Impurity effect of Mg on the generalized planar fault energy of Al

Abstract

Generalized Planar Fault Energy (GPFE) curves are widely used to evaluate the deformation behavior of metals and alloys. In the present work, a systematic analysis of the microscopic plastic deformation mechanism of face-centered cubic Al in comparison to Cu was conducted based on GPFE curves generated via first-principles calculations. Focus has been put on the effects of Mg impurities in terms of local concentration and local atomic arrangement nearby the deformation plane, upon the GPFE curve of Al, with the aim to investigate the twinnability of Al-Mg alloys subjected to plastic deformation.It is found that Mg exhibites a Suzuki segregation feature to the stacking fault of Al, either intrinsic or extrinsic. Mg atoms residing in the stacking fault plane can decrease the intrinsic stacking fault energy  ISFE and enhance the twinning propensity of Al. However, the  ISFE value does not decrease monotonically with increasing Mg concentration in the alloy, and a continuous twinnability increase with increasing Mg content is not observed. It is also seen that different local concentrations and atomic configurations of Mg atoms in the vicinity of deformation plane could yield a large variation of  ISFE and the twinning propensity of Al. It is proposed that Mg alloying cannot substantially enhance the twinning propensity of Al alloys.

Influence of Mg Content on Texture Development during Hot Plain-Strain Deformation of Aluminum Alloys

“…It should also be considered that the SFE of pure aluminum (annealed) is equal to 174 mJ/m 2 , while the SFE of the alloy with 6.28% magnesium content is 151.6 mJ/m 2 . In other words, even deformed alloys with extremely high magnesium content maintain a high level of SFE, compared to other materials [20]. Considering the data, presented by this source, it may be assumed that Al-95 alloy (with account for its high purity) energy will be equal to 177 mJ/m 2 , Al-Mg1-168.0 mJ/m 2 , Al-Mg4-154.7 mJ/m 2 , thus SFE difference for two extreme alloys will be slightly above 22 mJ/m 2 .…”

“…This texture pattern change is mainly associated with the effect of magnesium to maximally decrease the stacking fault energy. In pure aluminum, it reaches 174 mJ/m 2 , and in the alloy with 6.28% magnesium content, it reaches 151.6 mJ/m 2 [20].…”

Formation of Σ3{110} incoherent twin boundaries through geometrically necessary boundaries in an Al-8Zn alloy subjected to one pass of equal channel angular pressing

“…However, a recent first principles calculation based on density function theory (DFT) shows that an addition of Mg in Al can only slightly decrease the SFE and thus the twinning ability is slightly improved [24]. This has been confirmed by an experimental study on an Al-7Mg alloy subjected to dynamic plastic deformation (DPD) under a strain rate of ~10 2 s -1 [25], in which no deformation twins could be found.…”

Modelling of Creep in Alloys Strengthened by Rod-Shaped Particles: Al-Cu-Mg Age-Hardenable Alloys

“…Since the parameter A is traditionally considered to be proportional to the third-power of the stacking fault energy [20], a large reduction of this latter parameter [21,22] could indeed result in a decrease of one or even two orders of magnitude in the strain rate for a given effective stress. Yet, recent investigations present a quite different picture of the situation, since alloying actually only slightly reduces stacking fault energy, and this reduction is by far too modest to account for the dramatic reduction in the parameter A [23]. Thus, by Equation (1), one can still obtain an excellent description of the experimental data, but this description largely remains of a phenomenological nature, and any possible correlation with the microstructural evolution of the material is still based on weak bases.…”