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Al-Zn-Mg-Cu alloys (7xxx) belong to wrought aluminum alloys with high strength and toughness, which are widely used in aerospace and transportation fields [1,2] . Al-Zn-Mg-Cu alloys are generally formed through wrought process, which is much more expensive than the alternative casting route. However, Al-Zn-Mg-Cu alloys prepared by traditional casting methods are prone to casting defects such as shrinkage porosity and shrinkage cavities, which will deteriorate the mechanical properties of the alloys [3,4] . The semisolid metal processing technology discovered in 1971 provides the possibility for the direct casting of Al-Zn-Mg-Cu alloys [5] . This is because the semisolid

Despite the high cost and difficult production process, the 7xxx (Al-Zn-Mg-Cu) wrought aluminum alloys are still widely used in aerospace industry due to its wellperforming mechanical qualities and superior fatigue resistance [1][2][3] . Recently, there has been a booming interest in producing cast Al-Zn-Mg-Cu alloys with the goal of lowering production costs and developing shaped products while maintaining outstanding mechanical qualities [4] .Several processes, such as spray deposition, electromagnetic casting, powder metallurgy, semi-solid casting and quick solidification, have been employed

The microstructure and mechanical properties of semisolid rheo-diecasting Al-xZn-2Mg-1.5Cu alloys with different Zn contents were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness testing (HV) and room temperature tensile testing. Results show that the as-cast microstructure mainly consists of spherical α-Al and Mg(Al, Cu, Zn)2 phases. Furthermore, a small amounts of Al7Cu2Fe phases were also detected along the grain boundary. Increasing the Zn contents from 8–12%, the volume fraction of the Mg(Al, Cu, Zn)2 phases increases from 4.9–7.4%. After solution heat treatment at 470 °C for 8 h, most of the Mg(Al, Cu, Zn)2 dissolves into the α-Al matrix, while the Al7Cu2Fe phase keeps with remains. The yield strength linearly increases from 482 ± 5 MPa of 8% Zn to 529 ± 5 MPa of 12% Zn. While, the ultimate strength of 10% Zn is 584 ± 2 MPa, which is higher than that of the other two alloys. Moreover, the average elongation dramatically decreases from 13% for the 8% Zn alloy to 2% for the 12% Zn alloy.