低温对航空铝合金疲劳与裂纹扩展行为的影响

为了研究航空铝合金疲劳与裂纹扩展行为和机理,测试2种常用航空铝合金2524-T3和7050-T7451在常温25℃和低温–70℃下的疲劳与裂纹扩展性能,借助断口金相分析微观机理。结果表明:相同应力加载水平下,铝合金低温疲劳寿命延长而低温裂纹扩展速率减慢,–70℃低温对2种航空铝合金疲劳与裂纹扩展行为产生有益影响;–70℃低温环境下疲劳裂纹萌生区出现明显的台阶状小平面,两侧断面间形成凹凸错位,疲劳裂纹萌生困难;而在裂纹扩展区疲劳条带和韧窝特征减弱,且出现明显的沿晶特征,裂纹趋向于沿着晶界曲折扩展,疲劳和裂纹扩展寿命延长;随着加载应力水平提高,断口表面凹凸错位和沿晶特征减弱,而疲劳条带和韧窝特征增多。

Effect of low temperature on fatigue and crack propagation behavior of aeronautic aluminium alloy

Fatigue and crack growth tests were performed on two categories of the common aeronautic aluminum-alloys 2524-T3 and 7050-T7451 at ambient temperature of 25℃and cryogenic temperature of–70℃,in order to investigate the fatigue and crack propagation properties and micro mechanism.The test results show that the cryogenic fatigue life under the same amplitude loading rises and cryogenic crack growth rate decreases,which demonstrates the beneficial effect of cryogenic temperature on fatigue and crack growth properties.Furthermore,the fractographic micro mechanism reveals significant cleavage facets appeared during fatigue crack initiation at the cryogenic temperature of–70℃,leading to a concavo-convex morphology on fracture surfaces,and the fatigue crack initiation becomes difficult.On crack growth zones,the fatigue striations and dimples become unobvious,while evident intergranulars are occurred.As a result,the local fatigue crack tends to propagate zigzag and intergranularly,and fatigue and crack growth lives are increased.With the increasing loading stress level,the concavo-convex morphology and ductile transgranulars are reduced,while the fatigue striations and dimples are increased on fatigue surfaces,which demonstrates the cryogenic effect on fatigue crack initiation and propagation becomes weaker.This results have important theoretical and practical value.