The microstructure and mechanical properties of Al-Si-Zn-Mg alloys with different Zn contents were investigated by metallographic microscope（OM）

scanning electron microscope（SEM）

tensile testing machine and microhardness tester. The effects of Zn contents on aging precipitation behavior of Mg

2

Si phase in Al-Si-Mg alloy were analyzed by differential scanning calorimetry（DSC）

combined with Avrami-Johnson-Mehl（AJM） equation. The results indicate that peak aging strength and hardness of Al-Si-Zn-Mg alloys are gradually increased with the increase of Zn contents

while elongation is decreased and peak aging time is gradually shortened correspondingly. Zn is evenly distributed in the alloy

and addition of Zn has little effect on the microstructure

which

however

improves the precipitation activation energy of Mg-Si solute atomic clusters and G.P. zone by hindering the migration of Mg atoms to Si clusters

and accelerates the dissolution of Mg-Si solute atomic clusters and G.P. zone during the subsequent heating process

resulting in the dimension reduction of Mg-Si clusters. Furthermore

the lattice distortion energy of the matrix is increased

and the migration of Mg and Si atoms from the matrix to form more Mg-Si and Mg-Zn-Si clusters is promoted after Zn addition

which increase the nucleation particles of the β″ phase

promoting the precipitation of β″ phase and aging response rate.