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. (c) 2007 Elsevier B. V. All rights reserved.