The evolution behavior of cluster and subsequent precipitation in Al-Si-Cu-Mg alloys during aging procss were analyzed by means of three dimensional atom probe（3DAP）and first-principles calculations.3DAP experiment shows that dot-like Si-Si clusters

Si-Mg clusters and Si-Mg-Cu clusters appear in Al-1.0Si-1.5Cu-0.5Mg alloy with aging at 175℃for 0.25 h.First-principles calculation shows that the strong interaction exists between the solute atoms in structures mentioned.It consistents with the3 DAP experimental results.Meanwhile

the diffusion of Si atoms with a large number leads to the generation of Si-Cu clusters.As Si

Mg

Cu atoms continued to precipitation with aging for 0.25h

2

h

dot-like Si-Si clusters

Si-Cu clusters

Si-Mg clusters are grown into needle-like Si-Mg-Cu clusters.In further aging evolution

the aggregation of Si

Mg

Cu atoms promotes the growth of Si-Mg-Cu structures

and some Si-Mg-Cu structure is converted into lath-like Q′phase with generation of the Cu-rich structure.