Paper Titles
The ASTM International Standard Test Method for Determining the Superplastic Properties of Metallic Materials
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Tool Thermal Behavior in SPF Environment
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Analysis of Different Specimen Geometries for Tensile Tests in Superplastic Conditions for an Aluminium Alloy
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Forming Limit Diagrams for AA5083 under SPF and QPF Conditions
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Mechanisms of Microsuperplasticity
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On the Phenomenology and Mechanics of Super Plastic Flow in Advanced Structural Materials
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Superplastic Deformation Mechanism of a Zn-Al Eutectoid Alloy
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Study on the Interface Characteristic of Superplastic Diffusion Bonding Joint of Dissimilar Steels
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Mechanisms of Microsuperplasticity

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Abstract:

After superplastic deformation of Al-7475 and some other aluminium alloys, straininduced cavities are seen to be associated with long fibres parallel to the tensile direction. These fibres, whiskers or filaments are also observed on the fracture surface. This effect has become known as microsuperplasticity. The whisker characteristics are affected by the deformation conditions, particularly temperature and strain rate. To study the effect of these variables more fully, tensile samples of Al 7475 have been strained to failure at temperatures ranging from 480OC to 530OC and strain rates from 1.0E- 04s-1 to 5.0E-03s-1. Additional samples were deformed at 450OC and 420OC and a single strain rate. Some whiskering was observed under all testing conditions. The longest whiskers were generally seen at high temperatures and low strain rates. A TEM study of macroscopic whiskers produced under conditions of around 540OC and 1.0E-04 /s showed an amorphous structure. Annealing prior to deformation was shown to have little effect on whisker formation. EDX analysis showed the whole surface of the alloy to be enriched in alloying elements compared with the bulk alloy. The high levels of Mg detected were connected with the formation of magnesia as the surface oxide verified using Cr3+ fluorescence microscopy. Use of the differential scanning calorimeter (DSC) showed no conclusive evidence of partial melting below the testing temperatures. Considerations of capillarity and the DSC analysis suggest whiskering did not occur by a mechanism of viscous flow.

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Periodical:

Materials Science Forum (Volumes 551-552)

Pages:

135-145

DOI:

https://doi.org/10.4028/www.scientific.net/MSF.551-552.135

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Online since:

July 2007

Authors:

J.H. Robinson, Martin A. Rust, Richard I. Todd

Keywords:

AA7475, Fiber, Microsuperplasticity, Whisker

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© 2007 Trans Tech Publications Ltd. All Rights Reserved

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