First-principles study of alloy stability and diffusion on aluminum alloy surfaces

The stability of aluminum alloy surfaces has a critical influence on their ability to join to another material. This study employs first-principles density functional theory calculations to investigate the surface stability, configuration, and diffusion tendencies of alloying elements Mg, Si, Zr, and Sc on the crystal planes (001), (110), and (111) of an aluminum alloy. Utilizing asymmetric slab models, we introduce and apply an energy difference concept (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi mathvariant="normal">Δ</a:mi><a:msup><a:mi>E</a:mi><a:mtext>2D</a:mtext></a:msup></a:mrow></a:math>) to assess the stability of surface alloys relative to pure element covered surfaces. The findings reveal that surface stability is strongly dependent on both composition and atomic arrangement. Generally, mixed surface compositions, particularly a 50% coverage <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msub><c:mtext>Al</c:mtext><c:mn>2</c:mn></c:msub><c:msub><c:mi>M</c:mi><c:mn>2</c:mn></c:msub></c:mrow></c:math>, exhibit enhanced stability. And the next nearest neighbor is favored over the nearest-neighbor position of alloying atoms which are precursors to nearest precipitates. An analysis of the diffusion paths indicates that Mg and Si preferentially segregate to the outermost surface layer with Mg more strongly, whereas Zr and Sc exhibit a lower driving force to diffuse towards the outermost aluminum surface.