| Anodizing is a commonly used surface protection treatment technology for aluminum alloys,which forms a dense protective layer on the surface of aluminum alloys to provide effective friction resistance and corrosion resistance for aluminum alloys.However,the anodized film will affect the initiation and propagation of fatigue cracks in the aluminum alloy matrix during service.At present,the research on the influence of anodic oxide film on the fatigue properties of aluminum alloy mainly comes from experiments,and the experiment has the limitations of long research period and many interference factors in the preparation of oxide film samples,so that the influence of anodic oxide film on the fatigue properties of aluminum alloy matrix remains in the qualitative stage.In addition,due to the small thickness of the oxide film,the observation is difficult,and the stress-strain distribution characteristics of the oxide film and its weak position are not clear.In this paper,the crystal plastic finite element method(CPFEM)was used as the main research method,combined with certain experimental verification,6061-T6 aluminum alloy was used as the matrix material,considering the material properties and formation characteristics of aluminum alloy oxide film,a representative volume unit(RVE)model with different oxide film thicknesses was established,and the effects of anodic oxide film before and after cracking on the cracking driving force and fatigue hot spot position of aluminum alloy matrix were analyzed.Finally,the stress-strain distribution characteristics in the thickness direction and loading direction of the oxide film were studied,so as to determine the weak position of the oxide film.The main research contents and results of this paper are as follows:1.The Voronoi algorithm was implemented through MATLAB,and the crystalline plastic finite element model of 6061-T6 aluminum alloy with different oxide film thickness was established.The effect of oxide film on the fatigue properties of aluminum alloy matrix was analyzed by means of fatigue indicator factor(FIP).2.In order to study the influence of oxide film on the fatigue performance of aluminum alloy matrix,the driving force of fatigue crack initiation and the position of fatigue hot spots of aluminum alloy matrix before and after cracking of the oxide film were analyzed.The results show that the intact oxide film under low strain amplitude reduces the fatigue crack initiation driving force of the aluminum alloy matrix.After the crack is formed in the oxide film,the fatigue crack initiation driving force of the aluminum alloy matrix grain near the oxide film crack increases significantly,so that the oxide film crack will expand to the nearby aluminum alloy matrix after the oxide film crack is generated.3.In order to determine the weak position of the oxide film in the thickness direction,the thickness of the oxide film was divided into three layers of grid to represent different positions of the oxide film in the thickness direction,and the stress-strain distribution of different positions was compared.The results show that the weak position of the oxide film is located at the interface between the aluminum alloy matrix and the oxide film.4.In order to determine the weak position of the oxide film in the loading direction,the stress-strain variation in the loading direction of the RVE model was analyzed.The results show that the weak position of the uncracked oxide film in the loading direction is random,which is affected by the microstructure and grain orientation of the aluminum alloy matrix.The weak position of the oxide film fragment is located at both ends of the loading direction in the forward and reverse directions. |
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