| Rare earth magnesium alloys are widely used in aerospace,aviation,weapon equipment and other industries because of their excellent mechanical properties at high temperature and room temperature.They are also light metal structural materials required for carbon peak carbon neutralization.Taking Mg-9Gd-4Y-2Zn-0.5Zr alloy as the research material,this paper studies the mechanical behavior,microstructure and deformation mechanism under different thermal deformation conditions,discusses the relationship between mechanical behavior,microstructure and deformation mechanism,establishes fracture damage model,enriches the plastic deformation theory of rare earth magnesium alloy,and provides theoretical reference for its practical application.The main conclusions are as follows:(1)The stress-strain curve of the alloy basically shows that with the increase of strain,the flow stress first increases rapidly,reaches the peak and then decreases slowly.Under the conditions of low temperature?high strain rate and high temperature?low strain rate,it does not fully comply with the above laws:under the conditions of low temperature and high strain rate(350?/400?-0.1s-1),the flow stress reaches the peak value and decreases rapidly until it breaks;Under the condition of high temperature and low strain rate(450?0.0001s-1,500?-0.001s-1,500?-0.0001s-1),the flow stress first tends to be stable and then rises slowly.(2)The higher the temperature and the lower the strain rate,(the lower the Z value(Z=? exp(Q/RT))),the greater peak stress,fracture strain and the strain rate sensitivity coefficient m,and the smaller the deformation activation energy Q.Especially under the condition of high temperature and low strain rate,it shows superplastic mechanical characteristics;With the increase of deformation temperature and the decrease of strain rate,the fracture changes from cleavage fracture to dimple fracture.(3)The evolution trend and mechanical characteristics of the stress-strain curve of the alloy are dominated by the softening mechanism.With the decrease of the Z value,the trend of the softening mechanism changing from dynamic recrystallization to dynamic recrystallization+non-basal slip is more obvious.The lower the Z value,the smaller the deformation activation energy Q,the easier the non-basal slip system starts and the higher the softening degree,the greater the proportion of DRX and the higher the softening degree.However,under high temperature and low strain rate,it is easy to cause recrystallization growth and increase flow stress due to the influence of deformation parameters and second phase back dissolution.(4)Under the condition of low Z value(exhibiting superplasticity),the main deformation mechanism of the initial dynamic recrystallization grains is the cylinderslip accompanied by the coneslip,which makes the c-axis tend to be parallel stretched direction,resulting in a<0001>silk texture;if the deformation continues,the<0001>silk texture tends to weaken,the KAM value representing the dislocation density tends to increase,and the deformation activation energy is equal to the thermal diffusion activation energy,indicating that the deformation stage is accompanied by Grain boundary slip mechanism for thermal diffusion.(5)The the smaller the Z value,the greater the fracture damage value Df of the alloy.Df=E(T,?)×?-0.387[exp(160.5/RT)]-0.19 Using the established fracture damage model(E(T,?)=K1×(1000/T)+B;K1=-6.80ln(?)-70.74;B=11.226ln(?)+116.73),the maximum error is 8.8%... |
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