Thermally Stable Nanocrystalline Al-Mg Alloy Powders Produced by Cryomilling

Zhou, Fei; Rodriguez, Rodolfo-Martín; Lavernia, Enrique J.

doi:10.4028/www.scientific.net/msf.386-388.409

Cited by 35 publications

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“…Any excess Mg will form precipitates of Al 3 Mg 2 or Al 12 Mg 17 . Results reported by other investigators [10] have shown no evidence of the presence of Al-Mg precipitates in cryomilled Al-7.5 pct Mg, a finding that is in agreement with the present inference.The tensile specimens were machined along the extrusion direction with a gage length of 21.59 mm and a gage diameter of 3.175 mm. Tensile tests were carried out in liquid nitrogen using a universal testing machine at a strain rate of approximately 10 Ϫ3 s Ϫ1 .…”

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Mechanical behavior of a cryomilled nanostructured Al-7.5 pct Mg alloy

Han

Zhang

Lavernia

et al. 2004

Metall Mater Trans A

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Over the past several years, there has been considerable interest in phenomena that take place at nanometer (10 Ϫ9 m) length scales, and that may lead to novel mechanical properties in structural materials. As a result of this interest, a number of synthesis techniques that are capable of producing structural materials with grain sizes of 10 to 500 nm have been developed. Primary among these synthesis techniques is cryomilling, which consists of mechanical alloying/milling under liquid nitrogen. Furthermore, cryomilling is capable of producing bulk materials in large quantities. [1,2,3] Structural materials produced by cryomilling may be divided into ultrafine grained materials, which exhibit grain size larger than 200 nm, and bulk nanostructured materials, which are characterized by grain sizes less than 200 nm.In a very recent article, [4] the mechanical behavior of cryomilled Al-7.5 pct Mg alloy that exhibited an ultrafine grained microstructure with an approximate size of 300 nm was reported. The data of this alloy at room temperature, when plotted in terms stress-strain curves, have shown that the tensile behavior of the alloy is characterized by high strength, low strain hardening, and reasonably high ductility, compared to conventional 5083 Al. [4] Further, after yielding, there are well-defined stress drops. It has been suggested that a possible source for these stress drops is deformation twinning. In order to examine the possibility of deformation twinning, tests need to be performed under the following conditions: low temperature and small grain size. A decrease in temperature tends to favor twinning over slip, even in metallic systems with a high stacking fault energy such as Al (fcc). Also, when grain size is decreased, the twinning stress may become smaller than the stress for slip. This possibility is supported by the observation [5] that the twinning stress for Cu-15. at pct Zn increased linearly with d Ϫ1 and not with d Ϫ0.5 , which characterizes the grain size dependence of the stress for slip. In addition, deformation twinning was observed in nanostructured Al powers after cryomilling process using a high resolution electron microscope. [6,7] This article reports preliminary results on the mechanical behavior of nanostructured Al-7.5 pct Mg that was processed by cryomilling. The mechanical behavior of the alloy was investigated by performing tensile tests in liquid nitrogen.The primary purpose of the investigation was to determine if deformation twinning is operative during deformation.The extruded cryomilled nanostructured Al-7.5 pct Mg alloy used in the present investigation was manufactured at the Rocketdyne Division, Boeing Company (Canoga Park, CA), using the following procedures. [4] A mixture of pure aluminum powders and high-magnesium aluminum alloy powders was mechanically milled in liquid nitrogen. The milled powders were packed in aluminum cans in an inert atmosphere before hot degassing under vacuum and consolidated by hot isostatic pressing. The consolidated billets were finally ex...

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Mechanical behavior of a cryomilled nanostructured Al-7.5 pct Mg alloy

Han

Zhang

Lavernia

et al. 2004

Metall Mater Trans A

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“…Second, there is a shift in peak only slight barreling is observed in the circular or rectangular compressive specimens with an aspect ratio of 1, even after position to higher Bragg angles as the material condition corresponding decrease in the lattice parameter. Experimental evidence [21] has indicated that a decrease in the Mg conchanges from "as-extruded" to "furnace cooled" to "water quenched." This trend may be explained in terms of effects tent of Al leads to a decrease in the lattice parameter of the metal.…”

Section: Materials and Experimentalmentioning

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Mechanical properties of an ultrafine-grained Al-7.5 Pct Mg alloy

Han

Mohamed

Lee

et al. 2003

Metall Mater Trans A

138

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In the present study, the relationships between the structure and properties of a cryomilled Al-7.5 pct Mg alloy were investigated. The microstructure of the cryomilled Al-7.5 pct Mg alloy consisted of equiaxed grains with an approximate size of 300 nm. Thermal treatment had only a minor effect on microstructure, as evidenced by X-ray diffraction (XRD) and transmission electron microscopy (TEM) results. The tensile behavior was characterized by high strength, high ductility, and low-strain-hardening. The tensile deformation was relatively uniform, with limited necking deformation, and fracture surfaces were characterized by microdimples. The variation of strain rates from 4 и 10 Ϫ4 to 4 и 10 Ϫ2 s Ϫ1 had an insignificant effect on tensile behavior. Comparison of compressive and tensile behavior revealed similar moduli and yield strengths, although the postyield behavior was markedly asymmetric. The present results indicate that grain-size effects, solid-solution strengthening, Orowan strengthening, and dislocation strengthening contribute significantly to the properties of a cryomilled Al-7.5 pct Mg alloy.

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“…This type of thermal stability in ultrafine-grained aluminum alloys made from cryomilled powders has also been observed by other researchers. [12] It is believed that the high thermal stability of the microstructure in the present composite is due to the Zener pinning effect of the particles of oxides and nitrides formed during the cryomilling process, as well as the SiC particles, on the grain boundaries.…”

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confidence: 99%

Tensile Properties of a Nanostructured Al‐5083/SiC_p Composite at Elevated Temperatures

et al. 2007

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Recently, by combining particulate reinforced metal-matrix composites (MMCs) with nanotechnology, nanostructured metal-matrix composites (NMMCs), which have a nanocrystalline matrix and/or nano-sized reinforcing particles, have been developed. Experimental studies show that the mechanical properties of NMMCs have been significantly improved in comparison with those of the conventional MMCs. For instance, it has been reported that, with only 2 wt.% nano-sized SiC particles dispersed as a reinforcement using a melting method, the yield strength of as-cast aluminum alloy A356 was improved by 50 %, which is significantly higher than the reinforcing effect with the same amount of micron-sized particles. [1] Al/Si-N-C NMMCs with only 1 vol.% nano-sized Si-N-C particles fabricated by a powdermetallurgy process exhibited a tensile strength comparable to that of Al/SiC p MMCs with 15 vol.% SiC particles 3.5 lm in size, with higher ductility in the former than in the latter. [2] The yield strength of Al was doubled by the dispersion of 4 vol.% nano-sized Al 2 O 3 particles via a powder-metallurgy process. [3] NMMCs consisting of a nanocrystalline Ni matrix reinforced with up to 10.5 vol.% sub-micron SiC particulates were produced by pulse electro-deposition, and enhanced mechanical strength was obtained for these MMCs as compared with conventional Ni/SiC p MMCs with a matrix grain size in the micrometer range. [4] In an NMMC with a nanocrystalline or ultrafine-grained matrix, the dislocation movement in the matrix is restricted by the high-density grain boundaries and is qualitatively different from that in a coarse-grained matrix. [5] Therefore, the effect of reinforcing particles in an NMMC with a nanocrystalline or ultrafine-grained matrix should also have specific features. For example, an unexpected improvement in ductility has been observed in an NMMC consisting of a nanocrystalline nickel matrix reinforced with sub-micron size SiC particles, in comparison with pure nanocrystalline nickel without reinforcing particles. [4] So far, due to the complexities in the synthesis of NMMCs, systematic investigations on the mechanical properties of NMMCs are sparse, and thus, there is still not a thorough understanding of the microstructure/ properties relationship in the NMMCs.In the present paper, a bulk nanostructured Al-5083/SiC p composite, which consists of an ultrafine-grained Al-5083 matrix reinforced with nano-sized SiC particles, was fabricated with a powder cryomilling and consolidation technique. The tensile properties of this composite were investigated at various temperatures and fractography was conducted on the tensile specimens after failure. On the basis of these experimental results, the factors affecting the tensile properties and the fracture behavior of the nanostructured Al-5083/SiC p composite are discussed. ResultsAs described in a previous paper, [6] the microstructure of the present Al-5083/SiC p composite consists of regions dispersed with nano-scale SiC particles and regions free of SiC particles. T...

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Thermally Stable Nanocrystalline Al-Mg Alloy Powders Produced by Cryomilling

Cited by 35 publications

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Mechanical behavior of a cryomilled nanostructured Al-7.5 pct Mg alloy

Mechanical behavior of a cryomilled nanostructured Al-7.5 pct Mg alloy

Mechanical properties of an ultrafine-grained Al-7.5 Pct Mg alloy

Tensile Properties of a Nanostructured Al‐5083/SiC_p Composite at Elevated Temperatures

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Thermally Stable Nanocrystalline Al-Mg Alloy Powders Produced by Cryomilling

Cited by 35 publications

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Mechanical behavior of a cryomilled nanostructured Al-7.5 pct Mg alloy

Mechanical behavior of a cryomilled nanostructured Al-7.5 pct Mg alloy

Mechanical properties of an ultrafine-grained Al-7.5 Pct Mg alloy

Tensile Properties of a Nanostructured Al‐5083/SiCp Composite at Elevated Temperatures

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Tensile Properties of a Nanostructured Al‐5083/SiC_p Composite at Elevated Temperatures