A Study On Thermal Deformation Activation Energy And Deformation Mechanism Of AZ31 Magnesium Alloy

Magnesium alloy has a hexagonal close-packed crystal structure and few movable slip systems when deformed at room temperature,so the plasticity is poor.Therefore,it usually require plastic processing at higher temperatures.Deformation activation energy is a foundation to research deformation mechanism of magnesium alloy under hot deformation conditions,while the deformation mechanism is a base for making up the hot processing.In this paper,extruded AZ31 magnesium alloy is chosen for test alloy,the tensile text was conducted,at a temperature of 125 ~ 475 ?,strain rate within 3 × 10-2 ~ 10-4s-1,The changes of elastic modulus and deformation activation energy of the alloy with temperature and strain rate was investigated.The concrete rate constitutive equation was built and the deformation mechanism was studied under various deformation conditions.The results show that the modulus of elasticity of magnesium alloys decreases linearly with increasing temperature.At room temperature,the elastic modulus is insensitive to strain rate,but at high temperatures,the elastic modulus decreases with decreasing strain rate.According to relationship between flow stress and dislocation density,the cause for decrease of elastic modulus was discussed.According to the tensile tests at various temperatures and strain rate,three different forms of strain rate constitutive equation was adopted to calculate the deformation activation energy of the magnesium alloy at three ranges of temperature and strain rate.It was shown that the activation energy increases with increasing temperature.When deformed up to 325 ?,the activation energy values are similar by using either exponent or hyperbolic sine function type constitutive equation.However,when the temperature is higher than 350 ?,the activation energy values are related to the constitutive equation forms.According to the results of the activation energy and combined with the morphology of the fractures in macroscopic and microscopic samples,the deformation mechanism were analyzed.The basal slip and a small amount of non-basal slip is the main mechanism below 250?;thenon-basal slip is the dominated at temperature of 275 ~ 400 ?,the superplastic deformation is the dominated mechanism at temperature above 425 ?...