Kun Liu

Kun Liu
Université du Québec à Chicoutimi | UQAC · Department of Applied Sciences (DSA)

PhD

About

123
Publications
35,805
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2,045
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Introduction
Solidification and phase transforamtion of light alloys; Relationship between structure and properties of light alloys; New application of aluminum alloys at eleveted temperature; High-temperature behaviors of aluminum alloys, including the creep, LCF and TMF; Wire and Arc Additivie Manufacturing; Semi-solid and high pressure die casting
Additional affiliations
February 2013 - present
Université du Québec à Chicoutimi
Position
  • Researcher

Publications

Publications (123)
Article
Segregation is a type of harmful defect, especially for strips with high alloying content aluminum alloys produced by twin-roll casting, which seriously inhibits the mechanical properties. Mo is often used for the refiner in aluminum alloys, and, in this study, the effect of Mo on the segregation behavior of Al-Mg-Si-Mn alloy produced by twin-roll...
Article
Full-text available
The effects of minor additions of the transition elements Zr, Ti, and V on the microstructure, mechanical properties, and out-of-phase thermomechanical fatigue behavior of 224 Al-Cu alloys were investigated. The results revealed that the introduction of the transition elements led to a refined grain size and a finer and much denser distribution of...
Article
Full-text available
The influence of Si content (0.1–0.8 wt.%) on the development of precipitation microstructures and the resultant mechanical and creep properties during thermal exposure, up to 1000 h at 300 °C, in Al–Cu 224 cast alloys, was systematically investigated. The room and elevated temperature yield strength (YS) increased with increasing Si content under...
Article
Full-text available
Elevated temperatures and pressures in high-efficiency engines increases the risk of thermomechanical fatigue (TMF), constraining the utilization of aluminum cast alloys. Comprehensive understanding of TMF behavior is crucial for safety design of engine components. In this study, the out-of-phase thermomechanical fatigue (OP-TMF) performance of a n...
Chapter
Thermomechanical fatigue (TMF) that resulted from the cyclic changes of stress and temperature is considered to be one of the most detrimental failures for the automotive engine parts. To improve the service life of engine components, it is essential to understand their TMF behavior and hence improve the TMF resistance. In this work, the out-of-pha...
Chapter
Full-text available
The evolution of the Mn-bearing dispersoids in two Al-Mg-Mn 5xxx alloys with 3% and 5% Mg and their impact on the mechanical properties and recrystallization resistance have been investigated. A large number of Mn-dispersoids were precipitated in the aluminum matrix by applying a low-temperature homogenization, but the type, size, and number densit...
Article
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The microstructural evolution and mechanical properties of hot-rolled Al–Cu 2022 alloys were investigated to explore the effects of Zr addition and different homogenization procedures. Two-step low-temperature homogenization promoted a denser and finer distribution of Al3Zr particles in the Zr-containing alloy, which provided heterogeneous nucleati...
Article
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Herein, the precipitation behavior of Mn‐bearing dispersoids in Al‐3Mg‐0.8Mn (AA5454) alloy subjected to different heat treatments is investigated. The effects of Mn‐bearing dispersoids on the tensile properties and recrystallization resistance of the abovementioned alloy during hot/cold rolling and postrolling annealing are evaluated. The results...
Article
Full-text available
Thermo-mechanical fatigue (TMF) is one of the most detrimental failures of critical engine components and greatly limits their service life. In this study, the out-of-phase TMF (OP-TMF) behavior in Al-Si-Cu 319 cast alloys microalloyed with Mo was systematically investigated under various strain amplitudes ranging from 0.1-0.6% and temperature cycl...
Chapter
5xxx5xxxaluminum alloysAluminum alloys are traditionally considered non-heat-treatable. With the addition of Sc/Zr and multistep heat treatmentHeat treatment, two kinds of dispersoidsDispersoids (AlMn and Al3(Sc,Zr)) were formed. The effect of Sc additions (0.08–0.43 wt.%) on dispersoidDispersoids formation and mechanical propertiesMechanical prope...
Article
Precipitation-hardened Al–Si 356 cast alloys are widely used in fabricating the automotive engine parts due to their excellent castability and strength/weight ratio. However, with the increasing demand of the engine service temperature at 250–350°C, the mechanical properties of Al–Si 356 alloys greatly deteriorate owing to the rapid coarsening of p...
Article
Full-text available
The out-of-phase thermo-mechanical fatigue (TMF) behavior of the two Al-Si cast alloys most widely used for engine applications (319 and 356) were investigated under temperature cycling (60–300 °C) and various strain amplitudes (0.1–0.6%). The relationship between the microstructural evolution and TMF behavior was closely studied. Both alloys exhib...
Article
With the addition of Sc and Zr to AA5083 alloy, two populations of strengthening particles (submicron-sized AlMn dispersoids and nanosized Al3(Sc,Zr) precipitates) precipitate during three-step heat treatment. Here, their influence on the microstructure and mechanical properties of hot-rolled sheets at ambient and elevated temperatures was investig...
Article
The evolution of discontinuous and continuous Al3(Sc,Zr) precipitation in an Al-Mg-MnAA5083 alloy during heat treatment and hot rolling was investigated. The results showed that, at a high Sc content (0.43 wt%), a large number of line/fan-shaped structures were formed as discontinuous Al3(Sc,Zr) precipitation during solidification, while no such di...
Article
The influence of microalloying with Mg (0–0.36 wt%) on the elevated-temperature strength and creep resistance of Al–Cu 224 cast alloys was investigated. The Mg-containing alloys yielded finer and denser θ′ precipitates after high-temperature stabilization (300 °C/100 h) than the Mg-free alloy, which improved the yield strength at both room temperat...
Article
This work studied the precipitation characteristics of AlSi10Mg0.3Mn alloy produced by high-pressure vacuum die-casting in T5 and T6 conditions using transmission electron microscopy, differential scanning calorimetry and both electrical conductivity and microhardness measurements. Two different T6 tempers were used, involving partial solutionizing...
Article
Full-text available
Recrystallization can affect the mechanical properties of aluminum alloys by changing the grain structure, and even the secondary recrystallization will cause a sudden change in the grain size in the alloy. In this work, by choosing different annealing treatments on the cold-drawn 5056 aluminum wire, the microstructure evolution in the alloy homoge...
Article
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In the present study, the fatigue life and fatigue fracture characteristics of annealed 7005 aluminum alloy plates subjected to different pre-tensile deformations were investigated. The results obtained upon increasing the pre-tensile deformation of the alloy plate to 20% revealed that the second-phase particles did not show any obvious changes, an...
Article
The precipitation behavior of dispersoids in an Al-5% Mg-0.8% Mn alloy after various single-and multistep heat treatments and their effect on rolling performance were investigated. The results show a significant increase in the electrical conductivity and microhardness caused by the precipitation of submicron dispersoids after all heat treatments....
Article
Full-text available
In the present work, we investigated the possibility of introducing fine and densely distributed α-Al(MnFe)Si dispersoids into the microstructure of extruded Al-Mg-Si-Mn AA6082 alloys containing 0.5 and 1 wt % Mn through tailoring the processing route as well as their effects on room- and elevated-temperature strength and creep resistance. The resu...
Article
The evolution of precipitates and the elevated-temperature mechanical and creep properties of Al–Cu 224 cast alloys with the microalloyed transition metals (TMs) of Zr, V, and Sc were investigated. The results showed that the addition of TMs can generally delay the transformation from θ″ to θ′ during T7 aging and can effectively increase the coarse...
Article
The present work investigated the influence of Zr and Sc on the evolution of α-Al(FeMn)Si dispersoids (“α-dispersoids") in Al–Mg–Si alloys. Both the individual addition of Zr and the combined additions of Sc and Zr increased the size but decreased the number density of the α-dispersoids, indicating the reduction in the formation of α-dispersoids. H...
Article
The differences in the microstructure and elevated temperature tensile properties of gravity die cast, squeeze cast, and semi-solid thixoformed Al–Si–Cu–Mn–Fe alloys after thermal exposure at 300 °C were discussed. The results demonstrate that the elevated temperature tensile properties of semi-solid thixoformed alloys were significantly higher tha...
Article
Heterogeneous structure consisting of brittle-zones (BZs) rich of carbon nanotubes (CNTs) and ductile-zones (DZs) free of CNTs, was an effective way to improve the strength-ductility of CNT reinforced Al (CNT/Al) composites. Two heterogeneous CNT/2009Al composites with coarse grain (CG, ~2 μm) DZs or ultra-fine grain (UFG, ~500 nm) DZs were fabrica...
Article
Heterogeneous carbon nanotube (CNT)/Al-Cu-Mg composites, consisting of ductile zones (DZs) free of CNTs and brittle zones (BZs) rich of CNTs, were fabricated in powder metallurgy route. It was shown that the grain size and width of the DZs in the heterogeneous composites could be controlled by high energy ball milling (HEBM) on additional Al-Cu-Mg...
Article
Full-text available
Accurate determination of the materials’ strength and ductility in the semi-solid state at near-solidus temperatures is essential, but it remains a challenging task. This study aimed to develop a new method to determine the stress-strain evolution in the semi-solid state of aluminum alloys within the Gleeble 3800 unit. Stress evolution was determin...
Article
Full-text available
Mg-containing high-Si aluminum alloys are heat-treatable alloys that are widely used in industry. Substantial attention has been paid to increasing the performance of such alloys by adding a small amount of Mn, which is an effective and common alloying element in aluminum alloys. In the present work, the solidification process of Mn-free Al-5Si-0.8...
Article
Full-text available
Mg-containing high-silicon aluminum alloy is a heat-treatable aluminum alloy that is now widely used in the aerospace and automotive industries because of its high specific strength, high wear resistance and corrosion resistance, low thermal expansion coefficient, and low cost. More attention has been paid to optimizing the microstructure to increa...
Article
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The feasibility and efficacy of improving the mechanical response of Al-Mg-Si 6082 structural alloys during high temperature exposure through the incorporation of a high number of α-dispersoids in the aluminum matrix were investigated. The mechanical response of the alloys was characterized based on the instantaneous high-temperature and residual r...
Article
The effects of Al(MnFe)Si dispersoids, with different sizes and number densities, on the evolution of microstructure and ambient/elevated-temperature mechanical properties of extruded AA6082 alloys, with varying Mn content, under T5 conditions, were investigated. Compared to the low density of coarse dispersoids formed during conventional homogeniz...
Article
This study explored the effects of compositional variation of Al-Cu 206 alloys (Si and Mn concentrations, 0.12 versus 0.3 wt.% each) on the precipitation and thermal stability of θ′ precipitates, and the associated elevated-temperature strengths during long-term thermal exposure at 300 °C. The results indicated that both alloys under the T7 conditi...
Article
Full-text available
2020): Effects of thermal exposure on the microstructure and mechanical properties of Al-12Si-4Cu-1Ni-1Mg-2Mn piston alloys, International Journal of Cast Metals Research, ABSTRACT The effect of thermal exposure on the elevated-temperature mechanical properties of heat-treated Al-12Si-4Cu-1Ni-1 Mg-2Mn piston alloys was investigated using optical mi...
Article
The effect of transition elements, specifically Mn, Cr, V, and Mo, on dispersoid formation and mechanical properties in 6082 aluminum alloy was studied. The elevated-temperature mechanical properties were evaluated based on the compressive yield strength and creep resistance. The results indicated that the addition of Mn to the 6082 alloy resulted...
Article
Full-text available
Heat-treatable cast and wrought aluminum alloys are widely used for structural applications in the automobile and aerospace industries. To assess and diagnose the production and quality problems related to industrial heat treatments, differential scanning calorimetry (DSC) was used as a tool in the present work to determine the thermal histories of...
Article
Mechanical properties of the structural interface are significantly important for the wire + arc additively manufactured (WAAM) component who keeps the substrate as a part. Two deposition strategies using power sources of pulse advanced cold metal transfer (CMT-PA) and pulse metal inert gas (MIG-P) as the first layer were designed to build WAAM 231...
Article
The effects of microalloying with Mg (0–0.23 wt%) on the microstructural evolution and mechanical properties of Al–Cu 224 cast alloys at ambient and elevated temperatures are investigated using transmission electron microscopy, differential scanning calorimetry, and tensile/compression testing. The results show that microalloying with Mg significan...
Article
Eutectic Al-13%Si alloys are widely used in the automotive industry for manufacturing components, such as pistons and cylinder heads. To reduce greenhouse gas emissions and enhance the engine efficiency, their service temperature keeps increasing to 250-350 °C, leading to the deterioration of their mechanical properties and the creep resistance. In...
Article
Full-text available
In the present work, the hot rolling at 400°C and post-rolling annealing at 500°C were applied on heat-treated Al-Mg-Si 6082 alloys with different Mn contents to study the evolution of microstructure and elevated-temperature properties. During the pre-heat treatment before rolling (400°C/2h), a number of fine rod-like dispersoids formed in Mn-conta...
Article
Full-text available
In the present work, individual/combined additions of transition elements (V, Zr and Mo) were introduced into Al-7Si-0.6Cu-0.35Mg foundry alloy at different cooling rates to study their influence on the precipitation behaviour of dispersoids. Results showed that both individual and combined additions of V, Zr, Mo lead to the formation of dispersoid...
Article
Full-text available
In the present study, four Al-Mg-Mn 5xxx alloys with different Mg levels (2-5 wt.%) were investigated for better understanding the evolution of intermetallic phases formed during solidification. Optical and scanning electron microscopes, electron backscattered diffraction and differential scanning calorimetry analyses in combination with thermodyna...
Article
The effect of Ti content on the microstructure and mechanical properties of heat-treated Al–Si–Cu–Mn–Fe alloys was investigated. It was found that the mechanical properties increased with the increase of Ti content. This was attributed to the refinement of grain size, the increased amount of T (Al20Cu2Mn3), the α-Fe (Al15(FeMn)3(CuSi)2) precipitate...
Article
The creep resistance of an Al-Cu-Mn-Fe-Ni alloy, including the creep behavior and creep fracture mechanism, was studied using tensile creep tests, scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). This study is focused on the difference in the microstructures and creep resista...
Article
The present work investigated the evolution of dispersoids during various heat treatments via Mn and Mo additions and studied their effects on the yield strength (YS) and creep resistance at elevated temperature in Al-Si-Cu 319 cast alloys. The results showed that the individual addition of Mn or Mo promoted the precipitation of α-dispersoids; howe...
Article
The precipitation behavior of Mn-containing dispersoids in Al-Mg-Si 6082 alloys with different Mn contents (0, 0.5 and 1.0 wt.%) during various heat treatments (300-500 ℃) was investigated. The effects of dispersoids on elevated-temperature strength and recrystallization resistance during hot-rolling and post-rolling annealing were evaluated. The r...
Article
Full-text available
A practical approach to predict the yield strength and work-hardening exponent (n value) to evaluate the deep-drawing performance of annealed 3104 aluminum sheets is presented in the present work by only measuring and analyzing the grain size of the sheet. The various grain sizes were obtained through the different annealing treatment and then the...
Article
In the present work, Mo was added to an Al–Si–Mg foundry alloy to study its influence on the evolution of dispersoids during various heat treatments. The microhardness and the elevated-temperature tensile properties and creep resistance were measured to evaluate the contribution of dispersoids. Results showed that the addition of Mo greatly promote...
Article
In the present work, the precipitation and preferential selection of Fe-rich intermetallics in Al-Si-Cu 319 cast alloys with two Fe contents (0.3 and 0.7 wt pct) and various Mo contents (0 to 0.4 wt pct) were investigated. The results showed that two types of platelet β-Fe (defined as eutectic β-Fe and pre-eutectic β-Fe) and α-Fe can precipitate de...
Chapter
Al-Si foundry alloys are widely used in aerospace and automobile industries, such as the engine blocks and cylinder heads. These engine components are often exposed to cyclic mechanical stress at high operation temperature (250–350 ℃) and such dynamic loading frequently results in the occurrence of fatigue failure. Hence, a fully understanding of f...
Article
The mechanical behavior near the solidus temperature in Al-Si-Cu 319 cast alloys was studied in both the solid and semisolid states. Mn and Sr were introduced to modify the iron-bearing intermetallic from platelet β-Fe to Chinese script α-Fe and the eutectic Si particles from a flake to fibrous shape, respectively. During the high-temperature tensi...
Chapter
Full-text available
Iron is one of the most common impurity elements in Al–Cu 206 cast alloys as it often causes the precipitation of Fe-rich intermetallic phases during solidification due to its extremely low solid solubility in aluminum. The characteristics of the Fe-rich intermetallics, such as type, morphology, size, and distribution, have significant influences o...
Article
In present work, the hardenability and critical cooling rates of 7B50 alloy were investigated based on measured cooling curves obtained from the spray quenching test on modified Jominy specimen, electrical conductivity and hardness in different aging tempers, and microstructures evolution in natural aging temper. Results show that the hardened dept...
Article
Full-text available
The microstructure of Al-1.01Mg-1.11Si-0.38Cu-0.69Mn aluminum alloy plate hot-rolled from homogenization and homogenization-free ingots were investigated by optical microscopy and scanning electron microscopy assisted with energy dispersive spectroscopy (SEM/EDS). The results showed that there are 3 main kinds of constituents such as Mg 2 Si, AlCuM...
Article
The effects of quenching in different ways following solid-solution treatment on properties and precipitation behaviors of 7050 alloy were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED), hardness and electrical conductivity tests. Results show that after quenchin...
Article
Full-text available
Effects of added Al–5Ti–B master alloys on precipitation of iron-rich intermetallics and mechanical properties of A356 cast alloys with high Fe content (1.5 wt-%) were investigated using image analysis, scanning electron microscopy, and tensile testing. Results show that added Al–5Ti–B has apparent refinement on α (Al) grain size of A356 alloys tha...
Article
Full-text available
In the present work, the role of Mg atoms in the form of either Mg clusters or β phase on the moving dislocations in 5083 aluminum alloy sheet were investigated by comparing the plastic flow behavior and Portevin-Le Chatelier (PLC) character in annealed and quenched conditions. It is found that the tensile strength of quenched sheets at different s...
Article
Full-text available
The present work encompasses the effect of overaging on the strain-controlled low-cycle fatigue (LCF) behavior of an extruded AA6061 aluminum alloy at varying strain amplitudes. During the T7 aging treatment, the size of precipitates increased from 60 nm under T6 conditions to 220 nm after aging for 48 h at 200 ◦C, leading to a decrease in the mono...
Article
Full-text available
The present work has systematically investigated the evolution of dispersoids and elevated-temperature properties including strength and creep resistance during various multi-step heat treatments in Al-Mn-Mg 3004 alloys. Results show that only the α-Al(MnFe)Si dispersoid is observed in the studied temperature range (up to 625 • C), and that it coar...
Article
The microstructure of Al-1.01Mg-1.11Si-0. 38Cu-0. 69Mn aluminum alloy sheet hot-rolled from the homogenized and homogenization-free ingot were investigated by the optical microscopy and SEM/EDS. The results show that there are three main constituents AlMgSi,AlCuMgSi and AlFeMnSi in the as-cast Al-1. 01Mg-1.11Si-0. 38Cu-0. 69Mn aluminum alloy ingot....
Article
In the present work, continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests. Besides, the time–temperature–properties (TTP) curves of this alloy were obtained during isothermal treatments. Based on the accurate cooling curves and TTP curves, the hardness distribution along...
Preprint
Full-text available
Present work has systematically investigated the evolution of dispersoid and elevated-temperature properties including the strength and creep resistance during the various multi-step heat treatments in Al-Mn-Mg 3004 alloys. Results show that only α-Al(MnFe)Si dispersoid is observed in the studied temperature range (up to 625°C) and it coarsens with...
Article
Experimental investigations on cracking susceptibility were carried out for wire + arc additively manufactured (WAAM) Al-Cu-Mg alloys, which were designed and deposited with Al-Cu and Al-Mg wires in tandem. The influence of composition, heat input, mechanical properties and microstructure on cracking for ternary WAAM Al-Cu-Mg alloys were studied, a...
Article
Eutectic Al-13%Si alloys are widely used in automotive components, such as pistons and cylinder heads. Recently, the demand on the performance of piston alloys at high temperature is greatly increased to enhance the engine efficiency and to reduce exhaust emission. In the present work, Mn was added to strengthen the aluminum matrix via the formatio...
Article
In the present work, two-step heat treatments with preheating at different temperatures (175 °C, 250 °C, and 330 °C) as the first step followed by the peak precipitation treatment (375 °C/48 h) as the second step were performed in Al-Mn-Mg 3004 alloys to study their effects on the formation of dispersoids and the evolution of the elevated-temperatu...
Article
Applying inter-layer rolling to the wire+arc additively manufacturing (WAAM) process with increasing loads of 15 kN, 30 kN and 45 kN, achieves excellent mechanical properties for 5087 (Al-Mg4.5-Mn) alloys. Compared with the as-deposited alloy, the average micro hardness, yield stress and ultimate tensile strength of 45 kN rolled alloys reached to 1...
Poster
Precipitation-hardening Al-Si-Cu 319 casting alloy has been widely used in the automobile industry due to its good castablity and high strength/weight ratio. However, its application at elevated-temperatures is often compromised by coarsening of precipitates. Dispersoid strengthening is reported to improve the elevated-temperature properties via th...
Poster
High pressure vacuum die casting production is increasingly used in automobile industry since its massive production ability and achievable high properties for structural application. To make quick problem diagnostics and solving, it is necessary to know the different heat treatment conditions of alloys. Each alloy and temper can produce unique pea...
Poster
In the present work, the effects of Mn addition and homogenization on precipitation behavior of α-dispersoids and recrystallization resistance in 6082 aluminum alloys were studied using Vickers-hardness test, SEM and TEM observations. Alloys with various Mn contents were homogenized at temperatures ranging from 350 to 500℃ for up to 24 hours. Homog...
Poster
Al-Si alloys have been increasingly used in diesel engines due to their high strength-to-weight ratio. However, at high operation temperatures, the precipitate coarsening leads to severe loss of elevated-temperature mechanical properties. One possible way to overcome this problem is to design thermally stable dispersoids, which retain their effecti...
Article
Full-text available
In the present work, various Mn amounts (up to 2 wt. %) have been added into Al-Mn-Mg 3004 alloy to study their effect on the evolution of microstructure and elevated-temperature properties. Results showed that the dominant intermetallics are interdendritical Al6(MnFe) until to 1.5 wt. % Mn. With further addition of Mn to 2 wt. %, the blocky primar...
Article
Various heat treatments with different sequences between the peak precipitation treatment (375°C/48h, referred to as “P”) and the high temperature treatment (450-600 °C, referred to as “H”) were performed in Al-Mn-Mg 3004 alloys to simulate their thermal treatments during thermomechanical fabrication processes in the present work. Their influences...
Article
In the present work, two contents (1.5 wt. % and 3 wt. %) of TiB2 nanoparticles have been introduced in Al-Mn-Mg 3004 alloy to study their effect on the elevated-temperature properties. Results show that TiB2 nanoparticles were mainly distributed in the interdendritic grain boundaries with a size range of 20-80 nm, which is confirmed by Transmissio...
Article
The effects of minor Cu (0−0.29 wt.%) and Mg (0−0.1 wt.%) additions on the microstructure, electrical conductivity, mechanical and creep properties of 8xxx aluminum conductor alloys were studied. The microstructure evolution was investigated using an optical microscope and the electron backscattered diffraction technique. The creep property was cha...