Study Of Fatigue Behavior Of7A09Alloy

In this paper, with the aid of MYBP fatigue testing machine,metallographicmicroscope, scanning electron microscope and transmission electron microscopydevices such as studied fatigue behavior of7A09alloy at room temperature in air, RTin vacuum(10-3Pa) and at low temperature (83K) in vacuum (10-3Pa)Experimental results show that under the different environment with the increaseof stress amplitude the fatigue life of7A09alloy are reduced.In the case of the samestress amplitude,by comparison with RT in air fatigue life of7A09alloy at RT invacuum is longer;by comparison with RT in vacuum,fatigue life of7A09alloy at lowtemperature with vacuum is longer,the influence of low temperature environment on thefatigue life is better than vacuum environment.The scope of the fatigue limit of7A09alloy is120~140MPa at RT in air, thescope of the fatigue limit at RT in vacuum is less than130MPa,the scope of the fatiguelimit at low temperature in vacuum is240~250MPa.Under three conditions the characteristics of the crack initiation region of7A09alloy is formed by fatigue steps radial stripes,Crack initiation initiated in the defect ofthe processing and thick The second phase particles and inclusions,the characteristics ofthe crack propagation region is A large number of toughening nest,broken The secondphase particles and secondary crack. At RT in air and at RT in vacuum while lowerstress amplitude there are fatigue striations of toughness,the tyre pattern and furrowsthere are while higher stress amplitude;When the stress amplitude is170MPa at RT invacuum and at RT in air fatigue striations spacing are about1.1?m and1.5?m.fatiguestriations of brittleness there are at low temperature in vacuum.When the stressamplitude is260MPa, fatigue striations spacing are about0.7?m and1.7?m at lowtemperature in vacuum and at RT in vacuum.By comparison with the original sample, under the different environment thenumber of The second phase particles near fatigue fracture of7A09alloy decreases,butthe size increase;Under three conditions dislocation configuration is mainly curls linedislocation and dislocation loops;Under three conditions dislocation density is higherthan the original alloy specimen.Dislocation density at low temperature is the mosthigh,the second is at RT in vacuum.