【作者】 陈克豹；

【导师】 刘正；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2010， 博士

【摘要】 作为一种具有高比强度和比刚度的轻质金属材料,镁合金已在汽车、航空、计算机及通讯等工业领域获得了广泛的应用。疲劳是各种工程构件服役期间的主要失效形式之一,对于镁合金结构件亦不例外。因此,研究镁合金的疲劳变形和断裂行为不仅具有理论意义,而且也具有一定的实用价值。本文主要针对不同处理状态的AZ和AM系列挤压变形镁合金的低周疲劳行为进行了系统的研究,以期为此种镁合金的抗疲劳设计和合理使用提供可靠的理论依据。低周疲劳实验结果表明：不同处理状态的挤压变形AZ31镁合金在本实验所采用的外加总应变幅下均表现为循环应变硬化；挤压态和时效态AZ61镁合金在低的外加总应变幅下表现为循环稳定其后发生循环应变硬化,在其他外加总应变幅下则呈现循环应变硬化,而固溶态以及固溶+时效态AZ61镁合金在所有外加总应变幅下均表现为循环应变硬化；不同处理状态的挤压变形AM20和AM30镁合金可以表现为循环应变硬化、循环应变软化和循环稳定,主要取决于外加总应变幅的高低和热处理状态。热处理可以有效地提高热挤压AZ31镁合金在较高外加总应变幅区下的疲劳寿命,但降低合金在较低外加总应变幅区下的疲劳寿命；时效处理可以有效地提高挤压变形AZ61镁合金在较低外加总应变幅区间的疲劳寿命,而固溶+时效处理则降低挤压变形AZ61镁合金的疲劳寿命；固溶+时效处理可有效提高挤压变形AM20镁合金在较高外加总应变幅下的疲劳寿命,而固溶处理可提高挤压变形AM30镁合金在较高和较低外加总应变幅区间的疲劳寿命。不同处理状态的AZ和AM系列挤压变形镁合金的弹性应变幅、塑性应变幅与疲劳断裂时的载荷反向周次之间的关系可分别用Basquin和Coffin-Manson公式来描述,其循环应力幅与塑性应变幅之间呈线性关系；在较高的外加总应变幅下进行疲劳变形时,不同处理状态的AZ和AM系列挤压变形镁合金循环滞后回线上压缩变形部分的宽度大于拉伸变形部分的宽度,表现出明显的拉-压不对称循环变形行为。在总应变控制的疲劳加载条件下,不同处理状态的AZ和AM系列挤压变形镁合金的疲劳裂纹均是以穿晶方式萌生于疲劳试样表面,并以穿晶方式扩展且呈现典型的解理断裂特征。更多还原

【Abstract】 As the light metallic materials with high specific strength and high specific rigidity, magnesium alloys have been widely used in automobile, aeronautical, computer and communication fields. Fatigue is a main failure form of various structural components during operation. For the magnesium alloy components, the same case is also true. Therefore, the investigation concerning fatigue behavior of magnesium alloys is of both academic and practical significance. In this investigation, the strain-controlled fatigue deformation and fracture behaviors of extruded AZ and AM series magnesium alloys with different treatment states have been studied in order to provide a reliable theoretical foundation for both fatigue resistant design and reasonable usage of these magnesium alloys.The results of low-cyclic fatigue tests reveal that the extruded AZ31 magnesium alloys with different treatment states at various strain amplitudes exhibit the cyclic strain hardening. The as-extruded and aged AZ61 magnesium alloys exhibit the stable cyclic stress response followed by cyclic strain softening at lower total strain amplitude, while show the cyclic strain hardening at other imposed total strain amplitudes. For the extruded AZ61 magnesium alloys subjected to solid solution and solution plus aging treatment, the cyclic strain hardening can be observed at all the total strain amplitudes used in this investigation. The extruded AM20 and AM30 magnesium alloys with different treatment states exhibit cyclic hardening, softening and stability, which depends on the imposed total strain amplitudes and heat treatment states. It is noted that the heat treatment can enhance the fatigue lives of the hot-extruded AZ31 magnesium alloys at higher total strain amplitudes, while leads to a reduction in the fatigue lives of the hot-extruded AZ31 magnesium alloys at lower total strain amplitudes. Aging treatment can effectively enhance the fatigue lives of the extruded AZ61 magnesium alloys at lower total strain amplitudes, while solution plus aging treatment leads to a reduction in the fatigue lives of the AZ61 magnesium alloys. Solution plus aging treatment can effectively enhance the fatigue lives of the extruded AM20 magnesium alloy at higher total strain amplitudes, while solution treatment can prolong the fatigue lives of the extruded AM30 magnesium alloys in both higher and lower total strain amplitude regions. For the AZ and AM series magnesium alloys with different treatment states, the relations between elastic strain amplitude, plastic strain amplitude and reversals to failure can be described by Basquin and Coffin- Manson equations, respectively. In addition, a linear relationship between cyclic stress amplitude and plastic strain amplitude is also noted for the extruded AZ and AM series magnesium alloys with different treatment states. It has also been observed that when the extruded AZ and AM series magnesium alloys with different treatment states are subjected to fatigue deformation at higher total strain amplitudes, the width of theσεhysteresis loop in the compressivedirection is greater than that in the tensile direction. It means that the AZ and AM series magnesium alloys exhibit the pronounced anisotropic deformation behavior in the direction of tension and compression during strain-controlled fatigue deformation. For the extruded AZ and AM series magnesium alloys with different treatment states, the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly. In addition, the cleavage fracture feature can be found in the fatigue crack propagation region.更多还原