Reversion of natural ageing and restoration of quick bake-hardening response in Al-Zn-Mg-Cu alloy

The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction potential compared to the conventional Al alloys used for the automobile body panels.However,natural ageing(NA)significantly reduces the formability of Al-Zn-Mg-Cu alloy.The reversion of natural ageing has been systematically investigated by hardness test,tensile test,differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).Substantial reversion of natural ageing and thus hardness decrease occurs immediately upon thermal treatment at 120–210℃in an Al-Zn-Mg-Cu alloy.Although the hardness of the most reverted state decreases with increasing temperature,the lowest hardness is still higher than the as-quenched state by 30 HV.As revealed by the complementary DSC and TEM observations,this is ascribed to the synchronization of the dissolution and the re-precipitation of the solutes in the NA clusters during reversion ageing.Reversion at 180–210℃for less than 30 s leads to a hardness decline of 40 HV.The hardening kinetics during NA after reversion is slower than that during first-time NA due to the reduced vacancy concentration.Artificial ageing at 180℃for 30 min after secondary NA of less than 24 h induces intensive precipitation of plate-like pre-ηphases and a giant strength increase of 188–204 MPa.Potential use of high strength Al-Zn-Mg-Cu alloy in automobile body panels could be realized by appropriate reversion treatment improving the formability and the quick bake hardening response.

Natural aging mechanism of buried polyethylene pipelines during long-term service

Currently,accelerated aging tests are widely used to study the aging process of polyethylene pipelines.However,this approach can only simulate one or several main influencing factors in the natural environment,which are often quite different from the actual environment of the buried pipelines.In this study,five types of PE80 buried pipelines in service for 9e18 years were taken as the research object,while new PE80 pipelines were taken as the reference group.The aging process and mechanism of polyethylene buried pipelines were studied through mechanical and chemical property tests and microstructural analysis.The results showed that the pipeline exhibited cross-linking as the main aging mechanism after being in service for 0e18 years.The aging degree and law of the inner and outer surface of the pipeline were compared,and the observed mechanism of both surfaces was explained.After 18 years in service,the elongation at the break of the pipe decreased by 16.2%,and the toughness of the matrix in the main collapse area of the tensile sample was the fundamental reason responsible for changes in the mechanical properties.Finally,after 18 years in service,the oxidation induction time of the pipeline was 25.7 min,which was 28.5% higher than the national standard value.There were no potential safety hazards during continuous long-term service.The results of this paper provide reference data and theoretical guidance for the aging process study of buried polyethylene pipelines.

Microstructure and mechanical properties stability of pre-hardening treatment in Al-Cu alloys for pre-hardening forming process

The stability of the microstructure and mechanical properties of the pre-hardened sheets during the pre-hardening forming(PHF)process directly determines the quality of the formed components.The microstructure stability of the pre-hardened sheets was in-vestigated by differential scanning calorimetry(DSC),transmission electron microscopy(TEM),and small angle X-ray scattering(SAXS),while the mechanical properties and formability were analyzed through uniaxial tensile tests and formability tests.The results in-dicate that the mechanical properties of the pre-hardened alloys exhibited negligible changes after experiencing 1-month natural aging(NA).The deviations of ultimate tensile strength(UTS),yield strength(YS),and sheet formability(Erichsen value)are all less than 2%.Also,after different NA time(from 48 h to 1 month)is applied to alloys before pre-hardening treatment,the pre-hardened alloys possess stable microstructure and mechanical properties as well.Interestingly,with the extension of NA time before pre-hardening treatment from 48 h to 1 month,the contribution of NA to the pre-hardening treatment is limited.Only a yield strength increment of 20 MPa is achieved,with no loss in elongation.The limited enhancement is mainly attributed to the fact that only a limited number of clusters are transformed into Guinier-Preston(GP)zones at the early stage of pre-hardening treatment,and the formation ofθ''phase inhibits the nucleation and growth of GP zones as the precipitated phase evolves.

Identification of QTLs for seed storability in rice under natural aging conditions using two RILs with the same parent Shennong 265

Seed storability （SS） is an important trait for agronomic production and germplasm preservation in rice （Oryza sativa L.）. Quantitative trait locus （QTL） for seed storability in three storage periods was identified using two sets of recombinant inbred lines （RILs） derived from the crosses with a colnmon female parent Shennong 265 （SN265）. Ten QTLs for seed storability were detected on chromosomes 1, 2, 3, 4, 6, 8, and 12in SL-RILs （SN265/Lijiangxingtuanheigui （LTH））, and a total of 12 QTLs were identified on chromosomes 2, 3, 4, 6, 9, and 10 in SH-RILs （SN265/Luhui 99 （LH99））in different storage periods. Among these QTLs, five major QTLs were identified in more than one storage period. The qSS3-1, qSS3-2, qSS12-1, and qSS12-2 were detected in SL-RILs. Similarly, qSS2-2, qSS2-3, qSS6-2, qSS6-3, qSS6-4, qSS9-1, and qSS9-2 were detected in SH-RILs. In addition, the maximum phenotypic variation was derived from the qSS6-1 and qSS9-2, explaining 53.58 and 29.09%, respectively, while qSS6-1 was a new stable QTL for seed storability. These results provide an opportunity for pyramiding and map-based cloning major QTLs for seed storability in rice.

Effect of natural aging on microstructure and mechanical properties of friction stir welded 7050-T7451 joints

The microstructure and mechanical properties of friction stir welded 2. 5 mm 7050-T7451 aluminum alloy natural aging 72 h and 17 520 h were investigated, respectively. The uniaxial tensile test showed that yield strength, tensile strength and elongation of the joints 17 520 h natural aging were about 20%, 12% and 24% higher than those joints natural aging 72 h. Hardness profile of natural aging 17 520 h joint witnessed significant enhancement in nugget zone, compared with 72 h natural aging. Differential scanning calorimetry （ DSC ） and transmission electron microscopy （TEM） test revealed that more Guinier-Preston zone, η＇ and 71 phase emerged in nugget zone as natural aging duration increased, high density of dislocation located within grain boundary in nugget zone of joints natural aging 72 h. It is concluded that natural aging was feasible to enhalwe strength and plasticity of FSW joints simultaneously.

Influence of Trace Oxygen on the Mechanical Properties of High Pure Silver during Natural Aging

Two kinds of high pure silver materials with 5.3 ppm oxygen and 32.7 ppm oxygen were prepared by various melting processes, both samples were subjected to accumulative rolling with 95% thickness reduction. Their mechanical properties were tested during long natural aging. Results showed that the Ag sheet with 5.3 ppm oxygen is at full annealed state when natural aging 58 days or kept at 150℃ for 30 minutes, and the Ag sheet with 32.7 ppm oxygen is a little of recovery when natural aging a year. It is suggested that appropriate oxygen interstitial solute in Ag solid solution and a few of Ag2O particles at Ag grain boundaries impede the recovery and recrystallization of Ag sheets.

Damping Property of Supersaturated ZnA127Ce Alloy during Natural Aging

The microstructures and damping property of supersaturated ZnA127Ce alloy during natural aging have been investigated. H-800 TEM was mainly used to research the microstructures. The relationship between microstructure and damping property was primarily studied. The results showed that solution plus natural aging was the best heat treatment, which could improve the damping property. Both continuous precipitation and cellular reaction occurred during the aging. Continuous precipitation follows the sequence: β→spherical GP zones→elliptical GP zones→intermediate phase R→n. The cellular reaction can be written as follows:β→a+n+ε.

Natural-ageing-enhanced precipitation near grain boundaries in high-strength aluminum alloy

Artificial ageing above 165℃directly after quenching induces the formation of^50 nm wide precipitatefree zone(PFZ)and^100 nm wide precipitate-sparse zone(PSZ)consisting of coarse precipitates with a gradient in size and density toward the grain center in a commercial Al-Zn-Mg-Cu alloy.With the grain size decreasing,the fraction of PFZ and PSZ in a grain becomes larger and could even occupy the entire volume of the grain.This undesirable microstructure near the grain boundary is mitigated substantially by natural pre-ageing,leading to an exceptional enhancement of the age hardening potential at elevated temperatures.Natural ageing could fundamentally alter the precipitation near grain boundary,and is a promising method to optimize the precipitation hardening in high strength aluminum alloys with unconventionally small grains.

A new experimental way for the monitoring of the real/equivalent inservice- time of double base rocket propellant by coupling VST and PCA

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).

Precipitate evolution of 6005A-T6 aluminum alloy after FSW

The 6005A-T6 aluminum alloy was friction stir welded, and the peak temperature as well as microstructure was examined for the joints. A special attention was devoted to the precipitates evolution within different zones after post-weld natural aging time for 6 months. In the nugget zone （NZ） experiencing the highest peak temperature, the β′ precipitates dissolved into a-Al matrix and the GP zones re-precipitated after natural aging. In the thermo-mechanically affected zone （TMAZ）, which is characterized by a high density of dislocation, the Q＇ phases precipitated and part of them dissolved into α-Al matrix during FSW and the GP zones heterogeneously re-precipitated on dislocations after natural aging. The heat- affected zone （HAZ） contains the coarsening of β′ precipitates, the transformation of β″ to β′ and the precipitation of Q＇.

Extracellular vesicles from human urine-derived stem cells delay aging through the transfer of PLAU and TIMP1

Aging increases the risks of various diseases and the vulnerability to death.Cellular senescence is a hallmark of aging that contributes greatly to aging and aging-related diseases.This study demonstrates that extracellular vesicles from human urine-derived stem cells(USC-EVs)efficiently inhibit cellular senescence in vitro and in vivo.The intravenous injection of USC-EVs improves cognitive function,increases physical fitness and bone quality,and alleviates aging-related structural changes in different organs of senescence-accelerated mice and natural aging mice.The anti-aging effects of USC-EVs are not obviously affected by the USC donors’ages,genders,or health status.Proteomic analysis reveals that USC-EVs are enriched with plasminogen activator urokinase(PLAU)and tissue inhibitor of metalloproteinases 1(TIMP1).These two proteins contribute importantly to the anti-senescent effects of USC-EVs associated with the inhibition of matrix metalloproteinases,cyclin-dependent kinase inhibitor 2A(P16INK4a),and cyclin-dependent kinase inhibitor 1A(P21cip1).These findings suggest a great potential of autologous USC-EVs as a promising anti-aging agent by transferring PLAU and TIMP1 proteins.

Effects of Combined Pre-straining and Pre-aging on Natural Aging and Bakehardening Response of an Al-Mg-Si Alloy

For a series of Al-0.34／%Mg-1.05／%Si-0.08／%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differential scanning calorimetry （DSC） analysis was conducted to reveal corresponding precipitation mechanisms. The results showed that pre-straining and pre-aging alone couldn＇t completely suppress natural aging and improve bake hardening response simultaneously. The sensitivity of the pre-straining and pre-aging on the mechanical properties was evaluated. It was found that pre-aging was the main factor which greatly improved bake hardening response and pre-treatment had a weak influence on plasticity in pre-treated samples. DSC analysis showed that the dissolution trough of clusters disappeared in pre-treated samples, both β”and β＇ precipitation peak shifted to lower temperature and were reduced in pre-strained and pre-aged samples. It was concluded that the formation of Mg/Si clusters was replaced by the accelerated precipitation ofβ” andβ＇ phases, which caused the suppression of natural aging and the improvement of bake hardening response （BHR）.

Pre-treatment to Improve the Bake-hardening Response in the Naturally Aged Al-Mg-Si Alloy

This paper describes pre-treatment methods to improve the bake-hardening response of naturally aged AA6022 （Al-0.6Mg-1.0Si）, which is an alloy used in automotive body panels. These methods are used to accelerate the artificial aging process, which proceeds 30-day period of natural aging. The precipitation behavior of the sheets of this aluminum alloy was analyzed by differential scanning calorimetry （DSC） and electrical conductivity measurements, and subsequently confirmed by microstructure observations by transmission electron microscopy （TEM）. Tensile tests and microhardness measurements were performed to determine the mechanical properties of the samples. Under simulated paint-baking conditions （30 min at 170℃）, the microhardness and the yield strength （YS） of the pre-strained ＋ pre-aged samples were found to be I13 HV and 225 MPa, respectively. These values are considerably higher than those of pre-aged samples, and they did not decrease significantly during the initial stage of artificial aging.

Synchronous improvement of mechanical properties and stress corrosion resistance by stress-aging coupled with natural aging pre-treatment in an Al-Zn-Mg alloy with high recrystallization fraction

Enhancing the strength of Al-Zn-Mg alloys is critical to the weight-lightening of structural components in the application of high-speed trains and aerospace industries,while high stress corrosion cracking(SCC)susceptibility of Al-Zn-Mg alloys(especially the alloy with high recrystallization fraction)with high strength makes it difficult.In this study,the influence of tensile stress-aging coupled with natural aging pre-treatment on the mechanical properties and SCC resistance of Al-Zn-Mg alloy with high recrystallization fraction has been investigated.The results show that tensile stress-aging at 160℃can inhibit the dissolution of clusters/Guinier-Preston(GP)zones formed during long-term natural aging pre-treatment,which increases the number density of matrix precipitates(MPts),narrow the width of precipitate free zone(PFZ),and dramatically improve the mechanical properties of the experimental Al-Zn-Mg alloy.Meanwhile,the precipitation of the high density of MPts within the matrix will assume a large number of solute atoms during artificial aging,which will reduce the supplement of solute atoms to grain boundaries.As a result,the volume of anodic active grain boundary precipitates(GBPs)and the content of free solute atoms at grain boundaries are reduced,which reduces the possibility of initial nucleation and propagation of SCC crack.The coupled treatment method proposed in this study proves efficient in resolving the contradiction between the strength and SCC resistance in Al-Zn-Mg alloy.

Unraveling natural aging-induced properties change of sludge-derived hydrochar and enhanced cadmium sorption site heterogeneity

Hydrochar has potential applications in soil improvement and heavy metal remediation.Hydrochar would undergo the process of aging when introduced into the soil,altering its properties.However,recent studies have focused mainly on the artificial aging of hydrochar,which could not reveal the cumulative effect of multiple environmental factors.Therefore,the periodical monitoring of the property and sorption behavior of hydrochar after amending soils is necessary to better understand the multifaceted mechanisms associated with the natural aging of hydrochar.This study selected the sludge-derived hydrochar(SLHC)as a typical hydrochar and applied a 16-month rice-wheat-rice rotation to mimic the natural aging of hydrochar,focusing on changing properties and cadmium(Cd)sorption and literature contrast between aging strategies and biochar types.The porosity,O abundance,and ash content of 16-month aged SLHC increased by 37%,47%,and 8.5%,respectively,facilitating Cd sorption due to surface complexation,pore sorption,and precipitation.The sorption percentage of Cd to SLHC was in the range of 11-14%for SLHC-A0 and increased to 17-31%for SLHC-A4 and 20-32%for SLHC-A16 after natural aging.The natural aging of SLHC induced by ash content played an essential role in Cd sorption site heterogeneity.Linear regression analysis showed that aging strategies on sorption behavior significantly differed between biochars.Thus,studies involving natural aging with multiple environmental factors are preferred over those involving chemical or biological aging.Future studies should continue to explore the mechanisms of natural aging-induced heavy metal sorption between hydrochar and pyrochar.These results improve insights to appraise the potential of SLHC as soil amendments to alleviate the adverse effects of heavy metal contamination and provide an essential basis for researchers and staff in soil management and environmental prevention.

Ultra-high strength Mg-Li alloy with B2 particles and spinodal decomposition zones

The bcc-structured Mg-Li alloy is currently the engineering metallic material with the lowest density,but it has not been widely used due to its low strength.In this paper,alloying Zn effectively improves the strength of the bcc-structured Mg-Li alloy.Due to the semi-coherent B2 structured nanoparticles,the compressive yield strength of the as-cast Mg-13Li-9Zn alloy reaches higher than 300 MPa.Due to the solid solution strengthening of Zn and the spinodal zone,the compressive yield strength of the as-quenched Mg-13Li-15Zn(LZ1315)alloy immediately increases to 400 MPa.In addition,the as-quenched LZ1315 alloy exhibits natural aging strengthening behavior.Due to the precipitation of B2 nanoparticles,the yield strength of the peak aged alloy is up to 495 MPa.

Buses retrofitting with diesel particle filters: Real-world fuel economy and roadworthiness test considerations

Retrofitting older vehicles with diesel particulate filter（DPF） is a cost-effective measure to quickly and efficiently reduce particulate matter emissions. This study experimentally analyzes real-world performance of buses retrofitted with CRT DPFs. 18 in-use Euro III technology urban and intercity buses were investigated for a period of 12 months. The influence of the DPF and of the vehicle natural aging on buses fuel economy are analyzed and discussed. While the effect of natural deterioration is about 1.2%–1.3%, DPF contribution to fuel economy penalty is found to be 0.6% to 1.8%, depending on the bus type. DPF filtration efficiency is analyzed throughout the study and found to be in average 96% in the size range of 23–560 nm. Four different load and non-load engine operating modes are investigated on their appropriateness for roadworthiness tests. High idle is found to be the most suitable regime for PN diagnostics considering particle number filtration efficiency.

Tensile Properties and Deformation Behaviors of a New Aluminum Alloy for High Pressure Die Casting

Effects of natural aging and test temperature on the tensile behaviors have been studied for a highperformance cast aluminum alloy Al–10Si–1.2Cu–0.7Mn. Based on self-strengthening mechanism and spheroidization microstructures, the alloy tested at room temperature（RT） exhibits higher 0.2% proof stress（YS） of 206 MPa, ultimate tensile strength（UTS） of 331 MPa and elongation of 10%. Increasing aging time improves the YS and UTS and reduces the ductility of the alloy. Further increasing aging time beyond72 h does not signi？cantly increase the tensile strengths. Increasing test temperature significantly decreases the tensile strengths and increases the ductility of the alloy. The UTS of the alloy can be estimated by using the hardness. The Portevin–Le Chatelier effect occurs at RT due to the interactions between solid solution atoms and dislocations. Similar behaviors occurring at 250℃ are attributed to dynamic strain aging mechanism. Increasing aging time leads to decrease in the strain-hardening exponent（n） value and increase in the strain-hardening coeficient（k） value. Increasing test temperature apparently decreases the n and k values. Eutectic phase particles cracking and debonding determine the fracture mechanism of the alloy. Final failure of the alloy mainly depends on the global instability（high temperature, necking） and local instability（RT, shearing）. Different tensile behaviors of the alloy are mainly attributed to different matrix strengths, phase particle strengths and damage rate.

Effects of ultrasonic assisted friction stir welding on flow behavior,microstructure and mechanical properties of 7N01-T4 aluminum alloy joints

Conventional friction stir welding(FSW)and ultrasonic assisted friction stir welding(UAFSW)were employed to weld 6-mm thick 7 N01-T4 aluminum alloy plates.Weld forming characteristics and material flow behavior in these two different welding processes were studied and compared.Ultrasonic vibration was applied directly on the weld in axial direction through the welding tool.Metal flow behavior,microstructure characteristics in the nugget zone(NZ)and evolution of the mechanical properties of naturally aged joints were studied.Results show that the ultrasonic vibration can significantly increase the welding speed of defect-free welded joint.At the rotation speed of 1200 rpm,the UAFSW can produce defect-free welded joints at a welding speed that is 50%higher than that of the conventional FSW.Ultrasonic vibrations can also improve surface quality of the joints and reduce axial force by 9%.Moreover,ultrasonic vibrations significantly increase the volume of the pin-driven zone(PDZ)and decrease the thickness of the transition zone(TZ).The number of subgrains and deformed grains resulting from the UAFSW is higher than that from the FSW.By increase the strain level and strain gradient in the NZ,the ultrasonic vibrations can refine the grains.Ultrasonic energy is the most at the top of the NZ,and gradually reduces along the thickness of the plate.The difference in strengths between the FSW and the UAFSW joints after post-weld natural aging(PWNA)is small.However,the elongation of the UAFSW is8.8%higher than that of the FSW(PWNA for 4320 h).Fracture surface observation demonstrates that all the specimens fail by ductile fracture,and the fracture position of the UAFSW joint changes from HAZ(PWNA for 120 h)to NZ(PWNA for 720 and 4320 h).