航天铝合金变极性等离子弧焊焊接接头的腐蚀与疲劳交替研究

Study on Corrosion and Fatigue Alternation of Aerospace Aluminum Alloy Welded Joints by Variable Polarity Plasma Arc Welding

随着可重复使用航天器理念的提出,可重用航天器多次空天往返和地面修复过程的腐蚀与疲劳交替问题不可忽视。本工作以5A06铝合金变极性等离子弧焊焊接接头为研究对象,对焊接接头进行腐蚀与疲劳交替试验,研究不同单位腐蚀时间对腐蚀与疲劳交替工况下疲劳寿命的影响。通过扫描电子显微镜和激光共聚焦显微镜对其断口进行表征,分析了腐蚀与疲劳交替后焊接接头的损伤特性。结果表明,随着单位腐蚀时间的延长,腐蚀与疲劳交替寿命呈现先下降后平稳的趋势。这主要归因于腐蚀会钝化疲劳裂纹尖端,形成新的点蚀坑,同时钝化疲劳过程中的侵入/挤出和微裂纹降低了表面应力的集中程度,使疲劳寿命相对延长,从而反映出寿命保持稳定的状态。其中,断裂位置均处于热影响区,这主要因为焊接热影响区耐腐蚀性差,易造成严重腐蚀损伤,较大的腐蚀坑引起严重的应力集中,从而加速裂纹萌生。

With the concept of reusable spacecraft,multiple air-to-air round trips and ground repair processes have made alternating problems of corrosion and fatigue on reusable spacecraft cannot be ignored.In this work,variable polarity plasma arc welding was used to join 5 mm thick 5A06 aluminum magnesium alloy.The alternating corrosion-fatigue test was carried out to study the effect of different unit corrosion time on fatigue life.The specimens were characterized by scanning electron microscope and laser confocal microscope.The damage characteristics after the alternate action of corrosion and fatigue were analyzed.The results show that with the increase of unit corrosion time,the average alternating corrosion-fatigue life decrease first and then tend to be stable.That is mainly due to the fact that the corrosion passivated the fatigue crack tip and form new pitting pits.At the same time,the intrusion/extrusion and microcracks during the fatigue process reduce the surface stress concentration and increase the fatigue life relatively,thus the stable state of life reflects.The fracture locations are all in the heat affected zone,which mainly because the welding heat affected zone has poor corrosion resistance and easy to form serious corrosion damage.The large corrosion pits cause serious stress concentration and accelerates crack initiation.