Bulk Forming And Microstructure Evolution Simulation Of Casting AZ91D Magnesium Alloy

In this paper, form the AZ91D magnesium alloy cylindrical straight inner gear by shunt-type isothermal forging technology and determine the best process conditions. And combined with Yada model and Saito model, plasticity bulk forming process of the casting AZ91D magnesium alloy is simulated on the numerical platform composed of the Pro/Engineer, MSC.Mentat, MSC.Marc and Fortran. Based on the results of the experiment and the simulation, we can access the dynamic recrystallization grain size distribution pattern of the casting AZ91D magnesium alloy, thus supplying a reliable basis for the development and application for the casting bulk forming technology of Mg alloy.Based on the shunt-type isothermal forging technology, the casting AZ91D magnesium alloy was forged into good quality cylindrical straight inner gear. Graphite is an ideal lubricating material for casting AZ91D magnesium alloy. Liquid lubricants may cause crowded heap. As the temperature rises, forming load decreases, and the curves of load-stroke shows serrated periodicity rule. At 300℃, the forming load is up to 120 t; at 400℃, the forming load down to 40 t. The grain size of formed part is unequal due to forming temperature and deformation extent. The higher the temperature, the larger the grain size is. The more acute the deformation is, the more exiguous the grain is.Dynamic recrystallization kinetics of magnesium alloy can be described by Avrami equation which is calculated by the percentage of dynamic recrystallization. Different models adopt different forecast forms, and then gain different grain distribution. With a majorized function provided by the MATLAB Optimization Toolbox, we can get the parameters of the Yada model and the Saito model and carry out the relevant simulation and analysis. Compared With the metallography graph, it is obvious that:when forging temperature arrive at 300℃, simulation results from the Yada model agree well with the experimental results; when arrive at 400℃,simulation results from the Saito model are broadly in line with the experimental results. The Analysis shows that: in the Yada model, the level of recrystallization grain refinement and grain size distribution are mainly affected by the temperature and strain rate field in the region; in the Saito model, the level of recrystallization grain refinement is affected by the temperature and strain rate field which is consistent with Yada model, but the grain size distribution is primarily due to temperature and strain field in the region.