【作者】 计海涛；

【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】 铝合金具有密度低、比强度和比刚度高的特点,目前已在航空工业和汽车工业中得到了广泛的应用。为了进一步拓展铝合金的应用领域,需要采取一定的措施以改善铝合金的组织、提高铝合金的力学性能。稀土元素被认为是改善铝合金组织及力学性能的有效的合金元素。因此,研究稀土在铝合金中的作用,对于新型高强、高韧铝合金的开发和工程应用具有重要的意义。此外,等通道转角挤压(ECAP)技术因其可以有效地细化材料的组织,改善材料的力学性能,已经引起人们的普遍关注。作为工程结构材料,疲劳断裂是其主要失效方式之一。为此,本文主要针对不同处理状态的挤压变形Al-4Mg-0.3Ce合金、经过T6处理的Al-0.8Mg-0.6Si-x(Sc, Er)合金以及经过等通道转角挤压后的Al-0.8Mg-0.6Si-0.3Er合金的低周疲劳行为开展研究,以期为这些铝合金的抗疲劳设计和合理使用提供可靠的理论依据。实验结果表明,不同处理状态的挤压变形Al-4Mg-xCe合金、经过T6处理的挤压变形Al-0.8Mg-0.6Si-x(Sc, Er)合金以及等通道转角挤压Al-0.8Mg-0.6Si-0.3Er合金可表现为循环硬化、循环稳定和循环软化,主要取决于外加总应变幅的高低、热处理方式、添加稀土元素的种类以及等通道转角挤压的路径和道次等因素；固溶处理可以提高挤压变形Al-4Mg-0.3Ce合金在较高和较低外加总应变幅下的疲劳寿命,时效处理可以有效地提高挤压变形Al-4Mg-0.5Ce合金的疲劳寿命,而时效处理和固溶+时效处理均可有效地提高Al-4Mg-1.0Ce合金的疲劳寿命；不同成分和加工处理状态的合金的塑性应变幅、弹性应变幅与断裂时的载荷反向周次之间的关系分别服从Coffin-Manson和Basquin公式,其中经过T6处理的Al-0.8Mg-0.6Si-0.2Sc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。在低周疲劳加载条件下,不同处理状态的挤压变形Al-4Mg-xCe合金、经过T6处理的挤压变形Al-0.8Mg-0.6Si-x(Sc,Er)合金以及经过等通道转角挤压的Al-0.8Mg-0.6Si-0.3Er合金的疲劳裂纹均是以穿晶方式萌生于试样表面,并以穿晶方式扩展。更多还原

【Abstract】 Aluminum alloys have such characteristics as low density, high specific strength and rigidity, and have found a wide application in aeronautical and automotive industries. To extend the application field of aluminum alloys, some measures, which can improve the microstructures and mechanical properties of aluminum alloys, need to be taken. The rare earth elements are considered as the most effective elements available to enhance the microstructures and mechanical properties of aluminum alloys. Thus, the research concerning the effect of rare earth elements in aluminum alloys is of important significance for developing new aluminum alloys with high strength and ductility. In addition, the equal-channel angular pressing (ECAP) technology has been paid much attention because it can effectively refine the microstructures of materials and thus improve the mechanical properties of materials. As structural materials, the fatigue fracture is one of their main failure forms. In this investigation, the low-cycle fatigue behaviors of the extruded Al-4Mg-0.3Ce alloys with different treatment states, Al-0.8Mg-0.6Si-x(Sc, Er) alloys subjected to T6 treatment, and Al-0.8Mg-0.6Si-0.3Er alloys after ECAP have been studied in order to provide a reliable theoretical foundation for both fatigue resistant design and reasonable usage of these aluminum alloys.The experimental results reveal that the extruded Al-4Mg-xCe alloys with different treatment states, Al-0.8Mg-0.6Si-x(Sc, Er) alloys subjected to T6 treatment and Al-0.8Mg-0.6Si-0.3Er alloys after ECAP exhibit the cyclic strain hardening, softening and stability, which mainly depends on the imposed total strain amplitude, heat treatment state, type of added rare earth element as well as route and pass of ECAP. The solution treatment can enhance the fatigue lives of the extruded Al-4Mg-0.3Ce alloy at lower and higher total strain amplitudes, direct aging treatment can improve the fatigue lives of the extruded Al-4Mg-0.5Ce alloy, and both direct aging and solution plus aging treatments can increase the fatigue lives of the extruded Al-4Mg-1.0Ce alloy. For above-mentioned alloys, 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, for the extruded Al-0.8Mg-0.6Si-0.2Sc alloy, a bilinear relation between the plastic strain amplitude and reversals to failure has been noted.Under low-cycle fatigue loading condition, the fatigue cracks initiate transgranularly at the surface of fatigue samples and propagate in a transgranular mode.for the extruded Al-4Mg-xCe alloys with different treatment states, extruded Al-0.8Mg-0.6Si-x(Sc, Er) alloys subjected to T6 treatment and ECAPed Al-0.8Mg-0.6Si-0.3Er alloys.更多还原