Abstract：The microstructure and mechanical properties of friction stir welded 7020-T6 alloy were investigated by micro-hardness test, tensile mechanical properties test, metangraphic microscope, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the hardness distribution appears as the W-shaped profile in alloy weld zone and reaches to minimum in HMAZ/HAZ. The tensile strength, yield strength, elongation and welding coefficient of the welded joint are 352 MPa, 223 MPa, 9.8% and 86.9%, respectively. The grain structure shows significant difference in the welded zone. The fine and dispersive precipitates of CP zone and η° phase formed after artificial aging (90 ℃/8 h+135 ℃/16 h) in base metal are dissolved during the process of friction stir weld and re- precipitate later, but the size and density of precipitates in welded joint are much smaller than base metal.
[1] JU S D, MENG X C, LI Z W, et al.Investigation of vertical compensation friction stir-welded 7N01-T4 aluminum alloy[J]. The International Journal of Advanced Manufacturing Technology, 2016, 84(9): 1-9. [2] GUR C H, İ. YILDIZ. Non-destructive investigation on the effect of precipitation hardening on impact toughness of 7020 Al-Zn-Mg alloy[J]. Materials Science & Engineering A, 2004, 382(1): 395-400. [3] MAHONEY M W, RHODES C G, FLINTOFF J G, et al.Properties of friction-stir-welded 7075 T651 aluminum[J]. Metallurgical and Materials Transactions A, 1998, 29(7): 1955-1964. [4] JI S, XING J, YUE Y, et al.Design of friction stir welding tool for avoiding root flaws[J]. Materials, 2013, 6(12): 5870-5877. [5] JI S D, MENG X C, HUANG R F, et al.Microstructures and mechanical properties of 7N01-T4 aluminum alloy joints by active-passive filling friction stir repairing[J]. Materials Science & Engineering A, 2016, 664: 94-102. [6] DUDZIK K.Mechanical properties of 5083, 5059 AND 7020 aluminium alloys and their joints welded by mig[J]. Journal of Kones, 2011, 18: 73-77. [7] 彭小燕, 曹晓武, 段雨露, 等. 7020铝合金MIG焊焊接接头的组织与性能[J]. 中国有色金属学报, 2014(4): 912-918. PENG Xiaoyan, DUAN Xiaowu, DUAN Yulu, et al. Microstrucutre and property of7020 MIG 7020 alloy[J]. The Chinese Journal of Nonferrous Metals, 2014(4): 912-918. [8] 周友龙, 张力, 陈舟, 等. 7020铝合金搅拌摩擦焊与MIG焊接对比试验[J]. 电焊机, 2011, 41(11): 91-94. ZHOU YouLong, ZHANG Li, CHEN Zhou, et al.Study on the FSW process of 7020 aluminum alloy comparing with the MIG welding[J]. Electric Welding Machine, 2011, 41(11): 91-94. [9] STILLER K, WARREN P.Investigation of precipitation in an Al-Zn-Mg alloy after two-step ageing treatment at 100 degrees and 150 degrees C[J]. Journal of Power Sources, 2015, 274: 156-164. [10] GANG SHA, ALFRED CEREZO.Early-stage precipitation in Al-Zn-Mg-Cu alloy (7050)[J]. Acta Materialia, 2004, 52(15): 4503-4516. [11] DLUBEK G, KRAUASE R, BRUMMER O, et al.Study of formation and reversion of Guinier-Preston zones in Al-4.5 at%Zn-x, at%Mg alloys by positrons[J]. Journal of Materials Science, 1986, 21(3): 853-858. [12] WERENSKIOLD J C, DESCHAMPS A, BRECHET Y.Characterization and modeling of precipitation kinetics in an Al-Zn-Mg alloy[J]. Materials Science & Engineering A, 2000, 293(1): 267-274. [13] LOFFER H, KOVACS I, LENDVAI J.Decomposition processes in Al-Zn-Mg alloys[J]. Journal of Materials Science, 1983, 18(8): 2215-2240. [14] AYDIN H, BAYRAM A, UGUZ A, et al.Tensile properties of friction stir welded joints of 2024 aluminum alloys in different heat-treated-state[J]. Materials & Design, 2009, 30(6): 2211-2221. [15] Ø. FRIGAARD, Ø. GRONG, MIDLING O T. A process model for friction stir welding of age hardening aluminum alloys[J]. Metallurgical and Materials Transactions A, 2001, 32(5): 1189-1200. [16] KUMAR M, POLETTI C, DRGISCHER H P.Precipitation kinetics in warm forming of AW-7020 alloy[J]. Materials Science & Engineering A, 2013, 561(3): 362-370. [17] LIU H, FUJII H, MAEDA M, et al.Heterogeneity of mechanical properties of friction stir welded joints of 1050-H24 aluminum alloy[J]. Journal of Materials Science Letters, 2003, 22(6): 441-444.
2018, Vol. 23 
