拉伸孿晶形式存在。隨著應(yīng)力幅值的增加晶粒逐漸細化，這是由于在循環(huán)過程中，拉伸孿晶演變誘導(dǎo)晶粒細化。隨著應(yīng)力幅值的增加，織構(gòu)強度顯著減弱，這與試樣疲勞后的再結(jié)晶機制有關(guān)。通過對試樣疲勞斷口的分析，發(fā)現(xiàn)孿晶片層處容易引起裂紋萌生，隨著應(yīng)力的增加，試樣中裂紋擴展區(qū)面積逐漸減小，在疲勞裂紋擴展區(qū)觀察到明顯的疲勞輝紋。最終斷裂區(qū)表面粗糙，主要存在韌窩、撕裂脊以及二次裂紋等形貌。在最終斷裂區(qū)可觀察到韌窩，韌窩尺寸隨著循環(huán)應(yīng)力的增加，在較高加載頻率下，韌窩的尺寸與數(shù)量均減小。;Microstructure evolution and fracture morphology during high cycle fatigue in AZ31 magnesium alloy were investigated by fatigue test at different loading frequencies (3 and 30 Hz) and stress amplitudes (90, 95, 100, 105, 110 MPa). Electron back-scattered diffraction (EBSD) analysis results show that the number of residual twins in the matrix increases with the increase in loading stress, and the residual twins mainly exist in the form of {102} tensile twins. Gradual grain refinement is observed with increasing stress amplitude, which is due to the grain refinement induced by the evolution of tensile twinning during fatigue deformation. The significant weakening of the texture strength with increasing stress amplitude is related to the recrystallization mechanism after fatigue deformation. Through the scanning electron microscope (SEM) analysis of the fatigue fracture, it is found that the fatigue crack initiation (FCI) occurs in twin layer, the area of the fatigue crack growth (FCG) in the specimen gradually decreases with the increase in stress, and obvious fatigue striations (FS) are observed in FCG. The final fracture (FF) is rough surface, and there are mainly tear ridges and dimples. The dimple is observed in the final fracture, and the size and number of dimples decrease with the increase in stress."/>