Study On Anisotropy Of Fatigue Behavior Of5A06Aluminumalloy Based On Thermographic Method

Aluminum alloys with its advantages have been widely used in many fieldssuch as vehicles, chemical engineering and mechanical engineering and so on.As a kind of structure material used in various fields, aluminum alloy is hard toavoid fatigue problem. The traditional fatigue testing method is time-consuming.Infrared thermography is applied to identifying the superficial temperaturedistribution of a material or a component subjected to fatigue loading because ofits real-time, fast, and non-contact advantages. Planar anisotropy of alloy’smechanical properties will bring about many limitations to the usage of alloy.Engineering design can only base on the low performance direction. It has greatsignificance to research on anisotropy of high cycle fatigue property of5A06aluminum alloy based on infrared thermography.Infrared camera was used to record the temperature evolution during thetensile process, high cycle fatigue process and fatigue crack propagation processof5A06aluminum alloy in the two directions (longitudinal direction andtransverse direction) at room temperature. The fatigue properties and themechanism of heat generation of5A06aluminum alloy were studied. Thetemperature field information of the two directions during the process of tensile and fatigue was analyzed contrastively. The fatigue strength of the twodirections was also predicted using thermographic method, and the predictedresult was compared with the actual result. So the reliability of the fatiguestrength prediction based on the infrared thermography could be validated andbroaden the application of infrared thermography. The electron backscatterdiffraction (EBSD) method was used to measure the texture of5A06aluminumalloy. The effect of texture on the fatigue performance and fatigue crackpropagation performance in longitudinal direction and transverse direction of5A06aluminum alloy has been researched.The results show: The plasticity show obvious anisotropy in thelongitudinal direction and transverse direction of5A06aluminum alloy. Thefatigue strength achieved by traditional method in longitudinal direction andtransverse direction is113MPa and61MPa, respectively. The fatigue strengthof5A06aluminum alloy measured by infrared thermography in longitudinaldirection and transverse direction is114.6MPa and64MPa, respectively, andthe percentage error between the fatigue strength obtained by thermographicmethod and traditional method is1.4%and4.9%, respectively. So the fatiguestrength prediction based on infrared thermography and fatigue strengthachieved by traditional testing method have a good consistency. When stressabove the fatigue strength, the temperature evolution process can be divided intofour stages: initial temperature increase stage, slow temperature decline stage,rapid temperature rise stage and final temperature decline stage. Longitudinal direction and transverse direction have the same trend. During the tensile andfatigue testing process, the fracture temperature of transverse direction is higherthan that of longitudinal direction. It shows that when the transverse directionspecimen fractures, more energy will be released. It could also be found that thefatigue life of longitudinal direction is obviously longer than that of transversedirection under the same stress, which is because that the impeding ability offatigue crack initiation is stronger in longitudinal direction.For standard compact tension (CT) specimens in longitudinal direction andtransverse direction, under the same stress, with the increase of cycling times thefatigue crack propagation rate in parallel to the rolling direction is higher thanthat in perpendicular to the rolling direction. Infrared thermal imager was usedto record the temperature evolution in two directions during the process offatigue crack propagation of5A06aluminum alloy, the temperature evolutionduring fatigue crack propagation process showed three stages: initial slowtemperature rise stage, rapid temperature rise stage, and finial temperaturedecline stage. Under same stress the fracture temperature of perpendicular to therolling direction is higher than that of parallel to the rolling direction.Through using the electron backscatter diffraction (EBSD) method, thepole figures and inverse pole figures could be achieved. The maximumorientation density in longitudinal direction and transverse direction is7.79and8.14, respectively. It shows that there exists preferred orientation (texture) inbase metal grain of5A06aluminum alloy. The orientation density in transverse direction is bigger than that in longitudinal direction, so grain in transversedirection is more easily moved, the plastic deformation ability in transversedirection is more stronger. The corresponding relationship of strength andplasticity is opposite, this has good consistency with tensile and fatigue testresults.The peak index and average index of Schmid factor in longitudinaldirection of5A06aluminum alloy are all lower than transverse direction. So theplastic performance in transverse direction is better, and the mechanicalperformance in longitudinal direction is better. This has the good consistencywith the tensile and fatigue test result.