Multi-alloying effect of Sc, Zr, Cr on the Al-Mg-Si-Mn high-pressure die casting alloys

The alloying effects of small additions of Sc, Zr, Cr on the microstructure and mechanical properties of Al-5Mg-2Si casting alloys produced by High Pressure Die Casting (HPDC) were investigated. The microstructure of the Al-alloys consists primarily of the alpha-Al and Al-Mg2Si eutectic cells and the alpha-Al-15 (Mn,Fe)(3)Si-2 intermetallic phase as well as coarse Al7Cr and Al3Zr intermetallic phases. The most significant improvement in the mechanical properties was achieved in the alloys with Sc + Cr and Sc + Zr additions. Alloying with 0.2 wt% of Sc in combination with Zr and Cr additions exhibits the best combination of strength and ductility with a yield strength of 206 MPa, an ultimate tensile strength of 353 MPa and an elongation of 10% in the as-cast condition. Alloys with Cr + Zr addition have a higher hardness and tensile strength compared to the AlMg5Si2Mn base alloy (commercially known as "Magsimal-59") and the similar levels of yield strength and elongation. However, they have lower levels of all set of properties compared to the alloys with Sc + Cr and Sc + Zr additions, due to the presence of coarse Al7Cr sludge and Al3Zr intermetallic phases.