To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treat...To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.展开更多
The effects of heat treatment and strontium(Sr) addition on the microstructure and mechanical properties of ADC1_(2) alloys were investigated,and two-stage solution treatment was introduced.The results indicated that ...The effects of heat treatment and strontium(Sr) addition on the microstructure and mechanical properties of ADC1_(2) alloys were investigated,and two-stage solution treatment was introduced.The results indicated that the addition of Sr obviously refined the microstructure of ADC12 alloys.When 0.05 wt%Sr was added into the alloy,the eutectic Si phase was fully modified into fine fibrous structure;a-A1 andβ-A1_(5)FeSi phases were best refined;and the eutectic AlzCu phase was modified into block-like AlzCu phase that continuously distributed at the grain boundary.The ultimate tensile strength(UTS)(270.63 MPa)and elongation(3.19%)were increased by 51.2%and 73.4%respectively compared with unmodified alloys.After the two-stage solution treatment(500℃,6 h+520℃,4 h),for 0.05 wt%Sr modified ADC12 alloys,the Si phases transformed into fine particle structure and Al_(2)Cu phases were fully dissolved.The peak hardness value of the alloys processed by the two-stage solution treatment was increased by 8.3%and 6.8%respectively compared to solution treatment at 500℃and 520℃.After the aging treatment(175℃,7 h),the hardness and UTS were increased by 38.73%and 13.96%respectively when compared with the unmodified alloy.展开更多
A kind of Fe-Co-Ni-Cr-Mo-C alloy was designed for valve seat use. The effects of thequenching temperature, tempering time and tempering temperature on the mechanical properties and microstructure of the alloy were inv...A kind of Fe-Co-Ni-Cr-Mo-C alloy was designed for valve seat use. The effects of thequenching temperature, tempering time and tempering temperature on the mechanical properties and microstructure of the alloy were investigated. The results show that the hardness decreases, while tensile strength （σb）, transverse rupture strength (σbb ) and impact toughness(Kic) increase after the alloy is quenched and tempered. The best complex property (（σb , 446 MPa;） σbb ,793 MPa; Kic, 2.96 J/cm2 ) can be obtained when the alloy is quenched at 1 100 ℃ and tempered at 650 ℃. The results of X-ray diffraction and energy dispersive X-ray analysis （EDX） show that the major streng-（thening） phases are carbides such as （Fe,Cr）7C3 and Fe2MoC. The obvious secondary hardening appears when the alloy is tempered at 550 ℃,which results from the precipitated carbides of Cr and Mo in the alloy from the matrix and the heat-resistant retained austenite .展开更多
In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and m...In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and mechanical properties of the joint were studied. The pros and cons of the joint were identified and evaluated by measuring the tensile shear strength, microhardness and microstructure observation. The formation mechanism of various phases at the Mg/steel interface was analyzed. The results indicated that the galvanized layer could promote the metallurgical bonding between magnesium alloy and steel by improving the diffusion ability of molten magnesium alloy at the steel interface and reacting with Mg, so as to enhance the strength of the joint. A continuous dense layered eutectic structure(α-Mg+MgZn) was formed at the interface of the joint, while MgZn_(2)and MgZn phase was formed at the weld edge zone and heat affective zone(HAZ), whereas no reaction layer was generated between the uncoated steel and magnesium alloy. A sound joint could be obtained at 2.5 kW, and the corresponding tensile shear strength reached the maximum value of 42.9 N/mm. The strength was slightly reduced at 2.6 kW due to the existence of microcracks in the eutectic reaction layer.展开更多
An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 ...An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 °C(below Ac1 temperature of 710 °C). The spheroidization ratio of cementite and the average size of particles increase with increasing the cyclic number of heat treatment. After5-cycle heat treatment, the spheroidization ratio of cementite is 100%, and the average size of the cementite particles is about0.53 μm. After cyclic heat treatment, the hardness, ultimate tensile strength and yield strength of the experimental steel gradually decrease with increasing cyclic number of heat treatment. The elongation of the as-received specimens is about 7.4%, the elongation of the 1-cycle specimen is 14.3%, and the elongation of 5-cycle specimen reaches a peak value of 22.5%, thereafter marginally decreases to 18.3% after 6-cycle heat treatment. Accordingly, the fractured surface initially exhibits the regions of wavy lamellar fracture. By increasing the cyclic number of heat treatment cycles, the regions of dimples consume the entire fractured surface gradually. Some large dimples can be found in the fracture surface of the specimen subjected to six heat treatment cycles.展开更多
This paper reports the effects of post weld heat treatments, namely artificial ageing and solution treatment followed by artificial ageing, on microstructure and mechanical properties of 12 mm thick friction stir weld...This paper reports the effects of post weld heat treatments, namely artificial ageing and solution treatment followed by artificial ageing, on microstructure and mechanical properties of 12 mm thick friction stir welded joints of precipitation hardenable high strength armour grade AA7075-T651 aluminium alloy. The tensile properties, such as yield strength, tensile strength, elongation and notch tensile strength, are evaluated and correlated with the microhardness and microstructural features. The scanning electron microscope is used to characterie the fracture surfaces. The solution treatment followed by ageing heat treatment cycle is found to be marginally beneficial in improving the tensile properties of friction stir welds of AA7075-T651 aluminium alloy.展开更多
In this study,a mathematical model was developed to optimize the heat treatment process for maximum tensile strength and ductility of aluminum(8011) silicon carbide particulate composites.The process parameters are so...In this study,a mathematical model was developed to optimize the heat treatment process for maximum tensile strength and ductility of aluminum(8011) silicon carbide particulate composites.The process parameters are solutionizing time,aging temperature,and aging time.The experiments were performed on an universal testing machine according to centre rotatable design matrix.A mathematical model was developed with the main and interactive effects of the parameters considered.The analysis of variance technique was used to check the adequacy of the developed model.The optimum parameters were obtained for maximum tensile strength.Fractographic examination shows the cracks and dimples on the fractured surfaces of heat-treated specimen.展开更多
Mechanical properties and tribological behavior of a novel cast heat resisting copper based alloy are investigated. The corresponding properties of a commercial aluminum bronze C95500 (ASTM B30) are compared with the ...Mechanical properties and tribological behavior of a novel cast heat resisting copper based alloy are investigated. The corresponding properties of a commercial aluminum bronze C95500 (ASTM B30) are compared with the alloy. The results show that the alloy possesses better mechanical properties and tribological behaviors than that of C95500 at elevated temperature. The tensile strength, elongation and hardness at 500℃ are 470MPa, 2.5% and HB220, respectively. The wear rate of the developed alloy at ambient and elevated temperature is about one sixth and one fortieth of that of C95500, respectively. The alloy is very suitable for ma nufacturing heat resisting and wear resisting parts. Major strengthening mechanisms for the alloy are solution strengthening and the second phase strengthening.展开更多
The effects of heat treatment(heating temperature and pH) on the structures and emulsifying properties of caseins were systematically studied by spectroscopy.Heat treatment from 60to 100℃resulted in an increase in th...The effects of heat treatment(heating temperature and pH) on the structures and emulsifying properties of caseins were systematically studied by spectroscopy.Heat treatment from 60to 100℃resulted in an increase in their fluorescence intensity,hydrodynamic diameter,turbidity and emulsifying activity index,but decreased the size polydispersity of caseins.In the pH range of 5.5to 7.0,the fluorescence intensity,hydrodynamic diameter,turbidity and emulsifying properties decreased with increased heating pH,but the size polydispersity of caseins increased with increased pH.The relationship between the surface fluorescence intensity and emulsifying activity was also investigated,revealing a correlation coefficient of 0.90.These results suggested that heat treatment could be used to modify the structures and emulsifying properties of caseins by appropriately selecting heating conditions.展开更多
The microstructures and mechanical properties of Al-6Zn-2Mg-1.5Cu-0.4Er alloy under different treatment conditions were investigated by transmission electron microscopy （TEM） observation, and tensile properties and ...The microstructures and mechanical properties of Al-6Zn-2Mg-1.5Cu-0.4Er alloy under different treatment conditions were investigated by transmission electron microscopy （TEM） observation, and tensile properties and hardness test, respectively. The relationship between mechanical properties and microstructures of the alloys was discussed. With trace Er addition to A1-Zn-Mg-Cu alloy, Er and Al interact to form Al3Er phase, which is coherent with a（A1） matrix. The results show that Al-Zn-Mg-Cu alloy after retrogression and re-ageing （RRA） heat treatment exhibits higher tensile strength, ductility and conductivity.展开更多
The effects of rapid heating cyclic heat treatment on mechanical properties of a TiAl based alloy (Ti 33Al 3Cr) were studied by means of an induction heating machine. The results show that: 1) fine fully lamellar micr...The effects of rapid heating cyclic heat treatment on mechanical properties of a TiAl based alloy (Ti 33Al 3Cr) were studied by means of an induction heating machine. The results show that: 1) fine fully lamellar microstructure with colony size of about 50 μm and lamellar spacing of about 0.12 μm can be obtained; 2) the compression mechanical properties can be improved to a large extent and the best comprehensive compression mechanical properties can reach the yield stress 745 MPa, the large flow stress 1 672 MPa and the compression ratio 19.4%; and 3) the compression fracture at room temperature after induction heat treatment and aging is still typical cleavage fracture.展开更多
Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many meth...Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many methods to decrease the residual stress to prevent the structures from being broken and improve the mechanical properties.In this study,residual stress and mechanical properties of LAMed structures are analyzed,and the advanced measuring method,laser ultrasonic technique,is used to detect the residual stresses accumulated in the samples in time.The results show that when the solution temperature is less than T_(β)(992℃),the residual stress increases gradually with the increase of solution temperature,and when the temperature is more than T_(β)(992℃),Widmanstätten structure will significantly reduce the residual stress;the mechanical properties of the specimen decrease with the increase of the solution temperature,and the different cooling methods do not have much effect on the elastic properties of the specimen.Considering the residual stress and mechanical properties,the HT1 system used in this paper is the best.This study is of great significance for the reasonable suppression of residual stress and the regulation of mechanical properties of TC4 titanium alloy fabricated by laser additive manufacturing.展开更多
文摘To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.
基金Project(51364035)supported by the National Natural Science Foundation of ChinaProject(20133601110001)supported by the Ministry of Education Tied up with the Special Research Fund for the Doctoral Program for Higher School,China+1 种基金Project(KJLD14003)supported by the Loading Program of Science and Technology of College of Jiangxi Province,ChinaProject(2012-CYH-DW-XCL-002)supported by the Production and Teaching and Research Cooperation Plan of Naaachaaag Non-party Experts and Doctor,China
文摘The effects of heat treatment and strontium(Sr) addition on the microstructure and mechanical properties of ADC1_(2) alloys were investigated,and two-stage solution treatment was introduced.The results indicated that the addition of Sr obviously refined the microstructure of ADC12 alloys.When 0.05 wt%Sr was added into the alloy,the eutectic Si phase was fully modified into fine fibrous structure;a-A1 andβ-A1_(5)FeSi phases were best refined;and the eutectic AlzCu phase was modified into block-like AlzCu phase that continuously distributed at the grain boundary.The ultimate tensile strength(UTS)(270.63 MPa)and elongation(3.19%)were increased by 51.2%and 73.4%respectively compared with unmodified alloys.After the two-stage solution treatment(500℃,6 h+520℃,4 h),for 0.05 wt%Sr modified ADC12 alloys,the Si phases transformed into fine particle structure and Al_(2)Cu phases were fully dissolved.The peak hardness value of the alloys processed by the two-stage solution treatment was increased by 8.3%and 6.8%respectively compared to solution treatment at 500℃and 520℃.After the aging treatment(175℃,7 h),the hardness and UTS were increased by 38.73%and 13.96%respectively when compared with the unmodified alloy.
文摘A kind of Fe-Co-Ni-Cr-Mo-C alloy was designed for valve seat use. The effects of thequenching temperature, tempering time and tempering temperature on the mechanical properties and microstructure of the alloy were investigated. The results show that the hardness decreases, while tensile strength （σb）, transverse rupture strength (σbb ) and impact toughness(Kic) increase after the alloy is quenched and tempered. The best complex property (（σb , 446 MPa;） σbb ,793 MPa; Kic, 2.96 J/cm2 ) can be obtained when the alloy is quenched at 1 100 ℃ and tempered at 650 ℃. The results of X-ray diffraction and energy dispersive X-ray analysis （EDX） show that the major streng-（thening） phases are carbides such as （Fe,Cr）7C3 and Fe2MoC. The obvious secondary hardening appears when the alloy is tempered at 550 ℃,which results from the precipitated carbides of Cr and Mo in the alloy from the matrix and the heat-resistant retained austenite .
基金Projects(51705219, 51905227) supported by the National Natural Science Foundation of ChinaProject(BK20200915) supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(19KJB460013) supported by the General University Science Research Project of Jiangsu Province,China。
文摘In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and mechanical properties of the joint were studied. The pros and cons of the joint were identified and evaluated by measuring the tensile shear strength, microhardness and microstructure observation. The formation mechanism of various phases at the Mg/steel interface was analyzed. The results indicated that the galvanized layer could promote the metallurgical bonding between magnesium alloy and steel by improving the diffusion ability of molten magnesium alloy at the steel interface and reacting with Mg, so as to enhance the strength of the joint. A continuous dense layered eutectic structure(α-Mg+MgZn) was formed at the interface of the joint, while MgZn_(2)and MgZn phase was formed at the weld edge zone and heat affective zone(HAZ), whereas no reaction layer was generated between the uncoated steel and magnesium alloy. A sound joint could be obtained at 2.5 kW, and the corresponding tensile shear strength reached the maximum value of 42.9 N/mm. The strength was slightly reduced at 2.6 kW due to the existence of microcracks in the eutectic reaction layer.
文摘An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 °C(below Ac1 temperature of 710 °C). The spheroidization ratio of cementite and the average size of particles increase with increasing the cyclic number of heat treatment. After5-cycle heat treatment, the spheroidization ratio of cementite is 100%, and the average size of the cementite particles is about0.53 μm. After cyclic heat treatment, the hardness, ultimate tensile strength and yield strength of the experimental steel gradually decrease with increasing cyclic number of heat treatment. The elongation of the as-received specimens is about 7.4%, the elongation of the 1-cycle specimen is 14.3%, and the elongation of 5-cycle specimen reaches a peak value of 22.5%, thereafter marginally decreases to 18.3% after 6-cycle heat treatment. Accordingly, the fractured surface initially exhibits the regions of wavy lamellar fracture. By increasing the cyclic number of heat treatment cycles, the regions of dimples consume the entire fractured surface gradually. Some large dimples can be found in the fracture surface of the specimen subjected to six heat treatment cycles.
文摘This paper reports the effects of post weld heat treatments, namely artificial ageing and solution treatment followed by artificial ageing, on microstructure and mechanical properties of 12 mm thick friction stir welded joints of precipitation hardenable high strength armour grade AA7075-T651 aluminium alloy. The tensile properties, such as yield strength, tensile strength, elongation and notch tensile strength, are evaluated and correlated with the microhardness and microstructural features. The scanning electron microscope is used to characterie the fracture surfaces. The solution treatment followed by ageing heat treatment cycle is found to be marginally beneficial in improving the tensile properties of friction stir welds of AA7075-T651 aluminium alloy.
文摘In this study,a mathematical model was developed to optimize the heat treatment process for maximum tensile strength and ductility of aluminum(8011) silicon carbide particulate composites.The process parameters are solutionizing time,aging temperature,and aging time.The experiments were performed on an universal testing machine according to centre rotatable design matrix.A mathematical model was developed with the main and interactive effects of the parameters considered.The analysis of variance technique was used to check the adequacy of the developed model.The optimum parameters were obtained for maximum tensile strength.Fractographic examination shows the cracks and dimples on the fractured surfaces of heat-treated specimen.
文摘Mechanical properties and tribological behavior of a novel cast heat resisting copper based alloy are investigated. The corresponding properties of a commercial aluminum bronze C95500 (ASTM B30) are compared with the alloy. The results show that the alloy possesses better mechanical properties and tribological behaviors than that of C95500 at elevated temperature. The tensile strength, elongation and hardness at 500℃ are 470MPa, 2.5% and HB220, respectively. The wear rate of the developed alloy at ambient and elevated temperature is about one sixth and one fortieth of that of C95500, respectively. The alloy is very suitable for ma nufacturing heat resisting and wear resisting parts. Major strengthening mechanisms for the alloy are solution strengthening and the second phase strengthening.
基金International Science&Technology Cooperation Program of China(2011DFA32550)Ministry of Science and Technology of China(2012BAD12B08)
文摘The effects of heat treatment(heating temperature and pH) on the structures and emulsifying properties of caseins were systematically studied by spectroscopy.Heat treatment from 60to 100℃resulted in an increase in their fluorescence intensity,hydrodynamic diameter,turbidity and emulsifying activity index,but decreased the size polydispersity of caseins.In the pH range of 5.5to 7.0,the fluorescence intensity,hydrodynamic diameter,turbidity and emulsifying properties decreased with increased heating pH,but the size polydispersity of caseins increased with increased pH.The relationship between the surface fluorescence intensity and emulsifying activity was also investigated,revealing a correlation coefficient of 0.90.These results suggested that heat treatment could be used to modify the structures and emulsifying properties of caseins by appropriately selecting heating conditions.
基金Project(2005CB623706) supported by the National Basic Research Program of China
文摘The microstructures and mechanical properties of Al-6Zn-2Mg-1.5Cu-0.4Er alloy under different treatment conditions were investigated by transmission electron microscopy （TEM） observation, and tensile properties and hardness test, respectively. The relationship between mechanical properties and microstructures of the alloys was discussed. With trace Er addition to A1-Zn-Mg-Cu alloy, Er and Al interact to form Al3Er phase, which is coherent with a（A1） matrix. The results show that Al-Zn-Mg-Cu alloy after retrogression and re-ageing （RRA） heat treatment exhibits higher tensile strength, ductility and conductivity.
文摘The effects of rapid heating cyclic heat treatment on mechanical properties of a TiAl based alloy (Ti 33Al 3Cr) were studied by means of an induction heating machine. The results show that: 1) fine fully lamellar microstructure with colony size of about 50 μm and lamellar spacing of about 0.12 μm can be obtained; 2) the compression mechanical properties can be improved to a large extent and the best comprehensive compression mechanical properties can reach the yield stress 745 MPa, the large flow stress 1 672 MPa and the compression ratio 19.4%; and 3) the compression fracture at room temperature after induction heat treatment and aging is still typical cleavage fracture.
基金Project(51771051)supported by the National Natural Science Foundation of ChinaProject(2021-MS-102)supported by the Natural Science Foundation of Liaoning Province,China+1 种基金Project(N2105021)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(230032)supported by the National Training Program of Innovation and Entrepreneurship for Undergraduates,China。
文摘Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many methods to decrease the residual stress to prevent the structures from being broken and improve the mechanical properties.In this study,residual stress and mechanical properties of LAMed structures are analyzed,and the advanced measuring method,laser ultrasonic technique,is used to detect the residual stresses accumulated in the samples in time.The results show that when the solution temperature is less than T_(β)(992℃),the residual stress increases gradually with the increase of solution temperature,and when the temperature is more than T_(β)(992℃),Widmanstätten structure will significantly reduce the residual stress;the mechanical properties of the specimen decrease with the increase of the solution temperature,and the different cooling methods do not have much effect on the elastic properties of the specimen.Considering the residual stress and mechanical properties,the HT1 system used in this paper is the best.This study is of great significance for the reasonable suppression of residual stress and the regulation of mechanical properties of TC4 titanium alloy fabricated by laser additive manufacturing.
