Please wait a minute...
Acta Metall Sin  2016, Vol. 52 Issue (1): 60-70    DOI: 10.11900/0412.1961.2015.00201
Current Issue | Archive | Adv Search |
INVESTIGATION ON MECHANICAL AND STRESS CORROSION CRACKING PROPERTIES OF WEAKNESS ZONE IN FRICTION STIR WELDED 2219-T8 Al ALLOY
Ju KANG1,2,Jichao LI2,Zhicao FENG2,Guisheng ZOU1,Guoqing WANG4,Aiping WU1,3()
1 Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
2 Fontana Corrosion Center, The Ohio State University, Columbus, Ohio 43210-1185, USA
3 State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
4 China Academy of Launch Vehicle Technology, Beijing 100076, China
Download:  HTML  PDF(8969KB) 
Export:  BibTeX | EndNote (RIS)      
Abstract  

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.

Key words:  2219 Al alloy      friction stir welding (FSW)      weakness zone      micro-electrochemical characteristic      stress corrosion cracking (SCC)      in situ tensile testing     
Received:  07 April 2015     

Cite this article: 

Ju KANG,Jichao LI,Zhicao FENG,Guisheng ZOU,Guoqing WANG,Aiping WU. INVESTIGATION ON MECHANICAL AND STRESS CORROSION CRACKING PROPERTIES OF WEAKNESS ZONE IN FRICTION STIR WELDED 2219-T8 Al ALLOY. Acta Metall Sin, 2016, 52(1): 60-70.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2015.00201     OR     https://www.ams.org.cn/EN/Y2016/V52/I1/60

Fig.1  Schematic of test positions in the joints (RD—rolling direction, L—longitudinal, S—short transverse, T—transverse, AS—advancing side, RS—retreating side, DIC—digital image correlation)
Fig.2  Schematics of samples used for electrochemical experiments by microcell (unit: mm)
Fig.3  Schematic of microcell (a) and a 0.8 mm diameter tip for microcell test (b)
Fig.4  Schematic of modified ASTM G49 jig used to apply a constant stress at microcell test
Fig.5  Engineering stress-engineering strain curves for the base material (BM) and friction stir welding (FSW) joint of 2219-T8 Al alloy
Fig.6  Microhardness distributions of an FSW joint of 2219-T8 Al alloy (Inset shows a macroscopic metallographic image of the cross section of the joint)
Fig.7  DIC results for strain fields under different stresses of an FSW joint of 2219-T8 Al alloy
Fig.8  Engineering strain-engineering stress curve for the TMAZ at the position in Fig.2b
Fig.9  Fracture location and necking phenomenon in a fractured joint
Fig.10  Fracture process of a joint
Fig.11  Micro-electrochemical characteristics of different zones in the FSW 2219-T8 Al alloy joints with and without an applied stress (Microcell capillary 0.8 mm diameter tip, 0.5 mol/L NaCl, E—potential, i—current density)
Fig.12  OM images of the different zones in an FSW joint of 2219-T8 Al alloy before in situ tensile testing
Fig.13  Transgranular and intergranular cracks in the TMAZ after tensile testing at 191 MPa
Fig.14  OM image of fractured transverse section of an FSW joint of 2219-T8 Al alloy after in situ tensile testing
Fig.15  Schematic of crown side and root side in the joint (Lt—width of crown side in the NZ, Lb—width of root side in the NZ)
[1] Xu W F, Liu J H, Luan G H, Dong C L. Acta Metall Sin, 2008; 44: 1404
[1] (徐韦锋, 刘金合, 栾国红, 董春林. 金属学报, 2008; 44: 1404)
[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
[20] (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
[22] (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
[23] (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
[26] (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
[1] Ju KANG,Suying LIANG,Aiping WU,Quan LI,Guoqing WANG. Local Liquation Phenomenon and Its Effect on Mechanical Properties of Joint in Friction Stir Welded 2219 Al Alloy[J]. 金属学报, 2017, 53(3): 358-368.
[2] Fenjun LIU, Li FU, Haiyan CHEN. Microstructures and Mechanical Properties of Thin Plate Aluminium Alloy Joint Prepared by High Rotational Speed Friction Stir Welding[J]. 金属学报, 2017, 53(12): 1651-1658.
[3] Maocheng YAN,Shuang YANG,Jin XU,Cheng SUN,Tangqing WU,Changkun YU,Wei KE. STRESS CORROSION CRACKING OF X80 PIPELINE STEEL AT COATING DEFECT IN ACIDIC SOIL[J]. 金属学报, 2016, 52(9): 1133-1141.
[4] YAN Maocheng, WANG Jianqiu, HAN En-hou, SUN Cheng, KE Wei. CHARACTERISTICS AND EVOLUTION OF THIN LAYER ELECTROLYTE ON PIPELINE STEEL UNDER CATHODIC PROTECTION SHIELDING DISBONDED COATING[J]. 金属学报, 2014, 50(9): 1137-1145.
[5] DAI Qilei , LIANG Zhifang , WU Jianjun , MENG Lichun , SHI Qingyu . MICROSTRUCTURE CHANGE AND ENERGY RELEASE OF FRICTION STIR WELDED Al-Mg-Si ALLOY DURING DSC TEST[J]. 金属学报, 2014, 50(5): 587-593.
[6] HAO Wenkui,LIU Zhiyong,LI Xiaogang,DU Cuiwei. STRESS CORROSION CRACKING AND ITS MECHANISM OF 16Mn STEEL AND HEAT-AFFECTED ZONE IN ALKALINE SULFIDE SOLUTIONS[J]. 金属学报, 2013, 49(7): 881-889.
[7] KANG Ju LUAN Guohong FU Ruidong. MICROSTRUCTURES AND MECHANICAL PROPERTIES OF BANDED TEXTURES OF FRICTION STIR WELDED 7075-T6 ALUMINUM ALLOY[J]. 金属学报, 2011, 47(2): 224-230.
[8] LIU Zhiyong WANG Changpeng DU Cuiwei LI Xiaogang. EFFECT OF APPLIED POTENTIALS ON STRESS CORROSION CRACKING OF X80 PIPELINE STEEL IN SIMULATED YINGTAN SOIL SOLUTION[J]. 金属学报, 2011, 47(11): 1434-1439.
[9] DAN Tichun LU Zhanpeng WANG Jianqiu HAN Enhou SHOJI Testuo KE Wei. CRACK GROWTH BEHAVIOR FOR STRESS CORROSION CRACKING OF 690 ALLOY IN HIGH TEMPERATURE WATER[J]. 金属学报, 2010, 46(10): 1267-1274.
No Suggested Reading articles found!