| To realize the application and industrial promotion of aluminum FSW technology, joint fatigue behavior is essential to be one of the important targets. This study through high-frequency fatigue experiments, fatigue properties of the aerial aluminum LC4CS and 7075 - T6 FSW joints prefabricated crack wear through weld seam center, prefabricated crack through weld advance edge, prefabricated cracks through retreat side, prefabricated cracks vertical to welding seam samples have been studied. Microstructure observation, Vickers hardness experiment as a complementary test, through the regional organization, defects and hardness of FSW joints weld seam we can better understand the joint fatigue performance. The experiment provide an important basis to establish a reasonable friction stir welding joint fatigue assessing norms, thus promoting the application of friction stir welding technology in the field of aerospace.The IIW fatigue test standards are relatively conservative for FSW joints, the FSW fatigue test standards should be designed. The fatigue crack propagation rate equations of 7075 - T6 FSW joints prefabricated crack wear through weld seam center, prefabricated crack through weld advance side, prefabricated cracks through retreat side, prefabricated cracks vertical to welding seam samples are da/dN=2.5058×10-12 (△K)4.08,da/dN=4.6002×10-11 (△K)3.05,da/dN=1.8213×10-11(△K)3.16,da/dN= 4.9165×10-10 (△K)2.44 respectively. The fatigue crack propagation rate equations of LC4CS FSW joints prefabricated crack wear through weld seam center, prefabricated crack through weld advance side, prefabricated cracks through retreat side and prefabricated cracks vertical to welding seam samples are da/dN=1.8382×10-12 (△K)4.27,da/dN= 1.6872×10-11(△K )3.49,da/dN= 6.2811×10-11(△K )3.01,da/dN= 1.1229×10-10(△K)2.95 respectively.7075 - T6 aluminum FSW joint anti-fatigue crack propagation capacity is better than LC4CS aluminum alloy friction stir welded joints, but little difference. When△K is lower, the fatigue crack propagation rate of prefabricated cracks vertical to welding seam samples is the fastest. When△K is higher, the fatigue crack propagation rate of prefabricated cracks through retreat side sample is the lowest, prefabricated crack wear through weld seam center sample is the fastest. Weld seam formed a good shape, without any distortion. the border of two aluminum heat-affected zone of forward sides and stir zone are clear. welding nugget area are small, which is much smaller than base metal. Base metal are longer equiaxed grain along the direction of the rolling. It is showed that despite the nugget have small equiaxed grain, but anti-fatigue crack growth capacity is not the best, which may be related to the residual stress in the joints.The distribution of the Vickers hardness aluminum two friction stir welding joints are "W"-type, lowest hardness level is in the heat affected zone. There are oxide inclusion, penetrative type weak-bond defect and root defect in the two aluminum friction stir welding. They are disadvantage to joints fatigue performance. In reality we should optimize the process of welding technology, improve process accuracy, and other measures to reduce this defect.
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