| The extruded AZ31 magnesium alloy can be made easily and have a great broad prospects. However the key restriction of magnesium alloys application is poor workability because of its hexagonal close-packed(HCP)structure which has the very limted slips.Superplastic is the important way to improve the plastic processing capacity of AZ31 Mg alloy.In this paper, superplastic performance of the AZ31Mg-alloy is systematically studied,the superplastic degeneration mechanism and the constitutive equation are analysised in-depth and a deformation mechanism map is got.The results showed that When the strain rate=5×10-4s-1,AZ31 Mg alloy have the greatest elongation at 420℃.And it also showed that the value of the strain rate sensitive index m is the main parameters affecting superplasticity when the strain rate is high, and cavity is the main factor affecting superplasticity when the strain rate is low.The superplastic deformation mechanism of AZ31 Mg alloy changes with the differents of the temperature and strain rate.At the temperature of 400℃-420℃,deformation is conforms to dislocation creep mechanism controlled by the solute drag when the strain rate is low,but it is conforms to the dislocation climb controled creep mechanism when the strain rate is higher.At the temperature of 420℃-440℃,the deformation accord with the mechanism of dislocation creep controled by lattice diffusion.A process of stages disrupped deformation was proposed to improve the superplasticity of AZ31 Mg alloy,and effects of the deformation parameters on superplasticity of the alloy were experimental studied.The results showed that:the superplasticity of AZ31 Mg alloy was improved significantly by the stages disrupped deformation process at the temperature of 400℃-420℃and the strain rate less than 5×10-4s-1.The superplastic elongation up to 300 percent at the temperature of 420℃and the strain rate of 2.5×10-4s-1.The critical radius of the cavity growth was calculated.The relationship between strain,strain rate sensitivity index and the density of cavity was found based on the three cavity growth models of the DIF,SPD and PLA.The results showed that the numbers of cavityies was reduced in the deformation process which resulting in the decrease volumes of cavity,so as to improve the superplastic elongation. |
PDF Full Text Request