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Heat Treatment of Aluminum Alloys

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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (31 January 2019) | Viewed by 70903

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Prof. Dr. Salem Seifeddine

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Department of Materials and Manufacturing, School of Engineering, Jönköping University, P.O. Box 1026, SE-551 11, Jönköping, Sweden
Interests: molten metal quality; metal casting; solidification; in situ synchrotron X-ray techniques; deformation of metals; microstructure-properties relationships at room and elevated temperatures

Special Issue Information

Dear Colleagues,

Environmental awareness and resource efficiency, along with the development of high quality and high performing aluminum components, both wrought and cast, require alloy and process-parameter optimization. The microstructure, which is the result of alloy and process selections, and henceforward the mechanical and physical properties of aluminum alloys can be further tailored by proper selections of heat treatment parameters. The properties are then a function of temperature and time during the annealing or solution heat treatment and ageing steps, but also of the quenching operation. The complex relationship that exist between the alloy, process and heat treatment parameters can be modelled in order to bring this knowledge closer to the designer, enabling further component optimization, realizing less physical testing and hence faster components to market. This Special Issue aims, therefore, to present the latest research related to microstructure formation for optimized properties through heat treatment, as well as to demonstrate the latest modelling approaches that enable predictions of microstructural features, e.g., precipitates and their relation to properties of heat treated aluminum alloys.

Prof. Dr. Salem Seifeddine
Guest Editor

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Keywords

Annealing
solution heat treatment
ageing
quenching
mechanical and physical properties
modelling

Published Papers (13 papers)

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Research

9 pages, 20550 KiB

Open AccessArticle

Residual Stress Relief for 2219 Aluminum Alloy Weldments: A Comparative Study on Three Stress Relief Methods

by Shu-Guang Chen, Yi-Du Zhang, Qiong Wu, Han-Jun Gao and Dong-Yang Yan

Metals 2019, 9(4), 419; https://doi.org/10.3390/met9040419 - 08 Apr 2019

Cited by 20 | Viewed by 4089

Abstract

Thermal stress relief (TSR), vibration stress relief (VSR), and thermal and vibratory Stress relief (TVSR) have all been proven to be effective for residual stress relief. So far, no comparison has been made between the effects on residual stress relief of these three stress release methods. In this study, twelve 2219 aluminum alloy welding samples were divided into four groups. One of the groups is used as a reference without any stress relief treatment. The other three groups were processed by TSR, VSR, and TVSR, respectively. The residual stresses of depths of 0–1.2 mm are measured. Results show that small and uniform stresses are observed in the 2219 aluminum alloy welding samples after TSR, VSR, and TVSR treatment. TSR treatment decreased the peak residual stress much more than VSR and TVSR treatment. The maximum reduction of the peak residual stress is 50.8% (210 °C) in the transversal direction and 42.02% (185 °C) in the longitudinal direction after TSR treatment with the temperature range 140 °C to 210 °C. In terms of residual stress homogenization, although the TSR treatment has an advantage perpendicular to the weld direction, the effect parallel to the weld direction is not ideal. The TVSR has a good effect in both directions. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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11 pages, 2400 KiB

Open AccessArticle

Modeling Electrical Resistivity of Naturally Aged Al–Mg–Si Alloys

by Abbas Bahrami and Maryam Yazdan Mehr

Metals 2019, 9(3), 310; https://doi.org/10.3390/met9030310 - 08 Mar 2019

Cited by 8 | Viewed by 4262

Abstract

Isothermal ageing of Al–Mg–Si alloys, stored at room temperature for more than 5 months, is associated with an unexpected significant increase in the overall electrical resistivity. This unexpected anomalous increase is not observed in alloys with shorter storage (natural ageing) times. This phenomenon is explained with a scenario, based on the evolution of the size distribution of Guinier–Preston (GP) zones during natural ageing and during subsequent artificial ageing. The proposed scenario can explain the contribution of natural ageing atomic clusters to this anomalous increase in the electrical resistivity. A physically based combined precipitation–electrical resistivity model, with the former being based on simultaneous nucleation-growth-coarsening reactions and the latter based on the Bragg scattering of electrons from atomic clusters, has been used to explain the electrical resistivity evolution. It is shown that the proposed model is capable of reproducing the experimental data in both short natural ageing (less than 5 months) and long natural ageing (more than 5 months) regimes. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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16 pages, 6049 KiB

Open AccessArticle

Examination of the High Tensile Ductility Improvement in an As-Solutionized AA7075 Alloy with the Aid of a Friction Stir Process

by Ming-Hsiang Ku, Fei-Yi Hung and Truan-Sheng Lui

Metals 2019, 9(2), 196; https://doi.org/10.3390/met9020196 - 07 Feb 2019

Cited by 4 | Viewed by 2766

Abstract

The ductility enhancement of an AA7075 aluminum alloy aided by a friction stir process (FSP) and various heat treatments was investigated and compared in terms of outcome with full annealing (O). The results indicate that a big improvement in the tensile ductility was achieved by freezing the sample at temperatures below 0 °C after the solution treatment and water quenching (W treatment), and further improvement could be acquired via a friction stir process due to grain refinement (<6 μm). Thus, the observed improvement in tensile ductility can be explained by the fact that the W treatment and friction stir processing scheme had an increased strain-hardening effect and decreased the presence of intermetallic particles that are harmful to uniform tensile deformation, consequently causing strain localization in the early stage of tensile deformation, which suggests that these treatment are a potential solution for insufficient formability. In general, the elongation to failure values for the W and FSP-treated specimens (>40%) were at least 1.5-fold greater than that of the annealed alloy. In addition, serrated flow could be observed in the tensile flow curves, and both the Piobert–Lüders effect and the Portevin–LeChatelier (PL) effect could be observed. The enhancement in the tensile ductility was examined in terms of the existence of intermetallic particles and the supersaturated concentration of the solid solution. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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17 pages, 15223 KiB

Open AccessArticle

Investigation on Microstructural Evolution and Properties of an Al-Cu-Li Alloy with Mg and Zn Microalloying during Homogenization

by Hongying Li, Weichen Yu, Xiaoyu Wang, Rong Du and Wen You

Metals 2018, 8(12), 1010; https://doi.org/10.3390/met8121010 - 02 Dec 2018

Cited by 8 | Viewed by 2907

Abstract

The microstructural evolution and properties of an Al-Cu-Li alloy with Mg and Zn microalloying (Al-3.5Cu-1.5Li-0.5Mg-0.4Zn-0.3Mn-0.12Zr-0.06Ti) ingot subjected to homogenization (second-step annealing at 500 °C for 24 h following first-step annealing at 400 °C for 8 h) were investigated. Mg-Zn atom clusters were enriched at the end of dendrites as well as low-melting eutectic phases such as S (Al₂CuMg), T₂ (Al₆CuLi₃), T_B (Al_7.5Cu₄Li) and T₁ (Al₂CuLi) in the as-cast alloy. During homogenization, Mg-Zn atom clusters diffused from the segregation to the vacancies, leading to the dissolution of the low-melting eutectic phases. Not only Al₃Zr particles were observed at 500 °C, but more fine and uniform spherical dispersoids appeared, which were assumed as Al₃(Zr_xTi_yLi_1−x−y). Mg and Zn microalloying can promoted the nucleation of Al₃Zr and Al₃(Zr_xTi_yLi_1−x−y) dispersoids, as well as T (Al₂₀Cu₂Mn₃) phases, which all inhibited recrystallization effectively and improve the uniformity of the grains due to the strong pinning effect. The yield ratio was decreased from 0.81 to 0.52 with the yield strength decreased from 172 MPa to 61 MPa, which showed better plastic deformation ability of the alloy subjected to homogenization. In addition, the dissolution of low-melting eutectic phases and formation of Al₃(Zr_xTi_yLi_1−x−y) dispersoids resulted in the significant improvement on thermal stability. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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16 pages, 4805 KiB

Open AccessArticle

Optimization of A354 Al-Si-Cu-Mg Alloy Heat Treatment: Effect on Microstructure, Hardness, and Tensile Properties of Peak Aged and Overaged Alloy

by Stefania Toschi

Metals 2018, 8(11), 961; https://doi.org/10.3390/met8110961 - 17 Nov 2018

Cited by 36 | Viewed by 8501

Abstract

The aim of the present work is the study of T6 heat treatment of A354 (Al-Si-Cu-Mg) casting alloy. The heat treatment was optimized by maximizing mechanical strength of the alloy while keeping the treatment cost effective, reducing treatment time and temperature. Due to the presence of low melting compounds, a double stage solution treatment was proposed. The first stage was aimed at the homogenization and dissolution of the low melting phase while a second stage at a higher temperature was evaluated to foster dissolution of Cu/Mg rich intermetallics and keep the solution time and temperature as low as possible. Microstructural investigations were performed through optical and electronic microscopy, which allowed the assessment of the evolution of intermetallic phases during the solution treatment. Artificial aging was studied at different temperatures from 160 °C to 210 °C where the peak aging condition was identified. Over aging of the heat treated alloy was evaluated by soaking T6 samples at 200, 245, and 290 °C for up to 168 h. Tensile behavior of the T6 and over-aged alloy (i.e., after soaking at 210 °C for 50 h) was evaluated at room temperature. Results showed that the proposed treatment allowed the enhancement of mechanical properties of the alloy in comparison to industrial practice treatment, maintaining a good level of ductility and conferring a superior resistance to long-term high temperature exposure. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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18 pages, 7358 KiB

Open AccessArticle

Effect of T6 Heat Treatment on the Microstructure and Hardness of Secondary AlSi₉Cu₃(Fe) Alloys Produced by Semi-Solid SEED Process

by Alberto Fabrizi, Stefano Capuzzi, Alessandro De Mori and Giulio Timelli

Metals 2018, 8(10), 750; https://doi.org/10.3390/met8100750 - 23 Sep 2018

Cited by 30 | Viewed by 6357

Abstract

The effect of the T6 heat treatment on the microstructure and hardness of a secondary semi-solid AlSi₉Cu₃(Fe) alloy have been investigated by using optical, scanning and transmission electron microscopy and hardness testing. The semi-solid alloy was produced using the swirled enthalpy equilibration device (SEED). The solution heat treatments were performed at 450, 470 and 490 °C for 1 to 6 h followed by water quenching and artificial ageing at 160, 180 and 220 °C for holding times ranging from 1 to 30 h. The microstructural investigations have revealed the spheroidization of the eutectic Si and the dissolution of the majority of Cu-rich compounds after all the solution heat treatments; moreover, the greater the solution temperature and time, the higher the hardness of the alloy. Unacceptable surface blistering has been observed for severe solution condition, 490 °C for 3 and 6 h. The artificial ageing at 160 °C for 24 h has led to the highest alloy strengthening thanks to the precipitation of β” and Q’ (or L) phases within the α-Al matrix. The hardening peaks at higher temperatures have been early achieved due to faster hardening kinetic; however, the lower number density of β” and Q’ (or L) phases and the presence of coarser θ’ precipitates result in a reduction of hardness values for peak aged condition at 180 and 220 °C, respectively. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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14 pages, 6604 KiB

Open AccessArticle

Dissolution and Precipitation Behavior for Hot Forming of 7021 and 7075 Aluminum Alloys

by Benjamin Milkereit, Martin Österreich, Philipp Schuster, Georg Kirov, Ermal Mukeli and Olaf Kessler

Metals 2018, 8(7), 531; https://doi.org/10.3390/met8070531 - 09 Jul 2018

Cited by 30 | Viewed by 6343

Abstract

Due to their high strength, 7xxx aluminum sheets are increasingly used for structural automobile components. One of the major challenges is the formability of these alloys during the production process while retaining high strengths in service. One promising method is forming at elevated temperatures directly after solution annealing; this is known as hot forming. However, this thermomechanical process requires a detailed comprehension of the dissolution and precipitation behavior during heating, solution annealing, and subsequent combination of forming and cooling processes. Therefore, the kinetics of solid-solid phase transformations during continuous heating and continuous cooling of the aluminum alloys EN AW-7021 and EN AW-7075 were determined with differential scanning calorimetry and hardness testing. The suitable solution annealing conditions and the critical cooling rates were specified for both alloys and compared to the real hot forming processes. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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13 pages, 10229 KiB

Open AccessArticle

Enhancement of Mechanical Properties of Hot-Forged 6082 Suspension Parts via Rapid IR Heat Treatment

by Yi-Ling Chang, Fei-Yi Hung and Truan-Sheng Lui

Metals 2018, 8(7), 501; https://doi.org/10.3390/met8070501 - 29 Jun 2018

Cited by 10 | Viewed by 4195

Abstract

Post-forging heat treatment is often necessary to achieve the mechanical properties required for aluminum alloy forged parts. In this study, hot-forged 6082 suspension parts are used to study the effect of rapid infrared (IR) heat treatment. The insoluble particles present in the matrix after the solutionizing process are observed. Experimental results show that using rapid IR heat treatment leads to superior solutionizing, and thus a larger critical onset strain in serrated tensile flow. The rapid IR heat treatment also had a more significant precipitation effect, which enhanced the mechanical properties of the material. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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16 pages, 19250 KiB

Open AccessArticle

Influence of Solution-Annealing Parameters on the Continuous Cooling Precipitation of Aluminum Alloy 6082

by Hannes Fröck, Benjamin Milkereit, Philipp Wiechmann, Armin Springer, Manuela Sander, Olaf Kessler and Michael Reich

Metals 2018, 8(4), 265; https://doi.org/10.3390/met8040265 - 13 Apr 2018

Cited by 16 | Viewed by 5824

Abstract

We use a systematic approach to investigate the influence of the specific solution condition on quench-induced precipitation of coarse secondary phase particles during subsequent cooling for a wide range of cooling rates. Commercially produced plate material of aluminum alloy EN AW-6082 was investigated and the applied solution treatment conditions were chosen based on heating differential scanning calorimetry experiments of the initial T651 condition. The kinetics of the quench-induced precipitation were investigated by in situ cooling differential scanning calorimetry for a wide range of cooling rates. The nature of those quench-induced precipitates was analyzed by electron microscopy. The experimental data was evaluated with respect to the detrimental effect of incomplete dissolution on the age-hardening potential. We show that if the chosen solution temperature and soaking duration are too low or short, the solution treatment results in an incomplete dissolution of secondary phase particles. This involves precipitation during subsequent cooling to start concurrently with the onset of cooling, which increases the quench sensitivity. However, if the solution conditions allow the formation of a complete solid solution, precipitation will start after a certain degree of undercooling, thus keeping the upper critical cooling rate at the usual alloy-specific level. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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13 pages, 32765 KiB

Open AccessArticle

Enhancement of the Young’s Modulus through Infrared Heat Treatment: A Study of the Microstructure and the Mass Effect of Real Body 6082 Aluminum Forgings

by Yi-Ling Chang, Fei-Yi Hung and Truan-Sheng Lui

Metals 2018, 8(4), 239; https://doi.org/10.3390/met8040239 - 04 Apr 2018

Cited by 4 | Viewed by 4742

Abstract

To avoid the phenomenon of abnormal grain coarsening, and increase the Young’s modulus of forgings, an infrared heat treatment was used on different mass forgings and compared with the results of an air furnace heat treatment. This work focused on the effects of microstructural evolution and the mechanical properties of two different mass 6082 real forgings. The experimental results show that infrared heat treatment can effectively reduce the mass effect after heat treatment, inhibit the coarse grains formed, and keep the non-equiaxed grains along the metal flows, thus significantly improving the ductility of the material. In addition, the rapid heating characteristic of infrared can effectively shorten the duration of heat treatment and greatly enhance the Young’s modulus and the vibration resistance of 6082 entity forgings. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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11 pages, 4404 KiB

Open AccessArticle

Effects of Pre-Strain on the Aging Behavior of Al 7075 Alloy for Hot-Stamping Capability

by Seon-Ho Jung, Jongsup Lee and Megumi Kawasaki

Metals 2018, 8(2), 137; https://doi.org/10.3390/met8020137 - 16 Feb 2018

Cited by 20 | Viewed by 6305

Abstract

The present study investigates the significance of pre-strain on the T6 aging behavior of an Al 7075 alloy for evaluating the applicability of hot stamping. In practice, the alloy was pre-strained up to 15% during solution heat treatment at 480 °C prior to quenching, and artificial aging was conducted at 120 °C. The peak aging time and precipitation behavior were compared with the alloy with pre-straining at room temperature after quenching but immediately before the artificial aging. The results showed that increasing amounts of pre-strain tend to reduce the aging time up to 50% for achieving peak hardness, which is consistent with the alloy at the T6 condition. There is a limitation for the maximum attainable amount of pre-strain of 10% for the homogeneous distribution of strain when the alloy is strained at room temperature (RT) due to the low formability. The pre-strained alloy as hot stamping exhibited lowering of the peak reaction temperatures for dissolution and formation of Guinier–Preston (GP)-Zones and precipitated with increasing amounts of pre-strain towards 15% through the differential scanning calorimetry analysis, thereby confirming the shortening of the peak aging time. The present study confirms the excellent potential of the hot-stamping process to extend the capability of an Al 7075 alloy. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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9250 KiB

Open AccessArticle

Microstructure of Multi-Pass Friction-Stir-Processed Al-Zn-Mg-Cu Alloys Reinforced by Nano-Sized TiB₂ Particles and the Effect of T6 Heat Treatment

by Xiaofei Ju, Fengguo Zhang, Zhe Chen, Gang Ji, Mingliang Wang, Yi Wu, Shengyi Zhong and Haowei Wang

Metals 2017, 7(12), 530; https://doi.org/10.3390/met7120530 - 27 Nov 2017

Cited by 29 | Viewed by 5462

Abstract

In this work, a fine-grained structure with a uniform distribution of TiB₂ particles and precipitates was achieved in TiB₂ particle-reinforced (PR) Al-Zn-Mg-Cu alloys by friction stir processing (FSP). The effects of multi-pass FSP on the microstructure, and TiB₂ particle distribution, as well as the microstructural evolution in the following T6 treatment, were investigated by X-ray diffraction, scanning electron microscopy and associated electron backscattered diffraction. The results showed that the distribution of TiB₂ particles and alloy precipitates was further improved with an increase in the FSP passes. Moreover, compared with alloy segregation in the as-cast PR alloys during T6 treatment, a complete solution of the precipitates was achieved in the FSP-treated PR alloys. The fine-grained structure of the FSP-treated PR alloys was thermally stable without any abnormal growth at the high temperature of T6 treatment due to the pinning effect of dispersed TiB₂ particles. The strength and ductility of the PR alloys were simultaneously improved by the combination of FSP and T6 treatment. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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18110 KiB

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Effects of Porosity, Heat Input and Post-Weld Heat Treatment on the Microstructure and Mechanical Properties of TIG Welded Joints of AA6082-T6

by Bo Wang, Songbai Xue, Chaoli Ma, Jianxin Wang and Zhongqiang Lin

Metals 2017, 7(11), 463; https://doi.org/10.3390/met7110463 - 01 Nov 2017

Cited by 19 | Viewed by 6770

Abstract

Various heat input conditions and post-weld heat treatments were adopted to investigate the microstructure evolution and mechanical properties of tungsten inert gas (TIG) welded joints of AA6082-T6 with porosity defects. The results show that the fracture location is uncertain when an as-welded joint has porosities in the weld zone (WZ), and overaging in the heat-affected zone (HAZ) at the same time. When the fracture of the as-welded joint occurs in the HAZ, the total heat input has a linear relation with the tensile strength of the joint. An excess heat input induces the overgrowth of Mg₂Si precipitates in HAZ and the coarsening of α-Al grains in WZ, resulting in a decrease in the microhardness of the corresponding areas. After artificial aging treatment, the tensile strength of the welded joint is increased by approximately 9–13% as compared to that of as-welded joint, and fracture also occurs in HAZ. In contrast, for solution treated and artificial aging treated joint, fracture occurs suddenly at the rising phase of the tensile curve due to porosity defects throughout the weld metal. Furthermore, the eutectic Si particles of WZ coarsen and spheroidize after solution treatment and artificial aging treatment, due to the diffusion of Si to the surface of the original Si phases when soaking at high temperature. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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