Research On Naon-multilayer Magnesium Alloy By Accumulative Roll Bonding

Recent years, study on the processing technology, microstructure and properties of metal materials with nano-crystalline, ultra-fine grain and submicron crystalline is got much wide attention. In the methods of processing technologies of bulk nano-crystalline and ultra-fine grain materials, accumulative roll bonding (ARB) is seem the unique technology to be used in industrial production. In This paper, the ARB of AZ31magnesium alloy plates are investigated, and nano-multilayer materials of AZ31magnesium alloy plates are prepared by impregnating with carbon nano-tube, TiO2powder and pure copper plate between layers.Firstly, the AZ31magnesium alloy plates are deformed by ARB at different rolling temperatures, and the ARB process is repeated by seven times for one sample. In this paper, every ARB process is called one cycle and the sample after the nth ARB process is denoted as ARBn. Each cycle is realized by five rolling passes, and rolling reduction is15%. The rolling temperature is250℃,300℃and350℃respectively. The total rolling deformation of each cycle is75%. The conversion of grain boundaries near the layer interface from the instable low angle grain boundaries to the stable large angle grain boundaries resulted in the integration of the layer interface. Carbon nano-tube, TiO2powder and pure Cu plate are impregnated into layer interface of AZ31magnesium alloy plates in order to inhibit the integration of the layer interface and obtain AZ31magnesium alloy nano-multilayer materials.Meanwhile, In the ARB process of AZ31magnesium alloy plates without impregnating, through the pure aluminum as the coating material, the pure aluminum oxide to form A12O3in the effect of temperature and pressure. With the ARB process, the A12O3particle distribute in the matrix material dispersively, hinder the heat conduction of the layer interface and improve the integration of the layer interface. In the ARB7, the average grain size of matrix material reach1～2μm. With the increase of rolling temperatures, the grain size increase significantly and twin grain disappear gradually.Secondly, two different non-metallic powders are impregnated into layer interface of AZ31magnesium alloy plates, which are carbon nano-tube and TiO2powder respectively. After impregnating, the AZ31magnesium alloy plates are deformed seven cycles with300℃rolling temperature. After ARB7, the grain structure present long strip shape along the rolling direction, for the growth of one or other directions is restricted to the layer interface. And the average grain size is about8μm after impregnating with carbon nano-tube. The grain structure also present long strip shape along the rolling direction after impregnating with TiO2powder and much TiO2particles pinning the internal of grain, the average grain size of which is about5μm. The layer interface of AZ31magnesium alloy plates is obtained retention after impregnating non-metallic powders. Moreover, the size of layer interface is more uniform after impregnate carbon nano-tube.Finally, pure copper plate is impregnated in the AZ31magnesium alloy plates. After ARB7, the grain tissue obtains certain degree of refinement, but the grain tissue seems chaotic because of the solid solution reaction of magnesium and copper. The combining mechanism of layer interface tends to the softer magnesium phagocytosis the harder copper. Magnesium layer and copper layer are in solution reaction at certain temperature in order to disappear of layer interface.