Parameters Controlling High Temperature Deformability of Wrought Magnesium Alloys

2014 ◽  
Vol 783-786 ◽  
pp. 352-357
Author(s):  
Pierre Lhuissier ◽  
Luc Salvo ◽  
Jean Jacques Blandin
Keyword(s):  
High Temperature ◽  
Magnesium Alloys ◽  
Solute Drag ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Fine Grained ◽  
Significant Damage ◽  
Micro Tomography ◽  
Superplastic Properties ◽  
Deformation Tests

Due to limited deformability at room temperature, high temperature forming of magnesium alloys appears as an interesting alternative. Superplastic properties can be obtained in the case of fine grained magnesium alloys and in this regime, due to significant damage sensitivity, fracture strain is mainly controlled by nucleation, growth and coalescence of cavities. Magnesium alloys with large grained alloys can also exhibit interesting deformabilities at high temperature since dislocation movements can be controlled by a solute drag effect promoting plastic stability. Examples of such situations are presented in the case of wrought magnesium alloys, the associated damage mechanisms being investigated thanks to 3D X-ray micro tomography performed in continuous mode, namely directly during high temperature deformation tests.

Large Deformability of Wrought Magnesium Alloys: Is Superplasticity Needed?

2010 ◽  
Vol 433 ◽  
pp. 267-272 ◽  
Author(s):  
R. Boissière ◽  
Jean Jacques Blandin ◽  
Luc Salvo
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Magnesium Alloys ◽  
Rate Sensitivity ◽  
Solute Drag ◽  
Mg Alloys ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Fine Grained ◽  
Superplastic Properties

The deformability of wrought magnesium alloys at room temperature is limited and a way to overcome this limit is to carry out forming operations in warm or hot conditions. In the case of fine grained alloys, superplastic properties can be generally achieved but in this regime, the Mg alloys are sensitive to strain induced cavitation. However, large grained alloys can also exhibit quite large deformabilities when they are deformed at high temperature. This can be due to the fact that on one hand, the Mg alloys may quite easily dynamically recrystallize and on the other hand, that dislocation movements may be controlled by a solute drag effect leading to significant strain rate sensitivity parameters. These various mechanisms of deformation will depend on the composition, the mean grain size and the conditions of deformation (i.e. temperature and strain rate). In this work, the high temperature deformation mechanisms as well as the associated damage mechanisms of two wrought magnesium alloys are discussed.

High Temperature Deformation and Associated 3D Characterisation of Damage in Magnesium Alloys

2012 ◽  
Vol 706-709 ◽  
pp. 1128-1133 ◽  
Author(s):  
Pierre Lhuissier ◽  
A. Villanueva Fernandez ◽  
L. Salvo ◽  
Jean Jacques Blandin
Keyword(s):  
High Temperature ◽  
Magnesium Alloys ◽  
Room Temperature ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
X Ray ◽  
Plastic Stability ◽  
Micro Tomography ◽  
3D Information ◽  
Deformation Tests

A way to overcome the low deformability of magnesium alloys at room temperature is toincrease the temperature of forming operations. The stress exponent n, which is known to be a keyparameter in the control of plastic stability, generally decreases when temperature increases.Nevertheless, low n-values are not enough to ensure large capacity of deformation since fracturecan also result from strain induced cavitation. In the present investigation, both the mechanisms ofhigh temperature deformation and damage were studied in selected Mg alloys. Since damage datacan also give information on the deformation mechanisms, the strain induce cavitation behaviourwas mainly studied thanks to X-ray micro tomography which provides 3D information like thecavity shapes or the variation with strain of the number of cavities. Moreover, additionally toconventional post mortem analyses, it was attempted to perform the 3D damage characterisation inin situ conditions, namely directly during high temperature deformation tests.

Superplastic Elongation through Deformation Mechanism Transition during High-Temperature Deformation in Thermally Unstable Fine-Grained Aluminum Solid Solution Alloy

2016 ◽  
Vol 723 ◽  
pp. 21-26
Author(s):  
Tsutomu Ito ◽  
Takashi Mizuguchi
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Deformation Mechanism ◽  
Solute Drag ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Solid Solution Alloy ◽  
Fine Grained ◽  
Aluminum Solid Solution ◽  
Mechanism Transition

In this study, the superplastic behavior on a fine-grained aluminum solid solution alloy consisting of thermally unstable microstructures was investigated. In order to obtain the fine-grained microstructure, friction stir processing (FSP) was applied to a commercial 5083 aluminum alloy. An equiaxial fine-grained microstructure of 7.8 mm was obtained after FSP, but this microstructure was thermally unstable at high temperatures. Commonly, for fine-grained superplasticity to occur (or to continue grain boundary sliding (GBS)), it is necessary to keep the fine-grained microstructure to less than 10 mm during the high-temperature deformation. However, in this study, a large elongation of over 200% was observed at high temperatures in spite of the occurrence of grain growth. From the microstructural observations, it was determined that the fine-grained microstructure was maintained until the early stage of deformation, but the transgranular deformation was observed at a strain of over 100%. The microstructural feature of the abovementioned transgranular deformation is similar to the deformation microstructure of the solute drag creep occurring in "Class I"-type solid solution alloys. This indicates that the deformation mechanism transition from GBS to the solute drag creep occurred during high-temperature deformation. Here, the possibility of occurrence of the superplastic elongation through deformation mechanism transition is discussed as a model of the thermally unstable aluminum solid solution alloy.

4D Damage Characterization during Superplastic Deformation of Magnesium Alloys

2012 ◽  
Vol 735 ◽  
pp. 61-66 ◽  
Author(s):  
Pierre Lhuissier ◽  
Mario Scheel ◽  
Luc Salvo ◽  
Elodie Boller ◽  
Marco Di Michiel ◽  
...  
Keyword(s):  
Magnesium Alloys ◽  
Aluminium Alloys ◽  
Superplastic Deformation ◽  
Fracture Process ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Efficient Tool ◽  
X Ray ◽  
Micro Tomography ◽  
Deformation Tests

As for aluminium alloys, magnesium alloys are generally sensitive to strain induced cavitation when they are deformed in superplastic conditions. It has been widely shown that X-ray micro tomography is a particularly efficient tool for studying in 3D damage mechanisms during superplastic deformation. However, such characterisations are generally performed in post mortem conditions, namely on samples first deformed up to given strains and then characterised. In the present investigation, thanks to particularly short acquisition times offered by ESRF, damage induced by superplastic deformation of a magnesium alloy is studied thanks to tomography analyses performed in 4D conditions, namely directly during high temperature deformation tests. Such conditions provide unique opportunities for investigating nucleation, growth and coalescence of cavities since it is thus possible to follow each cavity up to the fracture process.

High-Temperature Deformation of Magnesium ElektronTM 43

2012 ◽  
Vol 735 ◽  
pp. 93-100
Author(s):  
Alexander J. Carpenter ◽  
Anthony J. Barnes ◽  
Eric M. Taleff
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Superplastic Forming ◽  
Solute Drag ◽  
Grain Boundary Sliding ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Fine Grained ◽  
Boundary Sliding

Complex sheet metal components can be formed from lightweight aluminum and magnesium sheet alloys using superplastic forming technologies. Superplastic forming typically takes advantage of the high strain-rate sensitivity characteristic of grain-boundary-sliding (GBS) creep to obtain significant ductility at high temperatures. However, GBS creep requires fine-grained materials, which can be expensive and difficult to manufacture. An alternative is provided by materials that exhibit solute-drag (SD) creep, a mechanism that also produces elevated values of strain-rate sensitivity. SD creep typically operates at lower temperatures and faster strain rates than does GBS creep. Unlike GBS creep, solute-drag creep does not require a fine, stable grain size. Previous work by Boissière et al. suggested that the Mg-Y-Nd alloy, essentially WE43, deforms by SD creep at temperatures near 400°C. The present investigation examines both tensile and biaxial deformation behavior of ElektronTM 43 sheet, which has a composition similar to WE43, at temperatures ranging from 400 to 500°C. Data are presented that provide additional evidence for SD creep in Elektron 43 and demonstrate the remarkable degree of biaxial strain possible under this regime (>1000%). These results indicate an excellent potential for producing complex 3-D parts, via superplastic forming, using this particular heat-treatable Mg alloy.

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