Investigation Of Mg Based Amorphous Alloys And Their Composites

Mg based amorphous alloys are regarded as a new family of the promising structural materials for their high strength and low density. However, it is impossible to use such kind of materials because most of Mg-based BMGs exhibit no macro-plastic deformation under compression and the fracture toughness is comparable to the ideal brittle materials, such as SiO₂. Therefore, how to improve the ductility of Mg-based BMGs has become a key issue in this area.In this paper, Mg based amorphous alloys and their composites were prepared by copper mould casting. The microstructures and phase constituent were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties of the bulk metallic glass composites were tested by universal electronic material testing machine and the fracture surface was observed by SEM. The microstructure, mechanical property, glass forming ability and phase constituent how to effect the mechanical property were investigated by means of the measurement of the strain-stress curves , phase ascertain and microstructure observation.The GFA and the mechanical properties of Mg-Cu-Ni-Nd-Y alloys were investigated. The glass formation for Mg_58.5Cu_27.5Ni₃Nd₅Y₆ alloy is as high as 13 mm in diameter. Furthermore, we suggest that the reliability in fracture stress can be evaluated by the relative difference between calculated stress and experimental stress. The smallest value was found for Mg_58.5Cu_27.5Ni₃Nd₅Y₆ BMG, which demonstrates that the fracture stress of this alloy can be reproduced.Mg₇₈Cu₁₀Y_6-xGd_xZn₅(x=0, 2,4) amorphous alloy matrix composite were prepared by copper mould casting. The microstructure and mechanical properties of Mg-Cu-Gd-Y-Zn amorphous alloy matrix composites were analyzed. The results show that the strength and plastic elongation is reduced with the increasing of Gd contents.Mg₇₇N_i8Y_10-xGd_xZn₅(x=0, 2, 4, 6) amorphous alloy matrix composite were fabricated by partial replacing Y with Gd. The microstructure and mechanical properties of Mg-Ni-Y-Gd-Zn amorphous alloy matrix composites were analyzed. The results indicate that the yield strength is decreased with the increasing of Mg solid solution. The plastic elongation of Mg_77+xNi₈Y₈Gd₂Zn₅ is 13%.Mg_77+xNi₈Y_8-xGd₂Zn₅(x=0, 2, 4) amorphous alloy matrix composite were prepared by copper mould casting. The effect of the Mg and Y on the microstructure and mechanical properties of Mg-Ni-Y-Gd-Zn amorphous alloy matrix composites were analyzed. The results show that the fracture strength and plastic strain for Mg₈₁Ni₈Y₄Gd₂Zn₅ are 583MPa and 21%, respectively. The plastic elongation is the largest one found up to now among Mg-Ni-Y-Gd-Zn amorphous matrix composites.