Activation Energy For Precipitation Research Articles

Study on the Aging Precipitation Behavior and Kinetics of Al-10.0Zn-3.0Mg-2.8Cu Alloy by Pre-Deformation Treatment.

In this paper, the effect of thermomechanical treatment process on the hardening behavior, grain microstructure, precipitated phase, and tensile mechanical properties of the new high-strength and high-ductility Al-10.0Zn-3.0Mg-2.8Cu alloy was studied, and the optimal thermomechanical treatment process was established. The strengthening and toughening mechanisms were revealed, which provided technical and theoretical guidance for the engineering application of this kind of high strength-ductility aluminum alloy. Al-10.0Zn-3.0Mg-2.8Cu alloy cylindrical parts with external longitudinal reinforcement were prepared by a composite extrusion deformation process (reciprocal upsetting + counter-extrusion) with a true strain up to 2.56, and the organizational evolution of the alloys during the extrusion deformation process and the influence of pre-stretching treatments on the subsequent aging precipitation behaviors and mechanical properties were investigated. The results show that firstly, the large plastic deformation promotes the fragmentation of coarse insoluble phases and the occurrence of dynamic recrystallization, which results in the elongation of the grains along the extrusion direction, and the volume fraction of recrystallization reaches 42.4%. Secondly, the kinetic study showed that the decrease in the activation energy of precipitation increased the nucleation sites, which further promoted the diffuse distribution of the second phase in the alloy and a higher number of nucleation sites, while limiting the coarsening of the precipitated phase. When the amount of pre-deformation was increased from 0% to 2%, the size of the matrix precipitated phase decreased from 5.11 μm to 4.1 μm, and when the amount of pre-deformation was increased from 2% to 7%, the coarsening of the matrix precipitated phase took place, and the size of the phase increased from 4.1 μm to 7.24 μm. The finalized heat treatment process for the deformation of the aluminum alloy tailframe was as follows: solution (475 °C/3 h) + 2% pre-stretching + aging (120 °C/24 h), at which the comprehensive performance of the alloy was optimized, with a tensile strength of 634.2 MPa, a yield strength of 571.0 MPa, and an elongation of 15.2%. The alloy was strengthened by both precipitation strengthening and dislocation strengthening. After 2% pre-stretching, the fracture surface starts to be dominated by dense tough nest structure, and most of them are small tough nests, and small and dense tough nests are the main reason for the increase in alloy toughness after 2% pre-stretching deformation.

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.

Achieving ultrahigh strength and ductility via high-density nanoprecipitates triggering multiple deformation mechanisms in a dual-aging high-entropy alloy with precold deformation

How to achieve high-entropy alloys (HEAs) with ultrahigh strength and ductility is a challenging issue. Precipitation strengthening is one of the methods to significantly enhance strength, but unfortunately, ductility will be lost. To overcome the strength–ductility trade-off, the strategy of this study is to induce the formation of high-density nanoprecipitates through dual aging (DA), triggering multiple deformation mechanisms, to obtain HEAs with ultrahigh strength and ductility. First, the effect of precold deformation on precipitation behavior was studied using Ni35(CoFe)55V5Nb5 (at.%) HEA as the object. The results reveal that the activation energy of recrystallization is 112.2 kJ/mol. As the precold-deformation amount increases from 15 % to 65 %, the activation energy of precipitation gradually decreases from 178.8 to 159.7 kJ/mol. The precipitation time shortens, the size of the nanoprecipitate decreases, and the density increases. Subsequently, the thermal treatment parameters were optimized, and the DA process was customized based on the effect of precold deformation on precipitation behavior. High-density L12 nanoprecipitates (∼3.21 × 1025 m−3) were induced in the 65 % precold-deformed HEA, which led to the simultaneous formation of twins and stacking fault (SF) networks during deformation. The yield strength (YS), ultimate tensile strength, and ductility of the DA-HEA are ∼2.0 GPa, ∼2.2 GPa, and ∼12.3 %, respectively. Compared with the solid solution HEA, the YS of the DA-HEA increased by 1,657 MPa, possessing an astonishing increase of ∼440 %. The high YS stems from the precipitation strengthening contributed by the L12 nanoprecipitates and the dislocation strengthening contributed by precold deformation. The synergistically enhanced ductility stems from the high strain-hardening ability under the dual support of twinning-induced plasticity and SF-induced plasticity.

Inhibition of precipitation structure transformation and enhancement of hardness by trace La addition in Cu-1Cr-0.1Zr alloy sheets

Cu-1Cr-0.1Zr and Cu-1Cr-0.1Zr-0.07La alloy sheets were prepared by the following process: vacuum casting– homogenization treatment– hot forging– solid solution treatment– cold rolling– aging treatment. The effect of trace La on the aging behavior and mechanical properties of Cu-1Cr-0.1Zr alloy was investigated. Compared to the Cu-1Cr-0.1Zr (0La) alloy, the Cu-1Cr-0.1Zr-0.07La (0.07La) alloy exhibited a significant increase in hardness and a slight decrease in electrical conductivity due to larger number of finer and coherent f.c.c Cr-rich precipitates. It was found that trace La can affects the evolution of precipitation phases. The thermodynamics calculation indicates that with La addition, the Cr-rich precipitates were much more inclined to nucleate with f.c.c structure, and the precipitation growth kinetics results indicate that the addition of La can reduce the activation energy of precipitation, promote the precipitation of f.c.c Cr phase and form Cr-poor zones, making it more difficult to form bcc nuclei. Thus, the transformation of nanoscale Cr-rich precipitates from f.c.c structure to bcc structure was inhibited due to trace La addition, causing higher hardness with appropriate conductivity.

Precipitation strengthening of Cu–Ni–Si-based alloys: Experimental and computational insights

The effects of interfacial energy on precipitation behavior and physical properties of Cu–Ni–Si–(Co) alloys were investigated. The Cu–1.3Ni–0.3Si and Cu–1.3Ni–0.6Si–1.0Co alloys (in weight %) were prepared by combined cold-rolling and aging processes. The addition of Co promoted the formation of (Ni,Co)2Si by replacing Ni with Co in Ni2Si. Ab initio calculations demonstrated that the small addition of Co considerably reduced the interfacial energy between the Cu matrix and (Ni,Co)2Si, which effectively decreased the activation energy for precipitation. As a result, the precipitation of fine rod-shaped (Ni,Co)2Si was accelerated during the aging process and the number density of the precipitates increased up to 9.0 × 1010 cm−2. The nano-scale (Ni,Co)2Si precipitates with an average size of 13.5 nm strengthened the alloy properly through the Orowan mechanism without much loss of electrical conductivity. The maximum hardness and electrical conductivity were 220 Hv and 51 % International Annealed Copper Standard, respectively, for the Cu–1.3Ni–0.6Si–1.0Co alloy aged for 4 h at 420 °C.

Examining the effect of intermediate aging temperature on intermetallics, microstructure evolution, and recrystallization in a thermomechanically processed Al-Cu-Mg alloy sheet

In this research, distinct thermomechanical processing routes, encompassing primary annealing, cold rolling, intermediate aging, and final heat treatment have been devised. The primary goal was to explore the critical impact of short intermediate aging temperature on the evolution of intermetallic particles, microstructure evolution, thermal stability, and recrystallization in Al-Cu-Mg alloy samples. The findings demonstrated that while each thermomechanical step exerted a significant influence on the microstructure and particles' evolution, interestingly, the composition of particles remained relatively unaffected by the processing steps. Throughout the experimental procedures, two major intermetallic compounds, namely Al7Cu2(Fe,Mn) and AlCuMnFeSi were consistently identified. It was observed that intermediate aging successfully suppressed recrystallization implying the higher thermal stability of the aged samples. Analysis of the changes in the volume fractions of particles, their size distribution pattern, and samples’ hardness revealed an optimal aging temperature of 170 °C, i.e., at which the lowest volume fraction of particles (6.33 vol%) was obtained concurrently with the greatest hardness (thus the highest thermal stability), as well as the lowest recrystallized fraction, hence effectively establishing an equilibrium between activation energy of precipitation and thermally activated diffusion mechanisms.

Effects of aging process on properties and precipitation kinetics of Cu–Cr–Zr alloy strips

Cu–1.0Cr–0.1Zr alloy strips were prepared by solution, cold rolling and aging processes. The effects of aging process on the conductivity, mechanical properties and microstructure of the alloy were studied, and the precipitation kinetics was analyzed. The results showed that the Cu–1.0Cr–0.1Zr alloy exhibited the best comprehensive properties after aging at 430 °C for 180 min, with an electrical conductivity of 85.86% IACS, a hardness of HV 176.54, and a tensile strength of 552 MPa. For the samples aged at 430 °C from 30 to 180 min, the fcc-Cr and Cu8Zr3 phases grew from ~5 to ~8 nm, and the relationship between the precipitates and matrix changed from coherent to semi-coherent. In addition, the rod-like and spherical coarse particles (≥300 nm) of bcc-Cr phase were observed. The precipitation kinetics equations at different aging temperatures were established, the time–temperature–transformation (TTT) curve was plotted, and the precipitation activation energy was obtained as 65 kJ/mol.

DSC Analysis of the Effect of Cold Deformation on the Precipitation Kinetics of a Binary Cu-Sc Alloy.

The present study aimed to investigate the effect of cold deformation on the precipitation kinetics of a binary CuSc alloy containing 0.4 wt.% scandium using the experimental analysis method of differential scanning calorimetry (DSC). Non-deformed and 75% cross-section-reduced cold-rolled supersaturated specimens were tested in non-isothermal DSC runs at up to five different heating rates. The DSC results showed that cold rolling significantly accelerated the precipitation process in the binary alloy, leading to a decrease in the initial and peak temperatures of the exothermic reactions. The activation energies calculated with the Kissinger method indicated that the precipitation activation energy decreased with increasing cold deformation. The findings of this study provide worthy implications to further optimize the processing of Cu-Sc alloys with improved mechanical properties.

Effect of La/Nd ratio on precipitation kinetics and tensile properties of squeeze-cast Mg-Al-Zn-La-Nd alloys

The current study investigated the effect of adding La and Nd on the precipitation kinetics and tensile properties of AZ91 magnesium alloy. Mg-Al-Zn-La-Nd alloys with different W La /W Nd ratios were developed by squeeze casting. Typical characterization was conducted using optical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy to analyze the effect of W La /W Nd on the aging behavior of Mg-Al-Zn-La-Nd alloys. Thermal analysis, Vickers hardness and tensile properties were measured using the differential scanning calorimetry, optical hardness tester and universal testing machine. The results show that the addition of RE increases the diffusion resistance of Al atoms in the matrix and increases the time interval to peak aging. The precipitation activation energy and tensile properties of Mg-Al-Zn-La-Nd alloys increase with the increase of W La /W Nd . The optimal tensile properties are obtained in the alloy with a W La /W Nd of 3/2. The co-addition of La and Nd increases the precipitation activation energy and atom diffusion resistance of the AZ91 alloy. The precipitation behavior of AZ91 alloy with the addition of rare earth elements is slower than that of AZ91 alloy.

Effects of Nb addition on the properties and microstructure of Cu-Ni-Si-Mg alloy

In this paper, the effects of Nb addition on the mechanical properties, electrical conductivity and microstructure of the Cu-Ni-Si-Mg alloy were investigated. The results show that, after the secondary aging at 460 °C for 120 min, the alloy with 0.2 wt% Nb exhibits the best comprehensive properties with a hardness of 245.9 HV, a tensile strength of 747.28 MPa, a breaking elongation of 8.6%, and an electrical conductivity of 47.74 %IACS. The addition of Nb element can promote the precipitation of Ni 2 Si phase. The Nb-doped alloy has a higher quantity of precipitates and a smaller size of precipitates. The Nb element promotes the transition of the Ni 2 Si phase from a coherent to an incoherent relationship with the matrix in the Cu-Ni-Si-Mg alloy. In the initial stage of precipitation, the precipitation activation energy of the alloy with 0.2 wt% Nb is 46.86% lower than that of the alloy without Nb. The addition of Nb increases the proportion of Σ3 n ( n = 1, 2, 3) grain boundary in the Cu-Ni-Si-Mg alloy. Furthermore, after the secondary aging, the Nb addition increases the recrystallized texture and recrystallized grains and decreases the cold-rolled texture and defects in the alloy. • The Nb addition improves the mechanical properties and conductivity of CuNiSiMg alloy. • The Nb addition promotes the Ni 2 Si phase from coherent to incoherent relationship. • The alloy with 0.2 wt% Nb reduces the precipitation activation energy by 46.86%. • The CuNiSiMgNb alloy has more Σ3 n ( n = 1, 2, 3) CSL boundaries.

Fast hardening response of martensitic stainless steel by copper-rich cluster formation under pulsed electric current

The pursuit of excellent comprehensive mechanical properties using a rapid aging process is of practical significance in the field of aging strengthening. A pulsed electric current assisted aging process can effectively accelerate aging and reduce the energy consumption caused by long-term thermal aging. The mechanism of a Cu-rich cluster formation promoted by a pulsed electric current was investigated to better understand the fast-hardening response process. The size and structure of the Cu-rich cluster were characterized using transmission electron microscopy (TEM); the results indicated that the pulsed electric current did not change the mechanism of aging strengthening but accelerated the process. The time required to achieve peak aging decreased owing to the athermal effect (interaction between atoms and electrons) induced by the pulsed electric current. The athermal effect decreased as the temperature increased, and a relationship between the athermal effect and temperature was obtained. When a current density of 7 × 107 A/m2 was applied, the precipitation activation energy of the Cu-rich clusters decreased by 91 kJ mol−1; this was owing to the following two aspects. (1) The pulsed electric current lowered the vacancy formation energy and resulted in an increase in vacancy concentration and (2) the current density gradient caused by the difference in conductivity between the matrix and Cu-rich clusters accelerated the substitution of the Cu atoms and vacancies and reduced the atomic migration energy. These results provide insights into the effect of a pulsed electric current on the kinetics of precipitation in the martensitic stainless steel and a deduction for the mechanism of the rapid growth of Cu-rich clusters.

Study of the Precipitation Kinetics, Microstructures, and Mechanical Properties of Al-Zn-Mg-xCu Alloys

Microstructures and mechanical properties of Al-5Zn-2.6Mg alloys with 0.24, 0.43, and 0.91 wt.% Cu were studied and the precipitation rate and activation energy at 378, 393, and 408 K were calculated using the Arrhenius equation in this work. The aging reaction rate k increased and the precipitation activation energy Ea decreased from 25.7 to 15.0 kJ/mol. The η’ distribution density of the precipitates clearly increased with increasing Cu content. However, the size and number of coarse second phase with Fe and Mn impurities also increased, which increased the tendency for crack initiation and propagation at the grain boundary, resulting in a decrease in dimple area. The fracture morphology transformed from plastic transgranular fracture to brittle intergranular fracture and the elongation of the alloys decreased by 3.8%. The contribution of Cu content to yield strength was predominantly due to precipitation strengthening rather than grain boundary strengthening and solid solution strengthening. The tensile strength of the Al-5Zn-2.6Mg alloys with 0.91 wt.% Cu subject to peak aging at 393 K increased by 10.2%.

Effects of Cu additions on the precipitation activation energy and mechanical properties of prestrained Al–Mg–Si alloys

We investigated the effect of different Cu additions (0.1 wt.% and 0.3 wt.%) on the precipitation activation energy and mechanical properties of Al–Mg–Si alloys under different prestraining levels (0%, 3%, and 5%). Tensile tests were performed before and after paint baking (PB). Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) analyses were conducted to explore the clustering and precipitation behavior. Our results show that the precipitation activation energy was reduced by higher Cu addition but increased with prestraining level. Before PB, higher Cu addition significantly improved the elongation and work-hardening behavior, and the improvement was more pronounced in the prestrained alloys than in the nonprestrained alloys. After PB, higher Cu addition slightly increased the bake hardening response (BHR) of the alloy, and this improvement was enhanced in the prestrained alloys. However, only by introducing an appropriate amount of prestraining (3%) could the high-Cu alloy increase the BHR more significantly than the low-Cu alloy. When 5% prestraining was introduced, the high-Cu alloy had no advantage in increasing the BHR. After the introduction of 3% prestraining, a small amount of pre-Q′ phases was additionally formed near the dislocation lines, but the β″ phase was still the main strengthening phase. Higher Cu addition significantly refined the β″ phase and increased its number density, thereby improving the BHR. The formation of pre-Q′ phases was more pronounced in the high-Cu alloy under 5% prestraining, which suppressed the formation of the β″ phase and limited the BHR.

Mechanism of an acceleration in T1 precipitation kinetics in an Al-Cu-Li alloy by electropulsing

Effect of electropulsing has been investigated on the microstructures and precipitation kinetics of an Al-Cu-Li alloy during artificial ageing. Electropulsing assisted ageing (EAA) and conventional ageing (CA) were carried out under various ageing temperature and time conditions. The maximum stable plateau of EAA samples happens for less ageing times, than that of CA samples from ageing hardening curves. It was found that precipitation activation energy in EAA is remarkably reduced by ~45% compared to CA. Dislocation reconfiguration was firstly found to happen via electropulsing during artificially ageing. Specifically, both the larger dislocation lines and the resultant dislocation network configuration were observed in the EAA sample of ageing for 1 h. Before the peak statue, the average length and number density of T1 plates in the EAA samples were much larger than those of the CA sample at the same ageing time. Based on the results analyzed, a new mechanism, which considering the formation of dislocation network configuration induced by electropulsing and the reduced average diffusion field size via dislocation network resulting in the absorption among T1 precursors in a shorter timescale, has been established to successfully explain an accelerated T1 precipitation during ageing assisted by electropulsing.

Study of aging stability and precipitation kinetic of the Al–Zn–Mg alloy applied for auto body structures

The aging stability and influence of Sn addition on precipitation kinetic were fully investigated for a novel Al–Zn–Mg aluminum alloy used for auto body structures. Microstructure evolution was characterized using Differential Scanning Calorimetry (DSC) analysis, Transmission Electron Microscopy (TEM and HRTEM), and Selected Area Electron Diffraction (SAED) techniques. Micro-hardness under different evolution was studied accordingly. Our results indicated that, the bake hardening ability was strongly improved by forming GPⅡ zone under the pre-aging treatment at 120 °C + 20 min，which is completely coherent with the matrix and has strong thermal stability. It was particularly found that the coupling of pre-aging process and Sn addition reduce the precipitation activation energy of the η′ phase from 95.38 kJ/mol in the natural aging state to 38.2 kJ/mol in the Sn-containing pre-aging state, which obviously enhances the bake hardening response.

Reactivity of Zinc Cations under Spontaneous Accumulation of Hydrophobic Coexisting Cations in Hydrophobic Nanoporous Silicon.

The ion enrichment behavior due to surface-induced phase separation and the concomitant phase transition of electrolyte solutions between a liquid and a solid confined within nanopores of porous silicon is examined using concentrated aqueous solutions. We performed open-circuit potential measurements and differential scanning calorimetry (DSC) while varying the concentration of aqueous tetraethylammonium chloride (TEACl) solution. Open-circuit potential measurements revealed that the local OH– concentration within the nanopores increases as the bulk TEACl concentration increases. DSC measurements indicated that TEA+ cations are enriched within the nanopores and an extremely high concentration of TEA+ remarkably increases the local OH– concentration. This increase in the local pH should realize the selective precipitation of metal hydroxides within the nanopores. However, such precipitation was not observed in our investigations using aqueous solutions containing zinc cations. The experimental results suggest that ionic species within the nanopores of porous silicon are more stable than those in a bulk solution due to the formation of ion pairs with enhanced stability as well as kinetic factors that increase the activation energy for precipitation.

Effect of Plastic Deformation on the Activation Energy for Precipitation of S' Phase in Al2024 Alloy

Effect of Plastic Deformation on the Activation Energy for Precipitation of S' Phase in Al₂₀₂₄ Alloy

Effects of Grain Refinement on Tensile Properties and Precipitation Kinetics of Al-Si-Mg Alloys Cast in Sand Molds

Effects of grain refinement on the tensile properties and precipitation kinetics of Al-Si-Mg alloys cast in sand molds by co-alloying of La–B elements were investigated in this work. The kinetics of precipitation after refinement were investigated, including the changes of the precipitation mechanism and decrease of the precipitation activation energy. The reduction of the Avrami exponent indicates the major precipitation mechanism transforms in A359 alloys. Meanwhile, a modified aging process is obtained, which considerably promotes the mechanical properties.

Precipitation kinetics of γ″ phase and its mechanism in a Nb-bearing nickel-based superalloy during aging

While understanding the precipitation kinetics of gamma double prime (γ″) phase is of vital importance in Inconel 718 superalloy, kinetics studies by Johnson–Mehl–Avrami–Kolmogorov (JMAK) and thermoanalysis techniques have not been conducted so far, and hence, investigating the mechanism of γ″ formation deserves more attention. In response, in the present work, the precipitation kinetics of γ″ phase was studied by JMAK analysis based on the hardness measurements during aging and differential thermal analysis (DTA) during continuous heating. Average Avrami exponent of 0.64 was obtained, which was interpreted as precipitation on dislocations on the theoretical front. Moreover, the activation energy of precipitation (Q) was found to be close to the activation energy for the diffusion of niobium in the matrix, which was also confirmed by the Kissinger's plot obtained from DTA analysis. As a result, the present work contributes to the kinetics and mechanism of the γ″ phase formation.

Effect of a Trace Addition of Sn on the Aging Behavior of Al-Mg-Si Alloy with a Different Mg/Si Ratio.

In this paper, the effect of trace Sn on the precipitation behavior and mechanical properties of Al–Mg–Si alloys with different Mg/Si ratios aged at 180 °C was investigated using hardness measurements, a room-temperature tensile test, transmission electron microscopy and differential scanning calorimetry. The results shown that Sn reduces the precipitation activation energy, increases the number density of β″ precipitates, and then increased the aging hardenability and mechanical properties of the Al–Mg–Si alloy. However, the positive effect of Sn on the mechanical properties of the Al–Mg–Si alloy drops with the decrease of the Mg/Si ratio of the alloy.