In order to analyze the effect of grain size on stress relaxation(SR) mechanism,the SR tests of TC4 alloy with three kinds of grain size were performed in a temperature range of 650-750℃.A modified cubic delay functi...In order to analyze the effect of grain size on stress relaxation(SR) mechanism,the SR tests of TC4 alloy with three kinds of grain size were performed in a temperature range of 650-750℃.A modified cubic delay function was used to establish SR model for each grain size.A simplified algorithm was proposed for calculating the deformation activation energy based on classical Arrhenius equation.The grain size distribution and variation were observed by microstructural methods.The experimental results indicate that smaller grains are earlier to reach the relaxation limit at the same temperature due to lower initial stress and faster relaxation rate.The SR limit at 650℃ reduces with decreasing grain size.While the effect of grain size on SR limit is not evident at 700 and 750℃ since the relaxation is fully completed.With the increase of grain size,the deformation activation energy is improved and SR mechanism at 700℃ changes from grain rotation and grain boundary sliding to dislocation movement and dynamic recovery.展开更多
Cold rolling and heat-treatment were used for the grain refinement of GH4169 superalloy plate.The effects of cold rolling reduction ratio and heat-treatment time on the precipitatedδphase,and the effects ofδ-phase c...Cold rolling and heat-treatment were used for the grain refinement of GH4169 superalloy plate.The effects of cold rolling reduction ratio and heat-treatment time on the precipitatedδphase,and the effects ofδ-phase content and morphology on the mechanical properties of the GH4169 alloy plates,are studied.The results demonstrate that coldrolling can promote the precipitation of theδphase and its transformation from theδ-Ni3Nb phase to theδ-NbNi4 phase.The comprehensive properties of the alloy are better when the heat treatment time is 1 h,with 132 MPa increase in the tensile strength and only 2.9%decrease in the elongation relative to those of the original material.The mechanical properties of the alloy are shown to change greatly with the change in theδ-phase morphology.展开更多
Against protection requirements for high-speed fragments on the ground weapons,we carried out the research work of crushing mechanism at different impact speeds ofφ8.7 mm spherical tungsten alloy,the penetration to 6...Against protection requirements for high-speed fragments on the ground weapons,we carried out the research work of crushing mechanism at different impact speeds ofφ8.7 mm spherical tungsten alloy,the penetration to 603 armor steel was completed by 20 mm ballistic gun,and the ANSYS/LS-DYNA software was used to complete the numerical calculation of the penetration.We find that there are different crushing mechanisms of spherical tungsten alloy with different speeds and low speed,the crushing mechanism of fragment is mainly controlled by overall plastic deformation,shearing stripping,and squeezing at a high pressure and a high speed.The crushing mechanism will have a spallation phenomenon in addition to the crushing mechanism under high pressure.展开更多
The microstructure evolution of the fine-grained 5083 Al alloy was investigated in annealing temperature range of 150−300℃.Then the effects of the different annealed microstructures on high-temperature deformation be...The microstructure evolution of the fine-grained 5083 Al alloy was investigated in annealing temperature range of 150−300℃.Then the effects of the different annealed microstructures on high-temperature deformation behavior were further studied.The results indicate that the initial recrystallization temperature is about 200℃.By tensile tests at 380−570℃and in strain rate range of 4.17×10^(−4)−1.0×10^(−2) s^(−1),the optimum superplastic parameters are obtained as follows:the annealed temperature 250℃,the tensile temperature 550℃and the strain rate 4.17×10^(−4) s^(−1).With the aid of scanning electronic microscopy(SEM),the fractography of the alloy after the superplastic deformation was analyzed.The results reveal that intergranular cavities with fine size and homogeneous distribution are beneficial to superplastic deformation.展开更多
The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture...The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture surface gradually transits from detachment of interface between W pellets and matrices to cleavage of W pellets. Meanwhile, low strength tungsten alloy has higher sensitivity to strain rate.展开更多
WC-Co hard metal was furnace brazed by Ag-Cu-Zn+Ni/Mn filler alloy using a tube furnace under high-purity argon at730°C.The influence of brazing time and gap size of joints was studied.The results revealed the ma...WC-Co hard metal was furnace brazed by Ag-Cu-Zn+Ni/Mn filler alloy using a tube furnace under high-purity argon at730°C.The influence of brazing time and gap size of joints was studied.The results revealed the maximum shear strength of(156±7)MPa for samples with150μm gap size at a holding time15min.The characterization and microstructure of the brazed joints were characterized by SEM,EDS and XRD.The results showed that increasing the time from5to15min could provide a better chance for the liquid interlayer to flow towards the base metal.However,the formation of some metallic phases such as Mn3W3C at brazing time longer than15min resulted in decreased shear strength of the joint.展开更多
The high-temperature mechanical properties of 95W-3.5Ni-1.5Fe and 95W-4.5Ni-0.5Co alloys were investigated in the temperature range of room temperature to1100℃. The yield strength and tensile strengths declined gradu...The high-temperature mechanical properties of 95W-3.5Ni-1.5Fe and 95W-4.5Ni-0.5Co alloys were investigated in the temperature range of room temperature to1100℃. The yield strength and tensile strengths declined gradually, and the ductility of both alloys increased as the testing temperature was increased to 300℃. All the three properties reached a plateau at temperatures between 300 and 500℃ in the case of 95W-3.5Ni-l.5Fe and at temperatures between 350 and 700℃ in the case of 95W-4.5Ni-0.5Co. Thereafter, the ductility as well as yield and tensile strengths decreased considerably.展开更多
New TiAl alloys, containing 45 at.% A1, 7 at.% Nb, x at.% W, and 0.15 at.% B （x = 0, 0.2, 0.4, and 0.7） were prepared by arc melting and drop casting consequently. Using optical microscopy, scanning electron microsc...New TiAl alloys, containing 45 at.% A1, 7 at.% Nb, x at.% W, and 0.15 at.% B （x = 0, 0.2, 0.4, and 0.7） were prepared by arc melting and drop casting consequently. Using optical microscopy, scanning electron microscopy （SEM）, and electron superprobe technologies, the effects of tungsten on the microstructural evolution of the TiA1 alloys, including the colony size and lamellar spacing, were analyzed. It was found that cellular structures and dendrites were formed in the as-cast TiA1 alloys, and heavy metals, such as niobium and tungsten, tend to segregate strongly at the interface of the cellular structures and dendrites. Trace tungsten can effectively impede the grain growth and narrow the interlamellar spacing. 0.4 at.% tungsten is more effective in refuting the microstructure of the TiAI alloys.展开更多
Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardnes...Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.展开更多
An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency...An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.展开更多
Double-V butt TIG welding process was performed on two plates of AA6061-T6 using ER5356 filler. The microstructure,mechanical and nanomechanical properties of the joint were evaluated in as-welded and after post weld ...Double-V butt TIG welding process was performed on two plates of AA6061-T6 using ER5356 filler. The microstructure,mechanical and nanomechanical properties of the joint were evaluated in as-welded and after post weld heat treatment (PWHT) usingXRD, FESEM, EBSD, nanoindentation and tensile tests. The results show that PWHT led to microstructural recovery of the heataffected zone (HAZ) in addition to the appearance of β-phase (Al3Mg2) at the grain boundaries of weld zone. The hardness (Hnano) inall zones increased after PWHT while the elastic modulus (Enano) was improved from 69.93 GPa to 81 GPa in weld area. All resultsindicate that PWHT has created a homogenous microstructure in the weld zone in addition to outstanding improvement inmechanical properties for the weld zone which surpass the base metal.展开更多
Ultrafine grain tungsten heavy alloys (WHAs) were successfully produced from the nano-crystalline powders using spark plasma sintering.The present study mainly discussed the effects of sintering temperature on the den...Ultrafine grain tungsten heavy alloys (WHAs) were successfully produced from the nano-crystalline powders using spark plasma sintering.The present study mainly discussed the effects of sintering temperature on the density,microstructure and mechanical properties of the alloys.The relative density of 98.12% was obtained at 1 050 ℃,and the tungsten grain size is about 871 nm.At 1 000 ℃-1 200 ℃,the mechanical properties of the alloys tend to first rise and then goes down.After SPS,the alloy exhibits improved hardness (84.3 HRA at 1 050 ℃) and bending strength (987.16 MPa at 1 100 ℃),due to the ultrafine-grained microstructure.The fracture mode after bending tests is mainly characterized as intergranular or intragranular fracture of W grains,interfacial debonding of W grains-binding phase and ductile tearing of binding phase.The EDS analysis reveals a certain proportion of solid solution between W and Ni-Fe binding phase.The good mechanical properties of the alloys can be attributed to grain refinement and solid solution strengthening.展开更多
The effects of Sn addition on the microstructure and mechanical properties of gas tungsten arc butt-welded Mg?6Al?0.3Mn (AM60) (mass fraction, %) alloy sheets were investigated by optical microscopy, scanning electron...The effects of Sn addition on the microstructure and mechanical properties of gas tungsten arc butt-welded Mg?6Al?0.3Mn (AM60) (mass fraction, %) alloy sheets were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and microhardness and tensile tests. The results indicate that both the average microhardness and joint efficiency of AM60 are improved by the addition of 1% Sn (mass fraction). The ultimate tensile strength of Mg?6Al?1Sn?0.3Mn (ATM610) reaches up to 96.8% of that of base material. Moreover, fracture occurs in the fusion zone ofATM610 instead of in the heat-affected zone of AM60 welded joint. The improvement in the properties is mainly attributed to the formation of Mg2Sn, which effectively obstructs the grain coarsening in the heat-affected zone, resulting in a relatively finemicrostructure. The addition of 1% Sn improves the mechanical properties of AM60 welded joint展开更多
The microstructure and mechanical properties of the gas tungsten arc welded cast A356 alloy were investigated with fillers ER1100,ER4043,ER4047 and ER5356 under the pulse frequencies of 1,3 and 5 Hz.Results showed tha...The microstructure and mechanical properties of the gas tungsten arc welded cast A356 alloy were investigated with fillers ER1100,ER4043,ER4047 and ER5356 under the pulse frequencies of 1,3 and 5 Hz.Results showed that the filler metal and pulse frequency affected the grain structure of fusion zone considerably.The highest fraction of eutectic（44%） was formed with filler ER4047.Tensile fracture of all specimens indicated that fracture did not occur in the fusion zone.The greatest impact toughness（about 4 J） was achieved for the welds with filler ER4047 while the largest hardness（HV 90） was obtained with filler ER5356.展开更多
A novel reduction technique has been developed to synthesize nano-sized tungsten heavy alloys powders and compared with the same powders processed by mechanical alloying technique. In the first method, nano-sized tung...A novel reduction technique has been developed to synthesize nano-sized tungsten heavy alloys powders and compared with the same powders processed by mechanical alloying technique. In the first method, nano-sized tungsten heavy alloys powders have been obtained by reduction of precursors obtained by spray drying of several appropriate aqueous solutions, which were made from salts containing tungsten, cobalt, and nickel. By adjusting the stoichiometry of the component of the solutions, it is possible to obtain the desired chemical composition of the tungsten heavy alloys powders. In the second method, highly pure elemental powders of tungsten heavy alloys have been mechanically alloyed in a tumbler ball mill for different milling time. The investigated tungsten heavy alloy powders with the composition (95%W-3.5%Ni-1.5%Fe), (93%W-4.5%Ni-1.0%Fe-1.5%Co), and (90%W-6%Ni-4%Cu) have been prepared using both methods. The prepared powders have been compacted at 70 bar (200 MPa) and sintered in vacuum furnace at 1400℃. Vacuum sintering was carried out to achieve full densification of the produced tungsten heavy alloys. The investigated materials were going to be evaluated the physical and mechanical properties of the sintered parts such as density;electrical conductivity, hardness, and transverse rupture strength. The results reveal that, the grain size of alloys fabricated by chemical reduction technique (53.1 - 63.8 nm) is smaller than that fabricated by mechanical alloying technique (56.4 - 71.4 nm).展开更多
TC4 titanium alloy was welded by double-sided gas tungsten arc welding(GTAW) process in comparison with conventional GTAW process, the microstructure and mechanical performance of weld were also studied. The results i...TC4 titanium alloy was welded by double-sided gas tungsten arc welding(GTAW) process in comparison with conventional GTAW process, the microstructure and mechanical performance of weld were also studied. The results indicate that double-sided GTAW is superior over regular single-sided GTAW on the aspects of increasing penetration, reducing welding deformation and improving welding efficiency. Good weld joint was obtained, which can reach 96.14% tensile strength and 70.85% elongation percentage of the base metal. The grains in heat-affected zone(HAZ) are thin and equiaxed and the degree of grain coarsening increases as one moves to the weld center line, and the interior of grains are α and α′ structures. The coarse columned and equiaxed grains, which interlace martensitic structures α′ and acicular α structures, are observed in weld zone. The fracture mode is ductile fracture.展开更多
The pitting corrosion characteristics of pulse TIG welded Ti-6Al-4V titanium alloy in marine environment were explained. Besides the rapid advance of titanium metallurgy, this is also due to the successful solution of...The pitting corrosion characteristics of pulse TIG welded Ti-6Al-4V titanium alloy in marine environment were explained. Besides the rapid advance of titanium metallurgy, this is also due to the successful solution of problems associated with the development of titanium alloy welding. The preferred welding process of titanium alloy is frequently gas tungsten arc(GTA) welding due to its comparatively easier applicability and better economy. In the case of single pass GTA welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The benefit of the process is utilized to obtain better quality titanium weldments. Four factors, five levels, central composite, rotatable design matrix are used to optimize the required number of experiments. The mathematical models have been developed by response surface method(RSM). The results reveal that the titanium alloy can form a protective scale in marine environment and is resistant to pitting corrosion. Experimental results are provided to illustrate the proposed approach.展开更多
Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed...Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed current gas tungsten arc welding(PCGTAW) was performed,to yield finer fusion zone grains,which leads to higher strength of AA6061 (Al-Mg-Si) aluminium alloy joints.In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints,the traditional Hooke and Jeeves pattern search method was used.The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints.The results indicate that the peak current (Ip) and base current (IB) are the most significant parameters,to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.展开更多
基金Projects(2016ZE57008,20163657004)supported by Aeronautical Science Foundation of ChinaProject(USCAST2016-20)supported by the SAST-SJTU Joint Research Centre of Advanced Aerospace Technology,ChinaProject(51875350)supported by the National Natural Science Foundation of China
文摘In order to analyze the effect of grain size on stress relaxation(SR) mechanism,the SR tests of TC4 alloy with three kinds of grain size were performed in a temperature range of 650-750℃.A modified cubic delay function was used to establish SR model for each grain size.A simplified algorithm was proposed for calculating the deformation activation energy based on classical Arrhenius equation.The grain size distribution and variation were observed by microstructural methods.The experimental results indicate that smaller grains are earlier to reach the relaxation limit at the same temperature due to lower initial stress and faster relaxation rate.The SR limit at 650℃ reduces with decreasing grain size.While the effect of grain size on SR limit is not evident at 700 and 750℃ since the relaxation is fully completed.With the increase of grain size,the deformation activation energy is improved and SR mechanism at 700℃ changes from grain rotation and grain boundary sliding to dislocation movement and dynamic recovery.
基金Project(E2019203005)supported by the Natural Science Foundation of Hebei Province,China。
文摘Cold rolling and heat-treatment were used for the grain refinement of GH4169 superalloy plate.The effects of cold rolling reduction ratio and heat-treatment time on the precipitatedδphase,and the effects ofδ-phase content and morphology on the mechanical properties of the GH4169 alloy plates,are studied.The results demonstrate that coldrolling can promote the precipitation of theδphase and its transformation from theδ-Ni3Nb phase to theδ-NbNi4 phase.The comprehensive properties of the alloy are better when the heat treatment time is 1 h,with 132 MPa increase in the tensile strength and only 2.9%decrease in the elongation relative to those of the original material.The mechanical properties of the alloy are shown to change greatly with the change in theδ-phase morphology.
基金Funded by the National Defense Technology Key Laboratory of Impact Environmental Materials。
文摘Against protection requirements for high-speed fragments on the ground weapons,we carried out the research work of crushing mechanism at different impact speeds ofφ8.7 mm spherical tungsten alloy,the penetration to 603 armor steel was completed by 20 mm ballistic gun,and the ANSYS/LS-DYNA software was used to complete the numerical calculation of the penetration.We find that there are different crushing mechanisms of spherical tungsten alloy with different speeds and low speed,the crushing mechanism of fragment is mainly controlled by overall plastic deformation,shearing stripping,and squeezing at a high pressure and a high speed.The crushing mechanism will have a spallation phenomenon in addition to the crushing mechanism under high pressure.
文摘The microstructure evolution of the fine-grained 5083 Al alloy was investigated in annealing temperature range of 150−300℃.Then the effects of the different annealed microstructures on high-temperature deformation behavior were further studied.The results indicate that the initial recrystallization temperature is about 200℃.By tensile tests at 380−570℃and in strain rate range of 4.17×10^(−4)−1.0×10^(−2) s^(−1),the optimum superplastic parameters are obtained as follows:the annealed temperature 250℃,the tensile temperature 550℃and the strain rate 4.17×10^(−4) s^(−1).With the aid of scanning electronic microscopy(SEM),the fractography of the alloy after the superplastic deformation was analyzed.The results reveal that intergranular cavities with fine size and homogeneous distribution are beneficial to superplastic deformation.
文摘The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture surface gradually transits from detachment of interface between W pellets and matrices to cleavage of W pellets. Meanwhile, low strength tungsten alloy has higher sensitivity to strain rate.
文摘WC-Co hard metal was furnace brazed by Ag-Cu-Zn+Ni/Mn filler alloy using a tube furnace under high-purity argon at730°C.The influence of brazing time and gap size of joints was studied.The results revealed the maximum shear strength of(156±7)MPa for samples with150μm gap size at a holding time15min.The characterization and microstructure of the brazed joints were characterized by SEM,EDS and XRD.The results showed that increasing the time from5to15min could provide a better chance for the liquid interlayer to flow towards the base metal.However,the formation of some metallic phases such as Mn3W3C at brazing time longer than15min resulted in decreased shear strength of the joint.
文摘The high-temperature mechanical properties of 95W-3.5Ni-1.5Fe and 95W-4.5Ni-0.5Co alloys were investigated in the temperature range of room temperature to1100℃. The yield strength and tensile strengths declined gradually, and the ductility of both alloys increased as the testing temperature was increased to 300℃. All the three properties reached a plateau at temperatures between 300 and 500℃ in the case of 95W-3.5Ni-l.5Fe and at temperatures between 350 and 700℃ in the case of 95W-4.5Ni-0.5Co. Thereafter, the ductility as well as yield and tensile strengths decreased considerably.
文摘New TiAl alloys, containing 45 at.% A1, 7 at.% Nb, x at.% W, and 0.15 at.% B （x = 0, 0.2, 0.4, and 0.7） were prepared by arc melting and drop casting consequently. Using optical microscopy, scanning electron microscopy （SEM）, and electron superprobe technologies, the effects of tungsten on the microstructural evolution of the TiA1 alloys, including the colony size and lamellar spacing, were analyzed. It was found that cellular structures and dendrites were formed in the as-cast TiA1 alloys, and heavy metals, such as niobium and tungsten, tend to segregate strongly at the interface of the cellular structures and dendrites. Trace tungsten can effectively impede the grain growth and narrow the interlamellar spacing. 0.4 at.% tungsten is more effective in refuting the microstructure of the TiAI alloys.
文摘Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.
文摘An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.
基金the financial support for this study from the Malaysian Ministry of Higher Education(MOHE) through the Fundamental Research Grant Scheme and Exploratory Research Grant Scheme
文摘Double-V butt TIG welding process was performed on two plates of AA6061-T6 using ER5356 filler. The microstructure,mechanical and nanomechanical properties of the joint were evaluated in as-welded and after post weld heat treatment (PWHT) usingXRD, FESEM, EBSD, nanoindentation and tensile tests. The results show that PWHT led to microstructural recovery of the heataffected zone (HAZ) in addition to the appearance of β-phase (Al3Mg2) at the grain boundaries of weld zone. The hardness (Hnano) inall zones increased after PWHT while the elastic modulus (Enano) was improved from 69.93 GPa to 81 GPa in weld area. All resultsindicate that PWHT has created a homogenous microstructure in the weld zone in addition to outstanding improvement inmechanical properties for the weld zone which surpass the base metal.
基金the National Key Research and Development Plan of China(2017YFB0310400)the National Natural Science Foundation of China(Nos.5167020705 and 51902233)the Self-determined and Innovative Research Funds of WHUT(2019III059XZ)。
文摘Ultrafine grain tungsten heavy alloys (WHAs) were successfully produced from the nano-crystalline powders using spark plasma sintering.The present study mainly discussed the effects of sintering temperature on the density,microstructure and mechanical properties of the alloys.The relative density of 98.12% was obtained at 1 050 ℃,and the tungsten grain size is about 871 nm.At 1 000 ℃-1 200 ℃,the mechanical properties of the alloys tend to first rise and then goes down.After SPS,the alloy exhibits improved hardness (84.3 HRA at 1 050 ℃) and bending strength (987.16 MPa at 1 100 ℃),due to the ultrafine-grained microstructure.The fracture mode after bending tests is mainly characterized as intergranular or intragranular fracture of W grains,interfacial debonding of W grains-binding phase and ductile tearing of binding phase.The EDS analysis reveals a certain proportion of solid solution between W and Ni-Fe binding phase.The good mechanical properties of the alloys can be attributed to grain refinement and solid solution strengthening.
基金Project(51474043)supported by the National Natural Science Foundation of ChinaProject(2014DFG52810)supported by the Ministry of Science and Technology of China+2 种基金Projects(SRFDR 20130191110018,CDJZR13130086)supported by the Ministry of Education of ChinaProject(CSTC2013JCYJC60001)supported by the Chongqing Municipal Government,ChinaProjects(CSTC2012gg B50003,CSTC2013jj B50006)supported by the Natural Science Foundation of Chongqing Science and Technology Commission,China
文摘The effects of Sn addition on the microstructure and mechanical properties of gas tungsten arc butt-welded Mg?6Al?0.3Mn (AM60) (mass fraction, %) alloy sheets were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and microhardness and tensile tests. The results indicate that both the average microhardness and joint efficiency of AM60 are improved by the addition of 1% Sn (mass fraction). The ultimate tensile strength of Mg?6Al?1Sn?0.3Mn (ATM610) reaches up to 96.8% of that of base material. Moreover, fracture occurs in the fusion zone ofATM610 instead of in the heat-affected zone of AM60 welded joint. The improvement in the properties is mainly attributed to the formation of Mg2Sn, which effectively obstructs the grain coarsening in the heat-affected zone, resulting in a relatively finemicrostructure. The addition of 1% Sn improves the mechanical properties of AM60 welded joint
基金the financial support of Shahid Chamran University through the Grant Number EN-636410
文摘The microstructure and mechanical properties of the gas tungsten arc welded cast A356 alloy were investigated with fillers ER1100,ER4043,ER4047 and ER5356 under the pulse frequencies of 1,3 and 5 Hz.Results showed that the filler metal and pulse frequency affected the grain structure of fusion zone considerably.The highest fraction of eutectic（44%） was formed with filler ER4047.Tensile fracture of all specimens indicated that fracture did not occur in the fusion zone.The greatest impact toughness（about 4 J） was achieved for the welds with filler ER4047 while the largest hardness（HV 90） was obtained with filler ER5356.
文摘A novel reduction technique has been developed to synthesize nano-sized tungsten heavy alloys powders and compared with the same powders processed by mechanical alloying technique. In the first method, nano-sized tungsten heavy alloys powders have been obtained by reduction of precursors obtained by spray drying of several appropriate aqueous solutions, which were made from salts containing tungsten, cobalt, and nickel. By adjusting the stoichiometry of the component of the solutions, it is possible to obtain the desired chemical composition of the tungsten heavy alloys powders. In the second method, highly pure elemental powders of tungsten heavy alloys have been mechanically alloyed in a tumbler ball mill for different milling time. The investigated tungsten heavy alloy powders with the composition (95%W-3.5%Ni-1.5%Fe), (93%W-4.5%Ni-1.0%Fe-1.5%Co), and (90%W-6%Ni-4%Cu) have been prepared using both methods. The prepared powders have been compacted at 70 bar (200 MPa) and sintered in vacuum furnace at 1400℃. Vacuum sintering was carried out to achieve full densification of the produced tungsten heavy alloys. The investigated materials were going to be evaluated the physical and mechanical properties of the sintered parts such as density;electrical conductivity, hardness, and transverse rupture strength. The results reveal that, the grain size of alloys fabricated by chemical reduction technique (53.1 - 63.8 nm) is smaller than that fabricated by mechanical alloying technique (56.4 - 71.4 nm).
文摘TC4 titanium alloy was welded by double-sided gas tungsten arc welding(GTAW) process in comparison with conventional GTAW process, the microstructure and mechanical performance of weld were also studied. The results indicate that double-sided GTAW is superior over regular single-sided GTAW on the aspects of increasing penetration, reducing welding deformation and improving welding efficiency. Good weld joint was obtained, which can reach 96.14% tensile strength and 70.85% elongation percentage of the base metal. The grains in heat-affected zone(HAZ) are thin and equiaxed and the degree of grain coarsening increases as one moves to the weld center line, and the interior of grains are α and α′ structures. The coarse columned and equiaxed grains, which interlace martensitic structures α′ and acicular α structures, are observed in weld zone. The fracture mode is ductile fracture.
文摘The pitting corrosion characteristics of pulse TIG welded Ti-6Al-4V titanium alloy in marine environment were explained. Besides the rapid advance of titanium metallurgy, this is also due to the successful solution of problems associated with the development of titanium alloy welding. The preferred welding process of titanium alloy is frequently gas tungsten arc(GTA) welding due to its comparatively easier applicability and better economy. In the case of single pass GTA welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The benefit of the process is utilized to obtain better quality titanium weldments. Four factors, five levels, central composite, rotatable design matrix are used to optimize the required number of experiments. The mathematical models have been developed by response surface method(RSM). The results reveal that the titanium alloy can form a protective scale in marine environment and is resistant to pitting corrosion. Experimental results are provided to illustrate the proposed approach.
基金Naval Research Board (NRB),Ministry of Defence,New Delhi for the financial support to carry out this investigation through sponsored project No.DNRD/05/4003/NRB/67.
文摘Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed current gas tungsten arc welding(PCGTAW) was performed,to yield finer fusion zone grains,which leads to higher strength of AA6061 (Al-Mg-Si) aluminium alloy joints.In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints,the traditional Hooke and Jeeves pattern search method was used.The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints.The results indicate that the peak current (Ip) and base current (IB) are the most significant parameters,to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.
