Microstructure and mechanical properties of bulk Mg–Zn–Ca amorphous alloys and amorphous matrix composites

Samples with different diameters for Mg–Zn–Ca alloys were fabricated by copper mold casting method. The microstructure, amorphous nature and mechanical properties of as-cast samples were investigated by SEM, XRD and compressive tests. The results show that amorphous alloys or amorphous matrix composites can be formed in the composition of 1–6 at.% Ca for the samples with 2, 3 or 4 mm in diameters. During which the highest strength up to 828 MPa and plastic deformation of 1.28% were obtained for Mg68Zn28Ca4 alloy with a monolithic amorphous structure. The best composition range defined both by strength and plastic deformation should be 3–5 at.% Ca for Mg72−xZn28Cax (x = 0–6) alloys. At least over 400 MPa of fracture strength was obtained for the samples with an amorphous matrix, indicating that Mg–Zn–Ca alloys can be good candidates for amorphous matrix composites fabrication. In order to further consider the amorphous matrix effect on mechanical properties, Mg95−xZnxCa5 (x = 15–33) alloys were investigated by the same methods. Mg80Zn15Ca5 alloy with no obviously amorphous structure exhibits a lower yielding strength of 307 MPa but it shows excellent plastic strain over 3.5%. We suggest that the amorphous matrix can enhance both the yielding strength and fracture strength of magnesium alloys.