Study On The Fabrication Of Mg-based Bulk Amorphous

The glass forming ability (GFA) of magnesium based bulk amorphous alloy is strong. Among Mg-Ln-TM alloy systems, Mg₆₅Cu₂₅Y₁₀ alloy has the largest value of ΔT_x (=T_x-T_g, where T_x is the crystallization point, T_g is the glass transition temperature) and supreme GFA. In the present paper, new Mg-based bulk amorphous alloys with low cost, fine room-temperature plasticity and strong glass forming ability are researched on based on the Mg-based bulk amorphous alloy now available. According to the systematic analysis about effects of different alloy elements on the glass forming ability, room-temperature mechanical properties, new Mg-based bulk amorphous alloys with low cost have been developed.Effects of adding other alloy elements into Mg-Cu-Y and the related alloy systems on the glass forming ability were studied and new Mg-based bulk amorphous alloy with larger critical glass forming size was then fabricated. In the present work, arc-melting furnace with magnetism-controlled tungsten electrode was employed to melt Cu-Y-M (M is the added element) master alloy. The master alloy is then smelted with pure magnesium in an electricity resistance furnace under the protection of argon atmosphere to get Mg-Cu-Y-M final alloy. Mg-Cu-Y-M bulk amorphous alloys were then prepared by casting the above alloy in a traditional copper mould. Melt-spinning machine with high vacuum was employed to prepare Mg-Cu-Y-M amorphous alloy ribbons of different composition. X-ray diffractometer was utilized to determine the phase constitution of the bulk amorphous alloys and the amorphous ribbons. DSC curves of Mg-Cu-Y-M bulk amorphous alloy were obtained by using the differential scanning calorimerter, and the glass transition temperatures and crystallization temperatures were confirmed. The glass forming ability was then analysed based on the differential scanning calorimeter curves. Mg-Cu-Y-M amorphous ribbons were heat treated in certain temperature range, and bending was carried out to determine the room-temperature plasticity of amorphous ribbons both before and after heat treatment, while tensile experiment was carried out to judge their strength. Utilizing optical microscope and scanning electron microscope, microstructures and the fracture morphology of ribbon sample were then observed.The experimental result shows that there will be no influence of the replacement of neodymium (Nd) by yttrium (Y) in the alloy on the glass forming ability. During thisprocess, Y was partly replaced by Nd, remembering that the price of Nd is much lower than that of Y. The room-temperature plasticity of Mg-based bulk amorphous alloys was improved as copper (Cu) was partly replaced by nickel (Ni), without influencing the glass forming ability. Then, the influence on the glass forming ability was discussed by comparing the contents and types of the addition elements. Mechanical properties of Mg-Cu-Y-M (M is the adding alloy element) bulk amorphous alloys were also examined systimatically. Influence of aging treatment on the room-temperature plasticity and mechanical properties of Mg65Cu2sYio, Mg-Cu-Y-Nd , Mg6sCu23Ni2Yio bulk amorphous alloys was discussed according to the results of mechanical examination and fracture morphology. A method to improve the room-temperature plasticity was then suggested. The crystallization of the amorphous alloy was also analyzed briefly.