[Objective]The aim was to study the effects of sunflower artificial aging on seed vigor and physiological characteristics.[Method] The varieties of seed germination capacity,vigor of germination,germination index,vigo...[Objective]The aim was to study the effects of sunflower artificial aging on seed vigor and physiological characteristics.[Method] The varieties of seed germination capacity,vigor of germination,germination index,vigor index,peroxidase（POD） activity,superoxide dismutase（SOD） activity and malondialdehyde（MDA） content for four sunflower germplasms such as＇SunM20＇,＇Deep Purple Minle＇,＇Da San Kui Hua 4＇and＇Ji Kui 24＇were studied under high temperature and high humidity conditions（100% RH,45 ℃） for different days（0 d,2 d,4 d,6 d,8 d,10 d）.[Result]The result showed that the germination capacity,vigor of germination,germination index,vigor index,POD activity,SOD activity declined gradually with the increase of seed aging days,whereas MDA content enhanced by degrees;The diggerences of resistance to artifical aging existed among the four accessions,＇SunM20＇was the most resistant one,and exhibited the strongest seed vigor,highest activities of two protective enzyme（POD,SOD） and lowest content of MDA at the uniform condition,moreover,the seed vigor and protective enzyme activities of＇SunM20＇changed slowest among the four materials during the aging process.[Conclusion]The distinct reduction of POD,SOD activities maybe the main reasons for the decrease of sunflower seed vigor at the artificial aging,and the gradual accumulation of a few MDA accelerated seeds aging.展开更多
In order to achieve good mechanical properties of Al-Cu alloys such as high strength and good toughness,precipitation hardening and artificial aging treatment were applied.As defined by the T6 heat treatment,the stand...In order to achieve good mechanical properties of Al-Cu alloys such as high strength and good toughness,precipitation hardening and artificial aging treatment were applied.As defined by the T6 heat treatment,the standard artificial aging treatment for Al-Cu alloy followed heat treatments of solution treatment at 510-530 ℃ for 2 h,quenching in water at 60 ℃ and then artificial aging at 160-190 ℃ for 2-8 h.The effects of solution treatment and artificial aging on the microstructure and mechanical properties of Al-Cu alloy were studied by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）,transmission electron microscopy（TEM） and tensile test.The results of solution treatment indicate that the mechanical properties of Al-Cu alloy increase and then decrease with the increase of solution temperature.This is because the residual phases dissolve gradually into the matrix,and the fraction of the precipitation and the size of the re-crystallized grain increased.Compared to the solution temperature,the solution holding time has less effect on the microstructure and the mechanical properties of Al-Cu alloy.The artificial aging treatments were conducted at 160-180 ℃ for 2-8 h.The results show that the ultimate tensile strength can be obtained at 180 ℃ for 8 h.Ultimate tensile strength increased with increasing time or temperature.Yield strength was found as the same as the ultimate tensile strength result.展开更多
The effect of pre-deformation followed by or together with artificial aging on the mechanical properties as strength and ductility of an AA6060 aluminium alloy was studied. AA6060 was initially cast, homogenized and e...The effect of pre-deformation followed by or together with artificial aging on the mechanical properties as strength and ductility of an AA6060 aluminium alloy was studied. AA6060 was initially cast, homogenized and extruded according to standard industrial practice. The extruded material was then subjected to a solution heat treatment and subsequently artificial aging after （sequential mode） and during （simultaneous mode） various combinations of deformation （0-10%） and heat treatments. The aging behaviour and mechanical properties were characterized in terms of Vickers hardness and tensile testing. It is found that precipitation kinetics and associated mechanical response, in terms of hardness and tensile properties are strongly affected by pre-deformations. In terms of aging behaviour, kinetics is accelerated and the peak strength generally increases. Comparing sequential mode and simultaneous mode, the latter seems to give overall better mechanical properties and after considerably shorter aging times. The results of the two modes of pre-deformation are compared and discussed in view of differences in processing conditions and microstructure characteristics.展开更多
The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry(DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were se...The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry(DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155, 165 and 180 °C, with heat treatment time from 40 min to 32 h. DSC analysis results show that cluster formation begins below room temperature(at around-10 °C). Since cluster formation influences the subsequent precipitation of the main strengthening β'' phase, it can be inferred that a delay between solutionizing and artificial aging has a detrimental effect on the mechanical properties of the alloy. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum values when β'' phase is completely developed during the artificial aging. This happens after 16 h for samples aged at 155 °C, after 6 h for samples aged at 165 °C and after 4 h for samples aged at 180 °C. A subsequent decrease of the mechanical properties, observed only in the sample aged at the highest temperature, with increasing aging time can be associated with the transformation of the coherent β'' phase into the semi-coherent β' phase. Finally, the activation energy associated with the precipitation of β'' phase was calculated to be 57.2 k J/mol.展开更多
The seeds of maize （Zea mays L.） variety Zhengdan 958 were used to study the change of ultraweak luminescence （UWL） intensity and its relationship with seed vigor, relative electric conductivity and ATP content du...The seeds of maize （Zea mays L.） variety Zhengdan 958 were used to study the change of ultraweak luminescence （UWL） intensity and its relationship with seed vigor, relative electric conductivity and ATP content during artificial aging. The results indicated that the germination percentage, germination potential, germination index, UWL intensity and ATP content decreased gradually, while the relative electric conductivity increased with the prolongation of artificial aging. The correlation analysis showed that UWL intensity was significantly positively correlated with ger- mination percentage, germination potential, germination index and ATP content, while significantly negatively correlated with relative electric conductivity. It was concluded that UWL was closely related to the energy level symbolized by ATP content, and as a fast nondestructive physical indicator with better sensitivity, it could be applied into the study of seed vigor nondestructive testing.展开更多
As shown by the changes in physiological characteristics and seed vigor of three Medicago ruthenica samples during artificial aging process, the germination potential, germination rate, germination index, vigor index ...As shown by the changes in physiological characteristics and seed vigor of three Medicago ruthenica samples during artificial aging process, the germination potential, germination rate, germination index, vigor index and simple vigor index declined with the extension of aging time on the whole. After artificial aging for 6 min, the vigor was higher than that of the control. The conductivity, malondialdehyde content and soluble polysaccharide content of seed leachate increased with the aging time and negatively correlated （ P 〈 0.05） with the seed vigor indicators. The physiological indicators were very significantly correlated （P 〈 0.01 ） with the vigor indicators in the Medicago ruthenica sample from Dorbod Qi, UIanqab City（China）.展开更多
In order to ascertain the effect of artificial aging on ultraweak lumines- cence （UWL） and the correlation between UWL and seed vigor, and explore a new way of seed vigor non-destructive testing, seeds of wheat vari...In order to ascertain the effect of artificial aging on ultraweak lumines- cence （UWL） and the correlation between UWL and seed vigor, and explore a new way of seed vigor non-destructive testing, seeds of wheat variety ‘Jimai 22＇ were used to study the change of UWL intensity and its relationship to seed vigor and ATP content during artificial aging. The results showed that with the extension of artificial aging time, the germination percentage, germination potential, germination index, UWL intensity and ATP content decreased gradually; after artificial aging for 48 h, they were reduced by 19.19%, 34.34%, 38.78%, 27.77% and 13.84%, re- spectively, compared with CK. Correlation analysis indicated that the UWL intensity was significantly positive correlated with germination percentage, germination poten- tial, germination index and ATP content. It was concluded that UWL as a fast, non- destructive and sensitive detection method could be applied in the study of seed vigor non-destructive testing.展开更多
The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling(-100 ° C,-190 ℃) or hot rolling(400 ℃) and subsequent aging at 160 ℃ for different times were investigated. The dy...The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling(-100 ° C,-190 ℃) or hot rolling(400 ℃) and subsequent aging at 160 ℃ for different times were investigated. The dynamic precipitation and dislocation characterizations were examined via transmission electron microscopy and X-ray diffraction. The grain morphologies and the fracture-surface morphologies were studied via optical microscopy and scanning electron microscopy. Samples subjected to cryorolling followed by aging exhibited relatively high dislocation densities and a large number of precipitates compared with hot-rolled samples. The samples cryorolled at-190 ℃ and then aged for 15 h presented the highest ultimate tensile strength(586 MPa), while the alloy processed via hot rolling followed by 10 h aging exhibited the highest uniform elongation rate(11.5%). The size of precipitates increased with the aging time, which has significant effects on the interaction mechanism between dislocations and precipitates. Bowing is the main interaction method between the deformation-induced dislocations and coarsened precipitates during tensile tests, leading to the decline of the mechanical properties of the alloy during overaging. These interesting findings can provide significant insights into the development of materials possessing both excellent strength and high ductility.展开更多
The effects of yttrium and artificial aging on AA2024 alloy were investigated.The developed samples were further subjected to artificial aging at 190℃for 1-10 h with an interval of 1 h.The metallurgical characterizat...The effects of yttrium and artificial aging on AA2024 alloy were investigated.The developed samples were further subjected to artificial aging at 190℃for 1-10 h with an interval of 1 h.The metallurgical characterization was done by scanning electron microscope and X-ray diffraction.The mechanical characterization like hardness and tensile strength of the samples was done using computerized Vickers hardness testing machine and universal testing machine.The microstructures revealed that addition of yttrium refined theα(Al)matrix and led to the formation of Al-Cu-Y intermetallic in the shape of Chinese script which strengthened the samples.Compared to the base metal,samples with yttrium addition showed better mechanical properties.The sample reinforced with 0.3 wt.%yttrium showed the highest mechanical properties with the hardness of 66 HV,UTS of 223 MPa,YS of 180 MPa,and elongation of 20.9%.The artificially aged samples showed that the peak hardening of all the samples took place within 5 h of aging at 190℃with Al2 Cu precipitation.Aging changed the intermetallic from Chinese script to the fibrous form.The optimum amount of yttrium addition to AA2024 was found to be 0.3 wt.%.展开更多
This research studied the mechanism of the corrosion resistance enhancement of artificially aged 7075 aluminium alloy using advanced Cs-corrected scanning transmission electron microscopy(STEM).The corrosion behaviors...This research studied the mechanism of the corrosion resistance enhancement of artificially aged 7075 aluminium alloy using advanced Cs-corrected scanning transmission electron microscopy(STEM).The corrosion behaviors of artificially aged 7075 aluminium alloys in a 3.5 wt.%NaCl solution were investigated by impedance spectra,equivalent circuit analyses,polarization measurements and immersion tests.The results show that a longer aging treatment leads to better corrosion resistance,which can be attributed to the following microstructural features,as revealed by STEM.The Cu segregation at grain boundaries under over-aged conditions helps retard intergranular corrosion.The Mg(Zn,Cu)_(2) precipitates formed on the surfaces of Al_(18)Mg_(3)(Cr,Mn)_(2) dispersoids effectively insulate the dispersoids as cathodes in corrosion,from the Al matrix.This study demonstrates a potential strategy to design corrosion-resistant alloys achieved by proper alloying and subsequent aging.展开更多
Yellow-seeded rapeseed (Brassica napus L.) is a new kind of breeding resources with yellow color, increased oil and protein content and less unwanted crude fiber content due to the thinner and transparent testa compar...Yellow-seeded rapeseed (Brassica napus L.) is a new kind of breeding resources with yellow color, increased oil and protein content and less unwanted crude fiber content due to the thinner and transparent testa compared with traditional black or brown-seeded rapeseed. To analyze the longevity of the yellow-seeded rapeseed during storage, the physiological differences between the yellow and black-seeded near-isogenic lines were studied by artificial ageing method. The testa rate, anthocyanin content and melanin content of yellow-seeded rapeseeds decreased by 20.1, 25.2, and 80.4% respectively than black-seeded rapeseed. During artificial ageing, the yellow-seeded rapeseed showed significantly different effect of ageing compared with the black-seeded, as demonstrated by faster deterioration with lower germination percentage, seed vigour index, reducing sugar and soluble protein contents than the black-seeded, as well as a drastic increase in electrical conductivity, malnodialdehyde (MDA) content and a rapid decrease in activities of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). The results suggested that the transparent testa of the yellow-seeded rapeseed lost some abilities to protect the embryo against adverse environmental conditions and thus led to a poor storability.展开更多
Al4Cu2Ni2Mg alloy is an age-hardenable aluminum alloy. The effect of different solution and aging heat treatment conditions on the microstructure, hardness and wear resistance of the alloy was studied. The cast specim...Al4Cu2Ni2Mg alloy is an age-hardenable aluminum alloy. The effect of different solution and aging heat treatment conditions on the microstructure, hardness and wear resistance of the alloy was studied. The cast specimens were solution treated and then artificially aged. Optical microscopy and scanning electron microscopy were used to investigate the microstructures of the specimens. The hardness and wear tests were applied to understanding the effects of heat treatment. After aging for 8 h, the hardness of the alloy increases from HV 10 96.5 to 151.1. Aging treatment for a longer duration causes a drop in the hardness because of over aging. Increasing the hardness of the alloy increases the wear resistance. As a result of all tests, solution heat treatment at 540 °C for 8 h and aging at 190 °C for 8 h were chosen for optimum heat treatment conditions for this alloy.展开更多
The assessment of the real in-service-time(RIST)and the equivalent in-service-time(EIST)of double base rocket propellants(DBRPs)is of utmost importance for the safe storage and use of weapon systems as well as the eff...The assessment of the real in-service-time(RIST)and the equivalent in-service-time(EIST)of double base rocket propellants(DBRPs)is of utmost importance for the safe storage and use of weapon systems as well as the efficiency of the accelerated aging plans.In this work,four DBRPs with similar chemical composition and different natural aging have been artificially aged at T?338.65 K for 4 months with sampling every 30 days.The unaged and artificially aged samples have been investigated by vacuum stability test(VST)at five isothermal temperatures(T?333.15 K,343.15 K,353.15 K,363.15 K,and 373.15 K).The volume of the evolved gases in VST was found to decrease with natural/artificial aging.Furthermore,the VST data were treated and subjected to principal component analysis(PCA).The results showed excellent discrimination of the DBRP samples according to their stability thermal properties.Most of the variance was described by the first principal component(PC1)whose scores were linearly correlated with the natural aging durations when PCA is applied on VST data obtained at T?363.15 K.In light of the obtained results,a new experimental way for the estimation of the real/equivalent IST was proposed,which takes into account the impact of the natural aging of the sample.The approach predicts successfully the RIST of two similar DBRPs with a relative deviation of less than 2%.At the specific heating temperature T?338.65 K,the developed model provides more conceivable EIST values,with asymptotic behavior against artificial aging duration evolution,thus overcoming some shortcomings of the common generalized van’t Hoff formula(GvH).展开更多
Many organisms have dormant stages with an extension of their life span to increase longevity, and deeper dormancy is usually related to greater longevity. In cereal crops, seed dormancy is significantly associated wi...Many organisms have dormant stages with an extension of their life span to increase longevity, and deeper dormancy is usually related to greater longevity. In cereal crops, seed dormancy is significantly associated with pre-harvest sprouting tolerance during seed development, as seed longevity is a valuable trait for seed banks and providing reliable crop seeds to farmers. In this study, we evaluated both seed dormancy and longevity in bread wheat based on germination and artificial aging tests. According to phenotypic clustering analysis, relative germination rate/potential and relative seedling vigor index were more effective to indicate seed longevity than relative electrical conductivity in wheat, while all the four investigated phenotypes of relative germination potential, relative germination rate, germination index and degree of seed dormancy fit well as a reflex of wheat seed dormancy. In the correlation analysis, the germination level of newly harvested grain negatively reflected its degree of seed dormancy, while the germination ability of grain after artificial aging reflected its seed longevity. However, in contrast to the current opinion in plant, seed dormancy was significantly negatively correlated to seed longevity in our study, and it was not an accidental phenomenon, for that the majority of accessions with high degree of seed dormancy had short seed longevity. To our knowledge, this is the first to report the negative association between seed dormancy and longevity in cereal crops. It would lead to further concerns about how to breed wheat with both prolonged seed longevity and deep dormancy to avoid pre-harvest sprouting.展开更多
Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy （TEM）, and differential scanning calorimetry （DSC）. The retrogression treatments...Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy （TEM）, and differential scanning calorimetry （DSC）. The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ＇ precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ＇ and θ＇ phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240°C causes the dissolution and coarsening of δ＇ and θ＇ precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T1, T2, δ＇, and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis.展开更多
The superplasticity of high strength superhard A1 alloy LC4 was improved to a great extent by modified thermomechanical treatment.Its maximum elongation may be up to 2100% un- der deformation at initial strain rate of...The superplasticity of high strength superhard A1 alloy LC4 was improved to a great extent by modified thermomechanical treatment.Its maximum elongation may be up to 2100% un- der deformation at initial strain rate of 8.33×10^(-4) S^(-1) at 510℃.Observations of the microstructure changes revealed that with the increase of the deformation,the grain grows and the alloy exhibits strain hardening.The excellent elongation of the alloy seems due to the in- crease of grain stability under deformation.展开更多
Aluminum casting alloys with silicon as the major alloying elements are the most important commercial casting alloys because of their superior casting characteristics and as it is well known that （AI-Si） alloys, whi...Aluminum casting alloys with silicon as the major alloying elements are the most important commercial casting alloys because of their superior casting characteristics and as it is well known that （AI-Si） alloys, which are widely applied in the aerospace and automotive industries. This research aims to study the effect of Ag element addition on hypo and hypereutectic （AI-Si） alloy. In this research microhardness and corrosion resistance was calculated by Vickers device and electrochemical method respectively to base alloys before and after the addition of Ag, and also the effect of artificial ageing time was studied at temperature （160 ℃） after the addition of Ag. The results shown that the addition of Ag led to increase microhardness, decrease corrosion resistance and the best time of artificial ageing was 10 hrs.展开更多
Five-layered Al/Al-Cu functionally graded material （FGM） was prepared by powder metallurgy technology, and the subsequent heat treatment was carried out for the graded material. The microstructures and distribution ...Five-layered Al/Al-Cu functionally graded material （FGM） was prepared by powder metallurgy technology, and the subsequent heat treatment was carried out for the graded material. The microstructures and distribution of Cu element under pressure sintering （F）, solution treatment （T4） and artificial aging treatment （T6） were investigated, and the Vickers hardness and flexural properties of different states were tested. The results showed that sintered compact with dense structure and compositional continuous change was obtained. The second-phase CuAl 2 was dispersively distributed along grain boundary of Al matrix. After solution treatment at 503 C for 3 h, CuAl 2 phase obviously decreased and dissolved into the Al matrix, and the flexural strength was thereupon enhanced to 228.5 MPa. With the subsequent aging treatment at 150 C for 15 h, the majority of flake shaped precipitates θ phases were uniformly distributed in the matrix. And the distribution of Cu element became gradual continuous compared to sintered compact. Meanwhile, the flexural strength increased further, which accompanied with the decline of plasticity.展开更多
The paper presented accelerated ageing test results of a durability study on ortho-phthalic anhydride-type unsaturated polyester resin （191#） and its glass-fiber reinforcement polyester composites （GFRPC）. The sam...The paper presented accelerated ageing test results of a durability study on ortho-phthalic anhydride-type unsaturated polyester resin （191#） and its glass-fiber reinforcement polyester composites （GFRPC）. The samples were exposed in an artificial xenon arc lamp ageing cell or a thermo-oxidative ageing cell. Morphology and gloss of the specimens were investigated by using a microscope and a gloss-meter, respectively. The tensile strength, bending strength and inter-laminar shear strength （ILSS） of GFRPC were tested before and after exposure, and were considered to evaluate the durability performance of this material. The polyester resin was analyzed by fourier transform infrared （FT-IR） spectroscopy. The results showed that the glossiness of the specimens got worse and some cracks appeared on their surface during the course of ageing, the tensile strength and bending strengths of the specimens first increased and then decreased. The ILSS of the composites decreased after they were aged in the xenon arc lamp cell, but increased while they were aged in the thermo-oxidative cell. The changes of these trends become more obvious during ageing in the xenon arc lamp cell, so the main influencing factor leading to the failure of this material is UV irradiation.展开更多
文摘[Objective]The aim was to study the effects of sunflower artificial aging on seed vigor and physiological characteristics.[Method] The varieties of seed germination capacity,vigor of germination,germination index,vigor index,peroxidase（POD） activity,superoxide dismutase（SOD） activity and malondialdehyde（MDA） content for four sunflower germplasms such as＇SunM20＇,＇Deep Purple Minle＇,＇Da San Kui Hua 4＇and＇Ji Kui 24＇were studied under high temperature and high humidity conditions（100% RH,45 ℃） for different days（0 d,2 d,4 d,6 d,8 d,10 d）.[Result]The result showed that the germination capacity,vigor of germination,germination index,vigor index,POD activity,SOD activity declined gradually with the increase of seed aging days,whereas MDA content enhanced by degrees;The diggerences of resistance to artifical aging existed among the four accessions,＇SunM20＇was the most resistant one,and exhibited the strongest seed vigor,highest activities of two protective enzyme（POD,SOD） and lowest content of MDA at the uniform condition,moreover,the seed vigor and protective enzyme activities of＇SunM20＇changed slowest among the four materials during the aging process.[Conclusion]The distinct reduction of POD,SOD activities maybe the main reasons for the decrease of sunflower seed vigor at the artificial aging,and the gradual accumulation of a few MDA accelerated seeds aging.
文摘In order to achieve good mechanical properties of Al-Cu alloys such as high strength and good toughness,precipitation hardening and artificial aging treatment were applied.As defined by the T6 heat treatment,the standard artificial aging treatment for Al-Cu alloy followed heat treatments of solution treatment at 510-530 ℃ for 2 h,quenching in water at 60 ℃ and then artificial aging at 160-190 ℃ for 2-8 h.The effects of solution treatment and artificial aging on the microstructure and mechanical properties of Al-Cu alloy were studied by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）,transmission electron microscopy（TEM） and tensile test.The results of solution treatment indicate that the mechanical properties of Al-Cu alloy increase and then decrease with the increase of solution temperature.This is because the residual phases dissolve gradually into the matrix,and the fraction of the precipitation and the size of the re-crystallized grain increased.Compared to the solution temperature,the solution holding time has less effect on the microstructure and the mechanical properties of Al-Cu alloy.The artificial aging treatments were conducted at 160-180 ℃ for 2-8 h.The results show that the ultimate tensile strength can be obtained at 180 ℃ for 8 h.Ultimate tensile strength increased with increasing time or temperature.Yield strength was found as the same as the ultimate tensile strength result.
基金Project (176816/I40) supported by the Research Council of Norway
文摘The effect of pre-deformation followed by or together with artificial aging on the mechanical properties as strength and ductility of an AA6060 aluminium alloy was studied. AA6060 was initially cast, homogenized and extruded according to standard industrial practice. The extruded material was then subjected to a solution heat treatment and subsequently artificial aging after （sequential mode） and during （simultaneous mode） various combinations of deformation （0-10%） and heat treatments. The aging behaviour and mechanical properties were characterized in terms of Vickers hardness and tensile testing. It is found that precipitation kinetics and associated mechanical response, in terms of hardness and tensile properties are strongly affected by pre-deformations. In terms of aging behaviour, kinetics is accelerated and the peak strength generally increases. Comparing sequential mode and simultaneous mode, the latter seems to give overall better mechanical properties and after considerably shorter aging times. The results of the two modes of pre-deformation are compared and discussed in view of differences in processing conditions and microstructure characteristics.
基金funded by Regione Lombardia-MIUR (Research Program "2 MILLIMETRI" ID 30152773)
文摘The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry(DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155, 165 and 180 °C, with heat treatment time from 40 min to 32 h. DSC analysis results show that cluster formation begins below room temperature(at around-10 °C). Since cluster formation influences the subsequent precipitation of the main strengthening β'' phase, it can be inferred that a delay between solutionizing and artificial aging has a detrimental effect on the mechanical properties of the alloy. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum values when β'' phase is completely developed during the artificial aging. This happens after 16 h for samples aged at 155 °C, after 6 h for samples aged at 165 °C and after 4 h for samples aged at 180 °C. A subsequent decrease of the mechanical properties, observed only in the sample aged at the highest temperature, with increasing aging time can be associated with the transformation of the coherent β'' phase into the semi-coherent β' phase. Finally, the activation energy associated with the precipitation of β'' phase was calculated to be 57.2 k J/mol.
基金Supported by Self-Innovation Program of Jinan Science&Technology Bureau and Jinan Colleges and Universities(201202062)~~
文摘The seeds of maize （Zea mays L.） variety Zhengdan 958 were used to study the change of ultraweak luminescence （UWL） intensity and its relationship with seed vigor, relative electric conductivity and ATP content during artificial aging. The results indicated that the germination percentage, germination potential, germination index, UWL intensity and ATP content decreased gradually, while the relative electric conductivity increased with the prolongation of artificial aging. The correlation analysis showed that UWL intensity was significantly positively correlated with ger- mination percentage, germination potential, germination index and ATP content, while significantly negatively correlated with relative electric conductivity. It was concluded that UWL was closely related to the energy level symbolized by ATP content, and as a fast nondestructive physical indicator with better sensitivity, it could be applied into the study of seed vigor nondestructive testing.
基金funded by National Key Technology R & DProgram during the 11th Five-Year Plan Period (2008BADB3B01)Crops Germplasm Resource Conservation Project of Ministry of Agriculture (NB08-2130135-43)
文摘As shown by the changes in physiological characteristics and seed vigor of three Medicago ruthenica samples during artificial aging process, the germination potential, germination rate, germination index, vigor index and simple vigor index declined with the extension of aging time on the whole. After artificial aging for 6 min, the vigor was higher than that of the control. The conductivity, malondialdehyde content and soluble polysaccharide content of seed leachate increased with the aging time and negatively correlated （ P 〈 0.05） with the seed vigor indicators. The physiological indicators were very significantly correlated （P 〈 0.01 ） with the vigor indicators in the Medicago ruthenica sample from Dorbod Qi, UIanqab City（China）.
基金Supported by the Independent Innovation Program for Universities and Institutions of Jinan,Jinan Science&Technology Bureau (201202062)~~
文摘In order to ascertain the effect of artificial aging on ultraweak lumines- cence （UWL） and the correlation between UWL and seed vigor, and explore a new way of seed vigor non-destructive testing, seeds of wheat variety ‘Jimai 22＇ were used to study the change of UWL intensity and its relationship to seed vigor and ATP content during artificial aging. The results showed that with the extension of artificial aging time, the germination percentage, germination potential, germination index, UWL intensity and ATP content decreased gradually; after artificial aging for 48 h, they were reduced by 19.19%, 34.34%, 38.78%, 27.77% and 13.84%, re- spectively, compared with CK. Correlation analysis indicated that the UWL intensity was significantly positive correlated with germination percentage, germination poten- tial, germination index and ATP content. It was concluded that UWL as a fast, non- destructive and sensitive detection method could be applied in the study of seed vigor non-destructive testing.
基金Project(2019YFB2006500) supported by the National Key Research and Development Program,ChinaProject(51674303) supported by the National Natural Science Foundation of China+3 种基金Project(2020GK2032) supported by Hunan High-tech Industry Science and Technology Innovation Leading Plan,ChinaProject (2018RS3015) supported by the Huxiang High-level Talent Gathering Project of Hunan Province,ChinaProject(2017YFA0700700) supported by the Ministry of Science&Technology of ChinaProject(2019CX006) supported by Innovation Driven Program of Central South University,China。
文摘The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling(-100 ° C,-190 ℃) or hot rolling(400 ℃) and subsequent aging at 160 ℃ for different times were investigated. The dynamic precipitation and dislocation characterizations were examined via transmission electron microscopy and X-ray diffraction. The grain morphologies and the fracture-surface morphologies were studied via optical microscopy and scanning electron microscopy. Samples subjected to cryorolling followed by aging exhibited relatively high dislocation densities and a large number of precipitates compared with hot-rolled samples. The samples cryorolled at-190 ℃ and then aged for 15 h presented the highest ultimate tensile strength(586 MPa), while the alloy processed via hot rolling followed by 10 h aging exhibited the highest uniform elongation rate(11.5%). The size of precipitates increased with the aging time, which has significant effects on the interaction mechanism between dislocations and precipitates. Bowing is the main interaction method between the deformation-induced dislocations and coarsened precipitates during tensile tests, leading to the decline of the mechanical properties of the alloy during overaging. These interesting findings can provide significant insights into the development of materials possessing both excellent strength and high ductility.
文摘The effects of yttrium and artificial aging on AA2024 alloy were investigated.The developed samples were further subjected to artificial aging at 190℃for 1-10 h with an interval of 1 h.The metallurgical characterization was done by scanning electron microscope and X-ray diffraction.The mechanical characterization like hardness and tensile strength of the samples was done using computerized Vickers hardness testing machine and universal testing machine.The microstructures revealed that addition of yttrium refined theα(Al)matrix and led to the formation of Al-Cu-Y intermetallic in the shape of Chinese script which strengthened the samples.Compared to the base metal,samples with yttrium addition showed better mechanical properties.The sample reinforced with 0.3 wt.%yttrium showed the highest mechanical properties with the hardness of 66 HV,UTS of 223 MPa,YS of 180 MPa,and elongation of 20.9%.The artificially aged samples showed that the peak hardening of all the samples took place within 5 h of aging at 190℃with Al2 Cu precipitation.Aging changed the intermetallic from Chinese script to the fibrous form.The optimum amount of yttrium addition to AA2024 was found to be 0.3 wt.%.
基金supported by the Open Fund of the State Key Laboratory of Refractories and Metallurgy,China(No.G201907)。
文摘This research studied the mechanism of the corrosion resistance enhancement of artificially aged 7075 aluminium alloy using advanced Cs-corrected scanning transmission electron microscopy(STEM).The corrosion behaviors of artificially aged 7075 aluminium alloys in a 3.5 wt.%NaCl solution were investigated by impedance spectra,equivalent circuit analyses,polarization measurements and immersion tests.The results show that a longer aging treatment leads to better corrosion resistance,which can be attributed to the following microstructural features,as revealed by STEM.The Cu segregation at grain boundaries under over-aged conditions helps retard intergranular corrosion.The Mg(Zn,Cu)_(2) precipitates formed on the surfaces of Al_(18)Mg_(3)(Cr,Mn)_(2) dispersoids effectively insulate the dispersoids as cathodes in corrosion,from the Al matrix.This study demonstrates a potential strategy to design corrosion-resistant alloys achieved by proper alloying and subsequent aging.
基金The authors thank 863 Project of the Ministry of Sci-ence and Technology of P.R.China(AA2003207150)948 Project of the Ministry of Agricutureof P.R.China(2003-Q04)for financial support.
文摘Yellow-seeded rapeseed (Brassica napus L.) is a new kind of breeding resources with yellow color, increased oil and protein content and less unwanted crude fiber content due to the thinner and transparent testa compared with traditional black or brown-seeded rapeseed. To analyze the longevity of the yellow-seeded rapeseed during storage, the physiological differences between the yellow and black-seeded near-isogenic lines were studied by artificial ageing method. The testa rate, anthocyanin content and melanin content of yellow-seeded rapeseeds decreased by 20.1, 25.2, and 80.4% respectively than black-seeded rapeseed. During artificial ageing, the yellow-seeded rapeseed showed significantly different effect of ageing compared with the black-seeded, as demonstrated by faster deterioration with lower germination percentage, seed vigour index, reducing sugar and soluble protein contents than the black-seeded, as well as a drastic increase in electrical conductivity, malnodialdehyde (MDA) content and a rapid decrease in activities of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). The results suggested that the transparent testa of the yellow-seeded rapeseed lost some abilities to protect the embryo against adverse environmental conditions and thus led to a poor storability.
文摘Al4Cu2Ni2Mg alloy is an age-hardenable aluminum alloy. The effect of different solution and aging heat treatment conditions on the microstructure, hardness and wear resistance of the alloy was studied. The cast specimens were solution treated and then artificially aged. Optical microscopy and scanning electron microscopy were used to investigate the microstructures of the specimens. The hardness and wear tests were applied to understanding the effects of heat treatment. After aging for 8 h, the hardness of the alloy increases from HV 10 96.5 to 151.1. Aging treatment for a longer duration causes a drop in the hardness because of over aging. Increasing the hardness of the alloy increases the wear resistance. As a result of all tests, solution heat treatment at 540 °C for 8 h and aging at 190 °C for 8 h were chosen for optimum heat treatment conditions for this alloy.
文摘The assessment of the real in-service-time(RIST)and the equivalent in-service-time(EIST)of double base rocket propellants(DBRPs)is of utmost importance for the safe storage and use of weapon systems as well as the efficiency of the accelerated aging plans.In this work,four DBRPs with similar chemical composition and different natural aging have been artificially aged at T?338.65 K for 4 months with sampling every 30 days.The unaged and artificially aged samples have been investigated by vacuum stability test(VST)at five isothermal temperatures(T?333.15 K,343.15 K,353.15 K,363.15 K,and 373.15 K).The volume of the evolved gases in VST was found to decrease with natural/artificial aging.Furthermore,the VST data were treated and subjected to principal component analysis(PCA).The results showed excellent discrimination of the DBRP samples according to their stability thermal properties.Most of the variance was described by the first principal component(PC1)whose scores were linearly correlated with the natural aging durations when PCA is applied on VST data obtained at T?363.15 K.In light of the obtained results,a new experimental way for the estimation of the real/equivalent IST was proposed,which takes into account the impact of the natural aging of the sample.The approach predicts successfully the RIST of two similar DBRPs with a relative deviation of less than 2%.At the specific heating temperature T?338.65 K,the developed model provides more conceivable EIST values,with asymptotic behavior against artificial aging duration evolution,thus overcoming some shortcomings of the common generalized van’t Hoff formula(GvH).
文摘Many organisms have dormant stages with an extension of their life span to increase longevity, and deeper dormancy is usually related to greater longevity. In cereal crops, seed dormancy is significantly associated with pre-harvest sprouting tolerance during seed development, as seed longevity is a valuable trait for seed banks and providing reliable crop seeds to farmers. In this study, we evaluated both seed dormancy and longevity in bread wheat based on germination and artificial aging tests. According to phenotypic clustering analysis, relative germination rate/potential and relative seedling vigor index were more effective to indicate seed longevity than relative electrical conductivity in wheat, while all the four investigated phenotypes of relative germination potential, relative germination rate, germination index and degree of seed dormancy fit well as a reflex of wheat seed dormancy. In the correlation analysis, the germination level of newly harvested grain negatively reflected its degree of seed dormancy, while the germination ability of grain after artificial aging reflected its seed longevity. However, in contrast to the current opinion in plant, seed dormancy was significantly negatively correlated to seed longevity in our study, and it was not an accidental phenomenon, for that the majority of accessions with high degree of seed dormancy had short seed longevity. To our knowledge, this is the first to report the negative association between seed dormancy and longevity in cereal crops. It would lead to further concerns about how to breed wheat with both prolonged seed longevity and deep dormancy to avoid pre-harvest sprouting.
基金supported by the Major State Basic Research Development Program of China (No.2005CB623705)
文摘Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy （TEM）, and differential scanning calorimetry （DSC）. The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ＇ precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ＇ and θ＇ phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240°C causes the dissolution and coarsening of δ＇ and θ＇ precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T1, T2, δ＇, and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis.
文摘The superplasticity of high strength superhard A1 alloy LC4 was improved to a great extent by modified thermomechanical treatment.Its maximum elongation may be up to 2100% un- der deformation at initial strain rate of 8.33×10^(-4) S^(-1) at 510℃.Observations of the microstructure changes revealed that with the increase of the deformation,the grain grows and the alloy exhibits strain hardening.The excellent elongation of the alloy seems due to the in- crease of grain stability under deformation.
文摘Aluminum casting alloys with silicon as the major alloying elements are the most important commercial casting alloys because of their superior casting characteristics and as it is well known that （AI-Si） alloys, which are widely applied in the aerospace and automotive industries. This research aims to study the effect of Ag element addition on hypo and hypereutectic （AI-Si） alloy. In this research microhardness and corrosion resistance was calculated by Vickers device and electrochemical method respectively to base alloys before and after the addition of Ag, and also the effect of artificial ageing time was studied at temperature （160 ℃） after the addition of Ag. The results shown that the addition of Ag led to increase microhardness, decrease corrosion resistance and the best time of artificial ageing was 10 hrs.
基金supported by the National Natural Science Foundation of China(No.50871025)
文摘Five-layered Al/Al-Cu functionally graded material （FGM） was prepared by powder metallurgy technology, and the subsequent heat treatment was carried out for the graded material. The microstructures and distribution of Cu element under pressure sintering （F）, solution treatment （T4） and artificial aging treatment （T6） were investigated, and the Vickers hardness and flexural properties of different states were tested. The results showed that sintered compact with dense structure and compositional continuous change was obtained. The second-phase CuAl 2 was dispersively distributed along grain boundary of Al matrix. After solution treatment at 503 C for 3 h, CuAl 2 phase obviously decreased and dissolved into the Al matrix, and the flexural strength was thereupon enhanced to 228.5 MPa. With the subsequent aging treatment at 150 C for 15 h, the majority of flake shaped precipitates θ phases were uniformly distributed in the matrix. And the distribution of Cu element became gradual continuous compared to sintered compact. Meanwhile, the flexural strength increased further, which accompanied with the decline of plasticity.
基金supported by the National Natural Science Foundation of China (No.50533060)
文摘The paper presented accelerated ageing test results of a durability study on ortho-phthalic anhydride-type unsaturated polyester resin （191#） and its glass-fiber reinforcement polyester composites （GFRPC）. The samples were exposed in an artificial xenon arc lamp ageing cell or a thermo-oxidative ageing cell. Morphology and gloss of the specimens were investigated by using a microscope and a gloss-meter, respectively. The tensile strength, bending strength and inter-laminar shear strength （ILSS） of GFRPC were tested before and after exposure, and were considered to evaluate the durability performance of this material. The polyester resin was analyzed by fourier transform infrared （FT-IR） spectroscopy. The results showed that the glossiness of the specimens got worse and some cracks appeared on their surface during the course of ageing, the tensile strength and bending strengths of the specimens first increased and then decreased. The ILSS of the composites decreased after they were aged in the xenon arc lamp cell, but increased while they were aged in the thermo-oxidative cell. The changes of these trends become more obvious during ageing in the xenon arc lamp cell, so the main influencing factor leading to the failure of this material is UV irradiation.
