异材焊接件应力腐蚀原因分析

Cause Analysis of Stress Corrosion of Welding between Different Alloys

对7020+7020和7020+6082合金板材进行焊接,并对2种焊接接头进行检测。使用光学显微镜对2种焊接板材的熔合区、热影响区及基材进行组织分析;使用SEM对焊接板材进行微观形貌观测和微区成分分析;结合模拟软件对焊接板材进行温度场分析。结果表明:腐蚀现象从热影响区开始,而异材焊接时7020合金一侧温度较高,冷却速率慢,导致晶粒尺寸长大,元素产生偏聚,腐蚀更严重;晶界及亚晶界上析出MgZn2,与晶粒基体及周围贫化区形成腐蚀微电池,其电位最低优先被腐蚀,导致腐蚀在热影响区发生及扩展,使得7系焊接接头的热影响区对晶间腐蚀最敏感。

In this paper,the welding of 7020+7020 and 7020+6082 plates was designed and then the two kinds of welded joints were tested.The microstructure of the fusion zone,heat-affected zone and substrate of the welded plates was analyzed by OM and SEM, the microstructure and composition of the welded plates were analyzed by SEM,and the temperature field of welded plates was analyzed using a simulation software.The results show that corrosion starts from the heat-affected zone,the 7020-side temperature is higher and the cooling rate is slower when different materials are welded,resulting in the increase of grain size and the polarization of elements.As a result,the corrosion is more serious.MgZn2 is precipitated on the grain boundary and the subgrain boundary,forming corrosion micro cells with the grain matrix and the surrounding depleted region.With the lowest potential, MgZn2 is first corroded,causing corrosion to occur and expand in the heat-affected zone,and making the heat affected zone of the 7- series welded joint most sensitive to intergranular corrosion.