Influence Of Heat Treatment On Fatigue Behavior Of Extruded Al-Mg-Ce Alloy

Aluminum alloys have such characteristics as low density, high specific strength and rigidity, and have found a wide application in aeronautical and automotive industries. As the engineering structural materials, the fatigue fracture is one of their main failure forms. Obviously, the investigation on the fatigue behavior of the extruded Al-4%Mg-%xCe alloy with different treatment statuses has important theory reference value and actual guiding significance for reliable usage and safety design of this alloy.In this investigation, the Al-4%Mg alloy is chosen as the master alloy. Through adding Ce as well as melting, casting, hot extrusion and heat treatment, the Al-4%Mg-xCe alloy with different processing statuses have been fabricated. The microstructures of the Al-4%Mg-xCe alloy are observed and analyzed using optical microscope. The low-cycle fatigue tests are performed at room temperature under different total strain amplitudes. The influence of heat treatment on both fatigue deformation and fracture behavior of the Al-4%Mg-xCe alloy is determined.The observations on microstructures reveal that the amount of secondary phases gets decreased after solid solution treatment. For the Al-4%Mg-xCe alloy subjected to solution plus aging treatments, the disperse secondary phases will precipitate inside grains and at grain boundaries. In addition, it is noted that in the Al-4%Mg-xCe alloy subjected to aging treatment, the much more and smaller secondary phases appear.The results of fatigue tests show that the Al-4%Mg-xCe alloy subjected to different treatments can exhibit the cyclic hardening, softening and stable cyclic stress response, which mainly depends on the imposed total strain as well as the treatment method. Compared with as-extruded Al-4%Mg-0.3%Ce alloy, the fatigue life of the alloy subjected to solution treatment increases at the higher or lower strain amplitude. for both Al-4%Mg-0.5%Ce and Al-4%Mg-1.0%Ce alloy, the fatigue lifetime increase after heat treatment. For the Al-4%Mg-xCe alloy with different processing statuses, the relation between plastic and elastic strain amplitudes as well as reversals to failure can be described by Coffin-Manson and Basquin equations, respectively. In addition, at the higher total strain amplitudes, a serrated flow can be observed on theσ-εhysteresis loop. It means that the so-called dynamic strain aging takes place during fatigue deformation.The fractographic observations reveal that under the fatigue loading conditions, the cracks initiate transgranularly at the surface of fatigue samples and propagate in a transgranular mode for the Al-4%Mg-xCe alloy with different treated statuses.