Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practic...Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practical application of as-printed components. This study examines the Mg-15Gd-1Zn-0.4Zr (GZ151K, wt.%) alloy, a prototypical high-strength casting Mg-RE alloy, fabricated through laser powder bed fusion (LPBF). Despite achieving ultra-high strength, the GZ151K alloy concurrently exhibits a pronounced cold-cracking susceptibility. The as-printed GZ151K alloy consists of almost fully fine equiaxed grains with an average grain size of merely 2.87 µm. Subsequent direct aging (T5) heat treatment induces the formation of dense prismatic β' precipitates. Consequently, the LPBF-T5 GZ151K alloy manifests an ultra-high yield strength of 405 MPa, surpassing all previously reported yield strengths for Mg alloys fabricated via LPBF and even exceeding that of its extrusion-T5 counterpart. Interestingly, as-printed GZ151K samples with a build height of 2 mm exhibit no cracking, whereas samples with build heights ranging from 4 to 18 mm demonstrate severe cold cracking. Thermal stress simulation also suggests that the cold cracking susceptibility increases significantly with increasing build height. The combination of high thermal stress and low ductility in the as-printed GZ151K alloy culminates in a high cold cracking susceptibility. This study offers novel insights into the intricate issue of cold cracking in the LPBF process of high-strength Mg alloys, highlighting the critical balance between achieving high strength and mitigating cold cracking susceptibility.展开更多
18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min,and then cooled to 950°C and compressed.The cracking behaviors were investigated using optical microscopy and sca...18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min,and then cooled to 950°C and compressed.The cracking behaviors were investigated using optical microscopy and scanning electron microscopy.The results showed that the hot workability of 18Mn18Cr0.5N steel gradually decreased with increasing preheating temperature between 1100 and 1200°C,and quickly deteriorated up to 1250°C.Above 1200°C,delta ferrite particles appeared in 18Mn18Cr0.5N steel,promoted cavity coalescence on grain boundary,and accelerated surface crack formation during the hot working process.展开更多
In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about th...In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about the partial working processes of the diesel engine, the amount of heat energy, enough to make the fuel self ignite at the end of compression process at different temperatures of coolant and intake air, was calculated. Several HY20 preheating plugs were used to heat up the intake air. Meanwhile, an electronic control system based on 8 bit micro controller unit (MCS 8031) was designed to automatically control the process of heating intake air. According to the various temperatures of coolant and ambient air, one plug or two plugs can automatically be selected to heat intake air. The demo experiment validated that the total system could operate successfully and achieve the scheduled function.展开更多
Gas Transmitting From West to East Project' is significant. It should ensure the welding quality and safety of pipeline. The task is very arduous to guarantee the quality of the project in the condition of long li...Gas Transmitting From West to East Project' is significant. It should ensure the welding quality and safety of pipeline. The task is very arduous to guarantee the quality of the project in the condition of long line, complex weather and geology features. In this paper, the welding cold cracking susceptibility of domestic X 70 pipeline steel adopted by the project, which is one of the most interesting questions of welding quality about petrol pipeline, was studied by means of oblique Y groove cracking test. The crack ratio of surface and section was tested under the conditions of different welding materials and preheat temperature .The thickness of plate steel was 14.7 mm and 10.3 mm . The results reveal that X 70 pipeline steel has good crack resistance. The research has important value for the construction of large scale pipeline engineering and the application of domestic X 70 pipeline steel.展开更多
In this investigation, an attempt has been made to study the influence of welding consumables on the factors that influence cold cracking of armour grade quenched and tempered （Q＆.T） steel welds. Flux cored arc wel...In this investigation, an attempt has been made to study the influence of welding consumables on the factors that influence cold cracking of armour grade quenched and tempered （Q＆.T） steel welds. Flux cored arc welding （FCAW） process were used making welds using austenitic stainless steel （ASS） and low hydrogen ferritic steel （LHF） consumables. The diffusible hydrogen levels in the weld metal of the ASS and LHF consumables were determined by mercury method. Residual stresses were evaluated using X-ray stress analyzer and implant test was carried out to study the cold cracking of the welds. Results indicate that ASS welds offer a greater resistance to cold cracking of armour grade Q＆T steel welds.展开更多
We optimized the gradation of cold recycled mixture(CRM)based on low-temperature performance.Firstly,the low-temperature crack resistance of CRM with different gradation and emulsified asphalt content was studied by i...We optimized the gradation of cold recycled mixture(CRM)based on low-temperature performance.Firstly,the low-temperature crack resistance of CRM with different gradation and emulsified asphalt content was studied by indirect tension(IDT)and semi-circular bending(SCB)test.Thereafter,the low-temperature performance evaluation index suitable for CRM was put forward.Then,the triangular coordinate statistical chart was used to analyze the optimal proportion of three grades of aggregate which are 2.36-4.75 mm,0.075-2.36 mm and below 0.075 mm.The results showed that the W_(f) and G_(f) could distinguish the low-temperature performance of CRM with different mixtures and emulsified asphalt dosage.For cold recycled fine aggregate,2.36-4.75 mm,0.075-2.36 mm and less than 0.075 mm account for 20%-25%,74.3%-80%and 5%-8%,respectively.The CRM with lower void fraction,higher W_(f) and G_(f) could be obtained.Based on the reported findings,it was suggested that the sieve passing percentage of 4.75,2.36,and 0.075 mm of CRM is 45%-55%,27%-52%and 1.5%-5%,respectively.展开更多
By mixing preheated high-aluminum bronze powders with different amounts of Al_2O_3 powder, a low-pressure cold-sprayed coating was prepared and sprayed onto a Cr12MoV steel substrate. The hardness of the coating and t...By mixing preheated high-aluminum bronze powders with different amounts of Al_2O_3 powder, a low-pressure cold-sprayed coating was prepared and sprayed onto a Cr12MoV steel substrate. The hardness of the coating and the bonding strength between the coating and the substrate were tested with a HV-1000 microhardness tester and a mechanical universal testing machine. The surface microstructure, cross-section and tensile fracture surface of the coating were observed with a scanning electron microscope(SEM). Correspondingly, the influences of the preheat treatment temperature of the bronze powder and the Al_2O_3 content on the coating performance were investigated. The results indicate that the hardness of bronze powders decreased and the coating deposition rate increased after the preheating treatment of the bronze powder. The Al_2O_3 content in the mixed powders contributed to the deformation of bronze powders during the spraying process. This trend resulted in varied performance of the coating.展开更多
Cracking morphology in the fusion zone of HQ130 high strength steel was researched by 'the y-slit test' and 'three-point bend test', ultrasonic test and microscope. HQ130 and QJ63 high strength steel w...Cracking morphology in the fusion zone of HQ130 high strength steel was researched by 'the y-slit test' and 'three-point bend test', ultrasonic test and microscope. HQ130 and QJ63 high strength steel was welded by Ar+CO2 gas shielded arc welding under the condition without preheating. Experimental results indicated that welding cracks were produced in the partially melted zone of the weld root of HQ130 steel side and propagated parallel to the fusion zone. The cracks were developed alternatively between the weld and the partially melted zone, and are not strictly ruptured at W/F (weld metal/fusion zone) boundary surface. Controlling weld heat input (E) about 16 kJ/cm could make the cracking rate lowest and satisfy the performance requirement of welded joint zone.展开更多
In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical ...In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical microscope. The morphology of cracks and surface defects were examined using scanning electron microscope. Macroscopic residual stresses produced in every process during manufacturing in the QSn6.5 0.1 strip were measured by X ray diffraction method and hole drilling method. The results show that the cracks in the QSn6.5 0.1 cold rolling strip were caused due to the derivation of metallurgical defects, such as SnO 2, S, fine looses,the inverse segregation unable to clear up when milling, and the accumulation of all kinds of resi dual stresses. When the accumulation of the residual stress reaches the material′s breaking strength, the cracks will be generated. Several measures to avoid the development of these kinds of cracks were put forward, such as: controlling the casting technology, improving homogenization annealing procedure (680 ℃/7 h) and milling quality(using the second milling when necessary), working out a more reasonable rolling technology to ensure intermediate annealing in time.展开更多
Uncontrolled residual stresses have significant effects on the service time and defects of the spun parts.Nowadays,X-Ray Diffraction(XRD)method has been widely used in the residual stress measurement of industry produ...Uncontrolled residual stresses have significant effects on the service time and defects of the spun parts.Nowadays,X-Ray Diffraction(XRD)method has been widely used in the residual stress measurement of industry products with different forming processes.The calculated residual stress is usually obtained from the data fitting slope of strain and angle with Ordinary Least Squares(OLS)method.But this fitting method is not always suitable for the big fluctuant data.In this paper,the Weighted Least Square(WLS)method is used for the data fitting and compared with the OLS method.The nickel-based superalloy GH3030 and iron-based superalloy GH1140 are applied in the multi-pass cold spinning experiments.The residual stress distributions of normal,potential crack and wrinkle workpieces are discussed with the grain structure.The results show that WLS method has better goodness of fit compared with OLS method.The residual stress distributions have special relationship with potential crack,wrinkle workpiece and grain structure.展开更多
基金supported by the National Key Research and Development Program of China(No.2021YFB3701000)the National Natural Science Foundation of China(Nos.51971130,52201129,U21A2047,51821001,U2037601)+2 种基金support by the China Postdoctoral Science Foun-dation(2023M742219)the Postdoctoral Fellowship Program of CPSF under Grant Number GZB20240419support by the Ministry of Education,Singapore,under its Academic Research Fund Tier 2(MOE-T2EP50221-0013).
文摘Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practical application of as-printed components. This study examines the Mg-15Gd-1Zn-0.4Zr (GZ151K, wt.%) alloy, a prototypical high-strength casting Mg-RE alloy, fabricated through laser powder bed fusion (LPBF). Despite achieving ultra-high strength, the GZ151K alloy concurrently exhibits a pronounced cold-cracking susceptibility. The as-printed GZ151K alloy consists of almost fully fine equiaxed grains with an average grain size of merely 2.87 µm. Subsequent direct aging (T5) heat treatment induces the formation of dense prismatic β' precipitates. Consequently, the LPBF-T5 GZ151K alloy manifests an ultra-high yield strength of 405 MPa, surpassing all previously reported yield strengths for Mg alloys fabricated via LPBF and even exceeding that of its extrusion-T5 counterpart. Interestingly, as-printed GZ151K samples with a build height of 2 mm exhibit no cracking, whereas samples with build heights ranging from 4 to 18 mm demonstrate severe cold cracking. Thermal stress simulation also suggests that the cold cracking susceptibility increases significantly with increasing build height. The combination of high thermal stress and low ductility in the as-printed GZ151K alloy culminates in a high cold cracking susceptibility. This study offers novel insights into the intricate issue of cold cracking in the LPBF process of high-strength Mg alloys, highlighting the critical balance between achieving high strength and mitigating cold cracking susceptibility.
基金supported by the National Science and Technology Support Plan of China(No.2007BAF02B01-03)
文摘18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min,and then cooled to 950°C and compressed.The cracking behaviors were investigated using optical microscopy and scanning electron microscopy.The results showed that the hot workability of 18Mn18Cr0.5N steel gradually decreased with increasing preheating temperature between 1100 and 1200°C,and quickly deteriorated up to 1250°C.Above 1200°C,delta ferrite particles appeared in 18Mn18Cr0.5N steel,promoted cavity coalescence on grain boundary,and accelerated surface crack formation during the hot working process.
文摘In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about the partial working processes of the diesel engine, the amount of heat energy, enough to make the fuel self ignite at the end of compression process at different temperatures of coolant and intake air, was calculated. Several HY20 preheating plugs were used to heat up the intake air. Meanwhile, an electronic control system based on 8 bit micro controller unit (MCS 8031) was designed to automatically control the process of heating intake air. According to the various temperatures of coolant and ambient air, one plug or two plugs can automatically be selected to heat intake air. The demo experiment validated that the total system could operate successfully and achieve the scheduled function.
文摘Gas Transmitting From West to East Project' is significant. It should ensure the welding quality and safety of pipeline. The task is very arduous to guarantee the quality of the project in the condition of long line, complex weather and geology features. In this paper, the welding cold cracking susceptibility of domestic X 70 pipeline steel adopted by the project, which is one of the most interesting questions of welding quality about petrol pipeline, was studied by means of oblique Y groove cracking test. The crack ratio of surface and section was tested under the conditions of different welding materials and preheat temperature .The thickness of plate steel was 14.7 mm and 10.3 mm . The results reveal that X 70 pipeline steel has good crack resistance. The research has important value for the construction of large scale pipeline engineering and the application of domestic X 70 pipeline steel.
基金Armament Research Board (ARMREB),New Delhi for funding this projectwork (Project No MAA/03/41)
文摘In this investigation, an attempt has been made to study the influence of welding consumables on the factors that influence cold cracking of armour grade quenched and tempered （Q＆.T） steel welds. Flux cored arc welding （FCAW） process were used making welds using austenitic stainless steel （ASS） and low hydrogen ferritic steel （LHF） consumables. The diffusible hydrogen levels in the weld metal of the ASS and LHF consumables were determined by mercury method. Residual stresses were evaluated using X-ray stress analyzer and implant test was carried out to study the cold cracking of the welds. Results indicate that ASS welds offer a greater resistance to cold cracking of armour grade Q＆T steel welds.
基金Funded by the Key Research and Development Plan of Jiangxi Province (No. 20223BBG74002)the Natural Science Foundation of China (Nos. 51778483, 51978521)the Fundamental Research Funds for the Central Universities (No. DUT24RC (3)100)。
文摘We optimized the gradation of cold recycled mixture(CRM)based on low-temperature performance.Firstly,the low-temperature crack resistance of CRM with different gradation and emulsified asphalt content was studied by indirect tension(IDT)and semi-circular bending(SCB)test.Thereafter,the low-temperature performance evaluation index suitable for CRM was put forward.Then,the triangular coordinate statistical chart was used to analyze the optimal proportion of three grades of aggregate which are 2.36-4.75 mm,0.075-2.36 mm and below 0.075 mm.The results showed that the W_(f) and G_(f) could distinguish the low-temperature performance of CRM with different mixtures and emulsified asphalt dosage.For cold recycled fine aggregate,2.36-4.75 mm,0.075-2.36 mm and less than 0.075 mm account for 20%-25%,74.3%-80%and 5%-8%,respectively.The CRM with lower void fraction,higher W_(f) and G_(f) could be obtained.Based on the reported findings,it was suggested that the sieve passing percentage of 4.75,2.36,and 0.075 mm of CRM is 45%-55%,27%-52%and 1.5%-5%,respectively.
基金financially supported by the National Key Research and Development Program of China(No.2016YFE0111400)the Program on Key Research Project of Gansu Province(No.17YF1WA159)the National High-end Foreign Experts Program of China(No.GTD20156200088)
文摘By mixing preheated high-aluminum bronze powders with different amounts of Al_2O_3 powder, a low-pressure cold-sprayed coating was prepared and sprayed onto a Cr12MoV steel substrate. The hardness of the coating and the bonding strength between the coating and the substrate were tested with a HV-1000 microhardness tester and a mechanical universal testing machine. The surface microstructure, cross-section and tensile fracture surface of the coating were observed with a scanning electron microscope(SEM). Correspondingly, the influences of the preheat treatment temperature of the bronze powder and the Al_2O_3 content on the coating performance were investigated. The results indicate that the hardness of bronze powders decreased and the coating deposition rate increased after the preheating treatment of the bronze powder. The Al_2O_3 content in the mixed powders contributed to the deformation of bronze powders during the spraying process. This trend resulted in varied performance of the coating.
文摘Cracking morphology in the fusion zone of HQ130 high strength steel was researched by 'the y-slit test' and 'three-point bend test', ultrasonic test and microscope. HQ130 and QJ63 high strength steel was welded by Ar+CO2 gas shielded arc welding under the condition without preheating. Experimental results indicated that welding cracks were produced in the partially melted zone of the weld root of HQ130 steel side and propagated parallel to the fusion zone. The cracks were developed alternatively between the weld and the partially melted zone, and are not strictly ruptured at W/F (weld metal/fusion zone) boundary surface. Controlling weld heat input (E) about 16 kJ/cm could make the cracking rate lowest and satisfy the performance requirement of welded joint zone.
文摘In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical microscope. The morphology of cracks and surface defects were examined using scanning electron microscope. Macroscopic residual stresses produced in every process during manufacturing in the QSn6.5 0.1 strip were measured by X ray diffraction method and hole drilling method. The results show that the cracks in the QSn6.5 0.1 cold rolling strip were caused due to the derivation of metallurgical defects, such as SnO 2, S, fine looses,the inverse segregation unable to clear up when milling, and the accumulation of all kinds of resi dual stresses. When the accumulation of the residual stress reaches the material′s breaking strength, the cracks will be generated. Several measures to avoid the development of these kinds of cracks were put forward, such as: controlling the casting technology, improving homogenization annealing procedure (680 ℃/7 h) and milling quality(using the second milling when necessary), working out a more reasonable rolling technology to ensure intermediate annealing in time.
基金supported by the Zhejiang Provincial Natural Science Foundation,China(No.LZ17E050001)the National Natural Science Foundation of China(No.51975301 and No.52075359)。
文摘Uncontrolled residual stresses have significant effects on the service time and defects of the spun parts.Nowadays,X-Ray Diffraction(XRD)method has been widely used in the residual stress measurement of industry products with different forming processes.The calculated residual stress is usually obtained from the data fitting slope of strain and angle with Ordinary Least Squares(OLS)method.But this fitting method is not always suitable for the big fluctuant data.In this paper,the Weighted Least Square(WLS)method is used for the data fitting and compared with the OLS method.The nickel-based superalloy GH3030 and iron-based superalloy GH1140 are applied in the multi-pass cold spinning experiments.The residual stress distributions of normal,potential crack and wrinkle workpieces are discussed with the grain structure.The results show that WLS method has better goodness of fit compared with OLS method.The residual stress distributions have special relationship with potential crack,wrinkle workpiece and grain structure.
