Characteristics and microstructure of newly designed Al-Zn-based alloys for the die-casting process

Al-Zn-based alloys with high strength of >470 MPa for die-casting were successfully fabricated without melt modification and post-casting heat treatment. We designed Al-based alloys containing more than 20 wt% of Zn for the die-casting process. The matrix phase of the alloy was angular α-Al surrounded by a very fine lamellar structure of α-Al and η-Zn. The average grain size of the matrix was relatively small (∼25 μm), and a complex network of eutectoid α + η, supersaturated η, β, and Cu-related intermetallic particles formed at the grain boundaries or non-equilibrium solidification phases. This microstructural feature obtained by the addition of more than 20 wt% Zn significantly enhanced the strength of the Al-Zn-based alloys. Furthermore, we investigated the fluidity and wear properties of the developed alloys, which improved as the Zn content was increased.