Effects of rare earth (RE) additions on microstructure and mechanical properties of the wrought AZ31 magnesium alloy were investigated. The results show that, by adding 0.3%, 0.6% and 1.0% RE elements, the as-cast mic...Effects of rare earth (RE) additions on microstructure and mechanical properties of the wrought AZ31 magnesium alloy were investigated. The results show that, by adding 0.3%, 0.6% and 1.0% RE elements, the as-cast microstructure can be refined, and the as-cast alloys′ elongation and tensile strength can be improved. After extrusion, the alloy with 0.3% and 0.6% RE additions obtain a finer microstructure and the best mechanical properties, but the alloy with 1.0% RE addition has the coarse Al-RE compound particles in grain boundaries which decreased elongation and tensile properties. Usually, Rare earth (RE) elements were used to improve the creep properties of aluminium-containing magnesium pressure die cast alloys at elevated temperatures. In this paper, it is also found that the high temperature strength of extruded materials can be increased by RE elements additions.展开更多
The effects of small amounts of the rare-earth element erbium on the microstructure and the mechanical properties of AZ31 magnesium alloy via the electromagnetic stirring (EMS) process have been studied. It has been...The effects of small amounts of the rare-earth element erbium on the microstructure and the mechanical properties of AZ31 magnesium alloy via the electromagnetic stirring (EMS) process have been studied. It has been shown that AZ31-Er alloys are mainly composed of α-Mg solid solution and β-Mg17TA112 phases. When the Er content reaches 0.12 wt.%, the characteristic peaks of A12Er can be observed. The micro- structure is obviously refined and the tensile strength of the AZ31-based alloy at ambient temperature is significantly improved by contents of 0.03 wt.% Er, especially the elongation (8= 19%). More addition of Er obviously decreases the tensile strength and elongation of the AZ31-based alloy because of the grain coarsening and the reduction of β-Mg17A112 phases.展开更多
The AZ31 material was selected for axisymmetric extrusion tests. After normal hot extrusion, the plasticity of magnesium alloy will be improved, but not noticeably. Further extrusion with extrusion ratio of 6.25 was a...The AZ31 material was selected for axisymmetric extrusion tests. After normal hot extrusion, the plasticity of magnesium alloy will be improved, but not noticeably. Further extrusion with extrusion ratio of 6.25 was adopted to commercial AZ31 magnesium alloy rods at different temperatures in order to research the effects of the different extrusion techniques on the elongation. And the correspondence between ductility and crystallite size was studied at the same time. Through experiments, it is proved that the plasticity of AZ31 magnesium alloy reduces with the increase of extrusion temperature. In order to insure the formability, the deformation temperature must reduce as low as it can be.展开更多
Equal channel angular pressing (ECAP) processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment ...Equal channel angular pressing (ECAP) processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 ℃ in a die having an included angle of 90o between two channels by the BCZ route with the sheets rotated by 90°about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 ℃. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value (CCV) than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.展开更多
Additive manufacturing(AM)of Mg alloys has become a promising strategy for producing complex structures,but the corrosion performance of AM Mg components remains unexploited.In this study,wire and arc additive manufac...Additive manufacturing(AM)of Mg alloys has become a promising strategy for producing complex structures,but the corrosion performance of AM Mg components remains unexploited.In this study,wire and arc additive manufacturing(WAAM)was employed to produce single AZ31 layer.The results revealed that the WAAM AZ31 was characterized by significant grain refinement with non-textured crystallographic orientation,similar phase composition and stabilized corrosion performance comparing to the cast AZ31.These varied corrosion behaviors were principally ascribed to the size of grain,where cast AZ31 and WAAM AZ31 were featured by micro galvanic corrosion and intergranular corrosion,respectively.展开更多
Mg alloys conventionally rolled often present strong basal textures that affect negatively further deformations,limiting their applications.The present research found that cross-rolling experiences in adequate conditi...Mg alloys conventionally rolled often present strong basal textures that affect negatively further deformations,limiting their applications.The present research found that cross-rolling experiences in adequate conditions can weaken those intense basal textures as a result of the interaction of deformation mechanisms and dynamic recrystallization.The effects of rolling temperature and strain rate on the microstructure and texture of an AZ31B magnesium alloy sheet generated heterogeneous microstructure where the initial basal texture was strengthened during cold cross-rolling and it was gradually weakening by the rolling reduction and the rolling temperature increases in such a way that a rather weak basal fiber was produced applying reductions higher than 15%at temperatures higher than 200℃.Their ODF functions supported the texture weakening,exhibiting a combination of two crystallographic orientations represented by{0001}<211^(-)0>and{0001}<101^(-)0>.展开更多
Microstructures, tensile properties, fracture characteristics of commercial AZ31 magnesium alloy thin sheet were studied by optical microscopy, scanning electron microscopy and uniaxial tensile test. Tensile tests wer...Microstructures, tensile properties, fracture characteristics of commercial AZ31 magnesium alloy thin sheet were studied by optical microscopy, scanning electron microscopy and uniaxial tensile test. Tensile tests were carried out at room temperature and 473K, with strain rates of 8.3×10 -44.2×10 -3s -1. The results show that grain refinement effects are better at high temperature, and it increases with the decrease of strain rate at 473K. Compared with that tested at room temperature, no apparent uniform plastic deformation stage exists in the stress—strain curves tested at 473K; afterwards, the stress—strain curve presents wavelike downward under condition of the small strain rate. Yield strength and tensile strength of the alloy decrease drastically while the elongation increases greatly. With the increase of strain rate, yield strength and tensile strength of the alloy increase, but the elongation decreases. The fracture of the alloy tested at room temperature is quasi-cleavage failure and ductile failure at 473K.展开更多
This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and trans...This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and transmission electron microscopy analysis,and the corrosion resistance is measured by an electrochemical corrosion test.Results show that the grains are obviously more uniform and finer along the wall thickness’s direction of the AZ31 alloy tube after the third spinning pass.The number of twins ascends first and then descends,while the varying trend of low-angle grain boundaries(LAGBs)is opposite to that of the twins as the spinning pass increases.With the increase of the total spinning deformation,the deformation texture initially increases and the c-axis of the{0001}crystal plane gradually rotates to the axial direction of the tube;the deformation texture then decreases and the orientation of grains becomes more random.The main mechanism of grain refinement is dynamic recrystallization by the twin-induced way and bowing out of the nucleation at grain boundaries during the first and second pass.However,the dominant mechanism of the refined grain is the high-temperature dynamic recovery in the third pass,and the microstructure mainly consists of substructured grains.After the spinning deformation,the corrosion resistance of the AZ31 alloy tube decreases due to the combined effect of twins and high density-dislocations.展开更多
Magnesium alloy AZ31 was caliber rolled at different temperatures viz.523K,573K,623K,673K and 723K imposing a total cumulative reduction of 92%and a cumulative strain of 2.6.The associated microstructure and texture e...Magnesium alloy AZ31 was caliber rolled at different temperatures viz.523K,573K,623K,673K and 723K imposing a total cumulative reduction of 92%and a cumulative strain of 2.6.The associated microstructure and texture evolution were studied using Electron Back Scattered Diffraction(EBSD)and X-ray macro-texture observations respectively.Grain refinement was observed in all the caliber rolled bars indicating the occurrence of dynamic recrystallization.Asymmetry parameter and texture index were used to study the evolution of texture.Near doubling of the yield strength at room temperature was observed by caliber rolling at a temperature of 573K.The improvement in mechanical properties was explained on the basis of the fine grain microstructures and suitable development of crystallographic texture.Based on the present study,warm caliber rolling can be used as a good production method for obtaining long bars of high strength magnesium alloy AZ31.展开更多
In-plane uniaxial tension of AZ31 magnesium alloy sheet with non-basal texture has been conducted in order to demonstrate the effects of loading direction on the microstructure evolution and mechanical properties at a...In-plane uniaxial tension of AZ31 magnesium alloy sheet with non-basal texture has been conducted in order to demonstrate the effects of loading direction on the microstructure evolution and mechanical properties at ambient temperature.Loading axes are chosen to be along five directions distributed between rolling direction(RD)and transverse direction(TD),allowing various activities in involved slip and twinning modes to take place.As for twinning modes,electron backscattered diffraction observations confirm that the contribution of{1011}compression twinning is minimal to the plastic deformation of all deformed samples.By comparison,{1012}extension twinning(ET)not only serves as an important carrier on sustaining and accommodating plastic strain but also contributes to the emergence of TD-component texture with the progression of plastic strain.In terms of slip modes,analysis on Schmid factor demonstrates that the increasing tilted angle between loading direction and RD of sheet is unfavorable to the activation of basalslip,whereas it contributes to the activation of prismaticslip.These observations consequently explain the increasing tendency of 0.2%proof yield stress.Moreover,the activations of basalslip and{1012}ET collectively contribute to the concentration of two tilted basal poles toward normal direction.With increasing angle between loading direction and RD,the activations of basalslip and{1012}ET are gradually weakened.This leads to a weakening tendency about concentration of two tilted basal poles,a generally increasing tendency about Lankford value(r-value)and a generally decreasing tendency about strain-hardening exponent(n-value).展开更多
A friction stirring welding to joint 5 mm rolled AZ31 magnesium had beendeveloped. The microstructures in various regions including the weld nugget, thermo-mechanicallyaffected zone (TMAZ) and heat affected zone (HAZ)...A friction stirring welding to joint 5 mm rolled AZ31 magnesium had beendeveloped. The microstructures in various regions including the weld nugget, thermo-mechanicallyaffected zone (TMAZ) and heat affected zone (HAZ) were investigated and compared with unaffectedparent metal using optical microscopy. The results showed that the heat and mechanical process hadgreat effect on the microstructure evolution. In weld nugget, the heat was enough to producesufficient superplastic material flow and the mechanical effect was greatest, and the dynamicrecrystallization was completed thoroughly. In TMAZ, the mechanical effect was indirectly affectedby the welding tool and only some grains had undergone dynamic recrystallization. The variousregions were studied in detail to better understand the microstructure evolution during frictionstirring welding (FSW). The cross section near the 'key hole' showed clear onion rings because thematerial was stirred only by the rotation of the probe and materials rotated with the probe and didnot move along welding direction and in vertical direction, there was no material flow and the flowmovement can be regarded as two dimensional layer flow.展开更多
Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magn...Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.展开更多
The microstructure and mechanical properties of extruded AZ31 magnesium at different extrusion temperature were investigated.The results show that,at 380℃,when the extrusion ratio is 23,the AZ31 magnesium alloy has a...The microstructure and mechanical properties of extruded AZ31 magnesium at different extrusion temperature were investigated.The results show that,at 380℃,when the extrusion ratio is 23,the AZ31 magnesium alloy has a dense recrystallized microstructure and good mechanical properties.On one hand,if the extrusion ratio is too small,grain crushing effect is not obvious,and part of the grain is not dynamic recrystallization.On the other hand,larger extrusion ratio can lead to grain growth and banded structure.Tensile fracture characteristics of extruded AZ31 magnesium alloy is quasi-cleavage.展开更多
A promising solid-state coating mechanism based on the cold spray technique provides highly advantageous conditions on thermal-sensitive magnesium alloys.To study the effect of heat balance in cold spray coating on mi...A promising solid-state coating mechanism based on the cold spray technique provides highly advantageous conditions on thermal-sensitive magnesium alloys.To study the effect of heat balance in cold spray coating on microstructure,experiments were designed to successfully coat AA7075 on AZ31B with two different heat balance conditions to yield a coated sample with tensile residual stress and a sample with compressive residual stress in both coating and substrate.The effects of coating temperature on the microstructure of magnesium alloy and the interfaces of coated samples were then analyzed by SEM,EBSD,TEM in high-and low-heat input coating conditions.The interface of the AA7075 coating and magnesium alloy substrate under both conditions consists of a narrow-band layer with very fine grains,followed by columnar grains of magnesium that have grown perpendicular to the interface.At higher temperatures,this layer became wider.No intermetallic phase was detected at the interface under either condition.It is shown that the microstructure of the substrate was affected by coating temperature,leading to stress relief,dynamic recrystallization and even dynamic grain growth of magnesium under high temperature.Reducing the heat input and increasing the heat transfer decreased microstructural changes in the substrate.展开更多
In this study, AZ31 Mg alloy was processed by a new severe plasticity deformation methodology with multi-pass lowered temperature, and the deformation behavior and microstructure evolution were investigated by finite ...In this study, AZ31 Mg alloy was processed by a new severe plasticity deformation methodology with multi-pass lowered temperature, and the deformation behavior and microstructure evolution were investigated by finite element method and electron back-scattered diffraction technique and hardness. The results show that with the increase of deformation pass, the strain gradually springs, and its interval distribution tends to homogenize. Meanwhile, the effective strain increases dramatically with the shear force sudden upgrade in the deformation process. Moreover, the new deformation technique can refine grain size remarkably. With the passes on, {10-12} tensile twins behavior and the pyramidal < c + a > slip are triggered more frequently, leading to the completeness of dynamic recrystallization (DRX) gradually, which weaken and disperse the basal texture obviously. Besides, the standard deviation of hardness is getting smaller, and the maximum can reach 78.40 HV on average, which can be attributed to the even large strain distribution, complete DRX, and the high geometrically necessary dislocation.展开更多
At the initial rolling temperature of 250 to 400 ℃, AZ31B magnesium alloy sheets were hot rolled by four different rolling routes. Microstructures and mechanical properties of the hot-rolled magnesium alloy sheets we...At the initial rolling temperature of 250 to 400 ℃, AZ31B magnesium alloy sheets were hot rolled by four different rolling routes. Microstructures and mechanical properties of the hot-rolled magnesium alloy sheets were analyzed by optical microscope and tensile tests respectively. Based on the Hall-Petch relation, considering the average grain size and grain size distribution, the nonlinear fitting analysis between the tensile strength and average grain size was carried on, and then the prediction model of tensile strength of hot-rolled AZ31B magnesium alloy sheet was established. The results indicate that, by rolling with multi-pass cross rolling, uniform, fine and equiaxial grain microstructures can be produced, the anisotropy of hot-rolled magnesium sheet can also be effectively weakened. Strong correlation was observed between the average grain size and tensile property of the hot-rolled magnesium alloy sheet. Grain size distribution coefficient d(CV) was introduced to reflect the dispersion degree about a set of grain size data, and then the Hall-Petch relation was perfected. Ultimately, the prediction accuracy of tensile strength of multi-pass hot-rolled AZ31B magnesium alloy was improved, and the prediction of tensile property can be performed by the model.展开更多
The electromagnetic free bulging experiment and the coupled-field numerical simulation of the EMF process were carried out to determine the possibility to improve the formability of magnesium alloy AZ31 sheets(1 mm th...The electromagnetic free bulging experiment and the coupled-field numerical simulation of the EMF process were carried out to determine the possibility to improve the formability of magnesium alloy AZ31 sheets(1 mm thick)at room temperature.Formability data were examined using strain measurements.The numerical simulation for the electromagnetic sheet free bulging is performed by means of ANSYS FEA software.Compared with quasi-static FLD results,increase in the major and minor principal strains of approximately 87%and 39%were achieved,respectively.The effects of various process parameters on electromagnetic bulging of AZ31 magnesium alloy sheets were evaluated. Three-dimensional(3D)FE model is established to predict the electromagnetic bulging of the sheet.The simulation results agreed well with experimental observations.展开更多
The effects of pulse current on the superplastic deformation of AZ31 magnesium alloy with different microstructures were examined. The results of TEM analysis showed that the dislocation movement was mainly glide, and...The effects of pulse current on the superplastic deformation of AZ31 magnesium alloy with different microstructures were examined. The results of TEM analysis showed that the dislocation movement was mainly glide, and the dislocation lines were approximate parallel with few dislocation tangles observed, which indicated that the dislocation movementwas promoted during the deformation, and therefore the formability of the coarse-grained AZ31 magnesium alloy was enhanced by the pulse current. This effect was also indicated by the asymmetrical contour of the free bulging sample, which was observed in the unidirectional pulses auxiliary equi-biaxial tensile test of coarse-grained alloy. In addition, the phenomenon of the restrained cavity growth caused by the thermoelectrical effect of the pulse current was discovered and studied.展开更多
Radial additive friction stir repairing(R-AFSR)assisted by stationary shoulder was put forward in the present study,which can be employed to repair the mechanical hole out of dimension tolerance of AZ31 magnesium allo...Radial additive friction stir repairing(R-AFSR)assisted by stationary shoulder was put forward in the present study,which can be employed to repair the mechanical hole out of dimension tolerance of AZ31 magnesium alloy sheet.The results show that the stationary shoulder has sealed-barrier,heat-sink and extra-forging effects.The heat-sink effect improves the microstructure uniformity along the stir zone(SZ)thickness and the surface appearance of repaired hole,and the sealedbarrier and extra-forging effects eliminate the super-fine grain band in the SZ.Therefore,these three effects improve the formation quality of repaired region,thereby enhancing the mechanical properties of repaired mechanical hole compared with conventional R-AFSR.The tensile and compressive shear strengths of the repaired hole by stationary shoulder R-AFSR both increase first and then decrease when the rotating speed changes from 1200 to 1800 rpm,and these maximum values,respectively,reach 190±3 MPa and 64.5±2 MPa at 1400 rpm.The addition of stationary shoulder during R-AFSR can obtain a higher-quality repaired hole and broaden the repairing process window.展开更多
文摘Effects of rare earth (RE) additions on microstructure and mechanical properties of the wrought AZ31 magnesium alloy were investigated. The results show that, by adding 0.3%, 0.6% and 1.0% RE elements, the as-cast microstructure can be refined, and the as-cast alloys′ elongation and tensile strength can be improved. After extrusion, the alloy with 0.3% and 0.6% RE additions obtain a finer microstructure and the best mechanical properties, but the alloy with 1.0% RE addition has the coarse Al-RE compound particles in grain boundaries which decreased elongation and tensile properties. Usually, Rare earth (RE) elements were used to improve the creep properties of aluminium-containing magnesium pressure die cast alloys at elevated temperatures. In this paper, it is also found that the high temperature strength of extruded materials can be increased by RE elements additions.
基金supported by the National Natural Science Foundation of China (Nos.50475157 and 50875031)the Key Project of the Ministry of Education of China (No.105052)
文摘The effects of small amounts of the rare-earth element erbium on the microstructure and the mechanical properties of AZ31 magnesium alloy via the electromagnetic stirring (EMS) process have been studied. It has been shown that AZ31-Er alloys are mainly composed of α-Mg solid solution and β-Mg17TA112 phases. When the Er content reaches 0.12 wt.%, the characteristic peaks of A12Er can be observed. The micro- structure is obviously refined and the tensile strength of the AZ31-based alloy at ambient temperature is significantly improved by contents of 0.03 wt.% Er, especially the elongation (8= 19%). More addition of Er obviously decreases the tensile strength and elongation of the AZ31-based alloy because of the grain coarsening and the reduction of β-Mg17A112 phases.
文摘The AZ31 material was selected for axisymmetric extrusion tests. After normal hot extrusion, the plasticity of magnesium alloy will be improved, but not noticeably. Further extrusion with extrusion ratio of 6.25 was adopted to commercial AZ31 magnesium alloy rods at different temperatures in order to research the effects of the different extrusion techniques on the elongation. And the correspondence between ductility and crystallite size was studied at the same time. Through experiments, it is proved that the plasticity of AZ31 magnesium alloy reduces with the increase of extrusion temperature. In order to insure the formability, the deformation temperature must reduce as low as it can be.
文摘Equal channel angular pressing (ECAP) processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 ℃ in a die having an included angle of 90o between two channels by the BCZ route with the sheets rotated by 90°about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 ℃. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value (CCV) than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.
基金the financial support by National Key Research and Development Project(Grand No.2020YFC1107202)Guangdong Basic and Applied Basic Research Foundation(Grand No.2020A1515110754)+3 种基金MOE Key Lab of Disaster Forest and Control in Engineering,Jinan University(Grand No.20200904008)Educational Commission of Guangdong Province(Grand No.2020KTSCX012)the Fundamental Research Funds for Central Universities(Grand No.21620342)the support from National Natural Science Foundation of China,NSFC(Grand No.51775556)。
文摘Additive manufacturing(AM)of Mg alloys has become a promising strategy for producing complex structures,but the corrosion performance of AM Mg components remains unexploited.In this study,wire and arc additive manufacturing(WAAM)was employed to produce single AZ31 layer.The results revealed that the WAAM AZ31 was characterized by significant grain refinement with non-textured crystallographic orientation,similar phase composition and stabilized corrosion performance comparing to the cast AZ31.These varied corrosion behaviors were principally ascribed to the size of grain,where cast AZ31 and WAAM AZ31 were featured by micro galvanic corrosion and intergranular corrosion,respectively.
基金supported by CAPES-(Coordenação de Aperfeiçoamento de Pessoal de Nível Su-perior),process no.PNPD20130250-22001018034P4.
文摘Mg alloys conventionally rolled often present strong basal textures that affect negatively further deformations,limiting their applications.The present research found that cross-rolling experiences in adequate conditions can weaken those intense basal textures as a result of the interaction of deformation mechanisms and dynamic recrystallization.The effects of rolling temperature and strain rate on the microstructure and texture of an AZ31B magnesium alloy sheet generated heterogeneous microstructure where the initial basal texture was strengthened during cold cross-rolling and it was gradually weakening by the rolling reduction and the rolling temperature increases in such a way that a rather weak basal fiber was produced applying reductions higher than 15%at temperatures higher than 200℃.Their ODF functions supported the texture weakening,exhibiting a combination of two crystallographic orientations represented by{0001}<211^(-)0>and{0001}<101^(-)0>.
文摘Microstructures, tensile properties, fracture characteristics of commercial AZ31 magnesium alloy thin sheet were studied by optical microscopy, scanning electron microscopy and uniaxial tensile test. Tensile tests were carried out at room temperature and 473K, with strain rates of 8.3×10 -44.2×10 -3s -1. The results show that grain refinement effects are better at high temperature, and it increases with the decrease of strain rate at 473K. Compared with that tested at room temperature, no apparent uniform plastic deformation stage exists in the stress—strain curves tested at 473K; afterwards, the stress—strain curve presents wavelike downward under condition of the small strain rate. Yield strength and tensile strength of the alloy decrease drastically while the elongation increases greatly. With the increase of strain rate, yield strength and tensile strength of the alloy increase, but the elongation decreases. The fracture of the alloy tested at room temperature is quasi-cleavage failure and ductile failure at 473K.
基金supported by the National Natural Science Foundation of China (Nos. 51805358 and 51775366)Key Research and Development Program of Jinzhong (No. Y201023)College Students’ Innovative Entrepreneurial Training Plan Program (No. 202010112011)
文摘This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and transmission electron microscopy analysis,and the corrosion resistance is measured by an electrochemical corrosion test.Results show that the grains are obviously more uniform and finer along the wall thickness’s direction of the AZ31 alloy tube after the third spinning pass.The number of twins ascends first and then descends,while the varying trend of low-angle grain boundaries(LAGBs)is opposite to that of the twins as the spinning pass increases.With the increase of the total spinning deformation,the deformation texture initially increases and the c-axis of the{0001}crystal plane gradually rotates to the axial direction of the tube;the deformation texture then decreases and the orientation of grains becomes more random.The main mechanism of grain refinement is dynamic recrystallization by the twin-induced way and bowing out of the nucleation at grain boundaries during the first and second pass.However,the dominant mechanism of the refined grain is the high-temperature dynamic recovery in the third pass,and the microstructure mainly consists of substructured grains.After the spinning deformation,the corrosion resistance of the AZ31 alloy tube decreases due to the combined effect of twins and high density-dislocations.
文摘Magnesium alloy AZ31 was caliber rolled at different temperatures viz.523K,573K,623K,673K and 723K imposing a total cumulative reduction of 92%and a cumulative strain of 2.6.The associated microstructure and texture evolution were studied using Electron Back Scattered Diffraction(EBSD)and X-ray macro-texture observations respectively.Grain refinement was observed in all the caliber rolled bars indicating the occurrence of dynamic recrystallization.Asymmetry parameter and texture index were used to study the evolution of texture.Near doubling of the yield strength at room temperature was observed by caliber rolling at a temperature of 573K.The improvement in mechanical properties was explained on the basis of the fine grain microstructures and suitable development of crystallographic texture.Based on the present study,warm caliber rolling can be used as a good production method for obtaining long bars of high strength magnesium alloy AZ31.
基金supported by the National Natural Science Foundation of China(Grant Nos.51805064,51822509,51701034)the Scientifi c and Technological Research Program of Chongqing Municipal Education Commission(Grant No.KJQN201801137)+1 种基金the Basic and Advanced Research Project of Chongqing Science and Technology Commission(Grant Nos.cstc2017jcyjAX0062,cstc2018jcyjAX0035)the Chongqing University Key Laboratory of Micro/Nano Materials Engineering and Technology(Grant No.KFJJ2003)。
文摘In-plane uniaxial tension of AZ31 magnesium alloy sheet with non-basal texture has been conducted in order to demonstrate the effects of loading direction on the microstructure evolution and mechanical properties at ambient temperature.Loading axes are chosen to be along five directions distributed between rolling direction(RD)and transverse direction(TD),allowing various activities in involved slip and twinning modes to take place.As for twinning modes,electron backscattered diffraction observations confirm that the contribution of{1011}compression twinning is minimal to the plastic deformation of all deformed samples.By comparison,{1012}extension twinning(ET)not only serves as an important carrier on sustaining and accommodating plastic strain but also contributes to the emergence of TD-component texture with the progression of plastic strain.In terms of slip modes,analysis on Schmid factor demonstrates that the increasing tilted angle between loading direction and RD of sheet is unfavorable to the activation of basalslip,whereas it contributes to the activation of prismaticslip.These observations consequently explain the increasing tendency of 0.2%proof yield stress.Moreover,the activations of basalslip and{1012}ET collectively contribute to the concentration of two tilted basal poles toward normal direction.With increasing angle between loading direction and RD,the activations of basalslip and{1012}ET are gradually weakened.This leads to a weakening tendency about concentration of two tilted basal poles,a generally increasing tendency about Lankford value(r-value)and a generally decreasing tendency about strain-hardening exponent(n-value).
文摘A friction stirring welding to joint 5 mm rolled AZ31 magnesium had beendeveloped. The microstructures in various regions including the weld nugget, thermo-mechanicallyaffected zone (TMAZ) and heat affected zone (HAZ) were investigated and compared with unaffectedparent metal using optical microscopy. The results showed that the heat and mechanical process hadgreat effect on the microstructure evolution. In weld nugget, the heat was enough to producesufficient superplastic material flow and the mechanical effect was greatest, and the dynamicrecrystallization was completed thoroughly. In TMAZ, the mechanical effect was indirectly affectedby the welding tool and only some grains had undergone dynamic recrystallization. The variousregions were studied in detail to better understand the microstructure evolution during frictionstirring welding (FSW). The cross section near the 'key hole' showed clear onion rings because thematerial was stirred only by the rotation of the probe and materials rotated with the probe and didnot move along welding direction and in vertical direction, there was no material flow and the flowmovement can be regarded as two dimensional layer flow.
基金supported by the National High Technique Development Foundation of China(No.2002AA331160).
文摘Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.
文摘The microstructure and mechanical properties of extruded AZ31 magnesium at different extrusion temperature were investigated.The results show that,at 380℃,when the extrusion ratio is 23,the AZ31 magnesium alloy has a dense recrystallized microstructure and good mechanical properties.On one hand,if the extrusion ratio is too small,grain crushing effect is not obvious,and part of the grain is not dynamic recrystallization.On the other hand,larger extrusion ratio can lead to grain growth and banded structure.Tensile fracture characteristics of extruded AZ31 magnesium alloy is quasi-cleavage.
基金The financial support of the Natural Sciences and Engineering Research Council of Canada(NSERC)through the Automotive Partnership Canada(APC)under APCPJ 459269-13 grant with contributions from Multimatic Technical centre,Ford Motor CompanyCenterline Windsor are acknowledged.Funds from NSERC-RTI program under EQPEQ458441-2014 grant also supported this research.
文摘A promising solid-state coating mechanism based on the cold spray technique provides highly advantageous conditions on thermal-sensitive magnesium alloys.To study the effect of heat balance in cold spray coating on microstructure,experiments were designed to successfully coat AA7075 on AZ31B with two different heat balance conditions to yield a coated sample with tensile residual stress and a sample with compressive residual stress in both coating and substrate.The effects of coating temperature on the microstructure of magnesium alloy and the interfaces of coated samples were then analyzed by SEM,EBSD,TEM in high-and low-heat input coating conditions.The interface of the AA7075 coating and magnesium alloy substrate under both conditions consists of a narrow-band layer with very fine grains,followed by columnar grains of magnesium that have grown perpendicular to the interface.At higher temperatures,this layer became wider.No intermetallic phase was detected at the interface under either condition.It is shown that the microstructure of the substrate was affected by coating temperature,leading to stress relief,dynamic recrystallization and even dynamic grain growth of magnesium under high temperature.Reducing the heat input and increasing the heat transfer decreased microstructural changes in the substrate.
基金supported by the National Natural Science Foundation of China(Grant Nos.52174362 and 51975207)the Xiangtan Special Project for Building a National Innovative City(Grant No.CG-YB20221043)the Yancheng“Talent Plan of Yellow Sea Pearl"for Leading Talent Project。
文摘In this study, AZ31 Mg alloy was processed by a new severe plasticity deformation methodology with multi-pass lowered temperature, and the deformation behavior and microstructure evolution were investigated by finite element method and electron back-scattered diffraction technique and hardness. The results show that with the increase of deformation pass, the strain gradually springs, and its interval distribution tends to homogenize. Meanwhile, the effective strain increases dramatically with the shear force sudden upgrade in the deformation process. Moreover, the new deformation technique can refine grain size remarkably. With the passes on, {10-12} tensile twins behavior and the pyramidal < c + a > slip are triggered more frequently, leading to the completeness of dynamic recrystallization (DRX) gradually, which weaken and disperse the basal texture obviously. Besides, the standard deviation of hardness is getting smaller, and the maximum can reach 78.40 HV on average, which can be attributed to the even large strain distribution, complete DRX, and the high geometrically necessary dislocation.
基金Funded by the National Natural Science Foundation of China(No.U1510131)the Key Research and Development Projects of Shanxi Province(No.201603D121010)+1 种基金the Science and Technology Project of Jincheng City(No.20155010)the Project of Young Scholar of Shanxi Province and the Leading Talent Project of Innovative Entrepreneurial Team of Jiangsu Province and the Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi(TYAL)
文摘At the initial rolling temperature of 250 to 400 ℃, AZ31B magnesium alloy sheets were hot rolled by four different rolling routes. Microstructures and mechanical properties of the hot-rolled magnesium alloy sheets were analyzed by optical microscope and tensile tests respectively. Based on the Hall-Petch relation, considering the average grain size and grain size distribution, the nonlinear fitting analysis between the tensile strength and average grain size was carried on, and then the prediction model of tensile strength of hot-rolled AZ31B magnesium alloy sheet was established. The results indicate that, by rolling with multi-pass cross rolling, uniform, fine and equiaxial grain microstructures can be produced, the anisotropy of hot-rolled magnesium sheet can also be effectively weakened. Strong correlation was observed between the average grain size and tensile property of the hot-rolled magnesium alloy sheet. Grain size distribution coefficient d(CV) was introduced to reflect the dispersion degree about a set of grain size data, and then the Hall-Petch relation was perfected. Ultimately, the prediction accuracy of tensile strength of multi-pass hot-rolled AZ31B magnesium alloy was improved, and the prediction of tensile property can be performed by the model.
基金Item Sponsored by National Basic Research Program of China[973 Program][2011CB012805]
文摘The electromagnetic free bulging experiment and the coupled-field numerical simulation of the EMF process were carried out to determine the possibility to improve the formability of magnesium alloy AZ31 sheets(1 mm thick)at room temperature.Formability data were examined using strain measurements.The numerical simulation for the electromagnetic sheet free bulging is performed by means of ANSYS FEA software.Compared with quasi-static FLD results,increase in the major and minor principal strains of approximately 87%and 39%were achieved,respectively.The effects of various process parameters on electromagnetic bulging of AZ31 magnesium alloy sheets were evaluated. Three-dimensional(3D)FE model is established to predict the electromagnetic bulging of the sheet.The simulation results agreed well with experimental observations.
基金supported by the National Natural Science Foundation of China(No. 51175112)Fundamental Research Funds for the Central Universities (Grant No. HIT.KLOF.2010039)
文摘The effects of pulse current on the superplastic deformation of AZ31 magnesium alloy with different microstructures were examined. The results of TEM analysis showed that the dislocation movement was mainly glide, and the dislocation lines were approximate parallel with few dislocation tangles observed, which indicated that the dislocation movementwas promoted during the deformation, and therefore the formability of the coarse-grained AZ31 magnesium alloy was enhanced by the pulse current. This effect was also indicated by the asymmetrical contour of the free bulging sample, which was observed in the unidirectional pulses auxiliary equi-biaxial tensile test of coarse-grained alloy. In addition, the phenomenon of the restrained cavity growth caused by the thermoelectrical effect of the pulse current was discovered and studied.
基金the National Natural Science Foundation of China(No.51874201)。
文摘Radial additive friction stir repairing(R-AFSR)assisted by stationary shoulder was put forward in the present study,which can be employed to repair the mechanical hole out of dimension tolerance of AZ31 magnesium alloy sheet.The results show that the stationary shoulder has sealed-barrier,heat-sink and extra-forging effects.The heat-sink effect improves the microstructure uniformity along the stir zone(SZ)thickness and the surface appearance of repaired hole,and the sealedbarrier and extra-forging effects eliminate the super-fine grain band in the SZ.Therefore,these three effects improve the formation quality of repaired region,thereby enhancing the mechanical properties of repaired mechanical hole compared with conventional R-AFSR.The tensile and compressive shear strengths of the repaired hole by stationary shoulder R-AFSR both increase first and then decrease when the rotating speed changes from 1200 to 1800 rpm,and these maximum values,respectively,reach 190±3 MPa and 64.5±2 MPa at 1400 rpm.The addition of stationary shoulder during R-AFSR can obtain a higher-quality repaired hole and broaden the repairing process window.