Effect of annealing and aging treatment on mechanical properties of ultrafine grained Al 6061 alloy
TL;DR: In this article, a comparative study of aging and a combined treatment of short annealing and aging on mechanical properties and microstructure of cryorolled (CR) Al 6061 alloy is investigated by using tensile tests, hardness tests, electron backscattered diffraction and transmission electron microscope.
Abstract: A comparative study of aging and a combined treatment of short annealing and aging on mechanical properties and microstructure of cryorolled (CR) Al 6061 alloy is investigated in the present work by using tensile tests, hardness tests, electron backscattered diffraction and transmission electron microscope. The pre-CR solid solution treatment combined with post-CR short annealing (200°C, 5 min) followed by aging treatment (100°C, 57 h) of the Al 6061 alloy showed an improved ductility and well defined ultrafine grain structure as compared to the samples subjected to pre-CR solid solution treatment followed by post-CR aging treatment (100°C, 60 h).
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TL;DR: In this article, an aluminum-magnesium (Al 5083) alloy was subjected to cryorolling and warm rolling followed by warm rolling in order to investigate the changes in mechanical behavior and microstructure evolution.
Abstract: Aluminum–Magnesium (Al 5083) alloy was subjected to cryorolling (CR) and cryorolling followed by warm rolling (WR) in order to investigate the changes in mechanical behavior and microstructure evolution in the present work. Al alloy specimens were first cryorolled up to 50% thickness reduction followed with warm rolling at 100 °C, 145 °C, 175 °C and 200 °C till to achieve total 90% thickness reduction. The final microstructure of all conditions were analyzed and compared through transmission electron microscopy (TEM), Electron back scattered diffraction (EBSD), and X-ray diffraction (XRD) techniques to investigate the effect of WR deformation temperatures on mechanical properties. The mechanical behavior of the processed samples were evaluated through hardness and tensile tests performed at room temperature. An increase in yield strength (522 MPa), ultimate tensile strength (539 MPa) and ductility (6.8%) was observed in WR specimens at 175 °C, hardness also increases to (146 HV) as compared to CR samples. These samples were annealed in temperature range from 150 °C to 300 °C to investigate their thermal stability. The CR samples exhibited severely deformed structure with high dislocation density network while cryorolled followed by warm rolled (WR) samples has shown formation of ultrafine grains associated with dynamic recovery. At elevated temperature of 200 °C, WR samples showed decrease in strength accompanied with increase in elongation due to dominant dynamic recovery effect led to reduction in dislocation density.
77 citations
TL;DR: In this paper, the mechanical properties and microstructural evolution of Al 6061 alloy subjected to cryorolling and warm rolling have been investigated in the present work and the effect of ageing on CR+WR samples was investigated and the optimum ageing condition was found to be 45h at 125°C.
Abstract: The mechanical properties and microstructural evolution of Al 6061 alloy subjected to cryorolling and warm rolling have been investigated in the present work. The Al 6061 alloy was subjected to thickness reduction of 70% by cryorolling followed by thickness reduction of 20% by warm rolling. The cryorolled + warmrolled (CR + WR) samples were characterized by Electron back scattered diffraction (EBSD) technique, Differential scanning calorimetry (DSC), X-Ray diffraction (XRD) analysis and Transmission electron microscopy (TEM) technique to substantiate the role of deformation strain and temperature on their microstructural features and compared with cryorolled (CR) samples. The CR + WR samples showed a significant improvement in tensile strength (376 MPa) and partial improvement in ductility (5%) as measured from tensile testing. It is mainly due to the combined effect of partial grain refinement, solid solution strengthening, dislocation hardening, dynamic recovery, and dynamic ageing during cryorolling and warm rolling. The effect of ageing on CR + WR samples was investigated and the optimum ageing condition was found to be 45 h at 125 °C, which gives improved tensile strength of (406 MPa) and good tensile ductility (10%). The tensile strength of cryorolled + warm rolled + peak aged (CR + WR + PA) sample (406 MPa) was found to be 11.2% more than that of cryorolled + peak aged (CR + PA) sample (365 MPa). During peak ageing treatment, the strength has been retained by pinning of dislocations through nanosized precipitates generated during warm rolling and it has been improved further by precipitation of the remnant dissolved second phase in the matrix. However, the observed ductility of CR + PA sample was 13% more than CR + WR + PA sample due to low dislocation density after ageing.
74 citations
Cites methods from "Effect of annealing and aging treat..."
...The effect of short annealing and static ageing treatment on mechanical properties of UFG 6061 alloy was reported in the author’s earlier work [17]....
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...EBSD analysis of CR Al 6061 alloy was discussed in our earlier study [17]....
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TL;DR: In this paper, the effects of short annealing and optimum heat treatment on tensile and impact-toughness behavior of Al 7075 alloy have been investigated by using tensile testing, hardness and Charpy impact testing.
Abstract: The effects of cryorolling and optimum heat treatment (short annealing + ageing) on tensile and impact-toughness behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its mechanical properties were studied by using tensile testing, hardness, and Charpy impact testing. The microstructural characterization of the alloy was carried out by using field emission scanning electron microscopy (FE-SEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain structure as observed from its FE-SEM micrographs. It is observed that the yield strength and impact toughness of the cryorolled material up to 70% thickness reduction have increased by 108% and 60% respectively compared to the starting material. The improved tensile strength and impact toughness of the cryorolled Al alloy is due to grain refinement, grain fragments with high angle boundaries, and ultrafine grain formation by multiple cryorolling passes. Scanning electron microscopy (SEM) analysis of the fracture surfaces of impact testing carried out on the samples in the temperature range of −200 to 100 °C exhibits ductile to brittle transition. cryorolled samples were subjected to short annealing for 5 min at, 170 °C, and 150 °C followed by ageing at 140 °C and 120 °C for both 40% and 70% reduced samples. The combined effect of short annealing and ageing, improved the strength and ductility of cryorolled samples, which is due to precipitation hardening and subgrain coarsening mechanism respectively. On the otherhand, impact strength of the cryorolled Al alloy has decreased due to high strain rate involved during impact loading.
68 citations
TL;DR: In this article, the influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied, and it was observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility.
Abstract: The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvements in strength and hardness. The ultimate tensile strength increases up to 340 MPa and 390 MPa for the 30% and 50% cryorolled samples, respectively. The cryorolled samples, with 30% and 50% reduction, were subjected to Charpy impact testing at various temperatures from −190°C to 100°C. It is observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility. Annealing of samples after cryorolling shows remarkable increment in impact toughness through recovery and recrystallization. The average grain size of the 50% cryorolled sample (14 μm) after annealing at 350°C for 1 h is found to be finer than that of the 30% cryorolled sample (25 μm). The scanning electron microscopy (SEM) analysis of fractured surfaces shows a large-size dimpled morphology, resembling the ductile fracture mechanism in the starting material and fibrous structure with very fine dimples in cryorolled samples corresponding to the brittle fracture mechanism.
53 citations
Cites methods from "Effect of annealing and aging treat..."
...Along with severe plastic deformation techniques, cryorolling (CR) has been used popularly to produce ultrafine grained structure in pure metals and alloys [8-11]....
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TL;DR: In this paper, an ultrafine grained structure developed in precipitation hardenable Al alloys through cryorolling by suppression of dynamic recovery followed by low temperature aging has received great research interest because of its high strength and very good ductility.
Abstract: An ultrafine grained (UFG) structure developed in precipitation hardenable Al alloys through cryorolling by suppression of dynamic recovery followed by low temperature aging has received great research interest because of its high strength and very good ductility. In the present work, Al 6061 alloy was solution treated and deformed by cryorolling up to an effective true strain of 2·6 and then subjected to annealing at the temperature range from 150 to 350°C to study the effect of annealing on the microstructure and mechanical properties. The evolution of microstructure and precipitates was investigated by employing X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Vickers hardness and tensile testings were performed at room temperature to evaluate the effect of annealing on the mechanical properties. It was observed that the strength and ductility increased upon annealing at 150°C, and further annealing at high temperatures (200–350°C) results in reduction in hardness ...
47 citations
References
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TL;DR: In this article, the authors present methods of severe plastic deformation and formation of nanostructures, including Torsion straining under high pressure, ECA pressing, and multiple forging.
Abstract: 2. Methods of severe plastic deformation and formation of nanostructures . . . . . . . 105 2.1. SPD techniques and regimes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 2.1.1. Torsion straining under high pressure . . . . . . . . . . . . . . . . . . . . . 106 2.1.2. ECA pressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 2.1.3. Multiple forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 2.2. Typical nanostructures and their formation . . . . . . . . . . . . . . . . . . . . . . . 115
5,763 citations
TL;DR: A thermomechanical treatment of Cu is described that results in a bimodal grain size distribution, with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine (<300 nm) grains, which impart high strength, as expected from an extrapolation of the Hall–Petch relationship.
Abstract: Nanocrystalline metals--with grain sizes of less than 100 nm--have strengths exceeding those of coarse-grained and even alloyed metals, and are thus expected to have many applications. For example, pure nanocrystalline Cu (refs 1-7) has a yield strength in excess of 400 MPa, which is six times higher than that of coarse-grained Cu. But nanocrystalline materials often exhibit low tensile ductility at room temperature, which limits their practical utility. The elongation to failure is typically less than a few per cent; the regime of uniform deformation is even smaller. Here we describe a thermomechanical treatment of Cu that results in a bimodal grain size distribution, with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine (<300 nm) grains. The matrix grains impart high strength, as expected from an extrapolation of the Hall-Petch relationship. Meanwhile, the inhomogeneous microstructure induces strain hardening mechanisms that stabilize the tensile deformation, leading to a high tensile ductility--65% elongation to failure, and 30% uniform elongation. We expect that these results will have implications in the development of tough nanostructured metals for forming operations and high-performance structural applications including microelectromechanical and biomedical systems.
2,531 citations
TL;DR: In this article, the authors reported a strategy to simultaneously increase the ductility and strength of bulk nanostructured materials, by engineering very small second-phase particles into a nanometre Al alloy matrix, while further gaining rather than sacrificing its yield strength.
Abstract: In this paper we report a strategy to simultaneously increase the ductility and strength of bulk nanostructured materials. By engineering very small second-phase particles into a nanostructured Al alloy matrix, we were able to more than double its uniform elongation, while further gaining rather than sacrificing its yield strength. The simultaneous enhancement of ductility and strength is due to the increased dislocation accumulation and resistance to dislocation-slip by second-phase particles, respectively. Our strategy is applicable to many nanostructured alloys and composites, and paves a way for their large-scale industrial applications. The material used in this model study is 7075 Al alloy. The alloy was solution-treated to obtain a coarse-grained (CG) solid solution. The CG sample was immediately cryogenically rolled to produce nanostructures with an average grain size of ca. 100 nm (designated as NS sample). The NS sample was then aged at low temperature to introduce very small secondphase particles (designated as NS+P sample). The engineering stress–strain curves of these samples are compared in Figure 1a. The 0.2 % yield strengths (marked by circles) of the CG, NS, and NS+P samples are 145 MPa, 550 MPa, and 615 MPa, respectively. Therefore, the low-temperature aging enhanced the yield strength of the NS sample by 12 %. The uniform elongation (marked by the symbol on the curves in Fig. 1a) was determined by the Considere criterion (Eq. 1) governing the onset of localized deformation [8]
703 citations
TL;DR: In this article, the microstructure of both 5000 and 6000 series alloy sheet can be controlled to provide the properties required for particular automotive applications, and the annealed strength and formability is strongly dependent upon grain size, Mg content, and, to a lesser extent, on crystallographic texture.
Abstract: The microstructure of both 5000 and 6000 series alloy sheet can be controlled to provide the properties required for particular automotive applications. The work-hardening 5000 series alloys, with between 3 and 6% Mg as the major alloying addition, are supplied to the automotive companies in the annealed temper and are characterized by a recrystallized grain structure which is influenced by the insoluble Fe-based intermetallics, dispersoids, and the work-hardening rate. The annealed strength and formability is strongly dependent upon grain size, Mg content, and, to a lesser extent, on crystallographic texture. The 6000 series alloys containing Cu, Mg, and Si are somewhat more complicated to control, because of precipitation of the age-hardening phases during fabrication. It is necessary to control the processes of dispersoid and precipitate formation so as to obtain the desired strength, grain size, and crystallographic texture in the final sheet. These alloys also offer a low solution-treated strength for high formability, combined with rapid age hardening to a relatively high strength in the formed component during the paint bake cycle.
266 citations
TL;DR: In this paper, a pre-ECAP solid-solution treatment combined with post ECAP aging treatment has been found to be more effective than preECAP peak-aging treatment in enhancing the strength of a 6061 Al alloy.
Abstract: Pre-ECAP solid-solution treatment combined with post-ECAP aging treatment has been found to be more effective than pre-ECAP peak-aging treatment in enhancing the strength of a 6061 Al alloy. An increase of ∼40% in UTS and yield stress was obtained in the post-ECAP aged material compared to the T6 treated commercial 6061 Al alloy.
192 citations