Microstructure evolution and mechanical properties of new die-cast Al-Si-Mg-Mn alloys

The microstructure evolution and mechanical properties of recently developed die-cast Al-Si-Mg-Mn alloys were investigated. CALPHAD modelling, based on the thermodynamic database, was carried out to design Al-Si-Mg-Mn alloys with different solid fractions of the eutectic mixture. Experimental results confirmed that the new Al-Si-Mg-Mn alloys have excellent yield strength of 230–280 MPa, ultimate tensile strength of 340–370 MPa and elongation to fracture of 2.3–4.3% from the standard tensile samples under as-cast condition. The as-cast microstructure consists of α-Al, α-AlFeMnSi, binary eutectic (Al + Mg2Si) and ultrafine quaternary eutectic (Si + α-Al + Mg2Si + π-AlFeMnSiMg). The high strength is induced by the formation of multi-scale eutectic mixtures and fine α-AlFeMnSi particles. The newly designed Al-Si-Mg-Mn alloys offer 20–50% increase in yield strength with good ductility, as compared with the commercially available die-cast aluminium alloys.