| Creep is a phenomenon in which alloy undergoes slow and continuous plastic deformation under a certain temperature and stress.At different creep temperatures,as the creep time increases,the second phase of the dispersion distribution will precipitate,the change of the size and volume content of the precipitated will have a great influence on the solution strengthening,precipitation strengthening and creep strain rate of the alloy,Therefore,taking into account the changes in the size and volume fraction of precipitates with time under different temperature in the creep constitutive equation has important guiding significance for the research on the rebound and creep mechanism of rare earth magnesium alloysThis article took WE43 high-performance rare earth magnesium alloy as the research object,observes the microstructure with the aid of metallographic microscope,XRD,TEM transmission electron microscope and other instruments,and uses the vickers hardness tester to measure the hardness of the sample after aging heat treatment,It was concluded that the time to reach the peak aging at temperatures of453 K and 473 K were 15 h and 12 h,the corresponding microhardness values were117 HV and 110 HV respectively,and the microhardness value after aging at 433 K for20h was 113HVAccording to the uniaxial hot tensile test,the maximum yield strength measured at 433 K,453K,and 473 K is 150 MPa.Since the creep test was performed below the yield strength,the creep stress was initially selected as 110 MPa,130MPa,150 MPa,creep temperature was 433 K,453K,473 K under different time creep test,the law of creep strain variation with time was obtained,the results show that when the stress was 110 MPa,the creep strain variation was too small,aging forming The efficiency was not high.When the stress strain was 150 MPa,the creep strain will change greatly and it may enter the third stage of creep.When the creep stress was130 MPa,the creep strain will change smoothly with time,and the aging formingefficiency was high,so the optimal creep stress determined in this paper was 130MPaObserved by optical microscope and TEM transmission electron microscope,WE43 rare earth magnesium alloy showed a trend of increasing size of grain and precipitated with increasing creep time under the conditions of 433 K,453K,and473 K respectively.The volume fraction of the precipitated phase increased first and then decreased,Quantitative analysis was performed with the help of Image-Pro Plus6.0 metallographic analysis software,and the size and volume fraction of the precipitated phase were macroscopically provided to provide data support for establishing the creep constitutive equationBased on the unified theory,growth dynamics and precipitation strengthening theory,on this basis,the constitutive equation established by Kowalewski was further simplified and the influence of temperature was taken into account.At the same time,the creep ageing constitutive model of aluminum alloy was checked.A cross-scale constitutive model of WE43 rare earth magnesium alloy was established.The constitutive model fully considered the effects of precipitation strengthening and solution strengthening on the creep strain rate,and it can accurately predict the change law of the size and volume fraction of the precipitated phase with the increase of creep time at different temperaturesMatlab genetic algorithm toolbox was used to fit and optimize the material parameters in the constitutive equation,and the optimal solutions of 22 material parameters in the constitutive equation were determined.The specific constitutive equation is obtainedComparing the predicted and experimental values of creep strain,precipitation phase size and volume fraction in the constructed aging constitutive equation of WE43 rare earth magnesium alloy,it was found that the error between the predicted value and the test value of the creep strain variable at a stress of 130 MPa and a temperature of 433 K was 14.8%.The error between the predicted value of the score and the experimental value ware 4.24% and 5.97%;At a stress of 130 MPa and a temperature of 453 K,the error between the predicted value of creep strain and the test value was 8.4%,and the error between the predicted value of the size and volume fraction of the precipitate and the test value were 4.52% and 4.07%;At a stress of130 MPa and a temperature of 473 K,the error between the predicted value of creep strain and the experimental value was 4.35%,and the error between the predicted value of the size and volume fraction of the precipitate and the experimental valuewere 5.55% and 1.6%,respectively... |
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