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2219-T8鋁合金攪拌摩擦焊接頭力學(xué)和應(yīng)力腐蝕性能薄弱區(qū)研究
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更新時間：2015-11-09
對2219-T8鋁合金攪拌摩擦焊 (FSW) 接頭在拉伸過程中, 熱機械影響區(qū) (TMAZ) 的變形行為、斷裂途徑和 190 MPa 下微區(qū)電化學(xué)性能進行了研究.
2219-T8鋁合金攪拌摩擦焊接頭力學(xué)和應(yīng)力腐蝕性能薄弱區(qū)研究INVESTIGATION ON MECHANICAL AND STRESS CORROSION?CRACKING PROPERTIES OF WEAKNESS ZONE IN FRICTION STIR?WELDED 2219-T8 Al ALLOY
對2219-T8鋁合金攪拌摩擦焊 (FSW) 接頭在拉伸過程中, 熱機械影響區(qū) (TMAZ) 的變形行為、斷裂途徑和 190 MPa 下微區(qū)電化學(xué)性能進行了研究. 結(jié)果表明, 焊接熱循環(huán)和攪拌作用加權(quán)強化效果最弱的區(qū)域是強度最差的位置; 拉伸時接頭變形主要發(fā)生在 TMAZ, 但由于受到焊核區(qū)的拘束程度不同, TMAZ 下層應(yīng)變更大, 導(dǎo)致裂紋起源于下層; 在相同的應(yīng)力水平下, TMAZ 表面的鈍化膜更易破裂, 甚至?xí)形⒘鸭y出現(xiàn), 這使得當接頭處于應(yīng)力腐蝕環(huán)境中時, TMAZ 更易發(fā)生局部腐蝕, 導(dǎo)致接頭的抗應(yīng)力腐蝕能力下降.?
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 a 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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