Formation of Mg-Cu-Ni-Ag-Zn-Y-Gd bulk glassy alloy by casting into cone-shaped copper mold in air atmosphere

A new Mg-Cu-Ni-Ag-Zn-Y-Gd alloy with significantly improved glass forming ability (GFA) was developed in this work. Mg₆₅Cu_7.5 Ni_7.5Ag₅Zn₅ Y₅Gd₅ bulk metallic glass (BMG) with a diameter of 14 mm was successfully fabricated by conventional copper mold casting method in air atmosphere. The critical cooling rate for glass formation was estimated to be about 20 K/s. When the maximum diameter for glass formation was compared with those previously reported for Mg-based alloys, the Mg₆₅Cu_7.5 Ni_7.5Ag₅Zn₅ Y₅Gd₅ alloy showed the highest GFA. However, when the GFA was compared with those of Mg-TM-RE alloys (TM: Cu, Ni, Zn, and Ag; RE: Y and Gd), the significant improved GFA of the Mg-Cu-Ni-Zn-Ag-Y-Gd alloy cannot be properly represented by ΔT_x, T_rg, K, and γ parameters. In contrast to most of the Mg-based BMGs reported so far, the Mg₆₅Cu_7.5 Ni_7.5Ag₅Zn₅ Y₅Gd₅ BMG exhibits yielding and plastic deformation during compressive loading.