Semi-solid Technology Of Magnesium Alloy By Gas Bubbles During Solidification

Semi-solid casting technology of Magnesium alloy, which fulfills the requirements of complex production to the near net forming, has been researched more in recent years because of its fine precision in size, high quality inside, good formability. However, the development of the semi-solid technology always be limited, as the high demand of equipment and the hard process control which lead to the vast production cost .Therefore, the mission of developing a new semi-solid technology seems more meaningful in the magnesium application, especially to improve the performance and reduce the cost. Considering the feasibility of the semi-solid forming, in this paper, gas bubbling technology is presented. For the sake of optimizing process, influences of technics parameters are investigated. In addition, the principles of semi-solid forming and evolvement also are mentioned initially.In this article, a new gas bubbling equipment for semi-solid structure has been designed firstly. The results show that it's feasible for obtaining the non-dendritic structure under the new technology. Moreover, the non-dendritic structure has the typically characteristics of semi-solid organization, which mainly be constituted of the primaryαphase and the rose-shaped phase. Secondly, the related parameters (agitate temperature, rotated speed, holding time, agitating time, cooling speed) of AZ91D semi-solid casting has been investigated. As a result, the fine non-dendritic structure can be acquired under the temperature about 600℃, which would not be higher or lower. Supposed the same slurry temperature, the liquid metal after slurry has more effect on the holding time than the slurry speed and time. If the other parameters are decided, the longer the holding time is, the more refine the grains are. When beyond the certain time, it may appear the coarse dendritic microstructure, and under 585℃, it can obtain the best. Also, it can get the ideal semi-solid structure under the iron scoop cooling condition. It has been systemic researched the principle about the gas bubble method to the semi-solid forming of AZ91D. The semi-solid structure is formed by strong convection and weak agitate, during the growing up of grain and the evolution. The strong turbulence, which is created from large number of broken bubbles with airflow in liquid metal, can make the dendritic crystalloid break up. Meanwhile, the graphite makes the chilled liquid metal more crystalloid. Obviously, the primaryαphase and the rose-shaped phase have been obtained by the turbulence and energy change.