Strain-controlled fatigue characteristics of peakaged and over-aged Mg_(96.47)Nd_(2.9)Zn_(0.21)magnesium alloys containing 0.42Zr,including stress response,strain resistance,hysteresis loops,strain-life and correspond...Strain-controlled fatigue characteristics of peakaged and over-aged Mg_(96.47)Nd_(2.9)Zn_(0.21)magnesium alloys containing 0.42Zr,including stress response,strain resistance,hysteresis loops,strain-life and corresponding lowcycle fatigue life prediction model,were studied.In the peak-aged state(T61:540℃×8 h+200℃×14 h),the alloy shows higher cyclic stress response,but lower ductility than the alloy in the over-aged state(T6_(2):540℃×8 h+200℃×400 h).The yield strength and ultimate tensile strength of the alloy under T6_(1)-and T6_(2)-treated conditions are close.Compared with T6_(1)-treated alloy,the steady stress amplitude occurred in T6_(2)-treated alloy is due to higher ductility and more homogenous deformation.In T6_(1)state,the fatigue cracks in the alloy first initiate along the cracked persistent slip bands and then propagate in the trans-granular mode,while in the T6_(2)state,the fatigue cracks initiate along grain boundaries and then propagate in the inter-granular mode.展开更多
By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-...By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-aging (120°C/24h + 160°C/8h + 120°C/24h), were characterized. It is found that compared with the Al-Zn-Mg-Cu alloys treated by T76 (120°C/24h + 160°C/8h), the new multi-stage aging treatment can improve the tensile strength, fracture toughness, hardness and conductivity of the alloys at the same time. This is mainly due to the pre-aging, over-aging and re-aging process of super high strength aluminum alloys. Compared with the two-stage over aging process, the formation of multi-stage multi-phase precipitation structure can improve the strength, toughness and corrosion resistance of the alloys at the same time. The polarization curve is consistent with the conclusion. Therefore, we conducted this study to test how the comprehensive properties of the alloy can be improved.展开更多
While pre-deformation is often conducted before aging treatment to increase the strength and microhardness of 2195 Al-Li alloy, it often increases the fatigue crack growth(FCG) rate and thus reduces the fatigue life o...While pre-deformation is often conducted before aging treatment to increase the strength and microhardness of 2195 Al-Li alloy, it often increases the fatigue crack growth(FCG) rate and thus reduces the fatigue life of the alloy.To determine the effects and causes of pre-deformation and heat treatment on the mechanical properties and FCG rate of2195 Al-Li alloy, and to provide a suitable calculation model for the FCG rate under different pre-deformation conditions, 2195 Al-Li alloy specimens with different degrees of pre-rolling(0, 3%, 6%, and 9%) were investigated. The experimental results indicate that with the increase of pre-rolling, the density of the T1phase and the uniformity of the S′distribution and the microhardness, tensile strength, and yield strength of the alloy increase and at the same time the FCG rate increases, and thus the fatigue life is reduced. It was also found that the normalized stress intensity factor of elastic modulus(E) can be applied to correlate the FCG rate of pre-rolled 2195 Al-Li alloy with constant C and K parameters.展开更多
Workers of Apis cerana cerana undergo an in-hive nursing to outdoor foraging transition,but the genes underlying this age-related transition remain largely unknown.Here,we sequenced the head transcriptomes of its 7-da...Workers of Apis cerana cerana undergo an in-hive nursing to outdoor foraging transition,but the genes underlying this age-related transition remain largely unknown.Here,we sequenced the head transcriptomes of its 7-day-old normal nurses,18-and 22-day-old normal foragers,7-day-old precocious foragers and 22-day-old over-aged nurses to unravel the genes associated with this transition.Mapping of the sequence reads to Apis mellifera genome showed that the three types of foragers had a greater percentage of reads from annotated exons and intergenic regions,whereas the two types of nurses had a greater percentage of reads from introns.Pair-and group-wise comparisons of the five transcriptomes revealed 59 uniquely expressed genes(18 in nurses and 41 in foragers)and 14 nurse-and 15 forager-upregulated genes.The uniquely expressed genes are usually low-abundance long noncoding RNAs,transcription factors,transcription coactivators,RNA-binding proteins,kinases or phosphatases that are involved in signaling and/or regulation,whereas the nurse-or forager-upregulated genes are often high-abundance downstream genes that directly perform the tasks of nurses or foragers.Taken together,these results suggest that the nurse-forager transition is coordinated by a social signal-triggered epigenetic shift from introns to exons/intergenic regions and the resulting transcriptional shift between the nurse-and forager-associated genes.展开更多
基金financially supported by the Key Research Project of Jiangxi Academy of Sciences(No.2017YZD2-03)the Introduction Doctoral Program of Jiangxi Academy of Sciences(No.2016-YYB-09)the Collaborative innovation GSP Project of Jiangxi Academy of Sciences(No.2016-XTPH1-09)。
文摘Strain-controlled fatigue characteristics of peakaged and over-aged Mg_(96.47)Nd_(2.9)Zn_(0.21)magnesium alloys containing 0.42Zr,including stress response,strain resistance,hysteresis loops,strain-life and corresponding lowcycle fatigue life prediction model,were studied.In the peak-aged state(T61:540℃×8 h+200℃×14 h),the alloy shows higher cyclic stress response,but lower ductility than the alloy in the over-aged state(T6_(2):540℃×8 h+200℃×400 h).The yield strength and ultimate tensile strength of the alloy under T6_(1)-and T6_(2)-treated conditions are close.Compared with T6_(1)-treated alloy,the steady stress amplitude occurred in T6_(2)-treated alloy is due to higher ductility and more homogenous deformation.In T6_(1)state,the fatigue cracks in the alloy first initiate along the cracked persistent slip bands and then propagate in the trans-granular mode,while in the T6_(2)state,the fatigue cracks initiate along grain boundaries and then propagate in the inter-granular mode.
文摘By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-aging (120°C/24h + 160°C/8h + 120°C/24h), were characterized. It is found that compared with the Al-Zn-Mg-Cu alloys treated by T76 (120°C/24h + 160°C/8h), the new multi-stage aging treatment can improve the tensile strength, fracture toughness, hardness and conductivity of the alloys at the same time. This is mainly due to the pre-aging, over-aging and re-aging process of super high strength aluminum alloys. Compared with the two-stage over aging process, the formation of multi-stage multi-phase precipitation structure can improve the strength, toughness and corrosion resistance of the alloys at the same time. The polarization curve is consistent with the conclusion. Therefore, we conducted this study to test how the comprehensive properties of the alloy can be improved.
基金Project(U21A20132) supported by the National Natural Science Foundation of ChinaProject(Gui Renzi2019(13))supported by the Guangxi Specially-invited Experts Foundation of Guangxi Zhuang Autonomous Region,China。
文摘While pre-deformation is often conducted before aging treatment to increase the strength and microhardness of 2195 Al-Li alloy, it often increases the fatigue crack growth(FCG) rate and thus reduces the fatigue life of the alloy.To determine the effects and causes of pre-deformation and heat treatment on the mechanical properties and FCG rate of2195 Al-Li alloy, and to provide a suitable calculation model for the FCG rate under different pre-deformation conditions, 2195 Al-Li alloy specimens with different degrees of pre-rolling(0, 3%, 6%, and 9%) were investigated. The experimental results indicate that with the increase of pre-rolling, the density of the T1phase and the uniformity of the S′distribution and the microhardness, tensile strength, and yield strength of the alloy increase and at the same time the FCG rate increases, and thus the fatigue life is reduced. It was also found that the normalized stress intensity factor of elastic modulus(E) can be applied to correlate the FCG rate of pre-rolled 2195 Al-Li alloy with constant C and K parameters.
基金This work was supported by the China Ministry of Agriculture Fujian Honeybee Biology Observation Station grant(2015-350426-G1203-053)National Natural Science Foundation of China(31401737,31171874 and 31321004)+3 种基金Beijing talents fund(2015000021223ZK29)Beijing Nova Program(Z1511000003150118)US Department of Agriculture National Institute of Food and Agriculture(hatch grant ARZT-1360890-H31-164 and multi state grant ARZT-1370400-R31-168)State Key Laboratory for Biology and of Plant Diseases and Insects(SKLOF201402 and SKLOF201504).
文摘Workers of Apis cerana cerana undergo an in-hive nursing to outdoor foraging transition,but the genes underlying this age-related transition remain largely unknown.Here,we sequenced the head transcriptomes of its 7-day-old normal nurses,18-and 22-day-old normal foragers,7-day-old precocious foragers and 22-day-old over-aged nurses to unravel the genes associated with this transition.Mapping of the sequence reads to Apis mellifera genome showed that the three types of foragers had a greater percentage of reads from annotated exons and intergenic regions,whereas the two types of nurses had a greater percentage of reads from introns.Pair-and group-wise comparisons of the five transcriptomes revealed 59 uniquely expressed genes(18 in nurses and 41 in foragers)and 14 nurse-and 15 forager-upregulated genes.The uniquely expressed genes are usually low-abundance long noncoding RNAs,transcription factors,transcription coactivators,RNA-binding proteins,kinases or phosphatases that are involved in signaling and/or regulation,whereas the nurse-or forager-upregulated genes are often high-abundance downstream genes that directly perform the tasks of nurses or foragers.Taken together,these results suggest that the nurse-forager transition is coordinated by a social signal-triggered epigenetic shift from introns to exons/intergenic regions and the resulting transcriptional shift between the nurse-and forager-associated genes.
