Of Az31b Magnesium Alloy Sheet Hot Rolling Deformation Behavior

In the dissertation, hot deformation behaviors of AZ31B magnesium alloy have been extensively investigated with physical and numerical simulation techniques.True stress-strain behaviors were investigated by hot compressive testing on Gleeble-1500 thermal simulator at temperature range of 250 to 500℃with strain rate varying from 0.01 to 10 s-1. The relationships between flow stress, strain rate and deformation temperature were analyzed. The coupled thermo-mechanical simulation analysis of rolling for the alloy was done by using elastic-plastic finite element method on the software platform of MSC.MARC. The results are as follows:1. True stress-strain behavior of the alloy at different strain rate and temperature is characteristic as dynamic recrystallization. And the flow stress decreases with the increase of temperature, while increases with the increases with strain rate. The constitutive equation established by Zener-Hollomo parameter method are: Where,2. Microstructure evolution of AZ31B magnesium alloy during hot-compressive deformation was observed. The results show that, dynamic recrystallization was the main strain softening mechanism during hot deformation. Dynamic recrystallization of AZ31B magnesium alloy start at the temperature of 300℃. Increase of temperature or decrease of strain rate is benefits for dynamic recrystallization or coursen of dynamic recrystallization grains.3. There is obvious temperature gradicent from surface to centre of the workpiece within a certain depth. And the surface temperature changes sharply during the rolling process, while the center temperature changes little. After rolling, the surface temperature is 400℃, while the temperature of center is 460℃. Maximum compressive stress and maximum tensile stress occurr in the surface and center in the deforming region. During the rolling process, strain of secondary surface layer is biggest.The equivalent strain gradually decreases from secondary surface to the center, and the smallest equivalent strain occurres in the center. The simulated results show a satisfactory coincidence with the industrial measured data.4. In this dissertation, three-dimensional simulation of rolling for the AZ31B alloy was done by using finite element method. As the study is limited by conditions, three-dimensional rolling processes were simulated only four passes. Forming law of rolling process of AZ31B magnesium alloy was simulated by finite element method.The effect of process parameters, including the deformation temperature and the deformation velocity on the equivalent stress, the equivalent strain, the temperature raise during rolling deformation has been studied by numerical simulation.5. The experiment simulation of multi-pass hot rolling of AZ31B magnesium alloy was done by Gleeble-1500 thermal mechanical simulator. By flow stress analysis, the flow stress of AZ31B magnesium alloy in the multi-pass hot rolling process shows work hardening stage-softening stage-the second work-hardening characteristics.