Artificial Aging Behavior Research Articles

Artificial aging behavior of SiCP/AA2009 composite by electric heating: Mechanisms and modelling

SiCP/Al composite is regarded as a superior alternative material in the aerospace industry due to its excellent properties. Meanwhile, electrically-assisted aging (EAA) heat treatment has emerged as a promising method for artificial aging to obtain better aging performances. This study explores the potential of EAA heat treatment to enhance the aging kinetics of SiCP/Al composite. The impact of EAA on the aging behavior of SiCP/AA2009 composites is investigated and compared with conventional furnace aging treatment, ranging from microstructure to macroscopic properties. The electric current has few effects on the evolution trend of aging strength, but can enhance the aging process of SiCP/AA2009 with higher yield strength (about 13.7 MPa improvement) and ultimate tensile strength (about 9.7 MPa improvement). Analysis of microstructures demonstrates that EAA can generate more nucleation sites and reduce consumption of Cu atoms by Cu–Mg co-clusters near SiCP interface, resulting in more θ’ phases compared to conventional aging (CA). Additionally, more fine precipitates and dislocations contribute to higher strength under EAA condition. Subsequently, a precipitation kinetic model based on the Lagrange-like approach is employed to predict the particular electric current effects on the particle size distribution and evolution during aging, and to calculate yield strength by establishing a relationship between microstructural characteristics and macroscopic performance, providing a model basis for the design of potential EAA processes.

Effect of Deep Cryogenic Treatment on the Artificial Aging Behavior of 6082 Aluminum Alloy

This study investigates the impact of cryogenic treatment duration on the mechanical properties and microstructural evolution of 6082 aluminum alloy subjected to subsequent artificial aging. Tensile tests were conducted using an electronic universal testing machine, and the microstructure was characterized by employing optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that both the tensile strength and elongation of the alloy first increase and then decrease with the extension of cryogenic treatment duration. The alloy treated with 12 h of cryogenic treatment followed by artificial aging at 180 °C for 8 h achieved a peak strength of 390 MPa. Meanwhile, the alloy treated with 8 h of cryogenic treatment and the same artificial aging process reached a maximum elongation of 13%. All specimens of 6082 aluminum alloy subjected to cryogenic and aging treatments exhibited ductile fracture under room temperature tensile conditions. The size of dimples at the fracture surface first increased and then decreased with increasing cryogenic treatment duration, indicating a transition from deeper to shallower dimples. The cryogenic treatment did not significantly affect the grain size of the alloy, which remained approximately 230 µm on average. Cryogenic treatment facilitated the precipitation of fine, densely distributed precipitates, enhancing the pinning effect of dislocations and thus improving the tensile strength. Additionally, cryogenic treatment increased the dislocation density and promoted the formation of subgrains, while the grain boundary precipitates transitioned from a continuous to a discontinuous distribution, all of which contribute to the enhancement of the plasticity.

The Influence of TiB2 Particles on the Artificial Aging Behavior of TiB2/Al–5Cu Composite

The Influence of TiB2 Particles on the Artificial Aging Behavior of TiB2/Al–5Cu Composite

Effects of Sn addition on precipitation of a pre-naturally aged Al–Zn–Mg alloy during artificial aging

The effect of Sn addition and pre-natural aging on the artificial aging behavior of Al–Zn–Mg alloy was investigated using both experimental approaches and first principle study. The result shows that Sn retards hardness increase at the initial stage of artificial aging by inhibiting the formation of Guinier-Preston zones (I). Atom probe tomography and density functional theory have revealed that the high binding energy of Mg-Sn disturbs Mg-Zn clustering and delays the formation of Guinier-Preston zones (I). However, the retardation effect of Sn on the artificial aging was found to be suppressed when the pre-natural aging was applied to the Al–Zn–Mg–Sn alloy: hardness at the initial stage increased rapidly compared to the Al–Zn–Mg alloy with pre-natural aging. The reason for the rapid increase of hardness in the Al–Zn–Mg–Sn alloy with pre-natural aging is that Guinier-Preston zones (II) was directly formed from vacancy-rich clusters in the Al–Zn–Mg–Sn alloy in contrast to the Al–Zn–Mg alloy with pre-natural aging. This means Mg-Sn and Zn-rich cluster formed during pre-natural aging can accelerate precipitation kinetic by providing nucleation site for Guinier-Preston zones (II) during artificial aging.

Effects of natural aging on the artificial aging kinetics and responses of Al–5Mg–3Zn–1Cu (wt.%) alloy

Effects of natural aging (NA) on artificial aging (AA) behavior of Al–5Mg–3Zn–1Cu alloy were studied from the perspectives of kinetics and microstructure evolution. The results show that short-term NA (24 h) has marginal effects on AA at any temperature, as well as long-term NA (>240 h) on low-temperature AA (120 °C), but long-term NA can accelerate aging kinetics and alleviate severe hardening ability attenuation at high temperatures (>150 °C). Analysis of the precipitates evolution demonstrates that such attenuation is primarily attributable to coarsening and reduction of intragranular precipitates and is also slightly related to the formation of precipitate-free zone (PFZ). Three main factors cause the unfavorable microstructure in NA-free alloy at high temperatures AA: (1) Insufficient nucleation of intragranular precipitates induced by weakened nucleation driving force, larger critical nucleation radius, and rapid vacancy annihilation; (2) The nucleated precipitates are prone to coarsening; (3) The precipitation near grain boundary is obstructed due to the depletion of vacancies and solutes. Clusters formed during NA can inhibit the unfavorable microstructure by delaying the annealing out of excess vacancies, promoting the nucleation of precipitates, and elevating the activation energy for precipitation coarsening, thereby enhancing the hardening potential. This work is instructive for the formulation of heat treatment strategies for Al–Mg–Zn–Cu alloys with high Mg/Zn ratios.

Effect of pulsed electromagnetic field treatment on dislocation evolution and subsequent artificial aging behavior of 2195 Al-Li alloy

In this paper, the pulsed electromagnetic field treatment (PEFT) is designed between the pre-stretching and artificial aging of the thermomechanical treatment. Using electron microscopy and hardness test, the effect of the PEFT on dislocation evolution and subsequent artificial aging behavior of spray deposited 2195 Al-Li alloy is studied. The results show that although the PEFT reduces the Vickers microhardness of the specimen, it improves the hardening kinetics and precipitation strengthening of the specimen during the subsequent artificial aging process. Besides, it is found that the PEFT reduces the dislocation density of the pre-stretching specimen and improves the dislocation uniformity. The PEFT makes the T 1 precipitate obtained by the subsequent artificial aging process more finely dispersed, a decrease of the average thickness by 57.6%. From simulation combined with theoretical analysis, it is found that the static recovery induced by temperature rise is an important reason for the decrease of dislocation density on the specimen during the PEFT. The magnetically induced stress is an important driving force for a more uniform dislocation distribution. The mechanism of the microstructure evolution of the material is systematically discussed and summarized. • The effect of pulsed electromagnetic field treatment (PEFT) on microstructure evolution of 2195 Al-Li alloy was studied. • PEFT reduced the dislocation density of the pre-stretching specimen and improves the dislocation uniformity. • PEFT made the T 1 precipitate obtained by the subsequent artificial aging process more finely dispersed. • The static recovery induced by temperature rise and magnetically induced stress was discussed.

Influence of Pre-Aging on the Artificial Aging Behavior of a 6056 Aluminum Alloy after Conventional Extrusion

In the present study, the influence of the initial heat-treatment conditions on the artificial aging behavior after conventional linear extrusion at room temperature was investigated for the precipitation hardening of a 6056 aluminum alloy. A solution-annealed condition was systematically compared to naturally-aged and pre-aged conditions. Differential scanning calorimetry was used for analyzing the precipitation sequence and its dependence on the initial heat treatment. The natural aging behavior prior to extrusion and the artificial aging behavior after extrusion were determined by microhardness measurements as a function of the aging time. Furthermore, the microstructure, dependent on the induced strain, was investigated using optical microscopy and transmission electron microscopy. As a result of pre-aging, following a solid-solution treatment, the formation of stable room-temperature clusters was suppressed and natural aging was inhibited. The artificial aging response after extrusion was significantly enhanced by pre-aging, and the achieved hardness and strength were significantly higher when compared with the equally processed solution-annealed or naturally-aged conditions.

Surface Characterization and Optical Properties of Reinforced Dental Glass-Ceramics Related to Artificial Aging.

The development of various dental glass-ceramic materials and the evolution of novel processing technologies lead to an essential change in the clinical and technical workflow. The long-term success of a dental restoration treatment is defined by its durability, which is directly influenced by the oral environment. This study’s purpose was to evaluate the artificial aging behavior of nanostructured, respective microstructured ceramics related to surface topography, roughness, and optical properties. Six monolithic restoration materials were selected: milled lithium disilicate glass-ceramic (LDS-M) MT (medium translucency), hot-pressed lithium disilicate glass-ceramic (LDS-P) MT and HT (high translucency), milled zirconia-reinforced lithium silicate ceramic (ZLS-M) MT and hot-pressed zirconia-reinforced lithium silicate ceramic (ZLS-P) MT and HT, resulting n = 96 surfaces. All the samples were artificially aged by thermal cycling, and all investigations were made before and after thermal cycling. In terms of optical properties, differences recorded between ZLS and LDS ceramics are not significant. Thermal cycling increases the translucency of ZLS and LDS glass-ceramic materials significantly, with the most harmful effect on the pressed and polished samples. Micro- and nano roughness are significantly influenced by in vitro aging and a negative correlation was recorded. Glazed samples are characterized by significant rougher surfaces for all types of materials. On nanolevel, ZLS materials are significantly smoothed by thermal cycling.

Influence of the heat-treatment prior to plastic deformation on the aging behavior and the hardness of the aluminum alloy 6056

Motivated by the improvement of the cost and resource efficiency of the manufacturing process of age-hardening aluminum components, the influence of an initial heat-treatment, prior to plastic deformation, on the artificial aging behavior and the hardness is investigated. Systematic work is done by comparing three initial heat-treatment conditions of the age-hardening aluminum alloy 6056 prior to low-temperature plastic deformation: a solid-solution heat-treated, a naturally aged and a stabilized one. Two plastic deformation processes, linear extrusion and compression, each with two different strains, respectively, were performed and followed by artificial aging. The hardness was measured prior to plastic deformation as a function of the natural aging time, and after plastic deformation as a function of the artificial aging time. Stabilization annealing of the aluminum alloy inhibited natural aging. After plastic deformation and artificial aging, the stabilized conditions showed an increased hardness, as compared to the solid-solution heat-treated, respectively naturally aged, condition. The artificial aging behavior of all tested conditions was only slightly influenced by the respective plastic deformation process. However, the hardness was similar for the extruded, respectively compressed, conditions in their respective initial heat-treatment conditions.

Influence of quenching temperature on peak aging time and hardness of Al-Mg-Si-Cu alloys strengthened by nano-sized precipitates

The quenching temperature plays a rather important role in the subsequent artificial aging behavior and resulting hardness of the Al-Mg-Si (or Al-Mg-Si-Cu) alloys, but related reports are limited. This paper presents a detailed investigation about the influence of the quenching temperature (ranging from 490 °C to 570 °C) on the precipitate microstructure, precipitation rate and aging hardness of a typical Al-Mg-Si-Cu alloy 6061. Methods such as TEM microscopy, real-time electrical resistivity monitoring and Vickers hardness testing were employed. The TEM results show that the main precipitate in peak aged status is needle shaped β″ with sizes of several nanometers in cross section and ten to twenty nanometers in length. It gradually grows up in size and transforms to Q′ phase in the over aged status. Hardness and resistivity measurement results show that the hardness increases while the resistivity decreases as the artificial aging proceeds. With higher quenching temperature, the size of the β″ phase gets finer and its total amount becomes more. Its precipitation kinetics also turns out to be much higher. The time for reaching the peak aging hardness prolongs from about 2–10 h as quenching temperature increases from 490 °C to 570 °C. But these effects becomes not so obvious when quenching temperature exceeds 550 °C, pointing out that it is the critical quenching temperature for this kind of alloy. Related mechanisms are explained from the aspects of super saturation solid solution level, quenched-in vacancy concentration, precipitate nucleation, growth rate etc. These results establish a significant heat-treatment guideline for mass production of these alloys.

A multi-method approach to quality control illustrated on the industrial powder coating process

Industrial powder coating processes offer a unique object of application for rheometers.Compared to classic coating procedures with liquid materials, powder coating is still a relatively young procedure. First industrial applications date back to the mid-1960s. Since then these applications have considerably increased, which can be mainly attributed to the desire for more environment-friendly coating systems. The powder coating process is dependent on one end on pneumatic conveyance behavior, namely the transport as a dense fluidized phase of powder and the associated bulk solid values, on the other end on bulk polymer behavior to determine and keep constant the curing point at which the applied powder bonds and produces an (ideally) smooth surface. This multivariant process is an ideal object of quality control for the MCR rheometers and two accessories: the Powder Cell and a disposable Plate–Plate Geometry with Peltier heated hood (P-PTD200, H-PTD200).In this work we will show the influence of both artificial aging behavior as well as flow aids on the powder flow properties (collapsed and fluidized) as well as the melting and polymerization steps and show a way to optimize processes utilizing this complex system.

The Influence of Composition on the Clustering and Precipitation Behavior of Al-Mg-Si-Cu Alloys

The natural aging (NA) and artificial aging (AA) behavior of Al-Mg-Si-Cu alloys with different Mg/Si ratios and Cu additions were systematically investigated by means of hardness test, atom probe tomography, transmission electron microscopy, and Monte Carlo simulation. The Si-rich low-Cu alloys displayed higher hardness compared to the Mg-rich equivalents because Si atoms play a dominant role in clustering of solute atoms during both natural and artificial aging. In the high-Cu alloys, Cu did not obviously change the cluster distribution during NA, but significantly refines the clusters and precipitates due to the strong interaction of Cu atoms with Mg atoms during AA. In contrast to the low-Cu alloys, the Mg-rich high-Cu alloys exhibit higher hardness in the early and over-aged stages of artificial aging, with similar or slightly higher hardness in the peak aging condition compared to their Si-rich counterparts. Three types of precipitates (β″, Q′, and L) are favored in the high-Cu alloys. The Mg-rich high-Cu alloy has more L phase, while the Si-rich variant is abundant in Q′ phase. The negative effect of NA on subsequent AA behavior is less dependent on Mg/Si ratio in the high-Cu alloys due to a synergistic action of the residual Si and Cu atoms, but is closely related to Mg/Si ratio in low-Cu alloys.

Influence of Aging Treatments on Alterations of Microstructural Features and Stress Corrosion Cracking Behavior of an Al-Zn-Mg Alloy

7xxx series Al-Zn-Mg-(Cu) alloys have higher strength in their peak-aged (T6) states compared with other age-hardenable aluminum alloys; however, the maximum strength peak-aged state is more susceptible to stress corrosion cracking (SCC) which leads to catastrophic failure. The over-aged (T7) temper with 10-15% lower strength has higher resistance to SCC requiring oversized structural aerospace component applications. The medium-strength AA7017 Al-Zn-Mg weldable alloy without Cu is also prone to SCC under certain environmental conditions. In the present investigation, the SCC behaviors of an AA7017 Al-Zn-Mg alloys of different tempers have been assessed. Specific aging schedules have been adapted to an AA7017 alloy to produce various tempers, e.g., under-, peak-(T6), over-(T7), and highly over-aged tempers. Artificial aging behavior of the AA7017 alloy has been characterized by hardness, electrical conductivity measurements, x-ray diffraction, differential scanning calorimetry, and electrochemical studies. Slow strain rate test technique was used to assess the SCC behaviors of the AA7017 alloys of under-, T6, T7, and highly over-aged tempers in 3.5 wt.% NaCl solution at free corrosion potential (FCP) and at applied anodic potential, as well. Results revealed that the AA7017 alloy tempers are not susceptible to SCC in 3.5 wt.% NaCl solution at FCP, but severely damaging to SCC at applied anodic potentials. Microstructural features, showing a non-recrystallized grain structure and the presence of discrete, widely spaced, not-interconnected η precipitates at the grain boundaries, are the contributive factors by virtue of which the alloy tempers at FCP did not exhibit SCC. However, the applied anodic potential resulted in rapid metal dissolution from the grain boundary region and led to SCC. The local anodic dissolution (LAD) is believed to be the associated SCC mechanism.

Feasibility Study on Die Quenching of AA2024 Aluminum Alloy Billet Using Servo Press

Die quenching of an AA2024 aluminum alloy billet was carried out using a servo press with ram motion control of WC-20mass%Co dies directly after solution heat treatment (SHT). The cylindrical billets were heated in an electric furnace and transferred to the press, then subjected to uniaxial compression with a reduction in height (Δh/h0) of 2%, 5% or 10% after SHT at 773 K or 823 K. The die quenching was successfully carried out without the precipitation hardening only on the billet after SHT at 823 K by sandwiching for 8 s. The subsequent artificial aging behavior at 463 K in an oil bath was investigated. It is found that the precipitation kinetics is accelerated in the die-quenched billets after SHT at 823 K. The peak hardness of the billet processed with 5% after SHT at 823 K is as high as that of the water-quenched billet, HV 149.0.

Interdependent effect of chemical composition and thermal history on artificial aging of AA6061

In this study, the interdependent effect of chemical composition and thermal history on artificial aging was investigated for the aluminum alloy AA6061. Based on thermodynamic calculations, including Al, Fe, Cr, Zn, Ti, Mg, Si and Cu, model alloys exhibiting a maximum variation of the reachable solute super-saturation of elements relevant for precipitation hardening within the compositional limits of AA6061 were produced. The artificial aging behavior of these alloys at 175°C was studied by tensile testing for two thermal histories, including very short- and long-term room temperature storage after quenching. Precipitation during artificial aging was investigated by an analysis of yield strength data. As generally expected, precipitation kinetics was found to depend strongly on the solute super-saturation in the case of very short room temperature storage. For artificial aging after long-term room temperature storage the kinetics showed almost no dependence on the chemical composition. This seems to be an exception from simple precipitation kinetics and can be explained based on the complex role of quenched-in vacancies in artificial aging of AA6061.

T4 and T6 Treatment of 6061 Al-15 Vol. % SiCP Composite

Aging temperature history has profound effect on the mechanical and corrosion behavior of 6061 Al/SiC composite. In order to understand the effect of aging on the corrosion resistance, the natural and artificial aging behavior of 15 vol. % 6061 Al-SiCP composites was studied using the aging treatment and the Brinell hardness measurements. The aging curves for the composite (T6 treated) were determined at various aging temperatures such as room temperature, 140, 160, 180, 200, 220, and 240°C. According to the peak hardness variation with temperature profile, it is found that the composite is underaged at 140°C and 160°C. Peak aging takes place at 180°C. Overaging takes place at 200°C, 220°C, and 240°C. The natural aging characteristics of the composite (T4 treated) are also studied using the Brinell hardness measurements.

Mechanisms controlling the artificial aging of Al–Mg–Si Alloys

In this study the artificial aging behavior of the Al–Mg–Si alloy AA 6061 was investigated in the temperature range 150–250 °C using atom probe tomography, hardness and resistivity measurements for various thermal histories. It was found that the precipitation kinetics and age-hardening response of artificial aging at temperatures below 210 °C are lowered by prior natural aging but enhanced above this temperature. An analysis of hardness data was used to evaluate the temperature dependence of precipitation kinetics and dissolution processes. Supported by theoretical considerations, it is assumed that artificial aging of Al–Mg–Si alloys is controlled via the concentration of mobile vacancies. The “vacancy-prison mechanism” proposed determines the mobile vacancy concentration in the case of natural pre-aging by temperature-dependent dissolution of co-clusters and solute–vacancy interactions.

Enhancing the performance of exterior waterborne coatings for wood by inorganic nanosized UV absorbers

Enhancing the durability of the architectural wood coatings is essential for a successful commercialization of the forest products. Therefore, this paper is focused on UV resistant waterborne nanocomposites coatings for exterior uses of wood, which were improved with inorganic UV absorbers such as zinc oxide and titanium dioxide nanoparticles. The performance of such nanocomposites coatings applied on black spruce boards was demonstrated trough accelerated weathering. Artificial aging behavior of the coatings was followed by color, gloss and thickness changes. Scanning electron microscopy and transmission electron microscopy was used to investigate nanoparticles dispersion in nanocomposite dry films. Fourier Transform Infrared Spectroscopy was used to characterize the chemical modification of the weathered coatings surface. The results have shown significant improvement in UV-shielding of the nanocomposites coatings. Depending of aging criteria, a selection of the best nanocomposite coatings formulations for exterior wood could be done.

Artificial Aging Behavior of 6063 Alloy Studied Using Vickers Hardness and Positron Annihilation Lifetime Techniques

Many aluminum-based alloys are strengthened by a heat treatment process known as age hardening. The aim of this work was to produce a high-strength 6xxx series aluminum alloy by adjusting the processing conditions, namely solutionizing and artificial aging. It consists of heating the alloy to a temperature at which the soluble constituents will form an homogeneous mass by solid diffusion, holding the mass at that temperature until diffusion takes place, then quenching the alloy rapidly to retain the homogeneous condition. In the quenched condition, heat-treated alloys are supersaturated solid solutions that are comparatively soft and workable, and unstable; depending upon the composition. After solution treatment and quenching, hardening is achieved either at room temperature (natural aging) or by precipitation heat treatment at a suitable temperature (artificial aging). Precipitation heat treatments are generally low-temperature long-term processes. Temperatures range from 115 to 190°C and times vary from 5 to 48 h. Choice of time-temperature cycles for precipitation heat treatment should receive careful consideration. The objective is to select the cycle that produces the optimum precipitate size and distribution pattern. The mechanical characterization of heat-treatable 6xxx (Al-Mg-Si-Cu based) 6063 wrought aluminum alloys was studied. Their effects were investigated in terms of the microstructure, using positron annihilation lifetime techniques and mechanical properties monitoring via Vickers hardness measurements. The hardness is the resistance of a material to plastic deformation, which gives it the ability to resist deformation when a load is applied. The greater the hardness of the material, the greater the resistance it has to deformation. The hardness of 6063 alloy has its maximum value (58) when aged for 8 hours at 175oC after quenching from 520oC; which is the solution temperature of this alloy. The hardness conformed to the literature. We also test the aging ability of the 1xxx aluminum alloy: 1050.

Effects of natural aging and reversion treatments on artificial aging behavior of 6000 series aluminum alloys

Three 6000 series commercial alloys (6061, 6022 and 6 N01) were aged at room temperature, reverted at temperatures above 473 K and finally aged at 448 K. The negative effect of room-temperature pre-aging on age-hardening at 448 K in 6061 and 6022 alloys was not varied by times of pre-aging longer than 10 days. In the 6061 alloy, reversion treatment at 573 K for 30 s resulted in a significant reduction in age hardening at 448 K. It is conjectured that rapid precipitation occurred during the reversion treatment because of the high degree of super saturation caused by its high solute content. Hardening by paint baking at 448 K for 1.2 ks of automotive body panels was largely improved by reversion treatments for 30 s at 523 K in 6061, at 523 K or 548 K in 6022 and at 548 K in 6N01. Concerning with maximum age-hardening at 448 K, improvement by reversion in the negative effect was the same temperature that improved paint bake response the most. The range of reversion temperatures at which the hardening was most improved tended to become narrower with increasing Mg and Si contents.