Numerical Simulation Of Plastic Forming Process Optimization Of Magnesium Alloy

Magnesium alloys have the advantages of low density, high strength and good heat conduction, which can be widely used in the field of automobile, aeronautics and astronautics. At present, magnesium alloys products were produced by casting, and the products always have the shrinkage porosity and shrinkage cavity. However, the plastic deformation products have high strength and good plasticity and toughness. The magnesium alloys die forging can be influence by temperature and reduction velocity easily, which will result in the failure of the deformation. Therefore, the research of low-cost, high-efficiency magnesium alloys forging forming technology by designing the mold structure and optimizing the process are necessary. In this paper, the AZ31B magnesium alloys are researched, a thermal-mechanical-microstructure--workability analysis coupled finite model is established, the temperature, deformation, microstructure and workability in plastic deformation are calculated. On the basis of analyzing and validating the microstructure and workability analysis of the cylindrical sample, for the magnesium alloys spur gears deformation, the optimized process in forging deformation of the gears is determined, and the reliability of optimized method is validated by experiment. The main research contents and conclusions are given as following:(1) A thermal-mechanical-microstructure coupled finite element model for AZ31B is established to simulate the distribution of stress, strain, temperature and microstructure evolution of a cylindrical sample undergoing hot compression. The flow stress curve and the microstructure evolution model are defined in the subroutine section of Msc.Marc software. The distribution of stress, strain, temperature and microstructure evolution is simulated. It is shown that the distribution of equivalent strain, equivalent stress, equivalent strain rate and temperature is heterogeneity. Dynamic recrystallization occurs firstly in the central zone, and the grain size in this area is fine and uniform. The good agreement between the simulation results and the experimental results validates the established model(2) Hot workability of magnesium alloys is analyzed by integrating the FEM with three-dimensional processing maps. Based on the flow stress curves obtained from Gleeble testing, the variation of power dissipation coefficient and instability parameter with T, ε, and ε are calculated, and the three-dimensional processing maps are established. Then the tree-dimensional processing maps are coupled into the FEM. Thus the evolution of the flow instability domains and power dissipation of a hot compressed cylindrical sample is simulated and compared with the theoretical analysis results. The results show that, simulated flow instability domains are in good agreement line with the experiment.(3) For magnesium alloys spur gears forming, an optimization method based on the hot workability analysis is proposed to optimize the processing route of magnesium alloys die forging forming. At first, the forging temperature and punch velocity for simulation are generated by Latin Hypercube Sampling. Then the flow instability parameter, power dissipation coefficient and microstructure evolution in magnesium alloys die forging forming are simulated by the finite model coupled with the microstructure and workability. The processing domain with good workability is regressed by response surface method. The optimized process is determined by comparing the power dissipation coefficient and microstructure information comprehensively.