24/10/12

w w w . m a t e r i a l s . i m d e a . o r gComputational study of atomic mobility in hcp Mg-Al-Zn alloys and

anisotropic diffusion in hcp Mg-Al alloysJingya Wang1; Yuwen Cui1,3; Javier Llorca1,2

1 IMDEA Materials Institute, 28906 Madrid, Spain； 2 Department of Materials Science, Polytechnic University of Madrid, 28040 Madrid, Spain； 3 Institute for Advanced Metallic Materials & School of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, China

Ø Introduction1. Magnesium alloys possess low density, good castability as well as high

specific strength and are widely used in engineering applications. Theatomic mobility for the hcp phase of Mg-Al-Zn alloys is essential tounderstand processing (solidification, precipitation and creep).

2. Due to the anisotropic hcp structure of Mg, the lattice diffusion depends oncrystal orientation.

In this work, the atomic mobility database for bulk diffusion in hcp Mg-Al-Zn alloysis established based on the experimental data [1,2] and the anisotropic latticeinterdiffusion in hcp Mg-Al alloys is analyzed by extracting the interdiffusioncoefficients along the different orientations.

ØMethod

q Anisotropic diffusion in hcp Mg-Al alloys

q Atomic mobility in hcp Mg-Al-Zn alloys

θ: angle between the c-axis of the grain andthe diffusion direction

Experimental composition profilefrom the literature

Thermo-calc & DictraWorkspace: POLY-3 and PARROT

Diffusioncoefficient

Composition dependent

Orientation dependent

ØResultsq Atomic mobility in hcp Mg-Al-Zn alloys

Mg-Al system

Fig. 1(a) Impurity diffusion coefficients of Al in hcp Mg; (b) Interdiffusion coefficients of hcp Mg-Al alloys;(c) Composition profiles of Al at 723K

Fig. 2(a) Impurity diffusion coefficients of Zn in hcp Mg; (b) Interdiffusion coefficients of hcp Mg-Zn alloys;(c) Composition profiles of Zn at 723K

Mg-Zn system

la excelencia como clave tecnológicaexcellence as our technological key][

ØSummary1. The atomic mobility has been assessed based on the experimental values

in the literature and could successfully predict the diffusion behavior.2. Interdiffusion coefficients have been confirmed to be orientation dependent,

and atoms diffuse faster along the c-axis of grain.

ØReference1. C.C. Kammerer, N.S. Kulkarni, et.al, J.Alloy. Compd. 617 (2014) 968.2. C.C. Kammerer, N.S. Kulkarni, B. Warmack, Y.H. Sohn, J. Phase Equilib. Diffus. 37

(2016) 65.3. J.Y. Wang, N. Li, C.Y. Wang, J.I. Betran, J. Llorca, Y.W. Cui, CALPHAD. 54 (2016) 134.

673K 723K

Fig. 3(a) Interdiffusion coefficients in Mg-Al-Zn alloys at 673K; (b) Interdiffusion coefficients in Mg-Al-Zn alloys at 723K; (c) Calculated composition profiles of diffusion couple I at 673K along with the experimental values; (d) Calculatedcomposition profiles of diffusion couple II at 723K with the experimental values; (e) Calculated diffusion paths and available experimental data at 673K; (f) Calculated diffusion paths and available experimental data at 723K

The diffusion coefficients have been re-extracted and the diffusion behavior has been reproduced.

Mg-Al-Zn system

q Anisotropic diffusion in hcp Mg-Al alloysFig. 4 IPF map in the selected grainsto determine the diffusion coefficientsas a function of the declination angles(θ) and 3D crystal orientation plot (theout-of-plane direction isthe diffusiondirection)

Fig. 5(a) The compositionprofiles in the Grains A and B;

(b) The interdiffusioncoefficients.

θ , D

VIRMETAL project (Virtual Design, Virtual Processing and VirtualTesting of Metallic Materials), ERC Advanced Grant, EU H2020programme, grant agreement nº 669141