On the atomic model of Guinier-Preston zones in Al-Mg-Si-Cu alloys
Résumé
Structural feature of equiaxed Guinier-Preston zones with the diameter of ∼2 nm in an Al-Mg-Si-Cu alloy has been systematically investigated by three-dimensional atom probe analyses, high-resolution electron microscopy and first-principles calculations. The results suggest that Si and Mg planes alternate along [001]Al with Cu atoms diversely substituting for some Si sites. An fcc-based Mg1(Si,Cu)1 model was then proposed for the first time, with expanded a, b and compressed c lattice parameters compared to Al. Meanwhile the structural evolution of Mg1(Si,Cu)1 → (Mg,Cu)1(Si,Cu)1 → β″-(Mg,Cu)1Mg4(Al,Cu)2Si4 is suggested.