Aging Temperature Research Articles

Effect of temperature on dynamic strain aging and intermediate temperature embrittlement of nickel-based alloy N06625

Due to its excellent mechanical properties and good corrosion resistance at low to intermediate temperatures, nickel-based alloy N06625 has gradually become an ideal material for high-temperature gas-cooled reactor evaporators in nuclear power plants. It is currently receiving more and more attention. In this work, the tensile test of nickel-based alloy N06625 was carried out at room temperature to 900℃. The dynamic strain aging (DSA) process and microstructure evolution were studied by electron back-scatter diffraction (EBSD). The dynamic strain aging and intermediate temperature embrittlement of nickel-based alloy N06625 in the temperature range 25–900℃ were systematically studied. The results show that the stress-strain curve exhibits a serrated shape at 200–700℃, and with the increase in temperature, the serrated type changes from type A to type A+B and type C. The type A and type (A+B) serrations are related to the diffusion of interstitial carbon atoms. The interaction between substitutional elements Cr and Mo and movable dislocations causes the type C serration. As the temperature increases, high-density dislocations accumulate at the grain boundaries, and the proportion of substructural grains increases. A brittle fracture occurs at 600–800℃. The fracture mechanism may be due to the stress concentration at the grain boundary caused by the appearance of micropore, which weakens the grain boundary's strength and promotes the grain boundary's early failure. The continuous increase of strain makes the micropore fuse and grow to form a crack source.

Corrosion suppression and strengthening of the Al-10Zn alloy by adding silica nanorods

Aluminum alloys have been widely studied because of their current engineering applications. Due to their high strength and lightweight, cracking can easily initiate on their surface, deteriorating their overall functional and structural properties and causing environmental attacks. The current study highlights the significant influence of incorporating 1 wt% silica nanostructure in aluminum-10 zinc alloys. The characteristics of the composites were examined using Vickers hardness, tensile, and electrochemical testing (OCP, Tafel, and EIS) at various artificial aging temperatures (423, 443, and 463 K). Silica nanorods may achieve ultrafine grains, increase hardness by up to 13.8%, increase σUTS values by up to 79% at 443 K, and improve corrosion rate by up to 89.4%, surpassing Al-10 Zn bulk metallics. We demonstrate that silica nanorods contribute to the creation of a superior nanocomposite that not only limits failure events under loading but also resists corrosion. Our findings suggest that silica nanocomposite can produce unique features for use in a variety of automotive, construction, and aerospace applications. This improvement can be attributed mainly to the large surface area of nano-silica particles, which alters the Al matrix. Microstructural, mechanical, and electrochemical studies revealed that the effects of structure refinement were dependent on nano-silica.

Investigation of Influence of Variations of Ageing Conditions on Aluminium-Silicon: Pathway to Tailored Mechanical Properties

This study focuses on the investigation of the influence of the variations of ageing conditions on the mechanical properties of ferrosilicon-silicon carbide reinforced Aluminium metal matrix composites. The ageing temperature, reinforcement percentage volume fractions and ageing time of the composite were systematically varied during fabrication stages by keeping the Aluminium and Ferrosilicon compositions constant while varying the percentage volume fractions of Silicon Carbide (SiC). The samples produced were machined into hardness, impact and tensile tests specimens. Then the specimens were subjected to laboratory based accelerated solution heat treatment, quenching and artificial ageing. Array of comprehensive mechanical properties examination and characterization in line with the appropriate specifications of the American Society for Testing and Materials Standard manuals were conducted to determine the influence of ageing on the material’s strength, hardness, impact toughness and stress-strain characteristics. The study revealed significant enhancement in the mechanical properties of the material and the findings would provide valuable insight into the ageing behaviour of Aluminium-Silicon, thus, enabling the optimization of the material’s performance for use in diverse engineering applications.

Hygrothermal effects on the durability of resin‐infused thermoplastic E‐glass fiber‐reinforced composites in marine environment

AbstractThis paper presents a comparative assessment of hygrothermal effects on the mechanical and thermomechanical properties of resin‐infused thermoplastic E‐glass fiber‐reinforced composites (FRC) in the marine environment. The thermoplastic FRCs were immersed in seawater at two different aging temperatures, that is, 35 and 70°C. The quasi‐static tests were conducted on unaged and aged FRCs, followed by scanning electron microscopy (SEM) to determine the effect of the marine environment on the mechanical properties and damage progression. The specimens immersed at 70°C showed a significant drop of 46.7%, 39.7%, 22.6%, and 16% in mechanical properties (tensile, compression, flexural, and ILSS) mainly due to plasticization, matrix cracking, and fiber/matrix debonding. The specimens immersed at 35°C showed a reduction in tensile, compressive, and flexural strength of 10%, 14.7% and 1.9% respectively, with no significant effect on ILSS. In addition, dynamic mechanical analysis (DMA) reveals that prolonged aging induces an increase in glass transition temperature due to polymerization reactions. This work is intended to reveal the effect of extreme marine environment on the resin‐infused thermoplastic FRC and to provide a useful reference for their potential structural applications in the marine industry.Highlights Influence of aging conditions on the long‐term performance of FRCs. Hygrothermal aging leads to an increase in the glass transition temperature. The marine environment degrades mechanical properties of FRCs by up to 50%. Matrix cracking and fiber‐matrix debonding evolved as dominant failure modes.

Influence of Aging Condition on the Characteristics of Continuous Precipitates of AZ80 Magnesium Alloy

The aim of this work is to evaluate the characteristics of continuous precipitates (CP) developed within the grain and grain boundary precipitates through statistical analysis of the number density and size (i.e., length and width) at varying aging conditions of AZ80 Mg alloy. Scanning electron microscopy illustrates the characteristics and features of precipitates, distinctively. The results reveal an increment of number density, whereas the reduction in the size of precipitates with decrease in the aging temperature for the varying aging times. The variation in hardness values at different aging conditions has been ascribed to this.

Deciphering the composition-microstructure correlation in low-density FeMnAlC steels with machine learning

FeMnAlC steels have been regarded as prospective candidates for the advanced high-strength steel with reduced density. However, the correlation between the complex steel composition and the resulting microstructure remains unclear. This study presents a robust and efficient approach for establishing the correlation between the composition and microstructure of low-density FeMnAlC steel using a machine learning algorithm. By employing classification and regression models, we successfully predicted four significant characteristics: the existence of the κ phase, a dual-phase region (γ + κ) at the aging temperature, a solitary γ phase region, and the volume fraction of the κ phase. Notably, the elements Al and C, with a particular emphasis on Al, exert significant influence on the phase structure. For example, when the Mn element content is 30 wt%, an estimated minimum Al content of around 4 wt% is required to guarantee the existence of the κ phase. Furthermore, the anticipated content range of Al and C required for the existence of the (γ + κ) duplex region at the aging temperature spans from 4.5 to 9.3 wt% and 0.4 to 1.1 wt%, respectively. Ultimately, the Fe-30Mn-8Al-1C steel was chosen for experimental validation, and the predicted characteristics exhibited excellent agreement with the experimental results. Our research offers a roadmap for the development of low-density steel, and the approach we devised holds promise for application in other metallic materials as well.

Storage Life of Particle-Filled Polymer Composites Considering Aging Effects.

This study investigates the storage life of particle-filled polymer composites (PFPCs) under the influence of aging effects. High-temperature accelerated aging tests were conducted at 60 °C, 70 °C, and 80 °C for various days to analyze the impact of aging time and temperature on the mechanical behavior of the materials. A predictive model for crosslink density was established using the Arrhenius equation, and the relationship between crosslink density and relaxation modulus was determined based on polymer physics theory. On this basis, a viscoelastic constitutive model that incorporates aging effects was developed. Structural analyses of a PFPC column with a length of 2.3 m and outer diameter of 1.8 m were performed using the UMAT subroutine in ABAQUS. Subsequently, a safety margin assessment method based on dewetting strain was employed to predict the storage life of the PFPC column. The results indicate that the aging viscoelastic constitutive model effectively characterizes the hardening effects caused by aging in the composites during storage. The storage life for the PFPC column considering aging effects decreases from 22 years to 19 years compared to models that ignore such effects. This approach provides a reference for estimating the storage life of PFPC columns considering aging effects.

Exploring the effects of austenitizing conditions on the heterogeneous microstructure and mechanical properties of 11Cr–11Ni–Ti–Mo maraging stainless steel: Breakthrough in the strength-ductility trade-off

Based on the microstructure analysis, the present research investigated the influence of various austenitizing conditions on the transformation behavior of intermetallic compound particles, i.e. η-Ni3Ti, and the reversed austenite during ageing treatment in Ti–Mo maraging stainless steel, as well as the related mechanical properties. The results revealed numerous tiny rod-like intermetallic compound particles, i.e. η-Ni3Ti, having a Burgers orientation relationship, i.e., {101}α′//{0001}η ; <111‾>α′//<112‾0>η, with the martensite matrix, as well as blocky, lath, and granular reversed austenite of various sizes distributed within the tempered martensite matrix. Regardless of the austenitizing treatment condition, more reversed austenite was found in the samples aged at 520 °C than in those aged at 640 °C. Although this finding was not consistent with the Thermo-Calc predictions, it should be associated with the thermal stability of reversed austenite at different ageing temperatures. In other words, the greater amount of reversed austenite that formed at 640 °C did not remain at room temperature due to secondary martensite transformation during cooling, as was verified by EBSD analysis.

Mechanical properties of Sr inoculated A356 alloy by Taguchi-based gray relational analysis

Abstract In this study, Sr inoculated A356 alloy casted by sand-casting technique. Production parameters such as Sr concentration (wt.%), aging temperature (°C), aging time (h), and constant cooling rate were used. The effect of heat treatment on the microstructure and mechanical features of inoculated A356 materials was examined by using scanning electron microscopy, optical microscopy, and the Taguchi-based gray relational analysis method. The optimum production parameters for A356 alloy were determined as 0.03 Sr concentration, aging 300 °C temperature, and 3 h aging time. Multiple response optimization based on the interaction of these parameters provided a 30.15 % improvement in performance. Gray relational grade (GRG) experimental results showed that the most important parameter was Sr concentration, with a contribution of 76.51 %, according to the analysis by ANOVA statistical method.

Reptile responses to fire across the western Mediterranean Basin

AbstractEffects of anthropogenic activities, including climate change, are modifying fire regimes, and the dynamic nature of these modifications requires identification of general patterns of organisms’ responses to fire. This is a challenging task because of the high complexity of factors involved (including climate, geography, land use, and species‐specific ecology). We aimed to describe the responses of the reptile community to fire across a range of environmental and fire‐history conditions in the western Mediterranean Basin. We sampled 8 sites that spanned 4 Mediterranean countries. We recorded 6064 reptile sightings of 36 species in 1620 transects and modeled 3 community metrics (total number of individuals, species richness, and Shannon diversity) as responses to environmental and fire‐history variables. Reptile community composition was also analyzed. Habitat type (natural vs. afforestation), fire age class (time since the last fire), rainfall, and temperature were important factors in explaining these metrics. The total number of individuals varied according to fire age class, reaching a peak at 15–40 years after the last fire. Species richness and Shannon diversity were more stable during postfire years. The 3 community metrics were higher under postfire conditions than in unburned forest plots. This pattern was particularly prevalent in afforested plots, indicating that the negative effect of fire on reptiles was lower than the negative effect of afforestation. Community composition varied by fire age class, indicating the existence of early‐ and late‐successional species (xeric and saxicolous vs. mesic reptiles, respectively). Species richness was 46% higher in areas with a single fire age class relative to those with a mixture of fire age classes, which indicates pyrodiverse landscapes promoted reptile diversity. An expected shift to more frequent fires will bias fire age distribution toward a predominance of early stages, and this will be harmful to reptile communities.

Unraveling the complexity of Fe-based bulk metallic glasses: Insights into dynamic mechanical relaxation in atomic-scale

This research conducts a thorough investigation into the structural and mechanical evolution of Fe74B20Nb2Hf2Si2 bulk metallic glass (BMG) subjected to thermal aging. Utilizing X-ray diffraction (XRD) and selected area electron diffraction (SAED), the study verifies the amorphous structure of the as-cast BMG, highlighting evidence of short-range ordering (SRO). Thermal aging conducted between 342 and 570 K induces substantial changes, notably the formation of Fe23B6 and α-Fe phases and reduced defect concentrations. During dynamic mechanical analysis, a significant shift was observed, which is characterized by a decrease in the intensity of β-relaxation and an increase in β-activation energy from 333.3±2.1 kJ/mol (for the sample aged at 342 K) to 384.6±5.6 kJ/mol (for the sample aged at 570 K). Nanoindentation evaluations reveal an increase in hardness from 11.85±0.22 GPa (for the as-cast BMG) to 14.65±0.41 GPa (for the sample aged at 570 K), accompanied by an increase in Young’s modulus from 211.61±3.00–244.24±2.00 GPa. These changes imply tighter atomic packing and diminished free volume due to aging, suggesting an advanced stage of structural relaxation. Additionally, the material demonstrates a decrease in plastic strain from 0.0052 in its as-cast state to 0.0026 at 342 K, progressing to brittle behavior with further aging. This study shows the pivotal role of precise aging temperature control in optimizing BMGs for diverse applications, illustrating the intricate interplay between thermodynamics and kinetics in material science.

The influence of heat treatment process on the dynamic recrystallization evolution mechanism of Inconel 718 during high-speed machining

This study aims to investigate the cutting mechanisms of Inconel 718 alloy under different heat treatment processes and the grain refinement patterns of the transformed layer. By establishing a constitutive model suitable for cutting and importing it into DEFORM-3D for heat treatment processing and single-factor cutting experiment simulation, the effects of heat treatment processes and cutting parameters on cutting force, cutting temperature, and surface grain refinement were studied. The results indicate that the increase in cutting force is maximum, approximately 12 %, after the aging temperature is raised from 668 °C to 718 °C. The cutting force generated after aging heat treatment shows a negative correlation with cutting speed, whereas the cutting force after solution heat treatment rises significantly between 1400 and 1600 mm/s. The maximum cutting temperature occurs in workpieces after solution heat treatment, about 112 % of that of workpieces treated at 718 °C aging heat treatment. At the onset of cutting, the size relationship of the original grain volume is as follows: untreated < solution heat treatment < aging heat treatment; the number of nucleation points for dynamic recrystallization at grain boundaries is as follows: aging heat treatment < solution heat treatment < untreated. The most significant increase in the number of dynamic recrystallizations is observed after aging heat treatment at 621 °C, with the relationship of the number of recrystallizations in different cutting deformation zones being: secondary deformation zone < primary deformation zone < tertiary deformation zone. With the increase in cutting depth, the grain size of the workpiece after solution heat treatment first increases then decreases during the cutting process; the grain size of the workpiece after aging heat treatment first decreases then increases. The grain size of the workpiece during the cutting process after heat treatment is negatively correlated with cutting speed. Specifically, when the cutting speed is 600 mm/s, the grain size after solution heat treatment is the largest, about 1.1 times that of the 718 °C aging heat-treated workpiece.

Laser Powder Bed Fusion and Heat Treatment of the Martensitic Age‐Hardenable Steel (1.2709)

The primary objective of this study is to clarify the fundamental question of whether, in principle, it is possible to dispense with a prior solution annealing process in favor of a direct aging heat treatment for specimens of maraging stainless steel grade X3NiCoMoTi18‐9‐5 (1.2709) produced by laser powder bed fusion (LPBF). The waiver of a solution annealing process would significantly increase the process efficiency and thus support a sustainable and resource‐friendly production of such components. Therefore, the hardness, microstructure, and the present phases of specimens in as‐built + aged condition (AB + A) and solution‐annealed + aged (SOL + A) are examined during this study. Initially, an extended parameter study is performed using a Renishaw AM 250 LPBF system equipped with a pulsed mode laser system to achieve the highest possible apparent density. As test specimens, small cubes are produced for parameter study and are analyzed for porosity by means of optical microscopy. To investigate the relationship between microstructure and hardness in different material states, one series of specimens is aged directly after LPBF processing in the as‐built state (AB + A). For comparison, the other series was solution annealed at 820 °C for 60 min, quenched in water and then aged (SOL + A). A maximum hardness value of 614 HV1.0 is achieved for specimen aged at 490 °C for 120 min in as built condition (AB + A), while 624 HV1.0 was measured for specimen aged at 490 °C for 180 min in conventionally solution annealed + aged (SOL + A) condition. Significant austenite reversion is not observed at aging temperature of 490 °C in both cases. Aging of specimens at temperatures of 540 and 600 °C resulted in reduction of specimen hardness due to higher percentage of austenite reversion. No significant difference between the hardness values of AB + A and SOL + A specimens is observed. It can therefore be concluded that, in principle, conventional solution annealing and ageing can be dispensed with in favor of direct aging. However, as the results are based on small sized specimens, further investigations into the scalability are needed.

The phase transformation and enhancing mechanical properties in high Zn/Mg ratio Al–Zn–Mg–Cu(-Si) alloys

Aging behavior and phase transformation of Al–5Zn–1Mg–1Cu(-Si) alloys under different isothermal temperatures were investigated using transmission electron microscope (TEM) and mechanical tests. The aging temperature and Si addition significantly influenced to the types of precipitated phases and mechanical properties of the Al–Zn–Mg–Cu alloys. Adding Si in this alloy changed the precipitated phases from T′ and η′ phases to the dual-sized η and GPB-II phases. With increasing isothermal aging temperature, more GPB-II phases formed in alloys with the same composition, effectively improving the microhardness and mechanical properties. When aging at 150 °C, 0.5 wt%Si-containing alloy reached the highest peak hardness of about 150HV and maintained stable hardness, while an alloy without Si only reached 120HV and later declined by 15HV. The tensile strength and yield strength of the 0.5 wt%Si-containing alloy were higher than those of non-Si alloy by 132 MPa and 165 MPa, increasing 51% and 90%, respectively. This result was due to the presence of fine and dispersed 4–8 nm GPB-II phases in 0.5 wt%Si-containing alloy. The GPB-II phase had a core-shell structure, with the core region mainly enriched in Mg and Si, and the shell region mainly enriched in Cu and Zn. Compared with the stability of T′ and η′ phases, this core-shell structure of GPB-II effectively inhibited its growth and beneficially maintained a smaller-sized GPB-II phase. The strengthening effect of GPB-II phase was better than that of η or T phases when aging at 150 °C or 200 °C. The mechanical properties of high Zn/Mg ratios Al–Zn–Mg–Cu alloys can enhanced by adding Si.

Design and Rate Control of Large Titanium Alloy Springs for Aerospace Applications

During the separation between satellite and launch vehicles, large steel springs are often used as compression separation spring sets in a catapult separation system. Replacing the steel springs with titanium alloy springs could reduce weight by about 50%. Although titanium alloy springs have been widely used in the aerospace field due to their excellent performance, there are few reports on the design of high-precision titanium alloy springs. The current spring design standards mainly focus on steel springs with helix angles between 5° and 9°, which are not applicable to titanium springs. Moreover, the change in spring rate with ambient temperature should also be considered. In this paper, β-C titanium alloy was used to design and prepare large compression separation springs, replacing steel springs in the catapult separation system. The design of titanium alloy springs took into account the big helix angle. The relationship between helix angle and the number of active coils was calculated. The parameters of titanium alloy springs were determined by the shear stress of the spring at working length. The effects of aging temperature and aging duration on the mechanical properties and modulus of β-C alloy were studied. By adjusting the aging process, the β-C alloy spring rate was controlled to meet the design requirements. The effect of ambient temperature on the mechanical properties and modulus of β-C titanium alloy were also investigated. It was found that as the ambient temperature increased, the rate of the β-C alloy spring gradually decreased.

Enhancing the Mechanical Properties of a 6061 Aluminum Alloy by Heat Treatment from the Perspective of Taguchi Design-of-Experiments

This research investigates the heat treatment parameters of 6061-aluminum alloy to enhance its mechanical properties. The Taguchi design-of-experiments (DOE) method was employed to systematically examine the effects of solutionizing temperature, solutionizing time, aging temperature, and aging time on the tensile strength of the alloy. Mechanical testing suggested a major influence of solutionizing and aging temperatures on the ultimate tensile strength of the alloy. The samples subjected to a solutionizing temperature of 540 °C for 3 h, followed by aging at 170 °C for 18 h, exhibited the highest ultimate tensile strength (293.7 MPa). Conversely, the samples processed at the lowest levels of these parameters displayed the lowest ultimate tensile strength (193.7 MPa). Microstructural analysis confirmed the formation of equiaxed grains, strengthening precipitates, precipitate clusters, and β (Mg2Si) precipitates alongside Fe-Al-Si dispersoids. Energy-dispersive X-ray spectroscopy (EDS) analysis detected the presence of elemental precursors of β phase (Al-Mg-Si) and dispersoid-forming elements (Al-Fe-Si). X-ray diffraction spectroscopy (XRD) analysis revealed the persistence of the β phase in the alloy, indicating its contribution to the improved mechanical properties, which are mainly obtained by aging precipitation phases. Fracture analysis showed a ductile fracture mechanism, and examining fractured samples supported the findings of enhanced tensile properties resulting from the adequate selection of heat treatment parameters. We employed ANOVA (analysis of variance) to analyze the DOE results, using a multiple regression model to express the ultimate tensile strength of the alloy in terms of the variables used in the design. This yielded an adjusted coefficient of determination of 89.75%, indicating a high level of explained variability in the test data for evaluating the model’s predictive capacity.

Effect of heat treatment on the microstructure and properties of CuCrZr prepared by laser powder bed fusion

In this paper, CuCrZr alloys were prepared by laser powder bed fusion technique. Under optimum forming process conditions, a relative density of 99.7% was obtained and the specimens were analyzed for microstructure and properties. To enhance the mechanical properties of the copper alloy, the specimens are post-treated using both solution aging and direct aging heat treatments. The variation and influence mechanism of microstructure and mechanical properties, thermal conductivity and electrical conductivity were studied and analyzed. With direct aging heat treatment a large number of Cr nanoprecipitates can be obtained, significantly improving the properties of the alloy. The best synthesis properties obtained at an aging temperature of 450 °C were: microhardness 168.7 ± 3.1 HV, ultimate tensile strength 481.7 ± 7.6 MPa, electrical conductivity 73.9 ± 0.9 %IACS, thermal conductivity 314.3 ± 5.3 W/(m·K).

Effects of aging processes on the microstructure, texture, properties and precipitation kinetics of the Cu–Cr–Zr–Nb alloy

The Cu–Cr–Zr–Nb alloy bars were prepared by vacuum melting, hot forging, solution treatment, and drawing. The effects of aging processes on the microstructure, texture, mechanical properties and electrical conductivity of the alloy were studied, and the precipitation kinetics was analyzed. Besides, the effect of adding Nb to the Cu–Cr–Zr alloy was simulated by the first-principles calculation. The results showed that when the aging temperature increased from 400 °C to 460 °C, Cube texture and Brass texture were transformed into Copper texture. The Cu–Cr–Zr–Nb alloy exhibited superior comprehensive properties such as a hardness of 84.3 HRB, a tensile strength of 520 MPa, an elongation of 19.0 %, and an electrical conductivity of 83.5 International Annealed Copper Standard (%IACS) after being aged at 460 °C for 4 h. The precipitation kinetics and electrical conductivity equations under different aging temperatures were established, and the precipitation activation energy of 24 kJ/mol was obtained. Moreover, the precipitation process of the alloy was also described by the Avrami empirical equation. It was found that the reaction mechanism of the alloy changed from nucleation and growth to one-dimensional diffusion as the aging temperature increased from 400 °C to 520 °C. It was also confirmed that Nb and Cr formed the Cr2Nb compound according to the first-principles calculation.

Precipitation behaviors and the related strengthening mechanism in 2219 Al alloy fabricated by wire arc additive manufacturing

Normally, a large number of dislocations could be introduced into the metallic component in the additive manufacturing process. The effects of these thermal stress-induced dislocations on the precipitation of 2219 Al alloy have thus far not been comprehensively studied. In the present study, the precipitation behaviors of 2219 Al alloys fabricated by wire arc additive manufacturing are investigated in detail by multi-scale experimental methods, including transmission electron microscopy, scanning electron microscopy, and X-ray diffraction analyses. Our study suggests that the stress-induced dislocations could act as the heterogenous nucleation sites, facilitating the precipitation of θ′ and θ′′ phases in the deposition process. During the subsequent artificial aging, θ′ and θ′′ phases are present in the 160°C peak-aged sample. Raising the aging temperature from 160°C to 180°C could facilitate the transformation of θ′′ to θ′ phases. Moreover, for the 200°C peak-aged sample, the number density of θ′ phases appears to decrease with accompanied coarsening. An evident improvement occurs in the comprehensive mechanical properties of the as-deposited sample by appropriate heat treatment (540℃/3 h-180℃/14 h). The ultimate tensile strength significantly increases from 238 MPa to 408 MPa, exhibiting an enhancement of approximately 70 %, while the elongation increases from 14 % to 15 %. Additionally, a quantitative correlation is established between the precipitate characteristics and mechanical properties.

Effect of waste engine oil and warm mix additive on the physical, rheological, and short-term aging attributes of Styrene–Butadiene Rubber-modified asphalt binders

Styrene-butadiene rubber (SBR) latex is used widely to increase the low-temperature resistance of asphalt binders. However, the high content of butadiene copolymer in SBR-treated asphalt causes oxidation and aging. Furthermore, following the SBR modification, the compatibility and thermal storage stability of SBR-modified asphalt is not satisfactory. Therefore, the best approach to improve the quality of short-term aged SBR-modified asphalt is to lower the manufacturing temperatures of the SBR-modified asphalt mixture. In this study, to reduce the preparation temperatures of SBR-modified asphalt mixes and improve their performance after short-term aging, several additives i.e., waste engine oil (WEO), warm mix agent i.e., ZycoTherm, and WEO/ZycoTherm combination (WEO+ ZycoTherm) were selected. The rheological properties and aging performance of binder samples were evaluated through the rational viscosity, dynamic shear rheometer, bending beam rheometer and Fourier transform infrared spectroscopy tests. The results showed that adding WEO together with ZycoTherm into an SBR-modified binder contributed to reducing the compaction and mixing temperatures. The chemical analysis showed that the three additives i.e., WEO, ZycoTherm, and ZycoTherm/WEO declined the aromaticity and chemical aging indicators of aged SBR-modified binders. Furthermore, it was demonstrated that both the ZycoTherm and WEO/ZycoTherm improved the asphalt resistance to rutting at elevated temperatures in both conditions i.e., before and after short-term aging. In addition, the findings revealed ZycoTherm /WEO compound yielded the best performance to improve the minimal-temperature cracking resistance of the SBR-modified binder, resulting in lower short-term aging temperatures. In summary, this study highlights the necessity of lowering preparation temperatures in asphalt mixes containing SBR to enhance binder resistance to rutting and cracking and reduce susceptibility to oxidation during short-term aging.