为了研究冷金属与脉冲复合焊(cold metal transfer and pulse,CMT+P)的焊接行为,使用PCI数据采集卡、高速相机、红外成像仪及声发射采集系统对焊接过程进行同步监测.发现脉冲射滴过渡发生前,焊机输出电流突增,同时焊丝尖端释放猛烈电弧...为了研究冷金属与脉冲复合焊(cold metal transfer and pulse,CMT+P)的焊接行为,使用PCI数据采集卡、高速相机、红外成像仪及声发射采集系统对焊接过程进行同步监测.发现脉冲射滴过渡发生前,焊机输出电流突增,同时焊丝尖端释放猛烈电弧光,随后熔滴滴入焊道,熔池温度增加,声发射(acoustic emission,AE)信号显示出1个波峰.发生CMT短路过渡时,焊机输出电流同时为焊丝熔化和焊丝伸出提供能量,待到焊丝尖端接触基板瞬间形成短路,熔池温度持续降低,AE信号微弱,伴随着熔滴因过热收缩而爆断,熔滴短路过渡完成.对AE信号进行离散傅里叶变换(discrete Fourier transform,DFT)后,可通过特征频率对CMT+P各个周期及阶段进行过程识别.结果表明,575 kHz和415 kHz可作为脉冲电弧周期和CMT短路周期的特征频率,推断180 kHz是脉冲电弧的特有频率,575 kHz的频率则是基础电弧提供,415 kHz处的频率则在CMT短路接触瞬间产生.展开更多
The current efforts in production of low-alloyed steels are aimed at achieving high ultimate and yield strengths,while maintaining sufficient elongation and good weldability in these materials.Among advanced heat trea...The current efforts in production of low-alloyed steels are aimed at achieving high ultimate and yield strengths,while maintaining sufficient elongation and good weldability in these materials.Among advanced heat treatment processes capable of reaching this goal,there is also the Q-P process (Quenching and Partitioning).The process consists in rapid quenching of the material between the M s and M f temperatures in order to prevent full martensitic transformation.The immediately following heating leads to tempering of the martensite and to diffusion of excess carbon from martensite to retained austenite.This increases the stability of the latter.The aim of the Q-P process is to produce very fine martensite microstructure with retained austenite between martensite plates.The experimental programme was carried out on a high-strength low-alloyed steel containing 0.2% carbon and a higher amount of silicon about 1.5%.Higher silicon content in the microstructure contributes to stabilization of retained austenite by suppressing formation of carbides.This grade of steel is an advantageous material thanks to its low amount of alloying elements.This group of low-alloyed steels,if heat treated or thermomechanically treated in a suitable manner,offers a favourable combination of strength,elongation and toughness.The paper is aimed at possibility of the Q-P process optimization with the use of quenching dilatometer.The experimental material is CMnSiMo steel.Conventional process optimization consists of standard samples treatment in laboratory furnaces and baths.This procedure can be time consuming with higher requirements on the experimental material.Therefore,it was proposed that the Q-P process optimization can be done with the use of quenching dilatometer and in this way the development of new procedures can be accelerated.Q-P processes were conducted in the standard way and with the aid of a dilatometer.Comparison of the obtained results provided by the standard procedure and by the procedure using the quenching dilatometer showed very similar results.On the basis of the obtained results,it can be concluded that the quenching dilatometer can be a powerful tool in Q-P processes optimization.展开更多
Cold forming of high strength materials is accompanied by an undesirable spring-back effect and therefore the automotive industry prefers to produce components from high strength steels by hot stamping.Hot deformation...Cold forming of high strength materials is accompanied by an undesirable spring-back effect and therefore the automotive industry prefers to produce components from high strength steels by hot stamping.Hot deformation and cooling in a die are applied to obtain shaped components with martensitic microstructure and high yield strength and ultimate tensile strength.This article presents new applications of this forming technology by incorporating another innovative heat treatment by the Q-P process,which improves both strength and ductility of obtained structures at the same time.Ultimate strengths over 2000 MPa with ductility above 10% can be achieved by this processing.To test microstructure development,thin sheet was hot formed and a corresponding FEM simulation was created.This processing was applied to low alloyed AHS steel with 0.42% of carbon and with an alloying strategy based on Mn,Si and Cr.Martensitic microstructure with retained austenite was obtained by this processing with a strength of around 2000 MPa and ductility of 10%.展开更多
Based upon the composition of C-Si-Mn,four types of transformation induced plasticity（ TRIP） steels with different contents of Si and M n were designed,which are subjected to quenching and partitioning（ Q＆P）proce...Based upon the composition of C-Si-Mn,four types of transformation induced plasticity（ TRIP） steels with different contents of Si and M n were designed,which are subjected to quenching and partitioning（ Q＆P）processes with variable austenitizing temperatures. The as-treated steels exhibits good combination of high strength and substantial elongation. In particular,with austenitizing at 820 ℃,0. 18C-1. 8Si-2. 2M n（ %） steel and0. 18C-1. 8Si-2. 5M n（ %） steel possessed high elongation（ more than 20%） with the tensile strength over 1000 M Pa. The microstructures of the as-treated steels were obtained by scanning electron microscope,the volume fraction and carbon content of retained austenite has been quantified by X-ray diffraction. The designed Q＆P processed steels contained a multiphase microstructure including ferrite,lath martensite,and retained austenite. The volume fraction and carbon content of those steels were higher,which was treated by Q＆P processes with austenitizing at 820 ℃. Due to the TRIP effect during the deformation process,retained austenite gives better stability as well as effectively improves the formability of steels with slightly decreasing the strength,contributing to overall better performance.展开更多
On 25 April, 2015, an Mw7.9 earthquake occurred in Nepal, which caused great economic loss and casualties. However, almost no surface ruptures were observed. Therefore, in order to interpret the phenomenon, we study t...On 25 April, 2015, an Mw7.9 earthquake occurred in Nepal, which caused great economic loss and casualties. However, almost no surface ruptures were observed. Therefore, in order to interpret the phenomenon, we study the rupture process of the earthquake to seek answers. Inversion of teleseismic body-wave data is applied to estimate the rupture process of the 2015 Nepal earthquake. To obtain stable solutions, smoothing and non-negative constraints are introduced. 48 teleseismic stations with good coverage are chosen. Finite fault model is established with length and width of 195 km and 150 km, and we set the initial seismic source parameters referring to CMT solutions. Inversion results indicate that the focal mechanism of this earthquake is a thrust fault type, and the strike, dip and rake angle are in accordance with CMT results. The seismic moment is 0.9195 ×10^（21）Nm（Mw7.9）, and source duration is about 70s. The rupture nucleated near the hypocenter and then propagated along the dip direction to the southeast, and the maximum slip amounts to 5.2 m. Uncertainties on the amount of slip retrieved by different inversion methods still exist, the overall characteristics are inconsistent. The lack of shallow slip during the 2015 Gorkha earthquake implies future seismic hazard and this region should be paid more attention to.展开更多
Cathodic deposition current density of the composite coatings increases when SiC par-ticles and rare earth (RE) were added in the bath, which is profitable for Ni- W-P alloy to deposit in the cathod, forming Ni-W-P-Si...Cathodic deposition current density of the composite coatings increases when SiC par-ticles and rare earth (RE) were added in the bath, which is profitable for Ni- W-P alloy to deposit in the cathod, forming Ni-W-P-SiC and RE-Ni-W-P-SiC composite coatings. On the contrary, the addition of PTFE in the bath decreases cathodic deposition current density of the coatings. The current density increases a little when the amount of RE is 7-9g/l; however, the current density increases greatly when the amount of RE is increased to 11-13g/l. Bui ij the amount of RE is raised further, the current density decreases. Hardness and wear resistance of RE-Ni-W-P-SiC composite coating have been studied, and the results show that the hardness and wear resistance of RE-Ni-W-P-SiC composite coating increase with increasing heat treatment tempera-ture, which reach peak values at 400℃; while the hardness and wear resistance of the coating decrease with the rise of heat treated temperature continuously.展开更多
Let f∈C[-1,1]and R. (r≥1 ) be the reneralized Pal iner polation polynomials satisf ying the conditions Rn, where{xk} are the roots of n-th Jacobi polynomial Pn and are the roots of In this paper,we prove that Rn...Let f∈C[-1,1]and R. (r≥1 ) be the reneralized Pal iner polation polynomials satisf ying the conditions Rn, where{xk} are the roots of n-th Jacobi polynomial Pn and are the roots of In this paper,we prove that Rn holds uniformly on [0,1].展开更多
In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coa...In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and protect the Mg alloy substrate from the bath corrosion. The optimal plating bath composition is NiSO4·6H2O 20 g/L, NaH2PO2·H2O20g/L and C6H8O7·H2O 2.5 g/L, and optimal bath acidity and optimal plating temperature are pH 4.0 and 95℃, respectively. The present process flow is composed of ultrasonic cleaning→alkaline cleaning→acid pickling→activation→double immersing zinc→electroplating zinc→electroless nickel plating→passivation treatment. The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.展开更多
The runoff and runoff process of Eucalyptus plantations natural watershed were studied to provide guidance for scientific evaluation of water conservation capacities of Eucalyptus plantations,compared with the Pinus m...The runoff and runoff process of Eucalyptus plantations natural watershed were studied to provide guidance for scientific evaluation of water conservation capacities of Eucalyptus plantations,compared with the Pinus massoniana forest natural watershed. The runoff volumes of Eucalyptus plantations and P. massoniana forest natural watersheds were continuously monitored using the small watershed runoff monitoring method and the automatic data collection devices from August,2013 to December,2016,and effects of heavy rainfall and continuous rainfall on the runoff process were studied. Results showed that the annual runoff coefficient of Eucalyptus plantations natural watershed was 0. 050,and 55. 4% lower than P. massoniana forest（ 0. 112）,with the difference being significant（ P 〈 0. 01）. Total runoff duration,time of maximum runoff lagging behind rainfall peak,and runoff duration caused by a heavy rainfall process（ amounting to 147. 5 mm） between the two kinds of forest watersheds were significant different,those of Eucalyptus plantations were 35. 6 mm,0. 2 h and 13. 8 h,respectively,while those of P. massoniana forest were28. 5 mm,0. 7 h and 35. 5 h,respectively. Eucalyptus plantations natural watershed produced only 4-days runoff,and runoff depth amounted to3. 8 mm with a 7-days continuous precipitation process of rainfall with 125. 0 mm,while P. massoniana forest natural watershed produced continuously 13-days runoff,and the runoff depth was 10. 1 mm. In conclusion,water conservation capacity of Eucalyptus plantations is obviously lower than P. massoniana forest.展开更多
文摘为了研究冷金属与脉冲复合焊(cold metal transfer and pulse,CMT+P)的焊接行为,使用PCI数据采集卡、高速相机、红外成像仪及声发射采集系统对焊接过程进行同步监测.发现脉冲射滴过渡发生前,焊机输出电流突增,同时焊丝尖端释放猛烈电弧光,随后熔滴滴入焊道,熔池温度增加,声发射(acoustic emission,AE)信号显示出1个波峰.发生CMT短路过渡时,焊机输出电流同时为焊丝熔化和焊丝伸出提供能量,待到焊丝尖端接触基板瞬间形成短路,熔池温度持续降低,AE信号微弱,伴随着熔滴因过热收缩而爆断,熔滴短路过渡完成.对AE信号进行离散傅里叶变换(discrete Fourier transform,DFT)后,可通过特征频率对CMT+P各个周期及阶段进行过程识别.结果表明,575 kHz和415 kHz可作为脉冲电弧周期和CMT短路周期的特征频率,推断180 kHz是脉冲电弧的特有频率,575 kHz的频率则是基础电弧提供,415 kHz处的频率则在CMT短路接触瞬间产生.
基金the project GACR 106/09/1968: Development of New Grades of High-Strength Low-Alloyed Steels with Improved Elongation Values
文摘The current efforts in production of low-alloyed steels are aimed at achieving high ultimate and yield strengths,while maintaining sufficient elongation and good weldability in these materials.Among advanced heat treatment processes capable of reaching this goal,there is also the Q-P process (Quenching and Partitioning).The process consists in rapid quenching of the material between the M s and M f temperatures in order to prevent full martensitic transformation.The immediately following heating leads to tempering of the martensite and to diffusion of excess carbon from martensite to retained austenite.This increases the stability of the latter.The aim of the Q-P process is to produce very fine martensite microstructure with retained austenite between martensite plates.The experimental programme was carried out on a high-strength low-alloyed steel containing 0.2% carbon and a higher amount of silicon about 1.5%.Higher silicon content in the microstructure contributes to stabilization of retained austenite by suppressing formation of carbides.This grade of steel is an advantageous material thanks to its low amount of alloying elements.This group of low-alloyed steels,if heat treated or thermomechanically treated in a suitable manner,offers a favourable combination of strength,elongation and toughness.The paper is aimed at possibility of the Q-P process optimization with the use of quenching dilatometer.The experimental material is CMnSiMo steel.Conventional process optimization consists of standard samples treatment in laboratory furnaces and baths.This procedure can be time consuming with higher requirements on the experimental material.Therefore,it was proposed that the Q-P process optimization can be done with the use of quenching dilatometer and in this way the development of new procedures can be accelerated.Q-P processes were conducted in the standard way and with the aid of a dilatometer.Comparison of the obtained results provided by the standard procedure and by the procedure using the quenching dilatometer showed very similar results.On the basis of the obtained results,it can be concluded that the quenching dilatometer can be a powerful tool in Q-P processes optimization.
基金the project 1M06032 Research Centre of Forming Technology
文摘Cold forming of high strength materials is accompanied by an undesirable spring-back effect and therefore the automotive industry prefers to produce components from high strength steels by hot stamping.Hot deformation and cooling in a die are applied to obtain shaped components with martensitic microstructure and high yield strength and ultimate tensile strength.This article presents new applications of this forming technology by incorporating another innovative heat treatment by the Q-P process,which improves both strength and ductility of obtained structures at the same time.Ultimate strengths over 2000 MPa with ductility above 10% can be achieved by this processing.To test microstructure development,thin sheet was hot formed and a corresponding FEM simulation was created.This processing was applied to low alloyed AHS steel with 0.42% of carbon and with an alloying strategy based on Mn,Si and Cr.Martensitic microstructure with retained austenite was obtained by this processing with a strength of around 2000 MPa and ductility of 10%.
文摘Based upon the composition of C-Si-Mn,four types of transformation induced plasticity（ TRIP） steels with different contents of Si and M n were designed,which are subjected to quenching and partitioning（ Q＆P）processes with variable austenitizing temperatures. The as-treated steels exhibits good combination of high strength and substantial elongation. In particular,with austenitizing at 820 ℃,0. 18C-1. 8Si-2. 2M n（ %） steel and0. 18C-1. 8Si-2. 5M n（ %） steel possessed high elongation（ more than 20%） with the tensile strength over 1000 M Pa. The microstructures of the as-treated steels were obtained by scanning electron microscope,the volume fraction and carbon content of retained austenite has been quantified by X-ray diffraction. The designed Q＆P processed steels contained a multiphase microstructure including ferrite,lath martensite,and retained austenite. The volume fraction and carbon content of those steels were higher,which was treated by Q＆P processes with austenitizing at 820 ℃. Due to the TRIP effect during the deformation process,retained austenite gives better stability as well as effectively improves the formability of steels with slightly decreasing the strength,contributing to overall better performance.
基金supported by National Natural Science Foundation of China (41304046)
文摘On 25 April, 2015, an Mw7.9 earthquake occurred in Nepal, which caused great economic loss and casualties. However, almost no surface ruptures were observed. Therefore, in order to interpret the phenomenon, we study the rupture process of the earthquake to seek answers. Inversion of teleseismic body-wave data is applied to estimate the rupture process of the 2015 Nepal earthquake. To obtain stable solutions, smoothing and non-negative constraints are introduced. 48 teleseismic stations with good coverage are chosen. Finite fault model is established with length and width of 195 km and 150 km, and we set the initial seismic source parameters referring to CMT solutions. Inversion results indicate that the focal mechanism of this earthquake is a thrust fault type, and the strike, dip and rake angle are in accordance with CMT results. The seismic moment is 0.9195 ×10^（21）Nm（Mw7.9）, and source duration is about 70s. The rupture nucleated near the hypocenter and then propagated along the dip direction to the southeast, and the maximum slip amounts to 5.2 m. Uncertainties on the amount of slip retrieved by different inversion methods still exist, the overall characteristics are inconsistent. The lack of shallow slip during the 2015 Gorkha earthquake implies future seismic hazard and this region should be paid more attention to.
基金The project was supported by Yunnan Provincial Natural Science Foundation (95B11-5).
文摘Cathodic deposition current density of the composite coatings increases when SiC par-ticles and rare earth (RE) were added in the bath, which is profitable for Ni- W-P alloy to deposit in the cathod, forming Ni-W-P-SiC and RE-Ni-W-P-SiC composite coatings. On the contrary, the addition of PTFE in the bath decreases cathodic deposition current density of the coatings. The current density increases a little when the amount of RE is 7-9g/l; however, the current density increases greatly when the amount of RE is increased to 11-13g/l. Bui ij the amount of RE is raised further, the current density decreases. Hardness and wear resistance of RE-Ni-W-P-SiC composite coating have been studied, and the results show that the hardness and wear resistance of RE-Ni-W-P-SiC composite coating increase with increasing heat treatment tempera-ture, which reach peak values at 400℃; while the hardness and wear resistance of the coating decrease with the rise of heat treated temperature continuously.
基金Supported by the Science Foundation of CSBTB the Natural Science Foundatioin of Zhejiang.
文摘Let f∈C[-1,1]and R. (r≥1 ) be the reneralized Pal iner polation polynomials satisf ying the conditions Rn, where{xk} are the roots of n-th Jacobi polynomial Pn and are the roots of In this paper,we prove that Rn holds uniformly on [0,1].
基金Project(52001281)supported by the National Natural Science Foundation of ChinaProject(192102210012)supported by Key Scientific and Technological Research Projects in Henan Province,ChinaProject(202300410431)supported by Natural Science Foundation of Henan Province,China。
基金Projects(2020YFB2008300,2020YFB2008304)supported by the National Key Research and Development Program of ChinaProjects(52271102,52075198)supported by the National Natural Science Foundation of ChinaProject supported by the Analytical and Testing Center,Huazhong University of Science and Technology,China。
文摘In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and protect the Mg alloy substrate from the bath corrosion. The optimal plating bath composition is NiSO4·6H2O 20 g/L, NaH2PO2·H2O20g/L and C6H8O7·H2O 2.5 g/L, and optimal bath acidity and optimal plating temperature are pH 4.0 and 95℃, respectively. The present process flow is composed of ultrasonic cleaning→alkaline cleaning→acid pickling→activation→double immersing zinc→electroplating zinc→electroless nickel plating→passivation treatment. The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.
基金Supported by Special Project for Scientific Research of Public Welfare Industry of Ministry of Water Resources(201301044)
文摘The runoff and runoff process of Eucalyptus plantations natural watershed were studied to provide guidance for scientific evaluation of water conservation capacities of Eucalyptus plantations,compared with the Pinus massoniana forest natural watershed. The runoff volumes of Eucalyptus plantations and P. massoniana forest natural watersheds were continuously monitored using the small watershed runoff monitoring method and the automatic data collection devices from August,2013 to December,2016,and effects of heavy rainfall and continuous rainfall on the runoff process were studied. Results showed that the annual runoff coefficient of Eucalyptus plantations natural watershed was 0. 050,and 55. 4% lower than P. massoniana forest（ 0. 112）,with the difference being significant（ P 〈 0. 01）. Total runoff duration,time of maximum runoff lagging behind rainfall peak,and runoff duration caused by a heavy rainfall process（ amounting to 147. 5 mm） between the two kinds of forest watersheds were significant different,those of Eucalyptus plantations were 35. 6 mm,0. 2 h and 13. 8 h,respectively,while those of P. massoniana forest were28. 5 mm,0. 7 h and 35. 5 h,respectively. Eucalyptus plantations natural watershed produced only 4-days runoff,and runoff depth amounted to3. 8 mm with a 7-days continuous precipitation process of rainfall with 125. 0 mm,while P. massoniana forest natural watershed produced continuously 13-days runoff,and the runoff depth was 10. 1 mm. In conclusion,water conservation capacity of Eucalyptus plantations is obviously lower than P. massoniana forest.
