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The precipitation of intermetallic phases and the associated hardening by artificial aging treatments at elevated temperatures above 400 °C were systematically investigated in the commercially available AC2B alloy with a nominal composition of Al–6Si–3Cu (mass%). The natural age hardening of the artificially aged samples at various temperatures was also examined. A slight increase in hardness (approximately 5 HV) of the AC2B alloy was observed at an elevated temperature of 480 °C. The hardness change is attributed to the precipitation of metastable phases associated with the α-Al15(Fe, Mn)3Si2 phase containing a large amount of impurity elements (Fe and Mn). At a lower temperature of 400 °C, a slight artificial-age hardening appeared. Subsequently, the hardness decreased moderately. This phenomenon was attributed to the precipitation of stable θ-Al2Cu and Q-Al4Cu2Mg8Si6 phases and their coarsening after a long duration. The precipitation sequence was rationalized by thermodynamic calculations for the Al–Si–Cu–Fe–Mn–Mg system. The natural age-hardening behavior significantly varied depending on the prior artificial aging temperatures ranging from 400 °C to 500 °C. The natural age-hardening was found to strongly depend on the solute contents of Cu and Si in the Al matrix. This study provides fundamental insights into controlling the strength level of commercial Al–Si–Cu cast alloys with impurity elements using the cooling process after solution treatment at elevated temperatures above 400 °C.

Various long-lived mRNAs are stored in seeds, some of which are required for the initial phase of germination and are critical to seed longevity. However, the seed-specific long-lived mRNAs involved in seed longevity remain poorly understood in rice. To identify these mRNAs in seeds, we first performed aging experiment with 14 rice varieties, and categorized them as higher longevity (HL) and lower longevity (LL) rice varieties in conventional rice and hybrid rice, respectively. Second, RNA-seq analysis showed that most genes showed similar tendency of expression changes during natural and artificial aging, suggesting that the effects of these two aging methods on transcription are comparable. In addition, some differentially expressed genes (DEGs) in the HL and LL varieties differed after natural aging. Furthermore, several specific long-lived mRNAs were identified through a comparative analysis of HL and LL varieties after natural aging, and similar sequence features were also identified in the promoter of some specific long-lived mRNAs. Overall, we identified several specific long-lived mRNAs in rice, including gibberellin receptor gene GID1 , which may be associated with seed longevity.

Typical climatic environments such as UV radiation, high temperature and strong wind in cold and arid regions have a significant effect on asphalt aging. The intent of this work is to reveal the evolution law of natural aging of SBS-modified asphalt under the complex adverse climate environment in cold and arid regions. Furthermore, the contribution rate of various environmental factors of natural aging of asphalt in cold and arid regions was analyzed. Based on rheological parameters, this paper characterized the influence of natural aging on the viscoelastic properties, rutting resistance at a high temperature, fatigue resistance and cracking resistance at a low temperature of SBS-modified asphalt. The evolution law of natural aging performance of SBS-modified asphalt was revealed. A quantitative evaluation index (CIi) of natural aging contribution rate of asphalt was put forward and the contribution rate of various environmental factors to asphalt natural aging was analyzed. The results showed that the effects of simulated aging and natural aging on asphalt properties were similar. After aging, the viscoelastic properties of asphalt were deteriorated, and the risk of fatigue cracking and low temperature cracking was increased. It also enhanced the deformation resistance of asphalt and increased the rutting resistance at high temperature. The aging contribution index CIi obtained based on rheological parameters such as complex modulus and rutting factor could directly reflect the influence of different natural factors on the performance of asphalt during aging. Among them, the effect of thermal oxygen was more obvious on the natural aging of SBS-modified asphalt.

Laboratory-simulated aging fails to fully replicate the complex aging behavior of asphalt binder under actual environmental conditions. This study aims to preliminarily investigate and analyze the differences between natural aging and PAV aging of asphalt binder. To achieve this objective, the asphalt binder was aged using three distinct methods: PAV aging, natural thermal-oxidative aging, and all-weather aging. The divergence in asphalt binder aging behavior was systematically investigated through encompassing low-temperature performance, chemical structure, elemental composition, molecular weight, and macroscopic and microscopic performance correlation analyses. Key findings include: the harsh environment in the cold and arid regions resulted in inferior low-temperature performance of asphalt binder after 12 months of natural thermal-oxidative and all-weather aging compared to PAV-aged asphalt binder, with the stiffness modulus at −12 °C increasing by 114.8% and 105.3%, respectively. Natural aging induced more significant asphalt binder’s chemical structural changes than PAV aging but exhibited less prominent oxidative reactions and macromolecular structure formation. Whether from a macroscopic or microscopic perspective, thermal-oxidative conditions were identified as the primary driver behind both the natural aging behavior and the aging pathway of asphalt binder. The influence of other factors on the aging behavior of asphalt binder was not significant. The poor correlation (R2 < 0.62) between oxygen content, molecular weight, and low-temperature performance across different aging modes underscores a fundamental divergence in aging pathways between PAV and natural aging. This study preliminarily identifies the key differences between laboratory-accelerated aging and natural aging of asphalt binder and paves the way for optimizing the parameters of laboratory-accelerated aging protocols.

The need to recycle elastomeric waste requires studying its viability in industrial applications. This study investigates the feasibility of recycling elastomeric waste by analyzing whether virgin ethylene-propylene-diene monomer (EPDM) can be replaced by blends of virgin EPDM and thermomechanically and microwave devulcanized EPDM (EPDM) in industrial applications from the perspective of environmental degradation. Two types of samples were examined: conventional EPDM used to roof membranes, and EPDM blended with different amounts (20, 40, and 50 phr) of EPDMd. Samples were subjected to natural aging in coastal and mountainous environments. Results show that mechanical properties decline with higher EPDMd content and, to a lesser degree, with prolonged outdoor exposure. The coastal climate proved more aggressive than the mountainous one when EPDMd content exceeded 40 phr. Zinc stearate (ZnSt,), a byproduct of vulcanization, was found to influence the evolution of the mechanical behavior. The combined analysis of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), abrasion tests, and thermogravimetric analysis (TGA) provided insights into the degradation processes of these elastomeric blends.

Composite insulators operate in harsh field environments all year round. Their various properties and states of aging require attention. It is important to study the performance changes of composite insulator sheds after aging to evaluate the life of insulators operating on grids. For this reason, 22 composite insulator sheds from different factories, with different voltage levels and different ages years were selected to conduct mechanical properties testing. The mechanical properties include hardness, tensile strength, and elongation at break, and were investigated by thermogravimetric (TGA) testing, surface morphology, and nuclear magnetic resonance (NMR) characterization. The changes in mechanical properties of high temperature vulcanization (HTV) composite insulator silicone rubber aged in the natural environment were analyzed, including the reasons for these changes. The results showed that the transverse relaxation time T2 of the sample was closely related to its aging state. The more serious the silicone rubber’s aging, the smaller was the T2. The state of the composite insulator can be evaluated by using T2 and aging years simultaneously. With the actual degree of aging in the silicone rubber intensified, its tensile strength and elongation at break generally showed a downward trend.

The influence of processing parameters and several combinations of natural as well as artificial aging on the mechanical properties of friction stir welded AA7075-T6 is analyzed in the present investigation. Different sets of welding parameters were employed to obtain joints characterized by different peak temperatures and thermal cycles. The joint obtained with the highest welding speed has guaranteed the best mechanical properties. The latter were shown to be strongly correlated to heat input, which influences both densities of dislocations in nugget zone grains and growth and dissolution of strengthening precipitates in the heat-affected zone that establish the mechanical characteristics of friction stir welds. On the other hand, artificial aging has drastically reduced the strain at break due to strain localization in the heat affected zones while it has proved its effectiveness in stabilizing the mechanical properties when exposed to further natural aging at room temperature.

Natural aging for 11 days at room temperature was applied to 6063 industrial aluminium alloy after being solutionized and quenched in order to form clusters. The cluster formation led to increasing hardness and tensile strength. The samples were then subject to a high aging temperature at 250 °C for up to 5 min in the so-called reverse aging (RA) process. The effect of RA was measured using hardness and tensile measurements, differential scanning calorimetry (DSC) and a scanning electron microscope (SEM). The tensile fracture surface morphology was investigated using the SEM. The natural secondary aging following RA was investigated as well. An understanding of the microstructure behavior after RA is established. The results showed that even the state of maximum reversion still contains undissolved clusters that contribute to hardness, tensile strength and DSC. At longer RA times, clusters grow and form strengthening precipitates. A state of clusters dissolution and clusters formation and growth is expected as free atoms can surround the non-dissolved clusters.

This study investigated the effects of aging profiles on the precipitate formation and the corresponding strengthening and deformation behaviors of Al–Mg–Zn alloys. The alloys subjected to natural aging (NA) demonstrated significantly enhanced ductility at equivalent stress levels compared to those subjected to artificial aging (AA). In AA-treated alloys, η′ and η-phases with incoherent interfaces were formed, while GP zones and solute clusters were dominantly exhibited in the NA-treated alloy with a coherent interface with the matrix. Due to the change in interface bonding, the dislocation movement and pinning behavior after deformation are varied depending on the aging conditions of Al–Mg–Zn alloy sheet. Thus, the elongation to fracture of the NA alloy sheet was improved compared to that of the AA alloy sheet because of the enhanced work-hardening capacity and the thin precipitate-free zone (PFZ). Deformation textures and dislocation densities varied between NA and AA treatments, as revealed by electron backscatter diffraction (EBSD) and kernel average misorientation (KAM) analysis. The interactions between the precipitates, dislocations, and the PFZ in the AA- and NA-treated alloys were analyzed via transmission electron microscopy (TEM). The insights gained from this research provide a valuable foundation for industrial applications, particularly in sectors demanding lightweight, high-strength materials, where optimizing the aging process can lead to significant performance improvement and cost savings.

Three kinds of 6061 aluminum alloy thin-walled tubes rolled by Pilger cold rolling mill and three-high rolling mill were taken as the research objects. EBSD, SEM and tensile test were used to analyze the microstructure, texture and mechanical properties of the tubes under natural aging. The results show that the grain size near the mandrel in the tube wall is larger, and the grain near the roll is smaller. The grains on the transverse section are elongated and elongated along the rolling direction. Under the large deformation of 84 % ~ 87 %, the main textures of thin-walled 6061 aluminum alloy tube are V texture, Brass texture, γ fiber texture and H texture. Under natural aging, the tensile strength and yield strength of 6061 aluminum alloy tube gradually increase with time, and remain basically unchanged after 60 days. The higher processing deformation, the higher tensile strength of tube, the lower elongation.