Of Mg-gd-y - Zr Alloy Thermoplastic Deformation Of The Optimization Of Process Parameters

Combined with deform finite element simulation, rolling experiments and testing metholds of OM,SEM,TEM, this thesis based on Gleeble-1500 thermal simulation have studied the relationship of the thermoplastic flow stress during deformation, strain, strain rate and temperature of Mg-10Gd-4.8Y-0.6Zr alloy, and determined optimization of processing parameters under different deformation conditions. The temperature rise during the deformation processing of the alloy on the setting deformation conditions was investigated, the material constants of thermoplastic deformation were calculated by linear regression analysis, and the constitutive equation of the alloy in thermoplastic deformation was established, and the organization evolution with the change of the stresses, temperatures, strain rates, strains and deformation times. Using the corrected experimental data, the processing maps of the alloy was established, and combining with metallographic and scanning analysis, the safe processing region and optimal deformation process of the alloy were gained, the critical points for dynamic recrystallization of the alloy on different conditions were determined, and the models of dynamic recrystallization volume fractions and dynamic recrystallization sizes were established. By studying the mechanism of atomic activeties under the experimental conditions, the optimum deformation parameters were determined. The optimal deformation parameters were verified through deform finite element simulation, and same time, the changes and distribution of stress, strain and other parameters were analyzed. In order to validate the validity of optimization deformation parameters, using the optimization methods presented in this paper and combining with experimental conditons, the experiment programs were established, and then rolling experiments were conducted. Through this thesis, the following innovative conclusions were obtained:(1) When the strain rate is 0.001～10s-1, the peak stresses decrease with deformation temperatures, the peak strains advance with the deformation temperature. When the deformation temperature is 350～500℃, the peak stresses increase with the acceleration of the strain rates, that is to say, this alloy shows a positive strain rate sensitivity in the deformation temperature range; when the deformation temperature is 300℃, flow stresses increase firstly and then decrease with the strain rates. Under certain deformation temperature during deformation, the phenomenon with deformation temperature rise at low strain rate is not very obvious, but the temperature rise can reach 50℃at high strain rate. Besides, temperature rise showes more obvous at lower deformation temperature.(2) As the deformation temperature rise, the uniformity of deformation increases, the degree of dynamic recrystallization improves. When the deformation temperature is constant, non-uniformity of the magnesium alloy is more serious with the strain rate, and the more cavities are prone to be together, which results the detriment of plastic deformation of the alloy. At the same time, the grain size of dynamic recrystallization lessenes with the strain rate increases. When the deformation temperature and strain rate are unchanged, dynamic recrystallization grain fraction increases with the deformation continuing, but grain size keeps unchanged, and the matrix grains gradually are swallowed. When the deformation temperature, strain rate and deformation degree are fixed, the microstructure of the alloy after deformation shows more recrystallized grains with the deformation times reducing, but the recrystallized grain size is unchanged.(3) According to the processing map at the true strain of 0.7 shows that the power dissipation efficiency increases firstly and then decreases with the deformation temperatures. The power dissipation efficiency increases firstly and then decreases with the strain rate, and the efficiency decreases first and then increases, and finally reduces with the strain increasing. At the true strain of 0.7, the security processing region is that the deformation temperature is 400～500℃, the strain rate is 0.001～0.018s-1. According to optimization process principle, it is determined that the optimal process parameters at the true strain of 0.7 are 500℃-0.01s-1 and 450℃-0.001s-1. And these dynamic recrystallization volume fractions and size models of dynamic recrystallization of Mg-10Gd-4.8Y-0.6Zr alloy are established under the two optimal process parameters conditions.(4) Considering the atomic activities mechanisms, the final optimal deformation process parameters of Mg-10Gd-4.8Y-0.6Zr alloy under the experiment conditions of this thesis are 450℃-0.001s-1-0.7 and 500℃-0.01s-1-0.7. And four microstructure crasking forms of the alloy under the experimental conditions are summarized, which are the cracking along the matrix grain boundaries, cracking from the trigeminal grain boundaries, cracking along the twin boundaries and cracking owing to the matrix grain crushing.(5) The injuries circumstances of the Mg-10Gd-4.8Y-0.6Zr alloy at the deformation condition that the deformation termperature is 500℃, the strain rate is 0.01s-1, and the true strain is 0.7 are investigated by simulation software. And the variation regularity of the stress, strain, and load variation, and distribution situation of the deformation conditions, deformation stress and strain are analyzed. In order to transform the optimization theory to practice, three rolling deformation programs under laboratory conditions are set, and the results are fully consistent with the optimization process, which further confirms the correctness and practicalness of this optimization process.