The relationship between microstructure and tensile behaviors of fatigued AZ31 magnesium alloy was investigated. Axial fatigue tests were performed on PLG-100 fatigue machine at stresses of 50 and 90 MPa. Tensile samples were cut from the fatigued samples, named as L-sample and H-sample respectively, and the O-sample was cut from original rolled AZ31 alloy. The EBSD and TEM were used to characterize the microstructure. It is found that the twinning-detwinning was the main deformation mechanism in high stress fatigue test, while dislocation slipping was dominant in low stress fatigue test. After fatigue tests, the average grain size of the L-sample and H-sample decreased to 4.71 and 5.33 μm, and the tensile and yield strength of the L-sample and H-sample increased slightly. By analyzing SEM images, the ultimate fracture region of the L-sample consisted of dimples, while there were many microvoids in the ultimate fracture region of the H-sample. Consequently, the tensile behaviors of fatigued magnesium have a close relationship with microstructure.
Yang SHUXi-yan ZHANGJiang-ping YULi TANRui-sen YINQing LIU
In order to investigate the microstructure and properties evolution of the AZ31magnesium alloy in different cycles(including104(sample1),106(sample2)and none(sample3,no fatigue tests on the samples))of high cycle deformation,thescanning electron microscopy(SEM)and electron back-scattered diffraction technique(EBSD)were fully used.It is found that many{1012}tension twins(near21%,volume fraction),a few{1011}compression twins and{1011}?{1012}secondary twins aregenerated during tension?compression cyclic deformation.The volume fractions of{1012}twins in samples1,2and3are8%,21%and4%,respectively.By analyzing the fatigue fracture of the samples,larger area of fatigue striations and cleavage fracture insamples are also observed,as well as the shallower dimples.The twin laminae are likely to occur in the crack initiation zone whiledimples are in the final fracture region and the dimple size increases with the increase of the cycle number.The dimple diameters ofsamples1,2and3are14.8,31.2and8.5μm,respectively.It turns out that both the fatigue strength and elongation of the samplesslightly decrease with increasing the cycle number.
