The fatigue characteristics of the AZ91D-T6 alloy samples taken from engine blocks have been investigated at 20℃ and elevated temperature(150℃).The fatigue strength and cyclic stress amplitude of the alloy significa...The fatigue characteristics of the AZ91D-T6 alloy samples taken from engine blocks have been investigated at 20℃ and elevated temperature(150℃).The fatigue strength and cyclic stress amplitude of the alloy significantly decrease with the increase of the test temperature,although cyclic hardening occurs continuously until failure for both temperatures.With the increase of the temperature,the decreased fatigue life of the alloy tested at the same stress amplitude is mainly attributed to the decreased matrix strength and the increased hysteresis energies.Fatigue failure of the engine blocks made of AZ91D-T6 alloy is mainly controlled by casting defects.For the defect-free specimens,the crack initiation behavior is determined by the single-slip(20℃)and by environment-assisted cyclic slip(150℃)during fatigue,respectively.The low-cycle fatigue lives of the alloy can be predicted using the Coffin-Manson relation and Basquin laws,the three-parameter equation and the energy-based concepts,while the high-cycle fatigue lives of the alloy fitted well with the developed long crack life model and MSF life models.展开更多
Strain-controlled fatigue characteristics of peakaged and over-aged Mg_(96.47)Nd_(2.9)Zn_(0.21)magnesium alloys containing 0.42Zr,including stress response,strain resistance,hysteresis loops,strain-life and correspond...Strain-controlled fatigue characteristics of peakaged and over-aged Mg_(96.47)Nd_(2.9)Zn_(0.21)magnesium alloys containing 0.42Zr,including stress response,strain resistance,hysteresis loops,strain-life and corresponding lowcycle fatigue life prediction model,were studied.In the peak-aged state(T61:540℃×8 h+200℃×14 h),the alloy shows higher cyclic stress response,but lower ductility than the alloy in the over-aged state(T6_(2):540℃×8 h+200℃×400 h).The yield strength and ultimate tensile strength of the alloy under T6_(1)-and T6_(2)-treated conditions are close.Compared with T6_(1)-treated alloy,the steady stress amplitude occurred in T6_(2)-treated alloy is due to higher ductility and more homogenous deformation.In T6_(1)state,the fatigue cracks in the alloy first initiate along the cracked persistent slip bands and then propagate in the trans-granular mode,while in the T6_(2)state,the fatigue cracks initiate along grain boundaries and then propagate in the inter-granular mode.展开更多
The influence of heat treatment on the strain-controlled fatigue behavior of cast NZ30 K alloy was investigated. Compared with the as-cast and solutionized（T4） alloys, the peak-aged（T6） and over-aged（T7）counterp...The influence of heat treatment on the strain-controlled fatigue behavior of cast NZ30 K alloy was investigated. Compared with the as-cast and solutionized（T4） alloys, the peak-aged（T6） and over-aged（T7）counterparts have a higher cyclic stress and a lower plastic strain value due to the precipitation strengthening. The as-cast and T4-treated alloys have a higher fatigue strength/yield strength ratio than the aged alloys, which is mainly attributed to their higher cyclic hardening. Under stress-controlled loading,the aged alloys show lower hysteresis energies than the as-cast and T4-treated counterparts, leading to longer fatigue lifetimes. For the T4-treated alloy, the cyclic hardening and fatigue failure are controlled by the dislocations-slip and twinning, while for both the as-cast and T6-treated counterparts, they are controlled by the dislocation-slip. For the T7-treated alloy, cyclic deformation and failure behavior are mainly dependent on dislocations-slip and grain boundary sliding.展开更多
基金General Motors and Shanghai Jiao Tong University.This work was also supported by the Introduction Doctoral Program of Jiangxi Academy of Sciences(2016-YYB-09)the key Research Project of Jiangxi Academy of Sciences(2017-YZD2-03)the Soft Science Project of Jiangxi Provincial Science and Technology Department(20161ACA10026).
文摘The fatigue characteristics of the AZ91D-T6 alloy samples taken from engine blocks have been investigated at 20℃ and elevated temperature(150℃).The fatigue strength and cyclic stress amplitude of the alloy significantly decrease with the increase of the test temperature,although cyclic hardening occurs continuously until failure for both temperatures.With the increase of the temperature,the decreased fatigue life of the alloy tested at the same stress amplitude is mainly attributed to the decreased matrix strength and the increased hysteresis energies.Fatigue failure of the engine blocks made of AZ91D-T6 alloy is mainly controlled by casting defects.For the defect-free specimens,the crack initiation behavior is determined by the single-slip(20℃)and by environment-assisted cyclic slip(150℃)during fatigue,respectively.The low-cycle fatigue lives of the alloy can be predicted using the Coffin-Manson relation and Basquin laws,the three-parameter equation and the energy-based concepts,while the high-cycle fatigue lives of the alloy fitted well with the developed long crack life model and MSF life models.
基金financially supported by the Key Research Project of Jiangxi Academy of Sciences(No.2017YZD2-03)the Introduction Doctoral Program of Jiangxi Academy of Sciences(No.2016-YYB-09)the Collaborative innovation GSP Project of Jiangxi Academy of Sciences(No.2016-XTPH1-09)。
文摘Strain-controlled fatigue characteristics of peakaged and over-aged Mg_(96.47)Nd_(2.9)Zn_(0.21)magnesium alloys containing 0.42Zr,including stress response,strain resistance,hysteresis loops,strain-life and corresponding lowcycle fatigue life prediction model,were studied.In the peak-aged state(T61:540℃×8 h+200℃×14 h),the alloy shows higher cyclic stress response,but lower ductility than the alloy in the over-aged state(T6_(2):540℃×8 h+200℃×400 h).The yield strength and ultimate tensile strength of the alloy under T6_(1)-and T6_(2)-treated conditions are close.Compared with T6_(1)-treated alloy,the steady stress amplitude occurred in T6_(2)-treated alloy is due to higher ductility and more homogenous deformation.In T6_(1)state,the fatigue cracks in the alloy first initiate along the cracked persistent slip bands and then propagate in the trans-granular mode,while in the T6_(2)state,the fatigue cracks initiate along grain boundaries and then propagate in the inter-granular mode.
基金supported by the Key Research Project of Jiangxi Academy of Sciences(No.2017-YZD2-03)the Introduction Doctoral Program of Jiangxi Academy of Sciences(No.2016-YYB-09)the Collaborative innovation GSP Project of Jiangxi Academy of Sciences(No.2016-XTPH1-09)
文摘The influence of heat treatment on the strain-controlled fatigue behavior of cast NZ30 K alloy was investigated. Compared with the as-cast and solutionized（T4） alloys, the peak-aged（T6） and over-aged（T7）counterparts have a higher cyclic stress and a lower plastic strain value due to the precipitation strengthening. The as-cast and T4-treated alloys have a higher fatigue strength/yield strength ratio than the aged alloys, which is mainly attributed to their higher cyclic hardening. Under stress-controlled loading,the aged alloys show lower hysteresis energies than the as-cast and T4-treated counterparts, leading to longer fatigue lifetimes. For the T4-treated alloy, the cyclic hardening and fatigue failure are controlled by the dislocations-slip and twinning, while for both the as-cast and T6-treated counterparts, they are controlled by the dislocation-slip. For the T7-treated alloy, cyclic deformation and failure behavior are mainly dependent on dislocations-slip and grain boundary sliding.
