Research On Fatigue Property And Microstructure Of High Strength Aeronautic Aluminum Alloy

Aluminum and its alloys are widely applied to air field because of their good characteristic which include low density, strong corrosion resistance, good fracture toughness and high fatigue strength. Defects appear easily in the metal components which work in harsh environment like high temperature, high pressure and high speed. The defects lead to fatigue failure that caused a great loss of life and property. So, determining the fatigue life of components that work in fatigue load has an important scientific guiding significance for the aeronautic aluminum alloys’design and manufacturing.The fatigue life of1933and1161aluminum alloys, from which S-N curves can be deserved, is tested with GPS100high-frequency fatigue machine in room temperature. In this test, sine loading and stress ratio that is0.1are adopted. Microstructure morphology, fatigue fracture morphology, composition of separation phase, initiation and propagation behavior of fatigue crack of these two kinds of aluminum alloys are studied by analysis methods of OM, XRD, SEM and EDS. The results of the study show that:The fatigue limit of1933aluminum alloys (L direction, Kt=1, R=0.1) is315MPa. The fatigue limit of1933aluminum alloys (L direction, Kt=3, R=0.1) is108MPa. The fatigue limit of1161aluminum alloys (LT direction, Kt=1, R=0.1) is298MPa. The fatigue limit of1161aluminum alloys (LT direction, Kt=3, R=0.1) is128MPa.Fatigue fracture of1933and1161aluminum alloys have three parts that is fatigue source area, crack spreading area and transient breaking area. Crack propagation area exist obvious secondary cracks and fatigue strips. The transient breaking area exist many dimples which show that the material has good plastic. Failure of the specimens is typical fatigue fracture. Because fatigue cracks originate in the surface of samples, so improving the quality of the surface can retard the fatigue crack initiation..The stress ratio has a severe effect on fatigue life of1161and1933aluminum alloys. The fatigue strength of notch samples was significantly lower than the round mouth samples. It means that these two kinds of aluminum alloys have sensitive notch effect. So the materials fatigue strength can be increased by reducing the notch.The size of most precipitation phase particles which disperse in the aluminum alloys matrix and grain boundary is in nanometer size range. A small amount of coarse precipitation phase particles distribute in grain boundary. Precipitated phases of1933aluminum alloys are and MgZn. Precipitated phases of1161aluminum alloys are AlCu and Al3Zr.