Synthesis And Properties Of Mg-based Amorphous Alloys And Their Matrix Composites

More and more attention has been paid to the research on magnesium alloy due to its many attractive properties, including low specific gravity, high specificstrength, excellent damping capacity etc. However magnesium alloy has some limitation such as lower strength,worse ductility and poor corrosion resistance. Mg-based amorphous alloys exhibit great improvement in strength property and high corrosion resistance, which are particularly attractive for engineering applications. However Mg-based amorphous alloys are typically brittle at room temperature. It has become one of the challenging problems for their engineering applications. Therefore, the preparation of Mg-based amorphous matrix composites by using in situ or ex situ methods has been proven to be an effective way to overcome the brittleness of amorphous alloys. It is noticeable that most Mg-based amorphous matrix composites are prepared under the high vacuum with the high pure raw materials, which increase the cost and bad for their engineering applications. In addition, the corrosion behaviors of Mg-based amorphous matrix composites are different from that of the fully amorphous alloys or the conventional Mg alloys due to the effect of partially crystallization. It makes sense to develop new Mg-based amorphous matrix composites under the low vacuum with the raw materials and have fundamental corrosion studies on Mg-based amorphous matrix composites.In this paper, Mg-Cu-Y-Zn amorphous alloys and their matrix composites were prepared by water quenching and copper mold casting under the low vacuum, and the raw materials used in preparing the Mg-Cu-Y-Zn alloys were commercially pure materials. The microstructures of the bulk samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and the thermal stability of samples was investigated by using a differential scanning calorimeter (DSC). The alloy at x=5 prepared by copper mold casting exhibits a fully glass structure. The value of Tg, Tx andâ–³Tx (â–³Tx = Tx -Tg) of alloy are 409.8K, 446.2K and 36.4K. In addition, it is found that Mg solid solution flakes, Mg2Cu and MgZnY flakes are dispersed in the matrix of composites prepared by water quenching.The value of fracture strength and compression strain of all samples was evaluated by compression test. The composites exhibit significant improvement in mechanical properties, e.g. a compressive plastic strain of ~7% and ultimate strength of 1170 MPa have been measured in alloy at x=15 prepared by copper mold casting. It is suggested that the enhancement of the mechanical properties of the composites can be attributed to the generation of multiple shear bands and the quantity of the Mg solid solution flakes. But it can be found that the strength of composites decreased with the increasing of Mg content.The corrosion behavior of the Mg-Cu-Y-Zn amorphous alloys and their matrix composites was studied in borate solutions with pH 7-9 and NaCl solution at pH 7. The Mg2Cu phase which accelerates the corrosion of the Matrix and increases the dissolution of the sample. The Mg phase can have two roles in corrosion: (i) as sacrificial anodes and (ii) as a galvanic cathode. If the volume of Mg phase is low and surrounded by the amorphous matrix, the Mg phase serves mainly as sacrificial anodes and restrains the corrosion of the amorphous matrix. If the volume of Mg phase is higher, the phase serves mainly as a galvanic cathode and accelerates the overall corrosion of the alloy.