Zhiyi Liu

Zhiyi Liu
Central South University | CSU ·  School of Materials Science and Engineering

PhD

About

221
Publications
12,477
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2,284
Citations
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July 2000 - December 2015
Central South University
Position
  • Professor

Publications

Publications (221)
Article
Full-text available
In the present work, different aging treatments were performed to investigate the pre-aging effect on the formation of Ω phase and mechanical properties in Al-Cu-Mg-Ag alloy. The results showed that pre-strain could inhibit the formation of Ω phases, which was detrimental to the alloy strength. Due to the introduction of pre-aging treatment before...
Article
Microstructure and texture development of Al–Cu–Mg alloy with a high Cu/Mg ratio were investigated during homogenisation and hot rolling by using OM, SEM, DSC, XRD and TEM. The results showed that the Brass texture intensity increased by 2.4 times after hot rolling (90% rolling reduction), when the proportion of the second-phase particles in an are...
Article
In this paper, a methodology integrating crystal plasticity (CP), the eXtended finite element method (XFEM) and the cohesive zone model (CZM) is developed for an Al-Cu-Mg alloy to predict fatigue crack propagation (FCP) across grain boundary (GB) of Al-Cu-Mg alloy during stage ІІ. One GB model is incorporated into FCP constitutive law to describe g...
Article
The dislocation slips during the hot- and cold-rolling processes, the texture evolution and the Goss-oriented grain refinement during the annealing of the Al–Cu–Mg alloy were investigated using optical microscope (OM), scanning electron microscope (SEM), electron back-scatter diffraction (EBSD), transmission electron microscope (TEM) and X-ray diff...
Article
The microstructure evolution and its effect on the strength properties and fatigue performance of the Al-Cu-Mg alloy are investigated by using optical microscope (OM), scanning electron microscope (SEM), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM). Results show that the strength-duc...
Article
Stability of grain structure, dislocation ordering and strengthening mechanisms of the naturally aged Al-Cu-Mg alloy after solution treatment are investigated by using optical microscope (OM), scanning electron microscope (SEM), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM). Results s...
Article
The microstructures and mechanical properties of a hot extruded Al–Zn–Mg–Cu alloy pipe with variable cross-section are investigated by transmission electron microscopy, electron backscattering diffraction, hardness testing and finite element method. The results suggest that the variable temperature distribution at different positions along the extr...
Article
The Al-Cu-Mg-Ag alloy with a low Cu/Mg ratio was hot rolled at different temperatures (410 ℃, 440 ℃, 470 ℃) following by solution and under-aged treatment to reveal the effect of hot rolling temperature on microstructures, mechanical and corrosion properties. This work was investigated by transmission electron microscopy (TEM), scanning transmissio...
Article
Evolution of microstructure, texture, and hardness of the Al-Cu-Mg alloy was investigated by using scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and x-ray diffraction. Results have shown that the hardness and Brass texture intensity of the Al-Cu-Mg alloy can be enhanced during the annealing proces...
Article
Full-text available
The microstructures and mechanical properties of novel cast Al-Cu-Mg-Ag alloys with and without minor additions of Er (0.09 and 0.2 wt %) are investigated by Vickers hardness tests, tensile tests, optical metallographic examination, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results...
Article
Full-text available
In this communication, a bis-silane prepolymer was used to modify epoxy resin, aiming to enhance the corrosion resistance of epoxy coatings on aluminum alloy substrates. The bis-silane prepolymer was prepared by tetraethoxysilane (TEOS) and γ-glycidoxypropyl trimethoxysilane (GPTMS). The corrosion behavior of silane-epoxy coatings was studied. Comp...
Article
Full-text available
A method combining crystal plasticity (CP), the eXtended Finite Element Method (XFEM), and cohesive zone model (CZM) with traction separation law is developed for an Al-Cu-Mg alloy to predict the effect of grain orientation on fatigue crack propagation (FCP) during stage ΙΙ within a single crystal. The simulation results show that of all the orient...
Article
Full-text available
A dense alumina ceramic coating was formed on UNS A97075 Al alloy by plasma electrolytic oxidation (PEO). An efficient and environmentally friendly silane layer was prepared to seal the PEO coating. The scanning electron microscopy (SEM) results showed that the PEO coating was completely sealed by the silane layer. The electrochemical corrosion evo...
Article
Full-text available
Stress formation of monocrystal and bicrystals are investigated in specific oriented grains and grain boundaries of AA2024 alloy by using Crystal Plasticity Finite Element Method (CPFEM). The simulations show that the maximum Schmid factor (SF) value and the number of equivalent initial slip system (EISS) play a principal role in controlling the ma...
Article
Full-text available
The effect of solution treatments at high temperatures on the microstructure and fatigue performance of an Al-Cu-Mg alloy was investigated. Microstructural observation revealed that large secondary phases could be dissolved sufficiently by a strengthening solution at 507 °C for 20 min and shortening the solution time at the high temperature would b...
Article
The effects of microalloying with yttrium on the microstructures and mechanical properties of cast Al-Cu-Mg-Ag alloys at ambient and elevated temperatures are investigated using tensile testing, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The present results reveal that the...
Article
In this work, the microstructures of the electron-beam welded joints of cast Al–Cu–Mg–Ag alloy plate were investigated in terms of the element segregation, grain structure and precipitation behavior by scanning electron microscopy, transmission electron microscopy and atom probe tomography observation as well as differential scanning calorimetry an...
Article
The addition of 0.1 wt% Zr in Al-Cu-Mg alloy contributes to the formation of a stronger Brass and weaker Goss textures during hot rolling. Aiming at this observation, the related texture formation mechanisms are discussed from the aspect of dynamic recrystallization (DRX) behavior and phase particle effect on grain rotation. This work demonstrates...
Article
Thermal stability plays an important role in practical application of Al-Zn-Mg-Cu alloy for oil drilling. In this work, a new four-stage aging treatment by employing a natural aging prior to re-aging is designed to improve thermal stability of Al-Zn-Mg-Cu alloy. The effect of T6, four-stage aging, three-stage aging and T74 on thermal stability was...
Article
The localized corrosion behavior of Al-Cu and Al-Cu-Mg-Ag alloys was investigated in a naturally aerated 0.6 M NaCl solution by in situ observations and electrochemical techniques. The combined roles of Ag and Mg in affecting the corrosion resistance of Al-Cu alloys were observed using electron probe microanalysis and scanning Kelvin probe force mi...
Article
A bis-silane prepolymer-modified epoxy coating was applied to an Al-Zn-Mg-Cu alloy to improve corrosion protection. The bis-silane prepolymer was synthesized from tetraethoxysilane and γ-glycidoxypropyl trimethoxysilane. To study the mechanism of protection failure by the silane–epoxy hybrid coating and to determine an appropriate coating for prote...
Article
Full-text available
The hot deformation behavior of an Al-Zn-Mg-Cu alloy was investigated by hot compression test at deformation temperatures varying from 320 to 440 °C with strain rates ranging from 0.01 to 10 s−1. The results show that the Mg(Zn, Cu)2 particles as a result of the sufficient static precipitation prior to hot compression have an influence on flow soft...
Article
Evolution of Goss texture in an Al–Cu–Mg alloy during cold rolling was investigated by three-dimensional orientation distribution functions, electron back-scattered diffraction and transmission electron microscopy. The results showed that with increasing reduction from 23.7 to 80%, Goss textures gradually transformed into Brass texture through the...
Article
The microstructure and texture evolution of the Al–Cu–Mg–Ag alloy were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results shown that the dynamic dissolution of the second phase particles occurs preferentially in the grain boundaries of the small DRX grains during hot ro...
Article
The nucleation and growth processes of dynamic recrystallized (DRX) grains of Al–Cu–Mg alloy during hot rolling were investigated using optical microscopy (OM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), and the possible way to refine the grain size by Al12Cu2Mn3 phase (T-phase) was given. Results shown that the sub-grains...
Article
The surface residual stress as well as corrosion behavior of an Al-Zn-Mg-Cu alloy plate is investigated under various pre-deformation conditions via X-ray diffraction, transmission electron microscopy, laser scanning microscope, open circuit potentials and electrochemical impedance spectroscopy measurements. Results reveal that the major extent of...
Article
In this work, a new four-stage aging treatment by employing a natural aging prior to re-aging is designed to promote GP zones formation and subsequent shear-able strengthening effect in an Al–Zn–Mg–Cu alloy. The effects of natural aging on the microstructural evolution, tensile properties and stress corrosion cracking (SCC) behavior of Al–Zn–Mg–Cu...
Article
This paper presents an investigation on the influence of Mg content on the microstructures, tensile properties and three-point bending fatigue behavior of Al-Cu-Mg-Ag alloys. The results indicate that the alloy containing 0.70 wt.% Mg possesses lower tensile properties and higher fatigue performance compared to the one with 1.15 wt.% Mg. Increasing...
Article
Texture or grain orientation was of crucial importance to fatigue crack propagation (FCP) in aluminium alloys due to boundary character between neighbouring grains and crack closure effect. The current understanding of the relationship among texture, grain size, slipping and crack propagation at fatigue stage I to III was reviewed and discussed. Th...
Article
The control of the precipitation of Ω phase is the critical factor that determines the mechanical properties and performance of Al-Cu-Mg-Ag alloys at elevated temperatures. As the most important components for Ω nucleation, the Mg and Ag additions usually plays a key role in affecting the precipitation kinetics of Ω phase. In order to clarify the i...
Article
After extended aging at 200 °C for various periods, the microstructures of Al–Cu–Mg–Ag alloys with and without small Er addition is intentionally investigated by optical metallographic examination, scanning electron microscopy (SEM) and quantitative transmission electron microscopy (TEM) characterization to explore the potential effect of Er on the...
Article
A new four-stage aging treatment, which is composed of pre-aging, retrogression, natural aging (NA) and re-aging, is designed to increase the tensile properties and the fatigue life of forged 7050 aluminum alloy in this work. As compared to traditional T74 and RRA treatments, the four-stage aging-treated sample exhibits the highest tensile properti...
Article
The association between small Sc addition and different precipitates in an Al[sbnd]Cu[sbnd]Mg[sbnd]Ag alloy is investigated in the present work to explain the Sc-dependent microstructural evolution during extended aging at 180 °C. The age-hardening capacity and the strength properties of Al[sbnd]Cu[sbnd]Mg[sbnd]Ag alloy are found to be degraded by...
Article
The texture evolution and fatigue crack propagation (FCP) of 2000 series alloys were investigated, respectively, by using scanning electron microscopy and x-ray diffraction. Results showed that the intensity change in different textures (such as Goss, Copper, S and Brass) abides by a linear evolution law, and a new model for texture evolution is pr...
Article
Full-text available
P-texture effect on the fatigue crack propagation (FCP) resistance in an Al-Cu-Mg alloy containing a small amount of Ag, is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattering diffraction (EBSD). Results shows that the high intensity P-texture sheet has low...
Article
The effects of texture, including Brass, Goss + Cube and Cube, on the fatigue crack growth behavior in annealed Al-Cu–Mg alloy sheets were characterized in this investigation. Results showed that the Goss + Cube sheet possessed the greatest fatigue threshold value and the lowest fatigue crack propagation (FCP) rate, and the Brass sheet presented th...
Article
Full-text available
The fatigue property as well as stress corrosion cracking (SCC) resistance of an Al-Zn-Mg-Cu alloy thick plate in peak-aged and overaged tempers (T7351 and T7651) is systematically investigated by fatigue crack propagation (FCP) test and slow strain rate test (SSRT). Microstructural characterization is examined by transmission electron microscopy a...
Article
The current understanding of texture evolution during deformation by rolling in aluminum alloys was summarized. This included understanding the evolution mechanisms and several key factors of initial texture, microstructure, alloy composition, deformation temperature, stress–strain condition, and rolling geometry. Related models on predicting textu...
Article
It is well known that deformation prior to artificial aging considerably decreases the strength properties of Al-Cu-Mg-Ag alloys by suppressing the formation of the main strengthening Ω precipitates. This negative effect is the as-yet unresolved obstacle for the wide applications of Al-Cu-Mg-Ag alloys. In this work, preaging prior to deformation is...
Article
The texture evolution in the intermediate (the 1/4 thickness) layer of hot-rolled Al-Cu-Mg alloy sheets was investigated by the x-ray diffraction technique, electron backscattered diffraction analysis and transmission electron microscopy observation. The results showed that a texture transition from the shear texture {001}<110> to the β-fiber textu...
Article
The formation mechanism of recrystallized textures in an Al-Cu-Mg alloy was investigated by means of three dimensional orientation distribution functions (ODFs) and in-situ electron back-scattered diffraction (EBSD). The results showed that in the hot-rolled alloy with a very sharp Brass texture but weak Copper and S orientations, both Goss and Cub...
Article
The surface microhardness, as well as the fatigue crack propagation (FCP) resistance of 2524-T3 alloy, is improved by producing a 20-μm-thick amorphous electroless Ni-12% P coating on its surface. Compared to the substrate, this deposited EN coating possesses higher strength properties and exhibits a greater ability of accommodating the plastic def...
Article
In the present work, the effect of artificial aging on the Cu-Mg co-clustering and mechanical behavior in a pre-strained Al-Cu-Mg alloy are investigated by tensile and fatigue testing, X-ray diffraction (XRD), transmission electron microscope (TEM) and atom probe tomography (APT). Results show that in the pre-strained samples, sample with artificia...
Article
Goss texture intensity effect on fatigue crack propagation (FCP) resistance in an Al-Cu-Mg alloy sheet is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron back scattering diffraction (EBSD). Results show that sheet with high intensity Goss texture presents a lower FCP rate than relatively low intensity Goss-t...
Article
The damage tolerance of Al-Cu-Mg alloy sheet was successfully improved by pre-rolling with small reduction (6.1%) rather than large reduction (12.2% and 21.7%). By this 6.1% pre-rolling, most of deformation only occurs at the surface layer of sheet, but not at the center layer. A protected compressive stress gradient was created, i.e., compressive...
Article
The effect of 2.5% pre-stretching on the solute clustering and subsequent precipitation of an initial aged Al-Cu-Mg-Ag alloy is investigated by quantitative transmission electron microscopy (TEM) and atom probe tomography (APT) technique. In present work, 2.5% pre-stretching is found to restrict the dense precipitation of Ω phase, leading to the sl...
Article
Texture and tempered condition combined effects on fatigue behavior in an Al-Cu-Li alloy have been investigated using tensile testing, cyclic loading testing, scanning electron microscope (SEM), transmission electron microscopy (TEM) and texture analysis. Results showed that in near-threshold region, T4-tempered samples possessed the lowest fatigue...
Article
Quantitative and qualitative analyses on the dissolution behavior of various size Cu-Mg co-clusters near a fatigue crack tip of underaged Al-Cu-Mg alloy during cyclic loading were performed by means of transmission electron microscopy (TEM) and atom probe tomography (APT). Results showed that the driving force for dissolution of Cu-Mg co-clusters w...
Article
The close association between the Ω precipitation and various Ag additions is systematically investigated by quantitative transmission electron microscopy and atom probe tomography analysis. Our results suggest that the precipitation of Ω phase is strongly dependent on Ag variations. Increasing the bulk Ag content favors a denser Ω precipitation an...
Article
Effects of trace addition of Ag on the fatigue crack propagation behavior and microstructure of a medium-strength aged Al-Zn-Mg alloy were investigated in the present work. The results show that a combination of enhanced tensile strength and improved fatigue crack propagation resistance in Al-Zn-Mg alloys is achieved with small addition of Ag. The...
Article
The effects of Ge and Ag additions on quench sensitivity and mechanical properties of an Al–Zn–Mg–Cu alloy are investigated using tensile testing, hardness testing, differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Results show that a small addition of Ge...
Article
Texture and microstructure development of Al-4Cu-1.6Mg alloy during hot rolling was examined by using XRD, EBSD and TEM. The results showed that starting with a random texture during the early stages of rolling with reduction lower than 58.9% at blooming temperature of 430 °C, the materials developed a typical α-fiber texture in the center layer as...
Article
A new retrogression and re-aging (RRA) treatment was designed to enhance the fatigue crack propagation (FCP) resistance of a superhigh strength Al–Zn–Mg–Cu alloy in this work. As compared to traditional RRA treatments, a lower retrogression temperature and a longer retrogression and re-aging time were employed. This modified RRA processing obtained...
Article
Enhanced heat resistance of Al-Cu-Mg alloy by employing a combined effect of pre-stretching and underaging has been characterized by thermal exposure, tensile testing, transmission electron microscopy (TEM) examination, and quantitative analysis. Tensile testing results showed that the samples subjected to both pre-stretching and underaging process...
Article
The modulus hardening capability of various co-clusters in a low Cu/Mg ratio Al-Cu-Mg-Ag alloy aged at 165℃ is investigated by quantitative atom probe tomography analysis. Prolonged aging from 5 min to 2 h leads to the simultaneous increase in the critical shear stress of both Mg-Ag and Cu-Mg co-clusters. Regardless of the higher shear modulus of C...
Article
Analysis of the plastic deformation zone at crack tip in fatigue stage II of AA2524-T4 and AA2297-T87 alloys reveals the complex microstructural effects, such as second-phase particles, grain boundaries, Schmid factor and grain orientations etc., on the formation of slip bands. In AA2524-T4 alloy, slip band formation in plastic deformation zone rel...
Article
The texture evolution of AA2524 cold-rolled sheet during annealing process and texture effect on fatigue crack propagation (FCP) behavior were investigated. Results showed the sample annealed at 400 ℃ for 45 min and solid solution-treated at 490 ℃ for 20 min had the strongest Goss and P textures, and possessed the lowest FCP rates. EBSD examination...
Article
Full-text available
The tensile properties and fatigue behavior of an Al–Zn–Mg–Cu alloy were investigated by performing tensile tests and fatigue crack propagation (FCP) tests. The tensile results show that lower aging temperature modified retrogression and re-aging (RRA) process enhances the elongation, but reduces the strength of the alloy, as compared to convention...
Article
Based on the traditional retrogression and re-aging (RRA) technology, RRA treatment by decreasing pre-aging and re-aging temperature was performed on ultrahigh strength aluminum alloy extruded bar with high content of Fe and Si elements. The effect of RRA treatment on the mechanical properties and microstructure of ultrahigh strength aluminum alloy...
Article
Dislocation mechanism operating in dynamic recrystallization (DRX) during hot compression of Mg–5.51Zn–0.49Zr alloy was investigated by X-ray diffraction, optical microscopy and transmission electron microscopy. The results showed that the continuous DRX occurred at a low strain rate of 1×10−3 s−1, which was associated with the operation of the sin...
Article
Multi-step heat treatment effectively enhances the stress corrosion cracking (SCC) resistance but usually degrades the mechanical properties of Al-Zn-Mg-Cu alloys. With the aim to enhance SCC resistance as well as strength of Al-Zn-Mg-Cu alloys, we have optimized the process parameters during two-step aging of Al-6.1Zn-2.8Mg-1.9Cu alloy by Taguchi’...
Article
The effect of Cu-Mg cluster size and number density on the fatigue fracture behavior of Al-Cu-Mg alloy with various aging conditions was investigated by means of transmission electron microscopy (TEM), atom probe tomography (APT), scanning electron microscopy (SEM) and fatigue testing. Results showed that the fatigue crack propagation (FCP) resista...
Article
The fatigue behavior of three different AA2524 alloy sheets respectively with dominant Goss+Cube-grains, Cube-grains and Cube+Brass-grains was characterized in present work. Results showed Goss+Cube-grain sheet possessed a much lower fatigue crack propagation (FCP) rate than Cube-grain sheet and Cube+Brass sheet. The Cube+Brass sheet had the greate...
Article
The fatigue behavior of three different AA2524 alloy sheets respectively with dominant GossþCube- grains, Cube-grains and CubeþBrass-grains was characterized in present work. Results showed GossþCube-grain sheet possessed a much lower fatigue crack propagation (FCP) r