Research On The Initial Yield Behavior And Subsequent Yield Behavior Of Magnesium Alloy AZ91

People pay more and more attention to a kind of newly-developing metal material,magnesium alloy.A series of magnesium alloy with excellent performance was developed by researchers and put into application.Nowadays,magnesium alloy was widely used in automobile industry,aerospace industry,3C electronics industry,medical industry and so on.People's demand for magnesium alloy is increasing year by year.As a kind of structural material,magnesium alloy was always serviced in complex environment which required a more comprehensive understanding of its performance for the sake of a better application in people's daily life and industry.As an important parameter of material mechanical properties,the yield strength was noted by researchers.Numerous studies show that most of the toughness metal material observes Mises criterion.Due to the close-packed hexagonal structure of magnesium,the number of Slip systems in magnesium alloy is small and the mechanism of plastic deformation is complicated.There is no conclusive which kind of yield criterion fit magnesium alloy.Therefore,theprimary work of this paper contains the following three aspects :(1)Experimental research on the yield behavior of AZ91 magnesium alloy;(2)Comparing of theoretical initial yield surface with experimental initial yield loci to find a yield criterion fitting AZ91 magnesium alloy;(3)Theoretical derivation and experimental verification of the evolution of AZ91 magnesium alloy subsequent yield surface.The combined shear-compression experiments of cast magnesium alloy AZ91 under three different loading rates(4.8/48/480mm/min)were realized by the test method of shear-compression specimen(SCS)at room temperature.Then,combined with the test result of compression,tensile and shear,the initial yield loci of cast AZ91 can be plotted.The cast AZ91 shows strong strain rate negative sensitivity at elastic stage and its initial yield loci shrink inwardly when the strain rate increase.Comparing the proposed initial yield surfaces of theoretical criterion with experimental initial yield loci,we could find that Ellipse criterion is suitable to explain the initial yielding of AZ91 magnesium alloy.Based on the initial yield surface,second order polynomial function was introduced to describe the compression,tensile and shear behavior of AZ91 magnesium alloy.Then the subsequent yield function can be proposed combined with isotropic hardening model.The availability of the subsequent yield function was verified by comparing the predicted value with test results.Then,considering about the influence of strain rate on flow stress,the rate-dependence subsequent yieldfunction at room temperature can be acquired.According the rate-dependence subsequent yield function,the mechanical behavior under complicated stress state of AZ91 magnesium alloy could be predicted.This study provides a certain theoretical and data support on the engineering design and application of AZ91 magnesium alloy.