Aging Temperature Research Articles

A magnesium alloy with ultrahigh Gd content manufactured by laser directed energy deposition: Heat treatment and microstructure evolution

High RE content is able to improve the age-hardening response of Mg–RE alloys, thus enhancing mechanical properties. Here, we successfully produce a Mg–22Gd–2Zn–0.4Zr (wt%) alloy with ultrahigh Gd content using laser directed energy deposition (LDED) and investigate the microstructure evolution during heat treatment. Results show that for the studied alloy, the yield strength is 333 MPa after solution at 520 °C for 2 hours and aging at 200 °C for 64 hours, superior to most existing Mg–Gd alloys, due to the high number density of the strengthening β' phase resulting from high supersaturation. During solution treatment, increasing the temperature improves the solution efficiency by reducing the holding time, while preventing the overgrowth of grains. The peak hardness is around 139 Hv for both 175 °C and 200 °C aging, indicating that the peak hardness of Mg alloys with high Gd content is insensitive to aging temperature. This research can serve as guidance for the heat treatment and microstructure control of high-Gd-content magnesium alloys.

Thermal Treatment Effects on Structure and Mechanical Properties of Polybutylene Terephthalate and Epoxy Resin Composites Reinforced with Glass Fiber.

In this study, two types of composites, polybutylene terephthalate (PBT) and epoxy resin (ER), reinforced with 20% of glass fiber (GF) are used as the comparative research objects. Their mechanical properties after thermal aging at 85~145 °C are evaluated by tensile strength and fracture morphology analysis. The results show that the composites have similar aging laws. The tensile strength of GF/PBT and GF/ER decrease gradually with the increase of aging temperature, while their elastic moduli are independent of the thermal treatment temperature. Scanning electron microscopy study of the fracture surface shows that separation of glass fiber from PBT and ER matrix becomes more obvious at higher aging temperature. The fibers on the matrix surface appear clear and smooth, and the whole pulled out GFs can be observed. As a main mechanical strength degradation mechanism, the deterioration of interface adhesion between the matrix and GF is discussed. A large difference in coefficients of thermal expansion of the matrix and GF is a main factor of the mechanical degradation.

Shape memory effect enhancement via aging treatment of the Cu-Al-Mn-Si alloy manufactured using laser powder bed fusion

This study investigated the effects of aging treatments (200–500℃, 1 h) on the Cu-11.1Al-8.15Mn-0.37Si shape memory alloy manufactured using laser powder bed fusion (LPBF). As the aging temperature increased, the residual stress of the alloy decreased, and the microstructure transitioned from an austenite-martensite dual-phase structure to an austenite single-phase structure. A phenomenon of martensite stabilization induced by low-temperature aging at 200–300℃ was observed, leading to increased phase transformation temperatures and decreased mechanical properties. After aging at 400℃, the plasticity was improved and the shape memory effect (SME) recovery strain experienced a significant 48 % enhancement and reached a maximum value of 3.10 %. This enhancement was due to the improved ordering and texture homogenization of the austenite phase, confirmed by EBSD results. Meanwhile, EPMA analyses revealed the pinning effect of Mn5Si3 precipitations migrated from the grain interior to the grain boundaries which no longer obstructed the movement of martensitic habit planes during the recovery process. Thus, the SME improved. Additionally, after aging at 500℃, a large amount of α phase precipitated along grain boundaries leading to a decrease in mechanical properties. These findings underscore the importance of tailored aging treatments for optimizing shape memory properties in LPBF-manufactured Cu-based shape memory alloys.

Thermo-Mechanical Properties and Benefits of Borosilicate Glass for SOEC Sealants

Boro-silicate glass materials have ideal properties for sealing oxidizing and reducing environments and electrically insulating solid oxide electrolysis cells (SOEC), while maintaining a glassy phase at high temperatures (750-900°C) to minimize chemo-mechanical degradation and gas permeability 1,2. Glass seals are typically applied as a slurry; hence, they are also expected to have non-wetting properties to prevent glass infiltration into the porous electrode structures during manufacturing 3. During the first startup, the initial temperature ramp serves to evaporate any binder in the slurry and to go through the glass transition phase, which cures the glass and increases hardness to improve resistance to creep. Typical glass materials operate in visco-plastic regimes (i.e., beyond the material’s glass transition temperature) and must be chemically stable while operating in steam-rich and oxygen-rich environments. To fully understand the performance of borosilicate glass seals, optimize the manufacturing, assembly, and maintenance of SOEC, we must be able to measure and analyze the glass material properties (i.e., glass transition temperature, coefficient of thermal expansion, modulus, creep, hardness) at the same operating conditions relevant for SOEC operation. In this work, we characterize the thermo-mechanical properties of borosilicate glass powder and sintered samples at various temperatures (ranging from ambient to 850°C), and at different aging conditions (i.e., atmosphere composition, temperature, and duration). The atmosphere composition is changed between air, steam-N2 mixtures, and H2-N2 mixtures to evaluate the chemical stability of borosilicate glass relating to the possible depletion of boron and silicon via the formation of boron hydroxide and silicon vapor when exposed to steam- and hydrogen-rich environments. The aging temperature and duration is varied to evaluate the crystallization kinetics, particle size growth, and its effect on mechanical properties. We employ a combination of Simultaneous Thermal Analysis - STA (i.e., combined Thermogravimetric Analysis - TGA, Differential Scanning Calorimetry - DSC, Fourier Transform Infrared - FT-IR spectroscopy, and Quadrupole Mass Spectroscopy - QMS), and nanoindentation as characterization techniques, while surface roughness is estimated with a 3D confocal optical microscope.Surface roughness varies between 0.83-1.38 𝜇m ± 1.1-1.76 𝜇m (Sa ± Sq). Both powder and solid samples are analyzed via STA with sequential temperature ramps (constant heating rate at 10 K/min in Ar atmosphere) up to 1500°C to estimate the effect of crystallization and particle size on the glass transition onset. For a sample aged at 850°C for 340 h, the first ramp shows typical DSC exothermic peaks (mW/mg) at around 800°C, with a midpoint glass transition occurring at 900°C. However, on the second ramps, peaks lower to around 500°C and the glass transition is estimated to be around 700°C. Subsequent tests consistently mirrored the trend of the second temperature ramp, showing minimal deviation and influence of crystallization and particle growth. Nanoindentation is performed between room temperature and 600°C to characterize both sintered glass samples “as-received” and aged at temperatures between 750-950°C for 340 h. Comparing a sample aged at 750°C with an “as-received” sample, the elastic moduli equally decreased from 100 GPa at room temperature to 40 GPa at 600°C, with comparable hardness values ranging from 10 GPa at room temperature to 0.5-0.9 GPa at 600°C, respectively. A.G. Sabato, G. Cempura, D. Montinaro, A. Chrysanthou, M. Salvo, E. Bernardo, M. Secco, F. Smeacetto, Journal of Power Sources, 328, 262-270 (2016)Dilshat U. Tulyaganov, Allu Amarnath Reddy, Vladislav V. Kharton, José M.F. Ferreira, Journal of Power Sources, 242, 486-502 (2013)S.-B. Sohn, S.-Y. Choi, G.-H. Kim, H.-S. Song, G.-D. Kim, Stable sealing glass for planar solid oxide fuel cell, J. Non. Cryst. Solids. 297 (2002) 103–112. doi:10.1016/S0022-3093(01)01042-0 Figure 1

High Throughput Manufacturing of Highly Ordered Mesoporous Thin Film Oxides for Hybrid-Polymer Nanocomposite Dielectrics

Highly ordered mesoporous metal oxide thin films have potential to become integrated into widely impactful dielectric materials due to the tunable properties of the oxide and its polymer filling; however, current manufacturing techniques to form the mesoporous oxide greatly limit scalable fabrication. Sol-gel mesoporous metal oxides generated via traditional processes require multi-day aging and high temperature, prolonged curing processes to yield controlled porosity at the expense of manufacturability. Moreover, high cost and unstable alkoxide precursors require precision over the solution precursor pH and subsequent thin film aging humidity after deposition.Solution combustion synthesis (SCS) is a next-generation method of generating metal oxides at reduced process temperatures (often <300 ºC) and using green precursors compared to the sol-gel approach. The metal oxide is typically produced from a metal nitrate, which provides both the metal cation and oxidant and an organic chelator fuel. The fuel acts to stabilize the cation against hydrolysis and to participate in the exothermic redox reaction that results in the metal oxide.Here, we present porogen integrated rapid oxidation (PIRO) which utilizes the principles of SCS to fabricate large-area mesoporous thin films of AlOx in less than 1 hour and at a temperature of 230 ºC. The PIRO method uses low-cost precursors to generate micelles with a controllable open-cell porosity ranging from ~30 – 60% and with varying degrees of closed-packed cubic ordering at a nearly 95% reduction in overall processing time. We show the precursor chemistry can be deposited via ultrasonic spray or blade coating at up to 6 m/min to manufacture large area mesoporous oxides and demonstrate filling of the porous AlOx with TOPAS® polymer to generate a hybrid nanocomposite with a dielectric constant of 6.26.

In Situ Measurements of NiAl Precipitation During Aging of Dual Hardening Hybrid Steels

The performance of modern dual hardening steels strongly relies on a well-controlled precipitation processes during manufacturing and heat treatment. Here, the precipitation of intermetallic β-NiAl in recently developed dual hardening steels has been investigated during aging using combined high-energy synchrotron X-ray diffraction and small-angle scattering. The effects of heating rate and aging temperature on the precipitation kinetics and lattice mismatch in two alloys (Hybrid 55 and Hybrid 60) were studied. Precipitation starts already during heating, typically in the temperature range 450 °C to 500 °C. The precipitation process is significantly faster at 570 °C compared to 545 °C for both steel grades, and the number density reaches its maximum already within 1 hours during aging at 545 °C and within 15 minutes during aging at 570 °C. The effect of heating rate is limited, but the precipitation during heating increases in Hybrid 60 when slower heating rate is used. This led to slightly higher volume fractions during subsequent aging, but did not affect the particle size. The lattice mismatch between β-NiAl and the matrix initially develops rapidly with time during aging, presumably due to a developing chemistry of the β phase, until a particle size of around 1.5 nm is reached, whereafter it saturates. After saturation, the lattice mismatch is small, but positive, and independent of temperature during cooling.

The space of secondary α phase significantly affects the mechanical properties of metastable β-type Ti-4V-2Mo-2Fe alloy

In this study, the evolution of the α phase precipitated from metastable β-type Ti-4V-2Mo-2Fe alloy under various aging conditions and its impact on mechanical properties were investigated. With the increase of aging temperature and time, the yield strength of the alloy decreases from the highest 1435 MPa to 995 MPa, and the elongation increases from 3 % to 14 %. Comparing with the volume fraction of αs, the space of αs was identified as the principal factor affecting the alloy’s mechanical properties. The contribution of αs to strength increases as the αs spacing decrease, while elongation improves with the αs spacing increases.

On the microstructural evolution and mechanical property development of additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy with aging temperature

In this study, the microstructure and mechanical properties of a laser powder bed fusion processed eutectic high-entropy alloy, AlCoCrFeNi2.1, and the influence of aging temperature have been investigated. The as-printed material consists of a hierarchical cellular eutectic microstructure with γ cells and a B2 network along the cell boundaries. The γ matrix contains homogeneously distributed Al2O3 nanoparticles and sporadically distributed L12 long-range ordered (LRO) domains. Some B2 grains contain ultrafine body-centred cubic Cr-rich precipitates. Aging at 500–700 °C leads to disruption of the B2 network and coarsening of the B2 grains at the intersections of several cells and thinning of the rest of the regions. At 800 °C, the B2 cellular network completely disappears and turns into large isolated spherical or near-spherical B2 particles with the original γ cells being fully integrated. At 600 °C, numerous ultrafine γ′ nanoparticles form from the γ matrix and turn into elongated γ′ at 700 °C but completely disappear at 800 °C due to the formation of thermally more stable B2 precipitates. The as-printed samples show a high yield strength (YS∼ 1050 MPa) and good ductility (elongation ∼ 20 %) due to the strengthening effects from the LRO domains and the less deformable B2 and Al2O3 particles. Aging at 600–700 °C leads to significant strength improvement mainly owing to the γ′ particles. Aging at 800 °C results in a considerable decrease in YS but improves the ductility due to the disappearance of γ′ precipitates and the B2 cellular network.

Preparation and characterization of micro-cellular melamine foam supported SiO2 aerogel for building thermal insulation

This study aims to complement the advantages of SiO2 aerogel and melamine foam (MF) to produce high-performance building insulation materials. The optimal sol–gel scheme was determined by controlling system temperature, water content, amount of ethanol and amount of acid-base catalyst (orthogonal experiment). The density and porosity of MF/SiO2 aerogel were regulated by adjusting aging time, aging temperature and type of aging agent. Furthermore, the effects of different volume fractions hydrophobic modifier on the surface free energy and wettability of MF/SiO2 aerogel were also investigated. The experiment results showed that the prepared MF/SiO2 aerogel satisfies requirements for low density (0.089 g/cm3), low thermal conductivity at room temperature (0.0256 W m−1·K−1), and excellent hydrophobic performance (the contact angle was 140.1°). Meanwhile, it was found that SiO2 aerogel was stably and uniformly distributed in the pores of the MF and effectively enhanced the mechanical property (a maximum compressive strength of 0.2058 MPa), heat-shielding performance, flame retardant property, and sound absorption capacity(αmax = 0.76, αave = 0.31).Therefore, the MF/SiO2 aerogel composites exhibit exceptional application potential in comparison to conventional building insulation materials (such as EPS, Rock wool board, etc.) due to their significantly low thermal conductivity and remarkable flame retardant properties.

Effect of reagent addition and aging by microwave on the structure of layered double hydroxides

A series of MgAl-layered double hydroxides (MgAl-LDHs) were prepared by variable pH precipitation. The addition of the metal (M) containing solution to the base (B=NaOH) solution, either rapidly (r) or dropwise (d), led to the obtention of the MBr and MBd samples, respectively. In the other hand, by inverting the order of the added solution (pH increase methodology), BMr and BMd were obtained. The BMd sample was microwave aged at 80 °C, 150 °C and 220 °C for 45 min. The results of powder X-ray diffraction showed that rapid precipitation produces more crystalline LDHs than those obtained by dripping. The crystallinity of BMd was improved by microwave aging. All precipitation conditions produced nanoparticles with an average size of around 27.5 nm, which increased almost 5-fold with the microwave treatment. Precipitation by increasing pH gave LDHs with low pore volume, which increased during the heat treatment. Nevertheless, the specific surface area decreased significantly with aging temperature due to the increase in particle size.

Investigation and optimization of short-term aging test conditions for asphalt binders

The existing short-term aging test methods have disadvantages such as not being suitable for high viscosity modified asphalt, different aging degrees between them and poor testing convenience. Therefore, this paper investigated and optimized the aging test conditions of asphalt. The macroscopic rheology and microchemistry of aged asphalt prepared by different aging conditions were comprehensively evaluated. Finally, the most suitable aging test conditions for asphalt was determined by referring to the aging degree of loose asphalt mixture. The experiment results showed that after aging, the rutting factor, carbonyl index, asphaltene content, and creep stiffness of asphalt would increase. The aging degree of existing asphalt aging methods (TFOT and RTFOT) and the corresponding loose asphalt mixture was quite different, and the difference percentage could reach 86.6%. Based on the TFOT test, the asphalt aging conditions were optimized. The aging temperature was 163 ℃. For 70# and SBS modified asphalt, the recommended asphalt film thickness and aging time were 1.59 mm–85 min and 0.80 mm–85 min, respectively. The aging degree of high viscosity modified asphalt under the condition of 0.80 mm–85 min was close to the aging degree of loose asphalt mixture at 135 ℃, and the aging degree of 0.80 mm–100 min was close to the aging degree of loose asphalt mixture at 165 ℃. The proposed aging test conditions can not only accurately simulate the short-term aging behavior of asphalt, but also shorten aging time and save resources.

Effect of precipitation hardening on the microstructure, mechanical, and corrosion properties of additively manufactured A20X aluminum alloy

The effect of age hardening treatment on microstructure, tensile properties, and corrosion behavior of additively manufactured A20X alloy was investigated. Three single-step aging temperatures (150 °C, 175 °C, and 200 °C) and one double-step aging temperature (pre-aging at 165 °C followed by aging at 185 °C) along with varying heat treatment durations ranging from 30 min to 144 h, were studied systematically. Microstructural characterizations revealed that the co-existence of coherent/semi-coherent (Ω, θ′) and incoherent precipitates (θ) resulted in the maximum hardening effect (up to 30 % higher microhardness). This improved the yield strength at room and 150 °C by 33.4 % and 22.6 %, respectively. Double aging delivered the best combination of microstructure with fine grains and optimal precipitate assembly in a short duration (12–16 h). The heat-treated LPBF A20X showed higher ductility and similar mechanical properties compared to the cast A20X. However, optimal precipitate characteristics reduced the corrosion potential by 13–16 % due to a higher galvanic reaction. The highest corrosion potential (−0.622 V) was achieved in the solutionized state.

Effect of Heat Treatment on Structure Evolution and Mechanical Property Strengthening of Low-Cobalt Nickel-Based Superalloy

In this paper, the microstructure of an alloy was regulated by means of strengthening solution aging, and microstructure observation and composition analysis were carried out by means of an optical microscope and X-ray diffractometer. Combined with the Vickers hardness tester, electronic universal testing machine and high-temperature persistent creep testing machine, the mechanical properties and high-temperature properties of the alloy were tested, and the strengthening mechanism of the alloy was explored. The results showed that the dendritic morphology and structure of the alloy decreased with an increase in temperature during the solution process, and the γ′ phase morphology also changed with the solution temperature: oval → cross → cubic. The γ′ phase after solid solution at 1295 °C was closest to the cubic form. Therefore, it is believed that the 1295 °C solution treatment had the best effect. In the aging process, the uniform cubic degree of γ′ phase distribution was the highest at 1090 °C. On the basis of fixed aging temperature (1090 °C), it was found that the volume fraction of the γ′ phase increased significantly after 8 h. The γ′ phase, which was closest to the cubic form, had the largest proportion of precipitation, and the volume fraction increased to 70.3%. The minimum carbide volume was 1.0%. The hardness of the alloy reached 435.8 HV; the yield strength increased to 280.1 MPa; and the durability of the alloy under the conditions of 1000 °C/230 MPa and 870 °C/655 MPa was 99.7 h and 42.7 h, respectively, which achieved the purpose of alloy design.

Heat Treatment Post-Processing for the Improved Mechanical Properties of Scalmalloy® Processed via Directed Energy Deposition

As high-strength aluminum alloys present several processability issues with additive manufacturing (AM), Scalmalloy®, an Al-Mg-Sc-Zr-based alloy, has been developed. This alloy is age-hardenable, allowing it to precipitate out a strengthening precipitate phase, Al3(Sc,Zr). The manufacturer recommends a single-stage aging treatment at 325 °C for 4 h; however, the majority of the literature studies utilize a powder bed processing known as selective laser melting (SLM) over powder-fed processing directed energy deposition (DED). This study addresses the lack of information on heat treatments for DED fabrication by exploring the application of artificial aging temperatures of 300–400 °C for 2, 4, and 6 h to: 1. determine the impact on the microstructural evolution and mechanical performance and 2. determine whether the recommended treatment for Scalmalloy® is appropriate for DED fabrication. Tensile testing determined that low-temperature treatments exhibited no visible dependence on time (2–6 h); however, time becomes influential at higher temperatures starting at 350 °C. The temperature plays a considerable role in the mechanical and microstructural behaviors of DED Scalmalloy®. The highest tensile strength was noted at 300 °C (384 MPa, 21.6% increase), but all heat-treated cases resulted in an improvement over the as-built case. This investigation established that increasing the treatment temperature resulted in a decreasing trend for the tensile strength that held over time. Elongation at 2 h displayed a near parabolic trend that peaks at 350 °C (20%) and falls with higher temperatures. At the 4 h treatment, a slight decreasing trend was noticed for elongation. No visible change was observed for elongation at 6 h, with elongation values remaining fairly consistent. The microstructural evolution, including micron-sized and nano-sized Al3(Sc,Zr) and grain size, was examined, and coarsening effects were noted with the increase in the temperature. It is recommended that treatment be conducted at 300 °C to achieve the precipitation of the strengthening Al3(Sc,Zr) phase while minimizing coarsening.

Durability of partially cured GFRP reinforcing bars in alkaline environments with or without sustained tensile load

Corrosion of steel reinforcing bars (rebars) in reinforced concrete structures can be addressed by using corrosion-resistant materials like Fiber-Reinforced Polymers (FRP). However, in France, FRP rebars are primarily restricted to temporary applications due to lack of comprehensive durability data. While numerous studies have explored FRP durability in alkaline environments, understanding the combined effect of alkali ions and sustained loading remains limited. Furthermore, the impact of incomplete matrix curing on the long-term performance of FRP rebars is limited.Accordingly, this paper investigates the durability of Glass FRP (GFRP) rebars exposed to alkali environments at varying temperatures. A batch of partially cured rebars was selected for this study, with part of them undergoing post-curing to investigate the effect of curing state on the ageing behaviour. Additionally, some partially cured specimens were subjected to combined sustained tensile loading at 20 % and 40 % of ultimate strength. Mechanical, physico-chemical and microstructural characterizations were conducted after various exposure durations. Results revealed that incomplete curing minimally impacted long-term tensile properties but significantly affected the interlaminar shear strength of aged rebars. Moreover, applying a combined load had little influence on residual properties at 20°C but led to rapid reduction in GFRP residual tensile strength at higher ageing temperatures (40 and 60°C).

Surfactant-Free Synthesis of Melon Seed-Like CeO2 and Ho@CeO2 Nanostructures with Enriched Oxygen Vacancies: Characterization and Their Enhanced Antibacterial Properties.

To overcome the poor antibacterial performance of cerium oxide (CeO2) nanoparticles at low concentrations, melon seed-shaped CeO2 (MS-CeO2) and holmium (Ho)-doped CeO2 (Ho@MS-CeO2) nanoparticles were synthesized using a simple precipitation method without the addition of any surfactants. The surface morphology, phase structure, crystallinity, Ce3+ and Ce4+ valence, lattice defects, and reactive oxygen species (ROS) production of both synthesized nanostructures were examined using different techniques, i.e., scanning electron microscopy (SEM), energydispersive X-ray (EDX), resolution transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), Raman spectroscopy, ultraviolet (UV) spectra, fluorescence spectra, and zeta potential (ζ). The results show that under certain stirring and aging temperatures, CeO2 and Ho-doped CeO2 nanoparticles with a melon seed-like morphology can be prepared in a short period. Both nanoparticles were tested as antiseptic agents against G+ and G - bacteria (E. coli and S. aureus), and the results confirmed that the Ho@MS-CeO2 nanostructures exhibited remarkable antimicrobial activity at a low concentration (0.5 mg/L) compared with the control group, which is attributed to the reversible conversion of Ce3+ and Ce4+ in the ceria crystal lattice, enriched oxygen vacancy, ROS species production, and positive surface charge.

Effect of aging temperature on the microstructure and properties of alloyed high‐manganese steel

Effect of aging temperature on the microstructure and properties of alloyed high‐manganese steel

Effect of aging temperature on the lubricated wear resistance of multi-directionally forged Al-40Zn-3Cu alloy

The effect of aging temperature on the lubricated wear behavior of multi directionally forged Al-40Zn-3Cu alloy was systematically investigated at different loads and sliding speeds. Microstructural and worn surface examinations of the alloy samples were performed by scanning electron microscopy, scanning transmission electron microscopy and energy dispersive spectrometry while their tribological properties were investigated with a ball on disc type wear test apparatus. The results showed that aging treatment at different temperatures after multi-directional forging changed the morphology of Zn-rich nanoscale η precipitates and Cu-rich θ particles and their dispersion in α-Al matrix. Their changes brought about an increase in hardness, strength, and wear resistance of Al-40Zn-3Cu alloy but a decrease in its ductility. It was also observed that the aging temperature, load and sliding speed had a combined effect on their wear response. As the applied load and sliding speed increased, friction coefficient of the samples decreased while their mass loss increased continuously with load but decreased with sliding speed after showing an increase. The adhesion, abrasion and oxidation were observed to be operative wear mechanisms for the alloy. The wear results of the alloy samples were discussed in terms of their microstructures and mechanical properties, and oil lubrication. The aging treatment at 150 °C after multi-directional forging increased the wear resistance of Al-40Zn-3Cu alloy more than 50 percent by providing a moderate hardness (129 HB), yield strength (310.9 MPa), tensile strength (383.2 MPa), and ductility (9.9 %).

Influence of ageing and moisture conditions on the ravelling resistance of the micro-surfacing mix

ABSTRACT In this study, the durability of the micro-surfacing mix was assessed by investigating the synergistic effect of ageing and moisture conditioning on ravelling. A total of 30 combinations of conditioning protocols were considered. Ageing time and temperature were varied between 85–105°C and 24–120 h, whereas moisture conditioning time and temperature were varied between 25–60°C and 24–192 h. The results showed that after the mix was fully cured, increased stiffness led to a substantial decrease in ravelling. Synergistic assessment of ageing and moisture showed that ageing temperature had the highest, whereas moisture conditioning time had the least influence on ravelling. It was noticed that once the specimens were fully cured and subjected to further ageing, the effect of moisture conditioning temperature on ravelling became minimal. Overall, laboratory investigations pointed out that micro-surfacing should be applied during favourable environmental conditions, facilitating faster moisture loss and strength gain to improve durability.

Using fuzzy logic based-modeling and simulated annealing approaches to optimize the hardness distribution of 2024 aluminum alloy during precipitation hardening heat treatment cycles

The present study assesses the impact of age hardening parameters, including aging temperature, aging time, and solution time, on the ultimate hardness of heat-treated 2024 aluminum alloys. Using a numerical approach, fuzzy logic systems were utilized as a robust tool to forecast the mechanical characteristics of high copper aluminum solid solutions throughout the age hardening process. In addition, an attempt was made to use a novel simulated annealing technique to determine the optimum hardness and its corresponding process parameters to achieve the highest mechanical properties. Comparing a fuzzy logic model with experimental results obtained from the Brinell hardness test showed the accuracy and confidence of the fuzzy model in representing such properties. The optimization results indicated that the maximum hardness can be obtained with a solution aging temperature of 173.5 °C, an aging time of 19 hours, and a solution time of 58 minutes. Overall, the variation in the experimental peak hardness obtained using the optimized process parameters was the deciding factor in believing the model.