In order to investigate the microstructure and properties evolution of the AZ31magnesium alloy in different cycles(including104(sample1),106(sample2)and none(sample3,no fatigue tests on the samples))of high cycle defo...In order to investigate the microstructure and properties evolution of the AZ31magnesium alloy in different cycles(including104(sample1),106(sample2)and none(sample3,no fatigue tests on the samples))of high cycle deformation,thescanning electron microscopy(SEM)and electron back-scattered diffraction technique(EBSD)were fully used.It is found that many{1012}tension twins(near21%,volume fraction),a few{1011}compression twins and{1011}?{1012}secondary twins aregenerated during tension?compression cyclic deformation.The volume fractions of{1012}twins in samples1,2and3are8%,21%and4%,respectively.By analyzing the fatigue fracture of the samples,larger area of fatigue striations and cleavage fracture insamples are also observed,as well as the shallower dimples.The twin laminae are likely to occur in the crack initiation zone whiledimples are in the final fracture region and the dimple size increases with the increase of the cycle number.The dimple diameters ofsamples1,2and3are14.8,31.2and8.5μm,respectively.It turns out that both the fatigue strength and elongation of the samplesslightly decrease with increasing the cycle number.展开更多
The hot deformation behavior,microstructure evolution and fracture characteristics of bimodal microstructured Ti-6Al-2Zr-1Mo-1V alloy were investigated by isothermal tensile tests.Results reveal that flow softening is...The hot deformation behavior,microstructure evolution and fracture characteristics of bimodal microstructured Ti-6Al-2Zr-1Mo-1V alloy were investigated by isothermal tensile tests.Results reveal that flow softening is caused by dynamic globularization of the bimodal microstructure,which also results in a relatively high stress exponent and thermal activation energy.The corresponding SEM,EBSD and TEM observations indicate that the dynamic globularization at750and800℃is accomplished by the formation ofα/αsub-grain boundary and penetration of theβphase.However,dynamic recrystallization(DRX)is the main globularization mechanism at850℃,which was proved by the generation of fine grains with a necklace-like character due to the transformation of low-angle boundaries(LABs)into high-angle boundaries(HABs).With an increase in the deformation temperature or a decrease in the strain rate,the fracture mechanism changes from microvoid coalescence to intergranular fracture.展开更多
The dynamic tensile behavior of twin-roll cast-rolled and hot-rolled AZ31B magnesium alloy was characterized over strainrates ranging from 0.001 to 375 s^-1 at room temperature using an elaborate dynamic tensile testi...The dynamic tensile behavior of twin-roll cast-rolled and hot-rolled AZ31B magnesium alloy was characterized over strainrates ranging from 0.001 to 375 s^-1 at room temperature using an elaborate dynamic tensile testing method, and the relationshipbetween its mechanical properties and microstructures. It is observed that the sheet has a strong initial basal fiber texture andmechanical twinning becomes prevalent to accommodate the high-rate deformation. The yield strength and ultimate tensile strengthmonotonically increase with increasing the strain rate, while the strain hardening exponent proportionally decreases with increasingthe strain rate due to twinning-induced softening. The total elongation at fracture distinctly decreases as the strain rate increasesunder quasi-static tension, while the effect of strain rate on the total elongation is not distinct under dynamic tension. Fractographicanalysis using a scanning electron microscope reveals that the fracture is a mixed mode of ductile and brittle fracture.展开更多
基金Projects(51271208,51071183,50890170)supported by the National Natural Science Foundation of China
文摘In order to investigate the microstructure and properties evolution of the AZ31magnesium alloy in different cycles(including104(sample1),106(sample2)and none(sample3,no fatigue tests on the samples))of high cycle deformation,thescanning electron microscopy(SEM)and electron back-scattered diffraction technique(EBSD)were fully used.It is found that many{1012}tension twins(near21%,volume fraction),a few{1011}compression twins and{1011}?{1012}secondary twins aregenerated during tension?compression cyclic deformation.The volume fractions of{1012}twins in samples1,2and3are8%,21%and4%,respectively.By analyzing the fatigue fracture of the samples,larger area of fatigue striations and cleavage fracture insamples are also observed,as well as the shallower dimples.The twin laminae are likely to occur in the crack initiation zone whiledimples are in the final fracture region and the dimple size increases with the increase of the cycle number.The dimple diameters ofsamples1,2and3are14.8,31.2and8.5μm,respectively.It turns out that both the fatigue strength and elongation of the samplesslightly decrease with increasing the cycle number.
基金Project (LQ18E050007) supported by the Natural Science Foundation of Zhejiang Province,ChinaProject (20120006110017) supported by the Research Fund for the Doctoral Program of Higher Education,China
文摘The hot deformation behavior,microstructure evolution and fracture characteristics of bimodal microstructured Ti-6Al-2Zr-1Mo-1V alloy were investigated by isothermal tensile tests.Results reveal that flow softening is caused by dynamic globularization of the bimodal microstructure,which also results in a relatively high stress exponent and thermal activation energy.The corresponding SEM,EBSD and TEM observations indicate that the dynamic globularization at750and800℃is accomplished by the formation ofα/αsub-grain boundary and penetration of theβphase.However,dynamic recrystallization(DRX)is the main globularization mechanism at850℃,which was proved by the generation of fine grains with a necklace-like character due to the transformation of low-angle boundaries(LABs)into high-angle boundaries(HABs).With an increase in the deformation temperature or a decrease in the strain rate,the fracture mechanism changes from microvoid coalescence to intergranular fracture.
基金supported by the German Aerospace Center (DLR) project “Next Generation Car”
文摘The dynamic tensile behavior of twin-roll cast-rolled and hot-rolled AZ31B magnesium alloy was characterized over strainrates ranging from 0.001 to 375 s^-1 at room temperature using an elaborate dynamic tensile testing method, and the relationshipbetween its mechanical properties and microstructures. It is observed that the sheet has a strong initial basal fiber texture andmechanical twinning becomes prevalent to accommodate the high-rate deformation. The yield strength and ultimate tensile strengthmonotonically increase with increasing the strain rate, while the strain hardening exponent proportionally decreases with increasingthe strain rate due to twinning-induced softening. The total elongation at fracture distinctly decreases as the strain rate increasesunder quasi-static tension, while the effect of strain rate on the total elongation is not distinct under dynamic tension. Fractographicanalysis using a scanning electron microscope reveals that the fracture is a mixed mode of ductile and brittle fracture.
