2219-T8铝合金搅拌摩擦焊接头力学和应力腐蚀性能薄弱区研究
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摘要
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, re-spectively. 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.
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, re-spectively. 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.
引文
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[2]Malarvizhi S,Balasubramanian V.Mater Des,2011;32:1205
[3]Mishra R S,Ma Z Y.Mater Sci Eng,2005;R50:1
[4]Kang J,Fu R D,Luan G H,Dong C L,He M.Corros Sci,2010;52:620
[5]Liu H J,Zhang H J,Yu L.Mater Des,2011;32:1548
[6]Srinivasan P B,Arora K S,Dietzel W,Pandey S,Schaper M K.J Alloys Compd,2010;492:631
[7]Chen Y C,Feng J C,Liu H J.Mater Charact,2009;60:476
[8]Liu H J,Zhang H J,Huang Y X,Yu L.Trans Nonferrous Met Soc China,2010;20:1387
[9]Xu W F,Liu J H,Luan G H,Dong C L.Mater Des,2009;30:3460
[10]Paglia C S,Buchheit R G.Mater Sci Eng,2006;A429:107
[11]Zhang H J,Liu H J,Yu L.Sci Technol Weld Joining,2011;16:459
[12]Zhang H J,Liu H J.Mater Des,2013;45:206
[13]Li J Q,Liu H J.Mater Des,2013;43:299
[14]Li J Q,Liu H J.Mater Des,2013;45:148
[15]Malarvizhi S,Balasubramanian V.Trans Nonferrous Met Soc China,2011;21:962
[16]Suter T,B?hni H.Electrochim Acta,2001;47:191
[17]Liu X D,Frankel G S,Zoofan B,Rokhlin S I.Corros Sci,2004;46:405
[18]Yang B C,Yan J H,Sutton M A,Reynolds A P.Mater Sci Eng,2004;A364:55
[19]John M P.Metall Trans,1981;12A:269
[20]Xu W F,Liu J H,Luan G H,Dong C L.Acta Metall Sin,2009;45:490(徐韦锋,刘金合,栾国红,董春林.金属学报,2009;45:490)
[21]Cui G R,Ma Z Y,Li S X.Acta Mater,2009;57:5718
[22]Kang J,Luan G H,Fu R D.Acta Metall Sin,2011;47:224(康举,栾国红,付瑞东.金属学报,2011;47:224)
[23]Yan D Y,Shi Q Y,Wu A P,Juergen S,Zhang Z L.J Mech Eng,2010;46:106(鄢东洋,史清宇,吴爱萍,Juergen S,张增磊.机械工程学报,2010;46:106)
[24]Lei X F,Deng Y,Yin Z M,Xu G F.J Mater Eng Perform,2014;23:2149
[25]Xu W F,Liu J H,Chen D L,Luan G H.Int J Adv Manuf Technol,2014;74:209
[26]Dai Q L,Liang Z F,Wu J J,Meng L C,Shi Q Y.Acta Metall Sin,2014;50:587(戴启雷,梁志芳,吴建军,孟立春,史清宇.金属学报,2014;50:587)
[27]Woo W,Balogh L,Ungar T,Choo H,Feng Z L.Mater Sci Eng,2008;A498:308
[28]Du D X,Fu R D,Li Y J,Jing L,Ren Y B,Yang K.Mater Sci Eng,2014;A616:246
[29]Baek Y,Frankel G S.J Electrochem Soc,2003;150B:1
[30]Kim Y,Buchheit R G.Electrochim Acta,2007;52:2437
[31]Garcia V S,Colin F,Skeldon P,Thompson G E,Bailey P,Noakes T C Q,Habazaki H,Shimizu K.J Electrochem Soc,2004;151B:16
[32]Ramgopal T,Frankel G S.Corrosion,2001;57:702
[33]Muller I L,Galvele J R.Corros Sci,1977;17:179
[34]Newman R C,Healey C.Corros Sci,2007;49:4040
[35]Feng Z,Frankel G S,Matzdorf C A.J Electrochem Soc,2014;161C:42
[36]Feng Z,Boerstler J,Frankel G S,Matzdorf C A.Corrosion,2015;71:771
[37]Uhlig H H.Corrosion and Corrosion Control:an Introduction to Corrosion Science and Engineering.New York:John Wiley&Sons Inc,1971:309
[38]Birnbaum H K,Sofronis P.Mater Sci Eng,1994;A176:191