The Mechanics Behavior And Dynamic Recrystallization In Hot Deformation Of AZ31 Alloy

The AZ31 magnesium alloy has been deformed by isothermal compression in the range of temperature 200℃-500℃at 0.001-1s-1 strain rate. The behaviors of flow stress and microstructure have been investigated. The flow curves showed a peak and a decline towards a steady-state regime which lower as temperature T rose and strain rate declined. It is shown that an exponential law with an activation energy of 138.13kJ/mol can be used to describe the influence of temperature and strain rate on stress. Dynamic recrystallization(DRX) occurred at the condition from the flow curves and optical microscopy figures. In this study, the critical strain that characterizes the dynamic recrystallization was determined from the measured flow curves and verified metallographically. The data obtained on AZ31 indicated that the ratio of the critical strain to the peak strain falls in the range of 0.4-0.6. The mechanism of dynamic recrysltallization associated with twinning was developed by analyzing the evolution of microstructure in detail.During compressing at temperature range of 250℃to 500℃, the typical stable microstructure of asymmetrical deformed microstructure, necklace microstructure, at first time, was found at low temperature and strain rate, because of lack of non-basal slip system. As the temperature rising, the necklace microstructure disappear gradually and microstructure is symmetrical. The main mechanisms of deformation of AZ31 magnesium alloy at elevated temperature are slip and twinning. Twinning plays an important role in plastic deformation of AZ31 magnesium alloy when temperature is lower than 350℃, and the higher strain rate and lower temperature, the more twinning take place. The boundary of twin provide place for nucleation of DRX. The ratio of twin decrease when temperature rise over 350℃and the basal and non-basal slip in grain become main deforming mechanism. The mainly soften mechanism of AZ31B magnesium alloy compressing at elevated temperature is of DRX.Particle-stimulated nucleation(PSN) was investigated in magnesium alloy AZ31 during hot deformation.compression tests.These revealed that particle-stimulated DRX nucleation(PSN) was taking place during hot deformation and that this is facilitated by the fragmentation of the Mg17Al12 dissolves into the matrix at about 350℃,the (Al,Mg) particles remain effective in producing PSN at temperatures up to at least 400℃.This suggests that alloy design leading to a suitable distribution of second-phase particles can improve the properties and formability of wrought magnesium alloys .