Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading frequency （20 kHz） were investigated and compared with the results under conventional loading of rotating bending（50 Hz）.The growth of a...Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading frequency （20 kHz） were investigated and compared with the results under conventional loading of rotating bending（50 Hz）.The growth of a crack retarded at about 500μm in surface length under ultrasonic loading,while at about 20μm under rotating bending.Although striations being a typical fracture mechanism were observed under conventional loading,most of fracture surface was covered with many facets under ultrasonic loading.These facets were also observed under rotating bending in nitrogen gas.The difference in growth mechanism depending on the loading frequency and the retardation of a crack growth under ultrasonic loading may be caused by the environment at the crack tip due to high crack growth rate under ultrasonic loading.展开更多
The roles of Zn content and thermo-mechanical treatment in affecting microstructures and mechanical properties of Mg-x%Zn-1%Mn（mass fraction,x=4,5,6,7,8,9） wrought Mg alloys were investigated.The microstructure was ...The roles of Zn content and thermo-mechanical treatment in affecting microstructures and mechanical properties of Mg-x%Zn-1%Mn（mass fraction,x=4,5,6,7,8,9） wrought Mg alloys were investigated.The microstructure was extremely refined by dynamic recrystallization（DRC） during extrusion.With increasing Zn content,the DRC grains tended to grow up,at the same time,more second phase streamlines would be present,which restricted the further growing.During solution treatment,the DRC grains would rapidly grow up;however,higher Zn content could hinder the grain boundary expanding,which results in finer ultimate grains.MgZn2 dispersoid particles which are coherent with the matrix would precipitate from the supersaturated solid solution during the one-step aging process,and nano-sized GP zones formed during the pre-aging stage of the two-step aging provide a huge amount of effective nuclei for the MgZn2 phases formed in the second stage,which makes the MgZn2 particles much finer and more dispersed.The mechanical properties of as-extruded samples were not so sensitive to the variation of Zn content,the tensile strength fluctuates between 300 and 320 MPa,and the elongation maintains a high value between 11% and 14%.The strength of aged samples rises as a parabolic curve with increasing Zn content,specifically,the tensile strength of one-step aged samples rises from 278 to 374 MPa,and that of two-step aged ones rises from 284 to 378 MPa,yet the elongation of all aged samples is below 8%.When Zn content exceeds its solid solution limit in Mg-Zn system（6.2%,mass fraction）,the strength rises slowly but the elongation deteriorates sharply,so a Mg-Zn-Mn alloy with 6% Zn possesses the best mechanical properties,that is,the tensile strengths after one-and two-step aging are 352 and 366 MPa,respectively,and the corresponding elongations are 7.98% and 5.2%,respectively.展开更多
基金supported by the National Natural Science Foundation of China(51175298)the Key Project of Educational Commission of Hubei Province of China (D20011203)
文摘Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading frequency （20 kHz） were investigated and compared with the results under conventional loading of rotating bending（50 Hz）.The growth of a crack retarded at about 500μm in surface length under ultrasonic loading,while at about 20μm under rotating bending.Although striations being a typical fracture mechanism were observed under conventional loading,most of fracture surface was covered with many facets under ultrasonic loading.These facets were also observed under rotating bending in nitrogen gas.The difference in growth mechanism depending on the loading frequency and the retardation of a crack growth under ultrasonic loading may be caused by the environment at the crack tip due to high crack growth rate under ultrasonic loading.
基金Project(2007CB613700)supported by the National Basic Research Program of ChinaProject(2007BAG06B04)supported by the National Science and Technology Pillar Program During the 11th Five-Year Plan Period,China+1 种基金Project(50725413)supported by the National Natural Science Foundation of ChinaProject(CDJXS10132202)supported by the Fundamental Research Funds for the Central Universities,China
文摘The roles of Zn content and thermo-mechanical treatment in affecting microstructures and mechanical properties of Mg-x%Zn-1%Mn（mass fraction,x=4,5,6,7,8,9） wrought Mg alloys were investigated.The microstructure was extremely refined by dynamic recrystallization（DRC） during extrusion.With increasing Zn content,the DRC grains tended to grow up,at the same time,more second phase streamlines would be present,which restricted the further growing.During solution treatment,the DRC grains would rapidly grow up;however,higher Zn content could hinder the grain boundary expanding,which results in finer ultimate grains.MgZn2 dispersoid particles which are coherent with the matrix would precipitate from the supersaturated solid solution during the one-step aging process,and nano-sized GP zones formed during the pre-aging stage of the two-step aging provide a huge amount of effective nuclei for the MgZn2 phases formed in the second stage,which makes the MgZn2 particles much finer and more dispersed.The mechanical properties of as-extruded samples were not so sensitive to the variation of Zn content,the tensile strength fluctuates between 300 and 320 MPa,and the elongation maintains a high value between 11% and 14%.The strength of aged samples rises as a parabolic curve with increasing Zn content,specifically,the tensile strength of one-step aged samples rises from 278 to 374 MPa,and that of two-step aged ones rises from 284 to 378 MPa,yet the elongation of all aged samples is below 8%.When Zn content exceeds its solid solution limit in Mg-Zn system（6.2%,mass fraction）,the strength rises slowly but the elongation deteriorates sharply,so a Mg-Zn-Mn alloy with 6% Zn possesses the best mechanical properties,that is,the tensile strengths after one-and two-step aging are 352 and 366 MPa,respectively,and the corresponding elongations are 7.98% and 5.2%,respectively.
