An Investigation Of The High Temperature Creep And Superplasticity Deformation Of AZ31 Magnesium Alloy

Extruded AZ31 magnesium alloy is a deformable alloy with good prospect in application. In the text, the high-temperature creep property of this alloy is systematically studied at the first time, and the high-temperature creep mechanism is analyzed in depth. The results show that AZ31 magnesium alloy conforms to the Coble creep with the stress index n is equal to 1 when loaded by smaller stress at temperature above 420℃; however ,the creep behavior of this alloy is accorded with the Takeuchi and Argon model when the stress is bigger in the temperature range from 320℃to 480℃,and the stress index n is about 2.7. The critical stressσp which result in creep changing from n=1 to n=2.7 creep is calculated, and this stress relevant to the Nabarro-Peieris stress, the relation is ( )σp = 2 ?3τp.It is proved that the creep rupture has the characteristic of intergranular split by calculating Monkman-Grant constant of the AZ31 alloy (Monkman-Grant is 0.32) and analyzing SEM photograph of the fractured face.Superplasticity is an important way to improve plasticity ability of AZ31 magnesium alloy. The properties of superplasticity are studied experimentally under the different conditions in the thesis. It is shown that the AZ31 alloy perform superplasticity when the temperature reach 390℃and strain rate is controlled within the scopes. By analyzing the relation between strain rate sensitivity and temperature, it is demonstrated that strain rate sensitivity increases and the elongation of superplasticity is raised as temperature rises within the range of certain temperature.