Abstract: Fatigue crack propagation of AZ31B magnesium alloy in room temperature is studied. And the temperature on the surface of the samples is tested by infrared thermographic technology. The mechanism of magnesium crack propagation is studied according to the relationship between the temperature of crack tip and crack length, and the relationship between temperature distribution on the surface and the trend of crack propagation in this test. Results show that the temperature on the surface of the samples increases in the beginning and then decreases during the process of fatigue crack propagation, the temperature changes a little in the stabilize phase and obviously in the rapid phase. The highest temperature rise of three group samples is sample A 10.89 ℃, sample B 15.19 ℃ and sample C 12.37 ℃. By observing the crack tip and vicinity region of crack tip, the orientation of crack tip changed, most of the crack is transgranular fracture with some intergranular fracture. There is some plastic deformation in the vicinity region of crack tip. The maximum temperature area on the surface of samples is related to the damage mechanisms of materials. This area corresponding to the stress concentration zone, it is the site of which the fatigue micro-crack formation and expansion, the temperature change and the final section of the specimen is consistent.

Key words: AZ31B magnesium alloy, Fatigue crack propagation, Infrared thermographic technology, Plastic deformation