【作者】 孙雪盼；

【导师】 陈立佳； 马春艳；

【作者基本信息】 沈阳工业大学 ， 材料学， 2011， 硕士

【摘要】 铝合金以其优异的性能,受到越来越多的重视,广泛应用在航空航天、汽车等工业部门。为了进一步改善铝合金的性能,扩大铝合金的应用范围,本文选择稀土元素Sc作为铝合金中的合金化元素,研究了微量元素Sc和固溶+时效(T6)处理对铝合金疲劳变形行为的影响。根据合金成分配比,熔炼Al-0.8%Mg-0.6%Si-x%Sc铝合金,然后进行浇注、热挤压,最后加工成实验所需的疲劳试样,对部分试样进行T6处理,然后进行显微组织观察和低周疲劳实验。显微组织观察结果表明,加入一定量的稀土元素Sc可以有效地细化挤压变形Al-0.8%Mg-0.6%Si-x%Sc合金的显微组织,经过T6处理后,除了含0.2%Sc合金的晶粒尺寸变化不大外,其余合金的晶粒尺寸明显减小。低周疲劳实验结果表明,挤压(F)态Al-0.8%Mg-0.6%Si-x%Sc合金在疲劳变形过程中,可表现为循环应变硬化,循环应变硬化的程度主要取决于稀土元素Sc的含量以及外加总应变幅的高低,T6态Al-0.8%Mg-0.6%Si-x%Sc合金在疲劳变形过程中,除了表现为循环应变硬化外,还可表现为循环稳定和循环应变软化；F态和T6态挤压变形Al-0.8%Mg-0.6%Si-x%Sc合金的塑性应变幅、弹性应变幅与断裂时的载荷反向周次之间表现为线性行为,分别服从Coffin-Manson和Basquin公式,其中,T6态挤压变形Al-0.8%Mg-0.6%Si-0.2%Sc合金的塑性应变幅与断裂时的载荷反向周次之间呈双线性关系。低周疲劳断口形貌分析结果表明,在低周疲劳加载条件下,F态和T6态挤压变形Al-0.8%Mg-0.6%Si-x%Sc合金的疲劳裂纹均是以穿晶方式萌生于疲劳试样表面,并以穿晶方式扩展。更多还原

【Abstract】 Aluminum alloys are concerned by more and more people due to its excellent properties, and have been widely applied in aeronautics and astronauts, automobile industries, etc. For further improvement of the properties of aluminum alloys, expanding the applied scope of aluminum alloys, rare earth element Sc has been choosen as the alloying element added into the aluminum alloy, the effect of trace Sc and solution plus aging (T6) treatment on the fatigue deformation behavior are investigated.According to the composition of the alloys, Al-0.8%Mg-0.6%Si-x%Sc are melted, then by casting, extrusion, finally fatigue samples needed are fabricated, T6 treatment was taken on partial samples, then the observations on the microstructures and fatigue tests are performed. The microstructure observations show that the microstructures of the extruded Al-0.8%Mg-0.6%Si-x%Sc alloys can be refined effectively with certain Sc, after T6 treatment, grain size of the alloys decreased apparently except for the alloy with 0.2%Sc which changed a little. The results of low-cycle fatigue tests reveal that the as-extruded (F) Al-0.8%Mg-0.6%Si-x%Sc alloys exhibit the cyclic strain hardening, degree of cyclic strain hardening mainly depends on the content of Sc and imposed total strain amplitude, extruded Al-0.8%Mg-0.6%Si-x%Sc alloys at T6 state exhibit the cyclic strain hardening, cyclic strain softening, cyclic stability. For the extruded Al-0.8%Mg-0.6%Si-x%Sc alloys at F and T6 state, the relationship between plastic and elastic strain amplitudes with reversals to failure shows linear behavior, and can be well described by the Coffin-Manson and Basquin equations, and for the extruded Al-0.8%Mg-0.6%Si-0.2%Sc alloy after T6 treatment, the relationship between plastic strain amplitude and reversals to failure shows bilinear behavior. The observations on the fracture surfaces of fatigued specimens reveal that under the condition of fatigue loading, the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly for extruded Al-0.8%Mg-0.6%Si-x%Sc alloys at F and T6 state.更多还原