| ABSTRACT:Through the study of fatigue property of AZ80magnesium alloy, microstructure of AZ80under different heat treatment were observed by metallographic analysis, XRD and TEM. The cyclic stress response, fatigue life, Cyclic hysteresis loop and the cyclic stress-strain behavior of three different heat treatment, hot forging, aging state (T5) and solid solution aging state(T6), were investigated under total strain amplitude control in room temperature by cyclic tension and compression.And the fatigue fracture morphology was observed, for estimating its means of crack initiation and crack propagation. In this thesis, the main conclusions obtained are shown as below:(1) The tensile strength and yield strength of AZ80magnesium alloy T5(170℃,20h) are the biggest, but the elongation is the lowest; and the tensile strength, yield strength of hot forging AZ80magnesium alloy are the lowest, the elongation is the largest; and AZ80magnesium alloy of T6(420℃,2h;170℃,20h) is between.(2) Under the three different kinds of heat treatment, AZ80magnesium alloy are generally characterized as the cyclic strain hardening phenomenon.(3) The relationship between Strain fatigue life and plastic strain of AZ80magnesium alloy obey the Coffin-Manson equation, and the elastic strain amplitude obey Basquin equation respectively. With the total strain amplitude increasing, the fatigue life reduce. Under0.3%of the minimum total strain amplitude, the fatigue life of AZ80hot forging state is the longest; while under0.9%of the maximum total strain amplitude, the fatigue life of AZ80-T5is the longest and the hot forging is the shortest.(4) The fatigue fracture morphology observation results show that the fatigue crack initated in the sample surface, and extended in a transgranular manner.(5) Under different heat treatment system, the fatigue stripes of AZ80magnesium alloy have brittle fatigue stripe obviously, that appear as variable and irregular shape. |
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