Research On Hydrogenation Reaction And Microstructure Of ZK60 Magnesium Alloy By Reactive Ball Milling Under Hydrogen

Magnesium alloy is a light structure material with the lowest density in all the current metals. Due to its high specific strength, high specific stiffness, good damping capacity and good shielding properties, magnesium alloys have been widely used in the fields of aviation and aerospace industry, automobile industry, electronics industry, communication industry, and other important fields. ZK60(Mg-Zn-Zr) is one of the best magnesium alloys with high strength. However, because magnesium alloys have HCP crystalline structure which leads to low symmetry, few slip systems and bad plastic deformation processability, it is limited to be widely used. As we all know, one of significant ways treating this alloy to improve its processability and plasticity is grain refinement. At present, there are several ways refining magnesium alloy grain, such as incubation treatment during casting, semi-solid state deformation, die casting, severe plastic deformation, and so on. All of these treatment ways approximately can only reduce the grain to 0.5~1μm, and it is hard to reach nanometer size.HDDR(hydrogenation-disproportionation-desorption-recombination) is a new hydrogen treatment technics to prepare ultra-fine rare earth permanent magnetic powder material. Magnesium can react with hydrogen to get the product of magnesium hydride, and also this reaction is reversible, so, as a result, HDDR technics can be introduced to process magnesium alloys and to refine grains. Conventionally the reaction to get magnesium hydride needs high temperature and high hydrogen pressure, which are a little difficult to satisfy with. While high energy ball milling can provide the reactant system with mechanical energy, substituting the thermal energy, which can also make the reaction happen, so we combine the hydrogenation with mechanical milling to produce nanostructured magnesium hydride at room temperature.In this paper, the hydrogenation mechanism of ZK60 magnesium alloy and the structure evolution has been studied. The effects on kinetics of ZK60 hydrogenated by hydrogen pressure, the ratio of ball to material and the rotation speed have also been researched. Through XRD, SEM and TEM, we analyzed the discipline of structure evolution during the hydrogenation process. In this study, ZK60 magnesium alloy powder milled for 20 hours can be hydrogenated fully at room temperature when the ratio of ball to material is 60:1 and the rotation speed is 375r/min under 0.5MPa hydrogen pressure. By comparative experiments, the reaction rate can be accelerated when the experiment is carried out under a higher hydrogen pressure, a higher ratio of ball to material and a higher rotation speed. After ZK60 powder hydrogenated fully, magnesium hydride was prepared with 10nm~20nm grain size.