Copper diffusivities were measured in both α single phase and α plus Si phase Al–Cu–Si alloys by diffusion couple experiments. The results showed that Cu atoms had much faster diffusion rate in the α plus Si phase Al–Cu–Si alloy than in the α single phase Al–Cu–Si alloy, which meant that  Si phase played an important role in Cu diffusion in the alloy. Copper has very high diffusivity in the Si phase, Si particles became shortcuts for Cu diffusion in the alloy. How much the Si phase could increase Cu diffusivity depended on silicon's volume percentage and morphology.

The Fast Diffusion Paths of Copper Atoms in Al–Cu–Si Alloys. D.Zhang, J.Peng, T.Liu: Materials Science and Engineering A, 2006, 425[1-2], 78-82