Effect of Zr Addition on the Microstructure and Mechanical Properties of as-Cast Al-Mg-Mn-Sc Alloys

This research examines the influence of Zr additions on the microstructure and properties characteristics of as-cast Al-6.5Mg-0.50Mn-0.25Sc alloys. The casting microstructure evolution, primary phase, mechanical properties, and the fracture morphology of alloys were characterized by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness test and universal electronic testing machine. The conclusion reveals that incorporating Zr in the casting Al-6.5Mg-0.50Mn-0.25Sc alloy has an obvious effect on both the microstructure and comprehensive performance. This positive effect is primarily due to the Al₃(Sc, Zr) primary phase, which serves as a heterogeneous nucleation agent during solidification, thereby contributing to grain refinement and the second-phase strengthening, specifically, at 0.10 wt.% Zr; as-cast alloy achieves the smallest average crystal size of 63 μm and exhibits the best combination of performance. The ultimate tensile strength (UTS), yield strength (YS), elongation (EL), and microhardness of the alloy reached 327 MPa, 190 MPa, 12%, and 107 HV, respectively.