Abstract: By changing the magnesium content, four compositions of Al-6.0Zn-xMg alloys were designed. The effect of Mg content on microstructure and properties of the as-cast and homogenized Al-Zn-Mg alloy and T6 state properties was studies by means of optical microscope (OM), scanning electron microscope (SEM), differential scanning calorimetry (DSC), hardness, electrical conductivity and room temperature tensile tests. The results show that there are a large number of eutectic network structures and chain-like second phases near the grain boundaries of the four as-cast alloys, mainly α (Al)+ternary T (AlZnMg) phases, and a small number of Al₃ (Zr, Ti) phases and iron-rich phases, and increasing the Mg content will increase the non-equilibrium eutectic phase in the alloy structure. After homogenization treatment and followed air-cooling, a large number of fine and dispersed needle-like η(MgZn₂) phases are precipitated in the alloy matrix, and with the increase of Mg content, the number of precipitation of this needle-like η(MgZn₂) phase also gradually increases. As the Mg content increases, the hardness gradually increases, while the electrical conductivity gradually decreases, and the hardness and electrical conductivity of the homogenized alloy are higher than that of the as-cast alloy. Among the four alloys at T6 state, the Al-6.0Zn-2Mg alloy has the best comprehensive mechanical properties.

Key words: Mg content, Al-Zn-Mg alloy, as-cast microstructure, homogenized microstructure, T6 state, mechanical properties