Extrusion Processing And Low-cycle Fatigue Behavior Of Al-Mg Series Alloys

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.