对2219-T8铝合金搅拌摩擦焊 (FSW) 接头在拉伸过程中, 热机械影响区(TMAZ)的变形行为、断裂途径和190 MPa下微区电化学性能进行了研究. 结果表明, 焊接热循环和搅拌作用加权强化效果最弱的区域是强度最差的位置; 拉伸时接头变形主要发生在TMAZ, 但由于受到焊核区的拘束程度不同, TMAZ下层应变更大, 导致裂纹起源于下层; 在相同的应力水平下, TMAZ表面的钝化膜更易破裂, 甚至会有微裂纹出现, 这使得当接头处于应力腐蚀环境中时, TMAZ更易发生局部腐蚀, 导致接头的抗应力腐蚀能力下降.
Al alloy 2219 (AA2219) is widely used in the aerospace industry, and friction stir welding (FSW) is an ideal method to join it. The ultimate tensile strength of an FSW AA2219-T8 joint can be as high as 344 MPa which is significantly higher than that welded by other methods such as gas tungsten arc welding. However, the thermo-mechanically affected zone (TMAZ) in the FSW joints of AA2219-T6/T8 is a weakness zone of mechanical property and is susceptible to stress corrosion cracking (SCC), but the reasons are not been well understood. In this work, the mechanical and electrochemical properties of different zones in AA2219-T8 joints obtained by the FSW method were studied. The welding thermal cycles during welding were measured using an array of type K thermocouples. During the tensile process of the joints, digital image correlation (DIC) technique and high speed video technique were employed to investigate the deformational behavior and fracture pathway of the TMAZ, respectively. A microcell method was used to study the micro-electrochemical characteristics of the joints with and without stress. The results showed that the minimum strength located at a position where the weighted strengthening effects of both thermal cycles and stir action were the weakest. The DIC results revealed that the deformation concentrated mainly in the TMAZ during the tensile tests. However, due to the different restraints from the nugget zone (NZ) led to a large strain in the root side than that in the crown side. This made the root side susceptible to cracks initiation. In situ tensile testing indicated that cracks occurred only in the TMAZ at 190 MPa, indicating that the protective surface films in the TMAZ were more prone to crack than those in other zones of the joint. This led the TMAZ to be the weakest zone to pitting corrosion in an aggressive environment. Once pits generate in the TMAZ, the local stress will concentrate near the tip of the pitting, resulting in failure.
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