties of the welded joint.展开更多
Pre-cold rolling with low reductions(<3%)was used to improve the mechanical properties of rolled ZK60 plates.The effects of rolling path on mechanical properties were investigated in detail.Both pre-cold rolling al...Pre-cold rolling with low reductions(<3%)was used to improve the mechanical properties of rolled ZK60 plates.The effects of rolling path on mechanical properties were investigated in detail.Both pre-cold rolling along the transverse direction(TD)and pre-cold rolling along the normal direction(ND)can increase the yield strength.However,pre-cold rolling along the TD is more effective than pre-cold rolling along the ND in improving the comprehensive mechanical properties.After pre-cold rolling to 3%reduction,the sample rolled along the TD and the sample rolled along the ND have similar tensile yield strength(~270 MPa).However,the former has a higher compressive yield strength,lower yield asymmetry and larger toughness than the latter.Moreover,pre-cold rolling can also enhance precipitation hardening effect.However,aging treatment cannot further improve the yield strength of pre-cold rolled samples.Finally,the related mechanism is discussed.展开更多
In this work, the biodegradable and histocompatibility properties of pure Mg and ZK60 alloy wereinvestigated as new temporary implants for urinary applications. The corrosion mechanism in artificialurine was proposed ...In this work, the biodegradable and histocompatibility properties of pure Mg and ZK60 alloy wereinvestigated as new temporary implants for urinary applications. The corrosion mechanism in artificialurine was proposed using electrochemical impedance spectroscopy and potentiodynamic polarizationtests. The corrosion potential of pure magnesium and ZK60 alloy were -1820 and -1561 mV, respectively,and the corrosion current densities were 59.66 ± 6.41 and 41.94 ± 0.53 μA cm^-2, respectively. Thein vitro degradation rates for pure Mg and ZK60 alloy in artificial urine were 0.382 and 1.023 mm/y,respectively, determined from immersion tests. The ZK60 alloy degraded faster than the pure Mg in bothartificial urine and in rat bladders (the implants of both samples are ø 3 mm × 5 mm). Histocompatibilityevaluations showed good histocompatibility for the pure Mg and ZK60 alloy during the 3 weeks postimplantationin rat bladders, and no harm was observed in the bladder, liver and kidney tissues. Theresults provide key information on the degradation properties and corrosion mechanism of pure Mg andZK60 alloy in the urinary system.展开更多
The influence of impurity content on the microstructure and mechanical properties of ZK60 magnesium alloys was investigated by optical microscopy,scanning electron microscopy and tensile test.ZK60 alloys were prepared...The influence of impurity content on the microstructure and mechanical properties of ZK60 magnesium alloys was investigated by optical microscopy,scanning electron microscopy and tensile test.ZK60 alloys were prepared by changing holding time of alloy melt during semi-continuous casting in order to control the content of impurity elements.The alloy with lower purity content is found to have less second precipitates and larger grain size in the as-cast state.However,in the as-extruded state,reducing impurities brings about a decrease in grain size and an increase in yield strength from 244 MPa to 268 MPa,while the elongations in the as-extruded alloys with different contents of impurities are almost the same.After T5 treatment,impurity content is found to have more obvious effect on the yield strength of ZK60 alloy.The yield strength of ZK60-45 alloys with low impurity content is increased up to 295 MPa after T5 treatment.展开更多
Steady state rheological behavior of semi-solid ZK60-RE magnesium alloy during compression was studied. The alloy was prepared from ZK60 alloy and RE elements by casting, equal channel angular extruding, and liquidus ...Steady state rheological behavior of semi-solid ZK60-RE magnesium alloy during compression was studied. The alloy was prepared from ZK60 alloy and RE elements by casting, equal channel angular extruding, and liquidus forging. Semi-solid isothermal pre-treatment was carried out to make the grains spherical before compression. The apparent viscosity increases with decreasing the solid content and shear rate. Another very important factor is the grain size. When the solid content is high, the viscosity increases with decreasing the grain size at high strain rates and decreases with decreasing the grain size at low shear rates. Several fitting equations were obtained by using the power law equation, and the method of time-temperature superposition was used to get more information through a small number of experimental data.展开更多
基金Projects(50735005,50605059)supported by the National Natural Foundation of ChinaProject(2007021026)supported by the Shanxi Provincial Science Foundation for Youths, ChinaProject(20081027)supported by the Development for Science and Technology in Higher Educational Institutes, China
文摘The effect of aging on the microstructure and mechanical properties of AZ80 and ZK60 wrought magnesium alloys was studied with optical microscope and mechanical testers. The results demonstrate that both the tensile strength and elongation of AZ80 alloy increase firstly and then decrease as the aging temperature rises, the peak values appear when the aging temperature is 170 ℃ The hardness of ZK60 alloy increases firstly and then decreases as the aging temperature rises, and the hardness reaches its peak value at 170 ℃. However, the toughness of the alloy is just the opposite. Moreover, ZK60 alloy has good performances in both impact toughness and other mechanical properties at the aging temperature from 140 ℃ to 200 ℃.
文摘Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process and growth mechanism were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS),confocal laser scanning microscopy and X-ray diffraction(XRD).The results indicate that the growth process of MAO coating mainly goes through“forming→puncturing→rapid growth of micro-arc oxidation→large arc discharge→self-repairing”.The coating grows inward and outward at the same time in the initial stage,but outward growth of the coating is dominant later.Mg,Mg_(2)SiO_(4) and MgO are the main phases of ceramic coating.
基金the Scientific Research Projects of Karabuk University(BAP)with project no.KBUBAP-16/1-DR-075.
文摘In this study,the effect of Y addition(0,0.5,1 and 2 wt%)on microstructure and corrosion properties of Mg-6Zn-0.5Zr-1 Nd(wt%)alloy was investigated.The alloys were produced by low-pressure die casting method and extruded at 300℃and 400℃after homogenization treatment at 400℃for 24 h.The results showed that the as-cast microstructure of the alloy with no Y addition consisted ofα-Mg,Mg-Zn binary and Mg-Zn-Nd ternary phases.With increasing Y additions,the average grain size showed a substantial decrease and two kinds of ternary Mg-Zn-Y ternary phases,designated as I-phase(Mg3Zn6Y)and W-phase(Mg3Zn3Y2)were formed.Homogenization treatment resulted in a partial dissolution of second phase particles.Extrusion process gave rise to a remarkable grain refinement due to the DRX mechanism.The extruded alloys with no Y addition exhibited poor corrosion resistance due to the strong micro galvanic coupling effect.Y additions up to 1 wt%improved the corrosion resistance due to the formation of finer grains,fine and uniform distribution of second phase particles and more stable oxide film.
基金Projects (51074106, 50674067) supported by the National Natural Science Foundation of ChinaProject (09JC1408200) supported by the Science and Technology Commission of Shanghai Municipality, China+1 种基金Project (2011-079) supported by the Shaanxi Scholarship Council,ChinaProject (20102015) supported by the Doctoral Startup Fund of TUST, China
文摘Finite element method was used to study the strain distribution in ZK60 Mg alloy during multi-pass cyclic extrusion and compression （CEC）. In order to optimize the CEC processing, the effects of friction condition and die geometry on the distribution of total equivalent plastic strain were investigated. The results show that the strain distributions in the workpieces are inhomogeneous after CEC deformation. The strains of the both ends of the workpieces are lower than that of the center region. The process parameters have significant effects on the strain distribution. The friction between die and workpiece is detrimental to strain homogeneity, thus the friction should be decreased. In order to improve the strain homogeneity, a large corner radius and a low extrusion angle should be used.
基金Projects(51171113,51301107) supported by the National Natural Science Foundation of China
文摘The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of -0.2 to -0.8. The alloy experienced complete dynamic recrystallization （DRX） and showed good workability in the temperature range of 300-400 ℃ and the strain rate range of 0.01-0.001 s-Z, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over -0.5, strain rates above 0.1 s-1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.
基金This work was supported by the National Basic Research Program of China(973 Program)(No.2012CB619101)National Natural Science Foundation of China(No.81401773)National High Technology Research and Development Program of China(863 Program,No.2015AA033701).
文摘ZK60 magnesium alloy possess good mechanical properties and is a potential biodegradable material.But its high degradation rate is not desirable.In this study the effect of heat treatment on the biodegradable property of ZK60 alloy was investigated.T5 treated,T6 treated,as-cast and as-extruded ZK60 alloys were studied.Microstructure characterization,electrochemical measurement and immersion test were carried out.The results showed that both the mechanical properties and degradation behavior were improved after T5 treatment due to the formation of small and uniformly distributed MgZn phases.The as-cast alloys also exhibited good corrosion resistance.However,the as-extruded and T6 treated samples were severely corroded due to the formation of large amounts of second phases accelerating the corrosion rate owing to the galvanic corrosion.The corrosion resistance of ZK60 alloy was as following:T5 treated>as-cast>T6 treated>as-extruded.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Key Laboratory of Advanced Welding Technology of Jiangsu Province, China (No. JSAWT-11)
文摘Micro-arc oxidation （MAO） process was cartied out in an optimized dual electrolyte system to fabricate a compact, smooth, and corrosion resistant coating on ZK60 Mg alloy. The microstructural characteristics of coating were investigated by scanning electron microscopy （SEM） coupled with an energy dispersive spectrometer （EDS） and X-ray diffraction （XRD）. Test of mass loss was conducted at a 3.5 % NaCl solution to assess the resistance to corrosion. The bonding strength between the coating and ZK60 substrate was evaluated using scratch experiment. The results reveal that MgA1204 and MgO are the main phases of ceramic coating obtained in the dual electrolyte system. The corrosion rate of coating prepared in the optimized dual electrolyte is only 0.0061 g.m-2.h-1, which demonstrates excellent corrosion resistance. This is mainly due to the compact, uniform coating with high bonding strength.
基金Project(51771160)supported by the National Natural Science Foundation of ChinaProject(2018JJ4048)supported by the Provincial and Municipal Joint Fund for Natural Science of Hunan Province,China
文摘The dissimilar joints of AZ61 and ZK60 magnesium alloys were obtained by tungsten inert gas arc(TIG)welding and activating tungsten inert gas arc(A-TIG)welding processes.Microstructure characterization shows that,the fineα-Mg equiaxed dendrite crystals contained Mg17Al12 and MgZn2 particles in the fusion zone.The average size of theα-Mg grains in the fusion zone was refined to 19μm at welding current of 80 A,which resulted in the largest tensile strength of 207 MPa.The tensile strength and the width of the beam of the A-TIG welded AZ61/ZK60 joints showed strong dependence on the amount of TiO2.However,the inhomogeneity of the heat-affected zone near different base metals presented no significant effect on the mechanical properties of the welded joint.
基金financially supported by the National Natural Science Foundation of China (No. 51601154)the Fundamental Research Funds for the Central Universities, China (No. XDJK2019B003)+1 种基金the Natural Science Foundation of Jiangsu Higher Education Institutions of China (No. 17KJD430006)Chongqing Municipal Education Commission, China (No. KJZDK202001502)
文摘Pre-cold rolling with low reductions(<3%)was used to improve the mechanical properties of rolled ZK60 plates.The effects of rolling path on mechanical properties were investigated in detail.Both pre-cold rolling along the transverse direction(TD)and pre-cold rolling along the normal direction(ND)can increase the yield strength.However,pre-cold rolling along the TD is more effective than pre-cold rolling along the ND in improving the comprehensive mechanical properties.After pre-cold rolling to 3%reduction,the sample rolled along the TD and the sample rolled along the ND have similar tensile yield strength(~270 MPa).However,the former has a higher compressive yield strength,lower yield asymmetry and larger toughness than the latter.Moreover,pre-cold rolling can also enhance precipitation hardening effect.However,aging treatment cannot further improve the yield strength of pre-cold rolled samples.Finally,the related mechanism is discussed.
基金This work is supported by the National Natural Science Foundation of China(NSFC,No.51431002&No.51601222)China Postdoctoral Science Foundation funded project(2016M591040)the Air Force General Hospital Grant(kz2015054).
文摘In this work, the biodegradable and histocompatibility properties of pure Mg and ZK60 alloy wereinvestigated as new temporary implants for urinary applications. The corrosion mechanism in artificialurine was proposed using electrochemical impedance spectroscopy and potentiodynamic polarizationtests. The corrosion potential of pure magnesium and ZK60 alloy were -1820 and -1561 mV, respectively,and the corrosion current densities were 59.66 ± 6.41 and 41.94 ± 0.53 μA cm^-2, respectively. Thein vitro degradation rates for pure Mg and ZK60 alloy in artificial urine were 0.382 and 1.023 mm/y,respectively, determined from immersion tests. The ZK60 alloy degraded faster than the pure Mg in bothartificial urine and in rat bladders (the implants of both samples are ø 3 mm × 5 mm). Histocompatibilityevaluations showed good histocompatibility for the pure Mg and ZK60 alloy during the 3 weeks postimplantationin rat bladders, and no harm was observed in the bladder, liver and kidney tissues. Theresults provide key information on the degradation properties and corrosion mechanism of pure Mg andZK60 alloy in the urinary system.
基金Project(50725413)supported by the National Natural Science Foundation of ChinaProject(2007CB613704)supported by the National Basic Research Program of ChinaProject(20090191120013)supported by the PhD Program Foundation of Ministry of Education of China
文摘The influence of impurity content on the microstructure and mechanical properties of ZK60 magnesium alloys was investigated by optical microscopy,scanning electron microscopy and tensile test.ZK60 alloys were prepared by changing holding time of alloy melt during semi-continuous casting in order to control the content of impurity elements.The alloy with lower purity content is found to have less second precipitates and larger grain size in the as-cast state.However,in the as-extruded state,reducing impurities brings about a decrease in grain size and an increase in yield strength from 244 MPa to 268 MPa,while the elongations in the as-extruded alloys with different contents of impurities are almost the same.After T5 treatment,impurity content is found to have more obvious effect on the yield strength of ZK60 alloy.The yield strength of ZK60-45 alloys with low impurity content is increased up to 295 MPa after T5 treatment.
基金Projects(50475029 50605015) supported by the National Natural Science Foundation of China
文摘Steady state rheological behavior of semi-solid ZK60-RE magnesium alloy during compression was studied. The alloy was prepared from ZK60 alloy and RE elements by casting, equal channel angular extruding, and liquidus forging. Semi-solid isothermal pre-treatment was carried out to make the grains spherical before compression. The apparent viscosity increases with decreasing the solid content and shear rate. Another very important factor is the grain size. When the solid content is high, the viscosity increases with decreasing the grain size at high strain rates and decreases with decreasing the grain size at low shear rates. Several fitting equations were obtained by using the power law equation, and the method of time-temperature superposition was used to get more information through a small number of experimental data.
